diff --git a/src/arch/i386/interface/vmware/guestinfo.c b/src/arch/i386/interface/vmware/guestinfo.c
index aa10fc015..a0530c8d1 100644
--- a/src/arch/i386/interface/vmware/guestinfo.c
+++ b/src/arch/i386/interface/vmware/guestinfo.c
@@ -51,7 +51,7 @@ static int guestinfo_channel;
  */
 static int guestinfo_fetch_type ( struct settings *settings,
 				  struct setting *setting,
-				  struct setting_type *type,
+				  const struct setting_type *type,
 				  void *data, size_t len, int *found ) {
 	const char *parent_name = settings->parent->name;
 	char command[ 24 /* "info-get guestinfo.ipxe." */ +
diff --git a/src/arch/x86/core/cpuid_settings.c b/src/arch/x86/core/cpuid_settings.c
index e2ec9bde6..2da859ee9 100644
--- a/src/arch/x86/core/cpuid_settings.c
+++ b/src/arch/x86/core/cpuid_settings.c
@@ -117,7 +117,7 @@ enum cpuid_registers {
 #define CPUID_NUM_REGISTERS( tag ) ( ( ( (tag) >> 16 ) & 0x3 ) + 1 )
 
 /** CPUID settings scope */
-static struct settings_scope cpuid_settings_scope;
+static const struct settings_scope cpuid_settings_scope;
 
 /**
  * Check applicability of CPUID setting
@@ -127,7 +127,7 @@ static struct settings_scope cpuid_settings_scope;
  * @ret applies		Setting applies within this settings block
  */
 static int cpuid_settings_applies ( struct settings *settings __unused,
-				    struct setting *setting ) {
+				    const struct setting *setting ) {
 
 	return ( setting->scope == &cpuid_settings_scope );
 }
@@ -252,7 +252,7 @@ struct init_fn cpuid_settings_init_fn __init_fn ( INIT_NORMAL ) = {
 };
 
 /** CPUID predefined settings */
-struct setting cpuid_predefined_settings[] __setting ( SETTING_HOST_EXTRA ) = {
+const struct setting cpuid_predefined_settings[] __setting ( SETTING_HOST_EXTRA ) = {
 	{
 		.name = "cpuvendor",
 		.description = "CPU vendor",
diff --git a/src/core/memmap_settings.c b/src/core/memmap_settings.c
index f06b8750d..906fba128 100644
--- a/src/core/memmap_settings.c
+++ b/src/core/memmap_settings.c
@@ -108,7 +108,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #define MEMMAP_SCALE( tag ) ( (tag) & 0x3f )
 
 /** Memory map settings scope */
-static struct settings_scope memmap_settings_scope;
+static const struct settings_scope memmap_settings_scope;
 
 /**
  * Check applicability of memory map setting
@@ -118,7 +118,7 @@ static struct settings_scope memmap_settings_scope;
  * @ret applies		Setting applies within this settings block
  */
 static int memmap_settings_applies ( struct settings *settings __unused,
-				     struct setting *setting ) {
+				     const struct setting *setting ) {
 
 	return ( setting->scope == &memmap_settings_scope );
 }
@@ -231,7 +231,7 @@ struct init_fn memmap_settings_init_fn __init_fn ( INIT_NORMAL ) = {
 };
 
 /** Memory map predefined settings */
-struct setting memmap_predefined_settings[] __setting ( SETTING_MISC ) = {
+const struct setting memmap_predefined_settings[] __setting ( SETTING_MISC ) = {
 	{
 		.name = "memsize",
 		.description = "Memory size (in MB)",
diff --git a/src/core/nvo.c b/src/core/nvo.c
index 4c871b2fd..e135d2b41 100644
--- a/src/core/nvo.c
+++ b/src/core/nvo.c
@@ -193,7 +193,7 @@ static int nvo_save ( struct nvo_block *nvo ) {
  * @ret applies		Setting applies within this settings block
  */
 int nvo_applies ( struct settings *settings __unused,
-		  struct setting *setting ) {
+		  const struct setting *setting ) {
 
 	return ( ( setting->scope == NULL ) &&
 		 dhcpopt_applies ( setting->tag ) );
@@ -208,7 +208,7 @@ int nvo_applies ( struct settings *settings __unused,
  * @v len		Length of setting data
  * @ret rc		Return status code
  */
-static int nvo_store ( struct settings *settings, struct setting *setting,
+static int nvo_store ( struct settings *settings, const struct setting *setting,
 		       const void *data, size_t len ) {
 	struct nvo_block *nvo =
 		container_of ( settings, struct nvo_block, settings );
diff --git a/src/core/settings.c b/src/core/settings.c
index 03ef084af..e6cfc0d21 100644
--- a/src/core/settings.c
+++ b/src/core/settings.c
@@ -96,7 +96,7 @@ static inline void * generic_setting_data ( struct generic_setting *generic ) {
  */
 static struct generic_setting *
 find_generic_setting ( struct generic_settings *generics,
-		       struct setting *setting ) {
+		       const struct setting *setting ) {
 	struct generic_setting *generic;
 
 	list_for_each_entry ( generic, &generics->list, list ) {
@@ -116,7 +116,7 @@ find_generic_setting ( struct generic_settings *generics,
  * @ret rc		Return status code
  */
 int generic_settings_store ( struct settings *settings,
-			     struct setting *setting,
+			     const struct setting *setting,
 			     const void *data, size_t len ) {
 	struct generic_settings *generics =
 		container_of ( settings, struct generic_settings, settings );
@@ -551,7 +551,8 @@ struct settings * settings_target ( struct settings *settings ) {
  * @v setting		Setting
  * @ret applies		Setting applies within this settings block
  */
-int setting_applies ( struct settings *settings, struct setting *setting ) {
+int setting_applies ( struct settings *settings,
+		      const struct setting *setting ) {
 
 	/* Find target settings block */
 	settings = settings_target ( settings );
@@ -570,7 +571,7 @@ int setting_applies ( struct settings *settings, struct setting *setting ) {
  * @v len		Length of setting data
  * @ret rc		Return status code
  */
-int store_setting ( struct settings *settings, struct setting *setting,
+int store_setting ( struct settings *settings, const struct setting *setting,
 		    const void *data, size_t len ) {
 	int rc;
 
@@ -609,11 +610,12 @@ int store_setting ( struct settings *settings, struct setting *setting,
 }
 
 /**
- * Fetch value and origin of setting
+ * Fetch setting
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
- * @v origin		Origin of setting to fill in
+ * @v origin		Origin of setting to fill in, or NULL
+ * @v fetched		Fetched setting to fill in, or NULL
  * @v data		Buffer to fill with setting data
  * @v len		Length of buffer
  * @ret len		Length of setting data, or negative error
@@ -621,17 +623,19 @@ int store_setting ( struct settings *settings, struct setting *setting,
  * The actual length of the setting will be returned even if
  * the buffer was too small.
  */
-static int fetch_setting_and_origin ( struct settings *settings,
-				      struct setting *setting,
-				      struct settings **origin,
-				      void *data, size_t len ) {
+int fetch_setting ( struct settings *settings, const struct setting *setting,
+		    struct settings **origin, struct setting *fetched,
+		    void *data, size_t len ) {
 	struct settings *child;
+	struct setting tmp;
 	int ret;
 
 	/* Avoid returning uninitialised data on error */
 	memset ( data, 0, len );
 	if ( origin )
 		*origin = NULL;
+	if ( fetched )
+		memcpy ( fetched, setting, sizeof ( *fetched ) );
 
 	/* Find target settings block */
 	settings = settings_target ( settings );
@@ -641,22 +645,33 @@ static int fetch_setting_and_origin ( struct settings *settings,
 		return -ENOTSUP;
 
 	/* Try this block first, if applicable */
-	if ( setting_applies ( settings, setting ) &&
-	     ( ( ret = settings->op->fetch ( settings, setting,
-					     data, len ) ) >= 0 ) ) {
-		/* Record origin, if applicable */
-		if ( origin )
-			*origin = settings;
-		/* Default to string setting type, if not yet specified */
-		if ( ! setting->type )
-			setting->type = &setting_type_string;
-		return ret;
+	if ( setting_applies ( settings, setting ) ) {
+
+		/* Create modifiable copy of setting */
+		memcpy ( &tmp, setting, sizeof ( tmp ) );
+		if ( ( ret = settings->op->fetch ( settings, &tmp,
+						   data, len ) ) >= 0 ) {
+
+			/* Default to string type, if not yet specified */
+			if ( ! tmp.type )
+				tmp.type = &setting_type_string;
+
+			/* Record origin, if applicable */
+			if ( origin )
+				*origin = settings;
+
+			/* Record fetched setting, if applicable */
+			if ( fetched )
+				memcpy ( fetched, &tmp, sizeof ( *fetched ) );
+
+			return ret;
+		}
 	}
 
 	/* Recurse into each child block in turn */
 	list_for_each_entry ( child, &settings->children, siblings ) {
-		if ( ( ret = fetch_setting_and_origin ( child, setting, origin,
-							data, len ) ) >= 0 )
+		if ( ( ret = fetch_setting ( child, setting, origin, fetched,
+					     data, len ) ) >= 0 )
 			return ret;
 	}
 
@@ -664,52 +679,53 @@ static int fetch_setting_and_origin ( struct settings *settings,
 }
 
 /**
- * Fetch value of setting
+ * Fetch allocated copy of setting
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
- * @v data		Buffer to fill with setting data
- * @v len		Length of buffer
- * @ret len		Length of setting data, or negative error
+ * @v origin		Origin of setting to fill in, or NULL
+ * @v fetched		Fetched setting to fill in, or NULL
+ * @v data		Buffer to allocate and fill with setting data
+ * @v alloc		Allocation function
+ * @ret len		Length of setting, or negative error
  *
- * The actual length of the setting will be returned even if
- * the buffer was too small.
+ * The caller is responsible for eventually freeing the allocated
+ * buffer.
  */
-int fetch_setting ( struct settings *settings, struct setting *setting,
-		    void *data, size_t len ) {
-	return fetch_setting_and_origin ( settings, setting, NULL, data, len );
-}
+static int fetch_setting_alloc ( struct settings *settings,
+				 const struct setting *setting,
+				 struct settings **origin,
+				 struct setting *fetched,
+				 void **data,
+				 void * ( * alloc ) ( size_t len ) ) {
+	struct settings *tmp_origin;
+	struct setting tmp_fetched;
+	int len;
+	int check_len;
 
-/**
- * Fetch origin of setting
- *
- * @v settings		Settings block, or NULL to search all blocks
- * @v setting		Setting to fetch
- * @ret origin		Origin of setting, or NULL if not found
- *
- * This function can also be used as an existence check for the
- * setting.
- */
-struct settings * fetch_setting_origin ( struct settings *settings,
-					 struct setting *setting ) {
-	struct settings *origin;
+	/* Use local buffers if necessary */
+	if ( ! origin )
+		origin = &tmp_origin;
+	if ( ! fetched )
+		fetched = &tmp_fetched;
 
-	fetch_setting_and_origin ( settings, setting, &origin, NULL, 0 );
-	return origin;
-}
+	/* Avoid returning uninitialised data on error */
+	*data = NULL;
 
-/**
- * Fetch length of setting
- *
- * @v settings		Settings block, or NULL to search all blocks
- * @v setting		Setting to fetch
- * @ret len		Length of setting data, or negative error
- *
- * This function can also be used as an existence check for the
- * setting.
- */
-int fetch_setting_len ( struct settings *settings, struct setting *setting ) {
-	return fetch_setting ( settings, setting, NULL, 0 );
+	/* Check existence, and fetch setting length */
+	len = fetch_setting ( settings, setting, origin, fetched, NULL, 0 );
+	if ( len < 0 )
+		return len;
+
+	/* Allocate buffer */
+	*data = alloc ( len );
+	if ( ! *data )
+		return -ENOMEM;
+
+	/* Fetch setting value */
+	check_len = fetch_setting ( *origin, fetched, NULL, NULL, *data, len );
+	assert ( check_len == len );
+	return len;
 }
 
 /**
@@ -717,34 +733,55 @@ int fetch_setting_len ( struct settings *settings, struct setting *setting ) {
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
+ * @v origin		Origin of setting to fill in, or NULL
+ * @v fetched		Fetched setting to fill in, or NULL
+ * @v data		Buffer to allocate and fill with setting data
+ * @ret len		Length of setting, or negative error
+ *
+ * The caller is responsible for eventually freeing the allocated
+ * buffer.
+ */
+int fetch_setting_copy ( struct settings *settings,
+			 const struct setting *setting,
+			 struct settings **origin, struct setting *fetched,
+			 void **data ) {
+
+	return fetch_setting_alloc ( settings, setting, origin, fetched,
+				     data, malloc );
+}
+
+/**
+ * Fetch value of setting
+ *
+ * @v settings		Settings block, or NULL to search all blocks
+ * @v setting		Setting to fetch
+ * @v data		Buffer to fill with setting string data
+ * @v len		Length of buffer
+ * @ret len		Length of setting, or negative error
+ */
+int fetch_raw_setting ( struct settings *settings,
+			const struct setting *setting,
+			void *data, size_t len ) {
+
+	return fetch_setting ( settings, setting, NULL, NULL, data, len );
+}
+
+/**
+ * Fetch value of setting
+ *
+ * @v settings		Settings block, or NULL to search all blocks
+ * @v setting		Setting to fetch
  * @v data		Buffer to allocate and fill with setting data
  * @ret len		Length of setting, or negative error
  *
  * The caller is responsible for eventually freeing the allocated
  * buffer.
  */
-int fetch_setting_copy ( struct settings *settings, struct setting *setting,
-			 void **data ) {
-	int len;
-	int check_len;
+int fetch_raw_setting_copy ( struct settings *settings,
+			     const struct setting *setting,
+			     void **data ) {
 
-	/* Avoid returning uninitialised data on error */
-	*data = NULL;
-
-	/* Check existence, and fetch setting length */
-	len = fetch_setting_len ( settings, setting );
-	if ( len < 0 )
-		return len;
-
-	/* Allocate buffer */
-	*data = malloc ( len );
-	if ( ! *data )
-		return -ENOMEM;
-
-	/* Fetch setting */
-	check_len = fetch_setting ( settings, setting, *data, len );
-	assert ( check_len == len );
-	return len;
+	return fetch_setting_copy ( settings, setting, NULL, NULL, data );
 }
 
 /**
@@ -760,11 +797,23 @@ int fetch_setting_copy ( struct settings *settings, struct setting *setting,
  * The returned length will be the length of the underlying setting
  * data.
  */
-int fetch_string_setting ( struct settings *settings, struct setting *setting,
+int fetch_string_setting ( struct settings *settings,
+			   const struct setting *setting,
 			   char *data, size_t len ) {
+
 	memset ( data, 0, len );
-	return fetch_setting ( settings, setting, data,
-			       ( ( len > 0 ) ? ( len - 1 ) : 0 ) );
+	return fetch_raw_setting ( settings, setting, data,
+				   ( ( len > 0 ) ? ( len - 1 ) : 0 ) );
+}
+
+/**
+ * Allocate memory for copy of string setting
+ *
+ * @v len		Length of setting
+ * @ret ptr		Allocated memory
+ */
+static void * fetch_string_setting_copy_alloc ( size_t len ) {
+	return zalloc ( len + 1 /* NUL */ );
 }
 
 /**
@@ -779,36 +828,13 @@ int fetch_string_setting ( struct settings *settings, struct setting *setting,
  * The returned length will be the length of the underlying setting
  * data.  The caller is responsible for eventually freeing the
  * allocated buffer.
- *
- * To allow the caller to distinguish between a non-existent setting
- * and an error in allocating memory for the copy, this function will
- * return success (and a NULL buffer pointer) for a non-existent
- * setting.
  */
 int fetch_string_setting_copy ( struct settings *settings,
-				struct setting *setting,
-				char **data ) {
-	int len;
-	int check_len = 0;
+				const struct setting *setting, char **data ) {
 
-	/* Avoid returning uninitialised data on error */
-	*data = NULL;
-
-	/* Fetch setting length, and return success if non-existent */
-	len = fetch_setting_len ( settings, setting );
-	if ( len < 0 )
-		return 0;
-
-	/* Allocate string buffer */
-	*data = malloc ( len + 1 );
-	if ( ! *data )
-		return -ENOMEM;
-
-	/* Fetch setting */
-	check_len = fetch_string_setting ( settings, setting, *data,
-					   ( len + 1 ) );
-	assert ( check_len == len );
-	return len;
+	return fetch_setting_alloc ( settings, setting, NULL, NULL,
+				     ( ( void ** ) data ),
+				     fetch_string_setting_copy_alloc );
 }
 
 /**
@@ -821,12 +847,12 @@ int fetch_string_setting_copy ( struct settings *settings,
  * @ret len		Length of setting, or negative error
  */
 int fetch_ipv4_array_setting ( struct settings *settings,
-			       struct setting *setting,
+			       const struct setting *setting,
 			       struct in_addr *inp, unsigned int count ) {
 	int len;
 
-	len = fetch_setting ( settings, setting, inp,
-			      ( sizeof ( *inp ) * count ) );
+	len = fetch_raw_setting ( settings, setting, inp,
+				  ( sizeof ( *inp ) * count ) );
 	if ( len < 0 )
 		return len;
 	if ( ( len % sizeof ( *inp ) ) != 0 )
@@ -842,8 +868,10 @@ int fetch_ipv4_array_setting ( struct settings *settings,
  * @v inp		IPv4 address to fill in
  * @ret len		Length of setting, or negative error
  */
-int fetch_ipv4_setting ( struct settings *settings, struct setting *setting,
+int fetch_ipv4_setting ( struct settings *settings,
+			 const struct setting *setting,
 			 struct in_addr *inp ) {
+
 	return fetch_ipv4_array_setting ( settings, setting, inp, 1 );
 }
 
@@ -887,7 +915,8 @@ static int numeric_setting_value ( int is_signed, const void *raw, size_t len,
  * @v value		Integer value to fill in
  * @ret len		Length of setting, or negative error
  */
-int fetch_numeric_setting ( struct settings *settings, struct setting *setting,
+int fetch_numeric_setting ( struct settings *settings,
+			    const struct setting *setting,
 			    unsigned long *value, int is_signed ) {
 	unsigned long tmp;
 	int len;
@@ -896,7 +925,7 @@ int fetch_numeric_setting ( struct settings *settings, struct setting *setting,
 	*value = 0;
 
 	/* Fetch raw (network-ordered, variable-length) setting */
-	len = fetch_setting ( settings, setting, &tmp, sizeof ( tmp ) );
+	len = fetch_raw_setting ( settings, setting, &tmp, sizeof ( tmp ) );
 	if ( len < 0 )
 		return len;
 
@@ -912,7 +941,8 @@ int fetch_numeric_setting ( struct settings *settings, struct setting *setting,
  * @v value		Integer value to fill in
  * @ret len		Length of setting, or negative error
  */
-int fetch_int_setting ( struct settings *settings, struct setting *setting,
+int fetch_int_setting ( struct settings *settings,
+			const struct setting *setting,
 			long *value ) {
 
 	return fetch_numeric_setting ( settings, setting,
@@ -927,7 +957,8 @@ int fetch_int_setting ( struct settings *settings, struct setting *setting,
  * @v value		Integer value to fill in
  * @ret len		Length of setting, or negative error
  */
-int fetch_uint_setting ( struct settings *settings, struct setting *setting,
+int fetch_uint_setting ( struct settings *settings,
+			 const struct setting *setting,
 			 unsigned long *value ) {
 
 	return fetch_numeric_setting ( settings, setting, value, 0 );
@@ -940,7 +971,8 @@ int fetch_uint_setting ( struct settings *settings, struct setting *setting,
  * @v setting		Setting to fetch
  * @ret value		Setting value, or zero
  */
-long fetch_intz_setting ( struct settings *settings, struct setting *setting ){
+long fetch_intz_setting ( struct settings *settings,
+			  const struct setting *setting ) {
 	unsigned long value;
 
 	fetch_numeric_setting ( settings, setting, &value, 1 );
@@ -955,7 +987,7 @@ long fetch_intz_setting ( struct settings *settings, struct setting *setting ){
  * @ret value		Setting value, or zero
  */
 unsigned long fetch_uintz_setting ( struct settings *settings,
-				    struct setting *setting ) {
+				    const struct setting *setting ) {
 	unsigned long value;
 
 	fetch_numeric_setting ( settings, setting, &value, 0 );
@@ -970,11 +1002,12 @@ unsigned long fetch_uintz_setting ( struct settings *settings,
  * @v uuid		UUID to fill in
  * @ret len		Length of setting, or negative error
  */
-int fetch_uuid_setting ( struct settings *settings, struct setting *setting,
+int fetch_uuid_setting ( struct settings *settings,
+			 const struct setting *setting,
 			 union uuid *uuid ) {
 	int len;
 
-	len = fetch_setting ( settings, setting, uuid, sizeof ( *uuid ) );
+	len = fetch_raw_setting ( settings, setting, uuid, sizeof ( *uuid ) );
 	if ( len < 0 )
 		return len;
 	if ( len != sizeof ( *uuid ) )
@@ -1005,7 +1038,7 @@ void clear_settings ( struct settings *settings ) {
  * @ret 0		Settings are the same
  * @ret non-zero	Settings are not the same
  */
-int setting_cmp ( struct setting *a, struct setting *b ) {
+int setting_cmp ( const struct setting *a, const struct setting *b ) {
 
 	/* If the settings have tags, compare them */
 	if ( a->tag && ( a->tag == b->tag ) && ( a->scope == b->scope ) )
@@ -1036,7 +1069,7 @@ int setting_cmp ( struct setting *a, struct setting *b ) {
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-int setting_format ( struct setting_type *type, const void *raw,
+int setting_format ( const struct setting_type *type, const void *raw,
 		     size_t raw_len, char *buf, size_t len ) {
 
 	/* Sanity check */
@@ -1055,7 +1088,7 @@ int setting_format ( struct setting_type *type, const void *raw,
  * @v len		Length of buffer
  * @ret len		Length of raw value, or negative error
  */
-int setting_parse ( struct setting_type *type, const char *value,
+int setting_parse ( const struct setting_type *type, const char *value,
 		    void *buf, size_t len ) {
 
 	/* Sanity check */
@@ -1074,7 +1107,7 @@ int setting_parse ( struct setting_type *type, const char *value,
  * @ret value		Numeric value
  * @ret rc		Return status code
  */
-int setting_numerate ( struct setting_type *type, const void *raw,
+int setting_numerate ( const struct setting_type *type, const void *raw,
 		       size_t raw_len, unsigned long *value ) {
 
 	/* Sanity check */
@@ -1093,7 +1126,7 @@ int setting_numerate ( struct setting_type *type, const void *raw,
  * @v len		Length of buffer
  * @ret len		Length of raw value, or negative error
  */
-int setting_denumerate ( struct setting_type *type, unsigned long value,
+int setting_denumerate ( const struct setting_type *type, unsigned long value,
 			 void *buf, size_t len ) {
 
 	/* Sanity check */
@@ -1108,28 +1141,37 @@ int setting_denumerate ( struct setting_type *type, unsigned long value,
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
+ * @v origin		Origin of setting to fill in, or NULL
+ * @v fetched		Fetched setting to fill in, or NULL
  * @v buf		Buffer to contain formatted value
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-int fetchf_setting ( struct settings *settings, struct setting *setting,
+int fetchf_setting ( struct settings *settings, const struct setting *setting,
+		     struct settings **origin, struct setting *fetched,
 		     char *buf, size_t len ) {
+	struct setting tmp_fetched;
 	void *raw;
 	int raw_len;
 	int ret;
 
+	/* Use local buffers if necessary */
+	if ( ! fetched )
+		fetched = &tmp_fetched;
+
 	/* Fetch raw value */
-	raw_len = fetch_setting_copy ( settings, setting, &raw );
+	raw_len = fetch_setting_copy ( settings, setting, origin, fetched,
+				       &raw );
 	if ( raw_len < 0 ) {
 		ret = raw_len;
 		goto err_fetch_copy;
 	}
 
 	/* Sanity check */
-	assert ( setting->type != NULL );
+	assert ( fetched->type != NULL );
 
 	/* Format setting */
-	if ( ( ret = setting_format ( setting->type, raw, raw_len, buf,
+	if ( ( ret = setting_format ( fetched->type, raw, raw_len, buf,
 				      len ) ) < 0 )
 		goto err_format;
 
@@ -1144,22 +1186,34 @@ int fetchf_setting ( struct settings *settings, struct setting *setting,
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
+ * @v origin		Origin of setting to fill in, or NULL
+ * @v fetched		Fetched setting to fill in, or NULL
  * @v value		Buffer to allocate and fill with formatted value
  * @ret len		Length of formatted value, or negative error
  *
  * The caller is responsible for eventually freeing the allocated
  * buffer.
  */
-int fetchf_setting_copy ( struct settings *settings, struct setting *setting,
+int fetchf_setting_copy ( struct settings *settings,
+			  const struct setting *setting,
+			  struct settings **origin, struct setting *fetched,
 			  char **value ) {
+	struct settings *tmp_origin;
+	struct setting tmp_fetched;
 	int len;
 	int check_len;
 
+	/* Use local buffers if necessary */
+	if ( ! origin )
+		origin = &tmp_origin;
+	if ( ! fetched )
+		fetched = &tmp_fetched;
+
 	/* Avoid returning uninitialised data on error */
 	*value = NULL;
 
 	/* Check existence, and fetch formatted value length */
-	len = fetchf_setting ( settings, setting, NULL, 0 );
+	len = fetchf_setting ( settings, setting, origin, fetched, NULL, 0 );
 	if ( len < 0 )
 		return len;
 
@@ -1169,7 +1223,7 @@ int fetchf_setting_copy ( struct settings *settings, struct setting *setting,
 		return -ENOMEM;
 
 	/* Fetch formatted value */
-	check_len = fetchf_setting ( settings, setting, *value,
+	check_len = fetchf_setting ( *origin, fetched, NULL, NULL, *value,
 				     ( len + 1 /* NUL */ ) );
 	assert ( check_len == len );
 	return len;
@@ -1183,7 +1237,7 @@ int fetchf_setting_copy ( struct settings *settings, struct setting *setting,
  * @v value		Formatted setting data, or NULL
  * @ret rc		Return status code
  */
-int storef_setting ( struct settings *settings, struct setting *setting,
+int storef_setting ( struct settings *settings, const struct setting *setting,
 		     const char *value ) {
 	void *raw;
 	int raw_len;
@@ -1231,27 +1285,36 @@ int storef_setting ( struct settings *settings, struct setting *setting,
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
+ * @v origin		Origin of setting to fill in, or NULL
+ * @v fetched		Fetched setting to fill in, or NULL
  * @v value		Numeric value to fill in
  * @ret rc		Return status code
  */
-int fetchn_setting ( struct settings *settings, struct setting *setting,
+int fetchn_setting ( struct settings *settings, const struct setting *setting,
+		     struct settings **origin, struct setting *fetched,
 		     unsigned long *value ) {
+	struct setting tmp_fetched;
 	void *raw;
 	int raw_len;
 	int rc;
 
+	/* Use local buffers if necessary */
+	if ( ! fetched )
+		fetched = &tmp_fetched;
+
 	/* Fetch raw value */
-	raw_len = fetch_setting_copy ( settings, setting, &raw );
+	raw_len = fetch_setting_copy ( settings, setting, origin, fetched,
+				       &raw );
 	if ( raw_len < 0 ) {
 		rc = raw_len;
 		goto err_fetch_copy;
 	}
 
 	/* Sanity check */
-	assert ( setting->type != NULL );
+	assert ( fetched->type != NULL );
 
 	/* Numerate setting */
-	if ( ( rc = setting_numerate ( setting->type, raw, raw_len,
+	if ( ( rc = setting_numerate ( fetched->type, raw, raw_len,
 				       value ) ) < 0 )
 		goto err_numerate;
 
@@ -1269,7 +1332,7 @@ int fetchn_setting ( struct settings *settings, struct setting *setting,
  * @v value		Numeric value
  * @ret rc		Return status code
  */
-int storen_setting ( struct settings *settings, struct setting *setting,
+int storen_setting ( struct settings *settings, const struct setting *setting,
 		     unsigned long value ) {
 	void *raw;
 	int raw_len;
@@ -1357,8 +1420,8 @@ static unsigned int parse_setting_tag ( const char *name ) {
  * @v name		Name
  * @ret type		Setting type, or NULL
  */
-static struct setting_type * find_setting_type ( const char *name ) {
-	struct setting_type *type;
+static const struct setting_type * find_setting_type ( const char *name ) {
+	const struct setting_type *type;
 
 	for_each_table_entry ( type, SETTING_TYPES ) {
 		if ( strcmp ( name, type->name ) == 0 )
@@ -1461,7 +1524,7 @@ int parse_setting_name ( char *name, get_child_settings_t get_child,
  * @v len		Length of buffer
  * @ret len		Length of setting name, or negative error
  */
-int setting_name ( struct settings *settings, struct setting *setting,
+int setting_name ( struct settings *settings, const struct setting *setting,
 		   char *buf, size_t len ) {
 	const char *name;
 
@@ -1487,7 +1550,7 @@ int setting_name ( struct settings *settings, struct setting *setting,
  * @v len		Length of buffer
  * @ret len		Length of raw value, or negative error
  */
-static int parse_string_setting ( struct setting_type *type __unused,
+static int parse_string_setting ( const struct setting_type *type __unused,
 				  const char *value, void *buf, size_t len ) {
 	size_t raw_len = strlen ( value ); /* Exclude terminating NUL */
 
@@ -1509,7 +1572,7 @@ static int parse_string_setting ( struct setting_type *type __unused,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_string_setting ( struct setting_type *type __unused,
+static int format_string_setting ( const struct setting_type *type __unused,
 				   const void *raw, size_t raw_len, char *buf,
 				   size_t len ) {
 
@@ -1523,7 +1586,7 @@ static int format_string_setting ( struct setting_type *type __unused,
 }
 
 /** A string setting type */
-struct setting_type setting_type_string __setting_type = {
+const struct setting_type setting_type_string __setting_type = {
 	.name = "string",
 	.parse = parse_string_setting,
 	.format = format_string_setting,
@@ -1538,7 +1601,7 @@ struct setting_type setting_type_string __setting_type = {
  * @v len		Length of buffer
  * @ret len		Length of raw value, or negative error
  */
-static int parse_uristring_setting ( struct setting_type *type __unused,
+static int parse_uristring_setting ( const struct setting_type *type __unused,
 				     const char *value, void *buf, size_t len ){
 	char tmp[ len + 1 /* NUL */ ];
 	size_t raw_len;
@@ -1564,7 +1627,7 @@ static int parse_uristring_setting ( struct setting_type *type __unused,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_uristring_setting ( struct setting_type *type __unused,
+static int format_uristring_setting ( const struct setting_type *type __unused,
 				      const void *raw, size_t raw_len,
 				      char *buf, size_t len ) {
 	char tmp[ raw_len + 1 /* NUL */ ];
@@ -1578,7 +1641,7 @@ static int format_uristring_setting ( struct setting_type *type __unused,
 }
 
 /** A URI-encoded string setting type */
-struct setting_type setting_type_uristring __setting_type = {
+const struct setting_type setting_type_uristring __setting_type = {
 	.name = "uristring",
 	.parse = parse_uristring_setting,
 	.format = format_uristring_setting,
@@ -1593,7 +1656,7 @@ struct setting_type setting_type_uristring __setting_type = {
  * @v len		Length of buffer
  * @ret len		Length of raw value, or negative error
  */
-static int parse_ipv4_setting ( struct setting_type *type __unused,
+static int parse_ipv4_setting ( const struct setting_type *type __unused,
 				const char *value, void *buf, size_t len ) {
 	struct in_addr ipv4;
 
@@ -1619,7 +1682,7 @@ static int parse_ipv4_setting ( struct setting_type *type __unused,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_ipv4_setting ( struct setting_type *type __unused,
+static int format_ipv4_setting ( const struct setting_type *type __unused,
 				 const void *raw, size_t raw_len, char *buf,
 				 size_t len ) {
 	const struct in_addr *ipv4 = raw;
@@ -1630,7 +1693,7 @@ static int format_ipv4_setting ( struct setting_type *type __unused,
 }
 
 /** An IPv4 address setting type */
-struct setting_type setting_type_ipv4 __setting_type = {
+const struct setting_type setting_type_ipv4 __setting_type = {
 	.name = "ipv4",
 	.parse = parse_ipv4_setting,
 	.format = format_ipv4_setting,
@@ -1685,7 +1748,7 @@ static const char setting_type_int_name[][8] = {
  * @v type		Setting type
  * @ret index		Integer setting type index
  */
-static unsigned int setting_type_int_index ( struct setting_type *type ) {
+static unsigned int setting_type_int_index ( const struct setting_type *type ) {
 
 	return ( ( type->name - setting_type_int_name[0] ) /
 		 sizeof ( setting_type_int_name[0] ) );
@@ -1697,7 +1760,7 @@ static unsigned int setting_type_int_index ( struct setting_type *type ) {
  * @v type		Setting type
  * @ret index		Integer setting type width
  */
-static unsigned int setting_type_int_width ( struct setting_type *type ) {
+static unsigned int setting_type_int_width ( const struct setting_type *type ) {
 
 	return ( 1 << setting_type_int_index ( type ) );
 }
@@ -1708,7 +1771,7 @@ static unsigned int setting_type_int_width ( struct setting_type *type ) {
  * @v type		Setting type
  * @ret is_signed	Integer setting type is signed
  */
-static int setting_type_int_is_signed ( struct setting_type *type ) {
+static int setting_type_int_is_signed ( const struct setting_type *type ) {
 	return ( ( type->name - setting_type_int_name[0] ) & 1 );
 }
 
@@ -1721,7 +1784,7 @@ static int setting_type_int_is_signed ( struct setting_type *type ) {
  * @v len		Length of buffer
  * @ret len		Length of raw value, or negative error
  */
-static int denumerate_int_setting ( struct setting_type *type,
+static int denumerate_int_setting ( const struct setting_type *type,
 				    unsigned long value, void *buf,
 				    size_t len ) {
 	unsigned int size = setting_type_int_width ( type );
@@ -1747,7 +1810,7 @@ static int denumerate_int_setting ( struct setting_type *type,
  * @v value		Numeric value to fill in
  * @ret rc		Return status code
  */
-static int numerate_int_setting ( struct setting_type *type,
+static int numerate_int_setting ( const struct setting_type *type,
 				  const void *raw, size_t raw_len,
 				  unsigned long *value ) {
 	int is_signed = setting_type_int_is_signed ( type );
@@ -1771,8 +1834,8 @@ static int numerate_int_setting ( struct setting_type *type,
  * @v len		Length of buffer
  * @ret len		Length of raw value, or negative error
  */
-static int parse_int_setting ( struct setting_type *type, const char *value,
-			       void *buf, size_t len ) {
+static int parse_int_setting ( const struct setting_type *type,
+			       const char *value, void *buf, size_t len ) {
 	char *endp;
 	unsigned long num_value;
 
@@ -1794,8 +1857,9 @@ static int parse_int_setting ( struct setting_type *type, const char *value,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_int_setting ( struct setting_type *type, const void *raw,
-				size_t raw_len, char *buf, size_t len ) {
+static int format_int_setting ( const struct setting_type *type,
+				const void *raw, size_t raw_len,
+				char *buf, size_t len ) {
 	unsigned long value;
 	int ret;
 
@@ -1817,8 +1881,9 @@ static int format_int_setting ( struct setting_type *type, const void *raw,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_uint_setting ( struct setting_type *type, const void *raw,
-				 size_t raw_len, char *buf, size_t len ) {
+static int format_uint_setting ( const struct setting_type *type,
+				 const void *raw, size_t raw_len,
+				 char *buf, size_t len ) {
 	unsigned long value;
 	int ret;
 
@@ -1859,27 +1924,27 @@ static int format_uint_setting ( struct setting_type *type, const void *raw,
 }
 
 /** A signed 8-bit integer setting type */
-struct setting_type setting_type_int8 __setting_type =
+const struct setting_type setting_type_int8 __setting_type =
 	SETTING_TYPE_INT ( SETTING_TYPE_INT8 );
 
 /** A signed 16-bit integer setting type */
-struct setting_type setting_type_int16 __setting_type =
+const struct setting_type setting_type_int16 __setting_type =
 	SETTING_TYPE_INT ( SETTING_TYPE_INT16 );
 
 /** A signed 32-bit integer setting type */
-struct setting_type setting_type_int32 __setting_type =
+const struct setting_type setting_type_int32 __setting_type =
 	SETTING_TYPE_INT ( SETTING_TYPE_INT32 );
 
 /** An unsigned 8-bit integer setting type */
-struct setting_type setting_type_uint8 __setting_type =
+const struct setting_type setting_type_uint8 __setting_type =
 	SETTING_TYPE_UINT ( SETTING_TYPE_INT8 );
 
 /** An unsigned 16-bit integer setting type */
-struct setting_type setting_type_uint16 __setting_type =
+const struct setting_type setting_type_uint16 __setting_type =
 	SETTING_TYPE_UINT ( SETTING_TYPE_INT16 );
 
 /** An unsigned 32-bit integer setting type */
-struct setting_type setting_type_uint32 __setting_type =
+const struct setting_type setting_type_uint32 __setting_type =
 	SETTING_TYPE_UINT ( SETTING_TYPE_INT32 );
 
 /**
@@ -1918,7 +1983,7 @@ static int format_hex_setting ( const char *delimiter, const void *raw,
  * @v size		Integer size, in bytes
  * @ret len		Length of raw value, or negative error
  */
-static int parse_hex_setting ( struct setting_type *type __unused,
+static int parse_hex_setting ( const struct setting_type *type __unused,
 			       const char *value, void *buf, size_t len ) {
 	return hex_decode ( value, ':', buf, len );
 }
@@ -1933,7 +1998,7 @@ static int parse_hex_setting ( struct setting_type *type __unused,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_hex_colon_setting ( struct setting_type *type __unused,
+static int format_hex_colon_setting ( const struct setting_type *type __unused,
 				      const void *raw, size_t raw_len,
 				      char *buf, size_t len ) {
 	return format_hex_setting ( ":", raw, raw_len, buf, len );
@@ -1949,7 +2014,7 @@ static int format_hex_colon_setting ( struct setting_type *type __unused,
  * @v size		Integer size, in bytes
  * @ret len		Length of raw value, or negative error
  */
-static int parse_hex_hyphen_setting ( struct setting_type *type __unused,
+static int parse_hex_hyphen_setting ( const struct setting_type *type __unused,
 				      const char *value, void *buf,
 				      size_t len ) {
 	return hex_decode ( value, '-', buf, len );
@@ -1965,7 +2030,7 @@ static int parse_hex_hyphen_setting ( struct setting_type *type __unused,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_hex_hyphen_setting ( struct setting_type *type __unused,
+static int format_hex_hyphen_setting ( const struct setting_type *type __unused,
 				       const void *raw, size_t raw_len,
 				       char *buf, size_t len ) {
 	return format_hex_setting ( "-", raw, raw_len, buf, len );
@@ -1981,7 +2046,7 @@ static int format_hex_hyphen_setting ( struct setting_type *type __unused,
  * @v size		Integer size, in bytes
  * @ret len		Length of raw value, or negative error
  */
-static int parse_hex_raw_setting ( struct setting_type *type __unused,
+static int parse_hex_raw_setting ( const struct setting_type *type __unused,
 				   const char *value, void *buf, size_t len ) {
 	return hex_decode ( value, 0, buf, len );
 }
@@ -1996,28 +2061,28 @@ static int parse_hex_raw_setting ( struct setting_type *type __unused,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_hex_raw_setting ( struct setting_type *type __unused,
+static int format_hex_raw_setting ( const struct setting_type *type __unused,
 				    const void *raw, size_t raw_len,
 				    char *buf, size_t len ) {
 	return format_hex_setting ( "", raw, raw_len, buf, len );
 }
 
 /** A hex-string setting (colon-delimited) */
-struct setting_type setting_type_hex __setting_type = {
+const struct setting_type setting_type_hex __setting_type = {
 	.name = "hex",
 	.parse = parse_hex_setting,
 	.format = format_hex_colon_setting,
 };
 
 /** A hex-string setting (hyphen-delimited) */
-struct setting_type setting_type_hexhyp __setting_type = {
+const struct setting_type setting_type_hexhyp __setting_type = {
 	.name = "hexhyp",
 	.parse = parse_hex_hyphen_setting,
 	.format = format_hex_hyphen_setting,
 };
 
 /** A hex-string setting (non-delimited) */
-struct setting_type setting_type_hexraw __setting_type = {
+const struct setting_type setting_type_hexraw __setting_type = {
 	.name = "hexraw",
 	.parse = parse_hex_raw_setting,
 	.format = format_hex_raw_setting,
@@ -2033,7 +2098,7 @@ struct setting_type setting_type_hexraw __setting_type = {
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_uuid_setting ( struct setting_type *type __unused,
+static int format_uuid_setting ( const struct setting_type *type __unused,
 				 const void *raw, size_t raw_len, char *buf,
 				 size_t len ) {
 	const union uuid *uuid = raw;
@@ -2047,7 +2112,7 @@ static int format_uuid_setting ( struct setting_type *type __unused,
 }
 
 /** UUID setting type */
-struct setting_type setting_type_uuid __setting_type = {
+const struct setting_type setting_type_uuid __setting_type = {
 	.name = "uuid",
 	.format = format_uuid_setting,
 };
@@ -2062,7 +2127,7 @@ struct setting_type setting_type_uuid __setting_type = {
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_busdevfn_setting ( struct setting_type *type __unused,
+static int format_busdevfn_setting ( const struct setting_type *type __unused,
 				     const void *raw, size_t raw_len, char *buf,
 				     size_t len ) {
 	unsigned long busdevfn;
@@ -2080,7 +2145,7 @@ static int format_busdevfn_setting ( struct setting_type *type __unused,
 }
 
 /** PCI bus:dev.fn setting type */
-struct setting_type setting_type_busdevfn __setting_type = {
+const struct setting_type setting_type_busdevfn __setting_type = {
 	.name = "busdevfn",
 	.format = format_busdevfn_setting,
 };
@@ -2153,7 +2218,8 @@ char * expand_settings ( const char *string ) {
 			/* Fetch and format setting value.  Ignore
 			 * errors; treat non-existent settings as empty.
 			 */
-			fetchf_setting_copy ( settings, &setting, &value );
+			fetchf_setting_copy ( settings, &setting, NULL, NULL,
+					      &value );
 		}
 
 		/* Construct expanded string and discard old string */
@@ -2177,7 +2243,7 @@ char * expand_settings ( const char *string ) {
  */
 
 /** Hostname setting */
-struct setting hostname_setting __setting ( SETTING_HOST ) = {
+const struct setting hostname_setting __setting ( SETTING_HOST ) = {
 	.name = "hostname",
 	.description = "Host name",
 	.tag = DHCP_HOST_NAME,
@@ -2185,7 +2251,7 @@ struct setting hostname_setting __setting ( SETTING_HOST ) = {
 };
 
 /** Domain name setting */
-struct setting domain_setting __setting ( SETTING_IPv4_EXTRA ) = {
+const struct setting domain_setting __setting ( SETTING_IPv4_EXTRA ) = {
 	.name = "domain",
 	.description = "DNS domain",
 	.tag = DHCP_DOMAIN_NAME,
@@ -2193,7 +2259,7 @@ struct setting domain_setting __setting ( SETTING_IPv4_EXTRA ) = {
 };
 
 /** TFTP server setting */
-struct setting next_server_setting __setting ( SETTING_BOOT ) = {
+const struct setting next_server_setting __setting ( SETTING_BOOT ) = {
 	.name = "next-server",
 	.description = "TFTP server",
 	.tag = DHCP_EB_SIADDR,
@@ -2201,7 +2267,7 @@ struct setting next_server_setting __setting ( SETTING_BOOT ) = {
 };
 
 /** Filename setting */
-struct setting filename_setting __setting ( SETTING_BOOT ) = {
+const struct setting filename_setting __setting ( SETTING_BOOT ) = {
 	.name = "filename",
 	.description = "Boot filename",
 	.tag = DHCP_BOOTFILE_NAME,
@@ -2209,7 +2275,7 @@ struct setting filename_setting __setting ( SETTING_BOOT ) = {
 };
 
 /** Root path setting */
-struct setting root_path_setting __setting ( SETTING_SANBOOT ) = {
+const struct setting root_path_setting __setting ( SETTING_SANBOOT ) = {
 	.name = "root-path",
 	.description = "SAN root path",
 	.tag = DHCP_ROOT_PATH,
@@ -2217,7 +2283,7 @@ struct setting root_path_setting __setting ( SETTING_SANBOOT ) = {
 };
 
 /** Username setting */
-struct setting username_setting __setting ( SETTING_AUTH ) = {
+const struct setting username_setting __setting ( SETTING_AUTH ) = {
 	.name = "username",
 	.description = "User name",
 	.tag = DHCP_EB_USERNAME,
@@ -2225,7 +2291,7 @@ struct setting username_setting __setting ( SETTING_AUTH ) = {
 };
 
 /** Password setting */
-struct setting password_setting __setting ( SETTING_AUTH ) = {
+const struct setting password_setting __setting ( SETTING_AUTH ) = {
 	.name = "password",
 	.description = "Password",
 	.tag = DHCP_EB_PASSWORD,
@@ -2233,7 +2299,7 @@ struct setting password_setting __setting ( SETTING_AUTH ) = {
 };
 
 /** Priority setting */
-struct setting priority_setting __setting ( SETTING_MISC ) = {
+const struct setting priority_setting __setting ( SETTING_MISC ) = {
 	.name = "priority",
 	.description = "Settings priority",
 	.tag = DHCP_EB_PRIORITY,
@@ -2241,7 +2307,7 @@ struct setting priority_setting __setting ( SETTING_MISC ) = {
 };
 
 /** DHCP user class setting */
-struct setting user_class_setting __setting ( SETTING_HOST_EXTRA ) = {
+const struct setting user_class_setting __setting ( SETTING_HOST_EXTRA ) = {
 	.name = "user-class",
 	.description = "DHCP user class",
 	.tag = DHCP_USER_CLASS_ID,
@@ -2256,7 +2322,7 @@ struct setting user_class_setting __setting ( SETTING_HOST_EXTRA ) = {
  */
 
 /** Built-in setting scope */
-struct settings_scope builtin_scope;
+const struct settings_scope builtin_scope;
 
 /**
  * Fetch error number setting
@@ -2277,7 +2343,7 @@ static int errno_fetch ( void *data, size_t len ) {
 }
 
 /** Error number setting */
-struct setting errno_setting __setting ( SETTING_MISC ) = {
+const struct setting errno_setting __setting ( SETTING_MISC ) = {
 	.name = "errno",
 	.description = "Last error",
 	.type = &setting_type_uint32,
@@ -2305,7 +2371,7 @@ static int buildarch_fetch ( void *data, size_t len ) {
 }
 
 /** Build architecture setting */
-struct setting buildarch_setting __setting ( SETTING_MISC ) = {
+const struct setting buildarch_setting __setting ( SETTING_MISC ) = {
 	.name = "buildarch",
 	.description = "Build architecture",
 	.type = &setting_type_string,
@@ -2333,7 +2399,7 @@ static int platform_fetch ( void *data, size_t len ) {
 }
 
 /** Platform setting */
-struct setting platform_setting __setting ( SETTING_MISC ) = {
+const struct setting platform_setting __setting ( SETTING_MISC ) = {
 	.name = "platform",
 	.description = "Platform",
 	.type = &setting_type_string,
@@ -2359,7 +2425,7 @@ static int version_fetch ( void *data, size_t len ) {
 }
 
 /** Version setting */
-struct setting version_setting __setting ( SETTING_MISC ) = {
+const struct setting version_setting __setting ( SETTING_MISC ) = {
 	.name = "version",
 	.description = "Version",
 	.type = &setting_type_string,
@@ -2401,7 +2467,7 @@ static int builtin_fetch ( struct settings *settings __unused,
  * @ret applies		Setting applies within this settings block
  */
 static int builtin_applies ( struct settings *settings __unused,
-			     struct setting *setting ) {
+			     const struct setting *setting ) {
 
 	return ( setting->scope == &builtin_scope );
 }
diff --git a/src/crypto/clientcert.c b/src/crypto/clientcert.c
index 6f6bf1135..b09c880ac 100644
--- a/src/crypto/clientcert.c
+++ b/src/crypto/clientcert.c
@@ -128,8 +128,8 @@ static int clientcert_apply_settings ( void ) {
 
 		/* Fetch new client certificate, if any */
 		free ( cert );
-		if ( ( len = fetch_setting_copy ( NULL, &cert_setting,
-						  &cert ) ) >= 0 ) {
+		if ( ( len = fetch_raw_setting_copy ( NULL, &cert_setting,
+						      &cert ) ) >= 0 ) {
 			client_certificate.data = cert;
 			client_certificate.len = len;
 		}
@@ -140,8 +140,8 @@ static int clientcert_apply_settings ( void ) {
 
 		/* Fetch new client private key, if any */
 		free ( key );
-		if ( ( len = fetch_setting_copy ( NULL, &privkey_setting,
-						  &key ) ) >= 0 ) {
+		if ( ( len = fetch_raw_setting_copy ( NULL, &privkey_setting,
+						      &key ) ) >= 0 ) {
 			client_private_key.data = key;
 			client_private_key.len = len;
 		}
diff --git a/src/crypto/rootcert.c b/src/crypto/rootcert.c
index 2aa313340..cfeabb815 100644
--- a/src/crypto/rootcert.c
+++ b/src/crypto/rootcert.c
@@ -100,8 +100,8 @@ static void rootcert_init ( void ) {
 		/* Fetch copy of "trust" setting, if it exists.  This
 		 * memory will never be freed.
 		 */
-		if ( ( len = fetch_setting_copy ( NULL, &trust_setting,
-						  &external ) ) >= 0 ) {
+		if ( ( len = fetch_raw_setting_copy ( NULL, &trust_setting,
+						      &external ) ) >= 0 ) {
 			root_certificates.fingerprints = external;
 			root_certificates.count = ( len / FINGERPRINT_LEN );
 		}
diff --git a/src/drivers/block/ibft.c b/src/drivers/block/ibft.c
index 75ca51a9c..0700f8c4f 100644
--- a/src/drivers/block/ibft.c
+++ b/src/drivers/block/ibft.c
@@ -107,7 +107,7 @@ static void ibft_set_ipaddr ( struct ibft_ipaddr *ipaddr, struct in_addr in ) {
  * @v count		Maximum number of IP addresses
  */
 static void ibft_set_ipaddr_setting ( struct ibft_ipaddr *ipaddr,
-				      struct setting *setting,
+				      const struct setting *setting,
 				      unsigned int count ) {
 	struct in_addr in[count];
 	unsigned int i;
@@ -183,11 +183,13 @@ static int ibft_set_string ( struct ibft_strings *strings,
  */
 static int ibft_set_string_setting ( struct ibft_strings *strings,
 				     struct ibft_string *string,
-				     struct setting *setting ) {
+				     const struct setting *setting ) {
+	struct settings *origin;
+	struct setting fetched;
 	int len;
 	char *dest;
 
-	len = fetch_setting_len ( NULL, setting );
+	len = fetch_setting ( NULL, setting, &origin, &fetched, NULL, 0 );
 	if ( len < 0 ) {
 		string->offset = 0;
 		string->len = 0;
@@ -197,7 +199,7 @@ static int ibft_set_string_setting ( struct ibft_strings *strings,
 	dest = ibft_alloc_string ( strings, string, len );
 	if ( ! dest )
 		return -ENOBUFS;
-	fetch_string_setting ( NULL, setting, dest, ( len + 1 ) );
+	fetch_string_setting ( origin, &fetched, dest, ( len + 1 ));
 
 	return 0;
 }
diff --git a/src/drivers/bus/pci_settings.c b/src/drivers/bus/pci_settings.c
index a4d7b9334..db20452e0 100644
--- a/src/drivers/bus/pci_settings.c
+++ b/src/drivers/bus/pci_settings.c
@@ -32,7 +32,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
  */
 
 /** PCI device settings scope */
-static struct settings_scope pci_settings_scope;
+static const struct settings_scope pci_settings_scope;
 
 /**
  * Check applicability of PCI device setting
@@ -42,7 +42,7 @@ static struct settings_scope pci_settings_scope;
  * @ret applies		Setting applies within this settings block
  */
 static int pci_settings_applies ( struct settings *settings __unused,
-				  struct setting *setting ) {
+				  const struct setting *setting ) {
 
 	return ( setting->scope == &pci_settings_scope );
 }
diff --git a/src/drivers/net/phantom/phantom.c b/src/drivers/net/phantom/phantom.c
index 7f2fe0b63..e70ded08c 100644
--- a/src/drivers/net/phantom/phantom.c
+++ b/src/drivers/net/phantom/phantom.c
@@ -1455,7 +1455,7 @@ static struct net_device_operations phantom_operations = {
  */
 
 /** Phantom CLP settings scope */
-static struct settings_scope phantom_settings_scope;
+static const struct settings_scope phantom_settings_scope;
 
 /** Phantom CLP data
  *
@@ -1656,7 +1656,7 @@ static int phantom_clp_fetch ( struct phantom_nic *phantom, unsigned int port,
 /** A Phantom CLP setting */
 struct phantom_clp_setting {
 	/** iPXE setting */
-	struct setting *setting;
+	const struct setting *setting;
 	/** Setting number */
 	unsigned int clp_setting;
 };
@@ -1673,7 +1673,8 @@ static struct phantom_clp_setting clp_settings[] = {
  * @v clp_setting	Setting number, or 0 if not found
  */
 static unsigned int
-phantom_clp_setting ( struct phantom_nic *phantom, struct setting *setting ) {
+phantom_clp_setting ( struct phantom_nic *phantom,
+		      const struct setting *setting ) {
 	struct phantom_clp_setting *clp_setting;
 	unsigned int i;
 
@@ -1703,7 +1704,7 @@ phantom_clp_setting ( struct phantom_nic *phantom, struct setting *setting ) {
  * @ret applies		Setting applies within this settings block
  */
 static int phantom_setting_applies ( struct settings *settings,
-				     struct setting *setting ) {
+				     const struct setting *setting ) {
 	struct phantom_nic *phantom =
 		container_of ( settings, struct phantom_nic, settings );
 	unsigned int clp_setting;
@@ -1723,7 +1724,7 @@ static int phantom_setting_applies ( struct settings *settings,
  * @ret rc		Return status code
  */
 static int phantom_store_setting ( struct settings *settings,
-				   struct setting *setting,
+				   const struct setting *setting,
 				   const void *data, size_t len ) {
 	struct phantom_nic *phantom =
 		container_of ( settings, struct phantom_nic, settings );
diff --git a/src/hci/commands/nvo_cmd.c b/src/hci/commands/nvo_cmd.c
index 3fd684d04..e63dab08e 100644
--- a/src/hci/commands/nvo_cmd.c
+++ b/src/hci/commands/nvo_cmd.c
@@ -58,8 +58,10 @@ static int show_exec ( int argc, char **argv ) {
 	struct show_options opts;
 	struct named_setting setting;
 	struct settings *origin;
+	struct setting fetched;
 	char name_buf[32];
 	char *value;
+	int len;
 	int rc;
 
 	/* Parse options */
@@ -71,19 +73,16 @@ static int show_exec ( int argc, char **argv ) {
 		goto err_parse_setting;
 
 	/* Fetch formatted setting value */
-	if ( ( rc = fetchf_setting_copy ( setting.settings, &setting.setting,
-					  &value ) ) < 0 ) {
+	if ( ( len = fetchf_setting_copy ( setting.settings, &setting.setting,
+					   &origin, &fetched, &value ) ) < 0 ) {
+		rc = len;
 		printf ( "Could not find \"%s\": %s\n",
 			 setting.setting.name, strerror ( rc ) );
 		goto err_fetchf;
 	}
 
-	/* Fetch origin and format fully-qualified name */
-	origin = fetch_setting_origin ( setting.settings, &setting.setting );
-	assert ( origin != NULL );
-	setting_name ( origin, &setting.setting, name_buf, sizeof ( name_buf ));
-
 	/* Print setting value */
+	setting_name ( origin, &fetched, name_buf, sizeof ( name_buf ) );
 	printf ( "%s = %s\n", name_buf, value );
 
 	/* Success */
@@ -234,7 +233,8 @@ static int read_value ( struct named_setting *setting, char **args __unused,
 	/* Read existing value, treating errors as equivalent to an
 	 * empty initial setting.
 	 */
-	fetchf_setting_copy ( setting->settings, &setting->setting, &existing );
+	fetchf_setting_copy ( setting->settings, &setting->setting,
+			      NULL, &setting->setting, &existing );
 
 	/* Read new value */
 	if ( ( rc = readline_history ( NULL, existing, NULL, value ) ) != 0 )
@@ -294,12 +294,11 @@ static int inc_exec ( int argc, char **argv ) {
 	     ( ( rc = parse_integer ( argv[ optind + 1 ], &increment ) ) != 0))
 		goto err_parse_increment;
 
-	/* Fetch existing setting value, if any, allowing for the fact
-	 * that numeric settings are big-endian and variable-length.
+	/* Read existing value, treating errors as equivalent to a
+	 * zero-valued :int32 initial setting.
 	 */
 	if ( ( rc = fetchn_setting ( setting.settings, &setting.setting,
-				     &value ) ) != 0 ) {
-		/* Treat as a non-existent :int32 setting with a zero value */
+				     NULL, &setting.setting, &value ) ) != 0 ) {
 		value = 0;
 		if ( ! setting.setting.type )
 			setting.setting.type = &setting_type_int32;
diff --git a/src/hci/commands/pci_cmd.c b/src/hci/commands/pci_cmd.c
index f2d695697..f5145fb35 100644
--- a/src/hci/commands/pci_cmd.c
+++ b/src/hci/commands/pci_cmd.c
@@ -68,8 +68,8 @@ static int pciscan_exec ( int argc, char **argv ) {
 		goto err_parse_setting;
 
 	/* Determine starting bus:dev.fn address */
-	if ( ( len = fetch_uint_setting ( setting.settings, &setting.setting,
-					  &prev ) ) < 0 ) {
+	if ( ( len = fetchn_setting ( setting.settings, &setting.setting,
+				      NULL, &setting.setting, &prev ) ) < 0 ) {
 		/* Setting not yet defined: start searching from 00:00.0 */
 		prev = 0;
 	} else {
diff --git a/src/hci/tui/settings_ui.c b/src/hci/tui/settings_ui.c
index 77ef8108e..8fe13ad8b 100644
--- a/src/hci/tui/settings_ui.c
+++ b/src/hci/tui/settings_ui.c
@@ -72,11 +72,16 @@ struct setting_row_widget {
 	 * Valid only for rows that lead to new settings blocks.
 	 */
 	struct settings *settings;
+	/** Configuration setting origin
+	 *
+	 * Valid only for rows that represent individual settings.
+	 */
+	struct settings *origin;
 	/** Configuration setting
 	 *
 	 * Valid only for rows that represent individual settings.
 	 */
-	struct setting *setting;
+	struct setting setting;
 	/** Screen row */
 	unsigned int row;
 	/** Screen column */
@@ -85,8 +90,6 @@ struct setting_row_widget {
 	struct edit_box editbox;
 	/** Editing in progress flag */
 	int editing;
-	/** Setting originates from this block flag */
-	int originates_here;
 	/** Buffer for setting's value */
 	char value[256]; /* enough size for a DHCP string */
 };
@@ -115,7 +118,6 @@ struct setting_widget {
 static unsigned int select_setting_row ( struct setting_widget *widget,
 					 unsigned int index ) {
 	struct settings *settings;
-	struct settings *origin;
 	struct setting *setting;
 	unsigned int count = 0;
 
@@ -147,18 +149,13 @@ static unsigned int select_setting_row ( struct setting_widget *widget,
 		if ( ! setting_applies ( widget->settings, setting ) )
 			continue;
 		if ( count++ == index ) {
-			widget->row.setting = setting;
 
-			/* Read current setting value */
-			fetchf_setting ( widget->settings, widget->row.setting,
+			/* Read current setting value and origin */
+			fetchf_setting ( widget->settings, setting,
+					 &widget->row.origin,
+					 &widget->row.setting,
 					 widget->row.value,
 					 sizeof ( widget->row.value ) );
-
-			/* Check setting's origin */
-			origin = fetch_setting_origin ( widget->settings,
-							widget->row.setting );
-			widget->row.originates_here =
-				( origin == widget->settings );
 		}
 	}
 
@@ -209,7 +206,7 @@ static void draw_setting_row ( struct setting_widget *widget ) {
 
 		/* Construct dot-padded name */
 		memset ( text.name, '.', sizeof ( text.name ) );
-		string_copy ( text.name, widget->row.setting->name,
+		string_copy ( text.name, widget->row.setting.name,
 			      sizeof ( text.name ) );
 
 		/* Construct space-padded value */
@@ -222,8 +219,10 @@ static void draw_setting_row ( struct setting_widget *widget ) {
 	}
 
 	/* Print row */
-	if ( widget->row.originates_here || widget->row.settings )
+	if ( ( widget->row.origin == widget->settings ) ||
+	     ( widget->row.settings != NULL ) ) {
 		attron ( A_BOLD );
+	}
 	mvprintw ( widget->row.row, widget->row.col, "%s", text.start );
 	attroff ( A_BOLD );
 	move ( widget->row.row, widget->row.col + curs_offset );
@@ -237,7 +236,7 @@ static void draw_setting_row ( struct setting_widget *widget ) {
  * @ret key		Key returned to application, or zero
  */
 static int edit_setting ( struct setting_widget *widget, int key ) {
-	assert ( widget->row.setting != NULL );
+	assert ( widget->row.setting.name != NULL );
 	widget->row.editing = 1;
 	return edit_editbox ( &widget->row.editbox, key );
 }
@@ -248,8 +247,8 @@ static int edit_setting ( struct setting_widget *widget, int key ) {
  * @v widget		Setting widget
  */
 static int save_setting ( struct setting_widget *widget ) {
-	assert ( widget->row.setting != NULL );
-	return storef_setting ( widget->settings, widget->row.setting,
+	assert ( widget->row.setting.name != NULL );
+	return storef_setting ( widget->settings, &widget->row.setting,
 				widget->row.value );
 }
 
@@ -344,28 +343,26 @@ static void draw_title_row ( struct setting_widget *widget ) {
  * @v widget		Setting widget
  */
 static void draw_info_row ( struct setting_widget *widget ) {
-	struct settings *origin;
 	char buf[32];
 
 	/* Draw nothing unless this row represents a setting */
 	clearmsg ( INFO_ROW );
 	clearmsg ( INFO_ROW + 1 );
-	if ( ! widget->row.setting )
+	if ( ! widget->row.setting.name )
 		return;
 
 	/* Determine a suitable setting name */
-	origin = fetch_setting_origin ( widget->settings, widget->row.setting );
-	if ( ! origin )
-		origin = widget->settings;
-	setting_name ( origin, widget->row.setting, buf, sizeof ( buf ) );
+	setting_name ( ( widget->row.origin ?
+			 widget->row.origin : widget->settings ),
+		       &widget->row.setting, buf, sizeof ( buf ) );
 
 	/* Draw row */
 	attron ( A_BOLD );
-	msg ( INFO_ROW, "%s - %s", buf, widget->row.setting->description );
+	msg ( INFO_ROW, "%s - %s", buf, widget->row.setting.description );
 	attroff ( A_BOLD );
 	color_set ( CPAIR_URL, NULL );
 	msg ( ( INFO_ROW + 1 ), "http://ipxe.org/cfg/%s",
-	      widget->row.setting->name );
+	      widget->row.setting.name );
 	color_set ( CPAIR_NORMAL, NULL );
 }
 
@@ -384,7 +381,7 @@ static void draw_instruction_row ( struct setting_widget *widget ) {
 	} else {
 		msg ( INSTRUCTION_ROW,
 		      "%sCtrl-X - exit configuration utility",
-		      ( widget->row.originates_here ?
+		      ( ( widget->row.origin == widget->settings ) ?
 			"Ctrl-D - delete setting" INSTRUCTION_PAD : "" ) );
 	}
 }
@@ -479,7 +476,7 @@ static int main_loop ( struct settings *settings ) {
 		if ( widget.row.editing ) {
 
 			/* Sanity check */
-			assert ( widget.row.setting != NULL );
+			assert ( widget.row.setting.name != NULL );
 
 			/* Redraw edit box */
 			color_set ( CPAIR_EDIT, NULL );
@@ -530,10 +527,10 @@ static int main_loop ( struct settings *settings ) {
 				move = +widget.num_rows;
 				break;
 			case CTRL_D:
-				if ( ! widget.row.setting )
+				if ( ! widget.row.setting.name )
 					break;
 				if ( ( rc = delete_setting ( widget.settings,
-						widget.row.setting ) ) != 0 ) {
+						&widget.row.setting ) ) != 0 ) {
 					alert ( " %s ", strerror ( rc ) );
 				}
 				select_setting_row ( &widget, widget.current );
@@ -550,7 +547,7 @@ static int main_loop ( struct settings *settings ) {
 				}
 				/* Fall through */
 			default:
-				if ( widget.row.setting ) {
+				if ( widget.row.setting.name ) {
 					edit_setting ( &widget, key );
 					redraw = 1;
 				}
diff --git a/src/include/ipxe/net80211.h b/src/include/ipxe/net80211.h
index dd8bd2288..d752382ad 100644
--- a/src/include/ipxe/net80211.h
+++ b/src/include/ipxe/net80211.h
@@ -1093,7 +1093,7 @@ struct net80211_wlan
 
 
 /** 802.11 encryption key setting */
-extern struct setting net80211_key_setting __setting ( SETTING_NETDEV_EXTRA );
+extern const struct setting net80211_key_setting __setting ( SETTING_NETDEV_EXTRA );
 
 
 /**
diff --git a/src/include/ipxe/nvo.h b/src/include/ipxe/nvo.h
index 487f8b3f2..1a629da78 100644
--- a/src/include/ipxe/nvo.h
+++ b/src/include/ipxe/nvo.h
@@ -45,7 +45,8 @@ struct nvo_block {
 /** Name of non-volatile options settings block */
 #define NVO_SETTINGS_NAME "nvo"
 
-extern int nvo_applies ( struct settings *settings, struct setting *setting );
+extern int nvo_applies ( struct settings *settings,
+			 const struct setting *setting );
 extern void nvo_init ( struct nvo_block *nvo, struct nvs_device *nvs,
 		       size_t address, size_t len,
 		       int ( * resize ) ( struct nvo_block *nvo, size_t len ),
diff --git a/src/include/ipxe/settings.h b/src/include/ipxe/settings.h
index a6dfd2102..25665ca78 100644
--- a/src/include/ipxe/settings.h
+++ b/src/include/ipxe/settings.h
@@ -32,7 +32,7 @@ struct setting {
 	 * This identifies the type of setting (e.g. string, IPv4
 	 * address, etc.).
 	 */
-	struct setting_type *type;
+	const struct setting_type *type;
 	/** Setting tag, if applicable
 	 *
 	 * The setting tag is a numerical description of the setting
@@ -45,7 +45,7 @@ struct setting {
 	 * For historic reasons, a NULL scope with a non-zero tag
 	 * indicates a DHCPv4 option setting.
 	 */
-	struct settings_scope *scope;
+	const struct settings_scope *scope;
 };
 
 /** Configuration setting table */
@@ -90,7 +90,7 @@ struct settings_operations {
 	 * @ret applies		Setting applies within this settings block
 	 */
 	int ( * applies ) ( struct settings *settings,
-			    struct setting *setting );
+			    const struct setting *setting );
 	/** Store value of setting
 	 *
 	 * @v settings		Settings block
@@ -99,7 +99,8 @@ struct settings_operations {
 	 * @v len		Length of setting data
 	 * @ret rc		Return status code
 	 */
-	int ( * store ) ( struct settings *settings, struct setting *setting,
+	int ( * store ) ( struct settings *settings,
+			  const struct setting *setting,
 			  const void *data, size_t len );
 	/** Fetch value of setting
 	 *
@@ -136,7 +137,7 @@ struct settings {
 	/** Settings block operations */
 	struct settings_operations *op;
 	/** Default scope for numerical settings constructed for this block */
-	struct settings_scope *default_scope;
+	const struct settings_scope *default_scope;
 };
 
 /**
@@ -193,7 +194,7 @@ struct setting_type {
 	 * @v len		Length of buffer
 	 * @ret len		Length of raw value, or negative error
 	 */
-	int ( * parse ) ( struct setting_type *type, const char *value,
+	int ( * parse ) ( const struct setting_type *type, const char *value,
 			  void *buf, size_t len );
 	/** Format setting value as a string
 	 *
@@ -204,7 +205,7 @@ struct setting_type {
 	 * @v len		Length of buffer
 	 * @ret len		Length of formatted value, or negative error
 	 */
-	int ( * format ) ( struct setting_type *type, const void *raw,
+	int ( * format ) ( const struct setting_type *type, const void *raw,
 			   size_t raw_len, char *buf, size_t len );
 	/** Convert number to setting value
 	 *
@@ -214,7 +215,8 @@ struct setting_type {
 	 * @v len		Length of buffer
 	 * @ret len		Length of raw value, or negative error
 	 */
-	int ( * denumerate ) ( struct setting_type *type, unsigned long value,
+	int ( * denumerate ) ( const struct setting_type *type,
+			       unsigned long value,
 			       void *buf, size_t len );
 	/** Convert setting value to number
 	 *
@@ -224,7 +226,7 @@ struct setting_type {
 	 * @v value		Numeric value to fill in
 	 * @ret rc		Return status code
 	 */
-	int ( * numerate ) ( struct setting_type *type, const void *raw,
+	int ( * numerate ) ( const struct setting_type *type, const void *raw,
 			     size_t raw_len, unsigned long *value );
 };
 
@@ -256,7 +258,7 @@ struct settings_applicator {
 /** A built-in setting */
 struct builtin_setting {
 	/** Setting */
-	struct setting *setting;
+	const struct setting *setting;
 	/** Fetch setting value
 	 *
 	 * @v data		Buffer to fill with setting data
@@ -273,7 +275,7 @@ struct builtin_setting {
 #define __builtin_setting __table_entry ( BUILTIN_SETTINGS, 01 )
 
 /** Built-in setting scope */
-extern struct settings_scope builtin_scope;
+extern const struct settings_scope builtin_scope;
 
 /**
  * A generic settings block
@@ -291,7 +293,7 @@ typedef struct settings * ( *get_child_settings_t ) ( struct settings *settings,
 						      const char *name );
 extern struct settings_operations generic_settings_operations;
 extern int generic_settings_store ( struct settings *settings,
-				    struct setting *setting,
+				    const struct setting *setting,
 				    const void *data, size_t len );
 extern int generic_settings_fetch ( struct settings *settings,
 				    struct setting *setting,
@@ -304,42 +306,50 @@ extern void unregister_settings ( struct settings *settings );
 
 extern struct settings * settings_target ( struct settings *settings );
 extern int setting_applies ( struct settings *settings,
-			     struct setting *setting );
-extern int store_setting ( struct settings *settings, struct setting *setting,
+			     const struct setting *setting );
+extern int store_setting ( struct settings *settings,
+			   const struct setting *setting,
 			   const void *data, size_t len );
-extern int fetch_setting ( struct settings *settings, struct setting *setting,
+extern int fetch_setting ( struct settings *settings,
+			   const struct setting *setting,
+			   struct settings **origin, struct setting *fetched,
 			   void *data, size_t len );
-extern struct settings * fetch_setting_origin ( struct settings *settings,
-						struct setting *setting );
-extern int fetch_setting_len ( struct settings *settings,
-			       struct setting *setting );
 extern int fetch_setting_copy ( struct settings *settings,
-				struct setting *setting, void **data );
+				const struct setting *setting,
+				struct settings **origin,
+				struct setting *fetched, void **data );
+extern int fetch_raw_setting ( struct settings *settings,
+			       const struct setting *setting,
+			       void *data, size_t len );
+extern int fetch_raw_setting_copy ( struct settings *settings,
+				    const struct setting *setting,
+				    void **data );
 extern int fetch_string_setting ( struct settings *settings,
-				  struct setting *setting,
+				  const struct setting *setting,
 				  char *data, size_t len );
 extern int fetch_string_setting_copy ( struct settings *settings,
-				       struct setting *setting,
+				       const struct setting *setting,
 				       char **data );
 extern int fetch_ipv4_array_setting ( struct settings *settings,
-				      struct setting *setting,
-				      struct in_addr *inp,
-				      unsigned int count );
+				      const struct setting *setting,
+				      struct in_addr *inp, unsigned int count );
 extern int fetch_ipv4_setting ( struct settings *settings,
-				struct setting *setting, struct in_addr *inp );
+				const struct setting *setting,
+				struct in_addr *inp );
 extern int fetch_int_setting ( struct settings *settings,
-			       struct setting *setting, long *value );
+			       const struct setting *setting, long *value );
 extern int fetch_uint_setting ( struct settings *settings,
-				struct setting *setting,
+				const struct setting *setting,
 				unsigned long *value );
 extern long fetch_intz_setting ( struct settings *settings,
-				 struct setting *setting );
+				 const struct setting *setting );
 extern unsigned long fetch_uintz_setting ( struct settings *settings,
-					   struct setting *setting );
+					   const struct setting *setting );
 extern int fetch_uuid_setting ( struct settings *settings,
-				struct setting *setting, union uuid *uuid );
+				const struct setting *setting,
+				union uuid *uuid );
 extern void clear_settings ( struct settings *settings );
-extern int setting_cmp ( struct setting *a, struct setting *b );
+extern int setting_cmp ( const struct setting *a, const struct setting *b );
 
 extern struct settings * find_child_settings ( struct settings *parent,
 					       const char *name );
@@ -351,61 +361,68 @@ extern struct setting * find_setting ( const char *name );
 extern int parse_setting_name ( char *name, get_child_settings_t get_child,
 				struct settings **settings,
 				struct setting *setting );
-extern int setting_name ( struct settings *settings, struct setting *setting,
+extern int setting_name ( struct settings *settings,
+			  const struct setting *setting,
 			  char *buf, size_t len );
-extern int setting_format ( struct setting_type *type, const void *raw,
+extern int setting_format ( const struct setting_type *type, const void *raw,
 			    size_t raw_len, char *buf, size_t len );
-extern int setting_parse ( struct setting_type *type, const char *value,
+extern int setting_parse ( const struct setting_type *type, const char *value,
 			   void *buf, size_t len );
-extern int setting_numerate ( struct setting_type *type, const void *raw,
+extern int setting_numerate ( const struct setting_type *type, const void *raw,
 			      size_t raw_len, unsigned long *value );
-extern int setting_denumerate ( struct setting_type *type, unsigned long value,
-				void *buf, size_t len );
-extern int fetchf_setting ( struct settings *settings, struct setting *setting,
+extern int setting_denumerate ( const struct setting_type *type,
+				unsigned long value, void *buf, size_t len );
+extern int fetchf_setting ( struct settings *settings,
+			    const struct setting *setting,
+			    struct settings **origin, struct setting *fetched,
 			    char *buf, size_t len );
 extern int fetchf_setting_copy ( struct settings *settings,
-				 struct setting *setting, char **value );
+				 const struct setting *setting,
+				 struct settings **origin,
+				 struct setting *fetched, char **value );
 extern int storef_setting ( struct settings *settings,
-			    struct setting *setting,
-			    const char *value );
-extern int fetchn_setting ( struct settings *settings, struct setting *setting,
+			    const struct setting *setting, const char *value );
+extern int fetchn_setting ( struct settings *settings,
+			    const struct setting *setting,
+			    struct settings **origin, struct setting *fetched,
 			    unsigned long *value );
-extern int storen_setting ( struct settings *settings, struct setting *setting,
+extern int storen_setting ( struct settings *settings,
+			    const struct setting *setting,
 			    unsigned long value );
 extern char * expand_settings ( const char *string );
 
-extern struct setting_type setting_type_string __setting_type;
-extern struct setting_type setting_type_uristring __setting_type;
-extern struct setting_type setting_type_ipv4 __setting_type;
-extern struct setting_type setting_type_ipv6 __setting_type;
-extern struct setting_type setting_type_int8 __setting_type;
-extern struct setting_type setting_type_int16 __setting_type;
-extern struct setting_type setting_type_int32 __setting_type;
-extern struct setting_type setting_type_uint8 __setting_type;
-extern struct setting_type setting_type_uint16 __setting_type;
-extern struct setting_type setting_type_uint32 __setting_type;
-extern struct setting_type setting_type_hex __setting_type;
-extern struct setting_type setting_type_hexhyp __setting_type;
-extern struct setting_type setting_type_hexraw __setting_type;
-extern struct setting_type setting_type_uuid __setting_type;
-extern struct setting_type setting_type_busdevfn __setting_type;
+extern const struct setting_type setting_type_string __setting_type;
+extern const struct setting_type setting_type_uristring __setting_type;
+extern const struct setting_type setting_type_ipv4 __setting_type;
+extern const struct setting_type setting_type_ipv6 __setting_type;
+extern const struct setting_type setting_type_int8 __setting_type;
+extern const struct setting_type setting_type_int16 __setting_type;
+extern const struct setting_type setting_type_int32 __setting_type;
+extern const struct setting_type setting_type_uint8 __setting_type;
+extern const struct setting_type setting_type_uint16 __setting_type;
+extern const struct setting_type setting_type_uint32 __setting_type;
+extern const struct setting_type setting_type_hex __setting_type;
+extern const struct setting_type setting_type_hexhyp __setting_type;
+extern const struct setting_type setting_type_hexraw __setting_type;
+extern const struct setting_type setting_type_uuid __setting_type;
+extern const struct setting_type setting_type_busdevfn __setting_type;
 
-extern struct setting ip_setting __setting ( SETTING_IPv4 );
-extern struct setting netmask_setting __setting ( SETTING_IPv4 );
-extern struct setting gateway_setting __setting ( SETTING_IPv4 );
-extern struct setting dns_setting __setting ( SETTING_IPv4_EXTRA );
-extern struct setting hostname_setting __setting ( SETTING_HOST );
-extern struct setting domain_setting __setting ( SETTING_IPv4_EXTRA );
-extern struct setting filename_setting __setting ( SETTING_BOOT );
-extern struct setting root_path_setting __setting ( SETTING_SANBOOT );
-extern struct setting username_setting __setting ( SETTING_AUTH );
-extern struct setting password_setting __setting ( SETTING_AUTH );
-extern struct setting priority_setting __setting ( SETTING_MISC );
-extern struct setting uuid_setting __setting ( SETTING_HOST );
-extern struct setting next_server_setting __setting ( SETTING_BOOT );
-extern struct setting mac_setting __setting ( SETTING_NETDEV );
-extern struct setting busid_setting __setting ( SETTING_NETDEV );
-extern struct setting user_class_setting __setting ( SETTING_HOST_EXTRA );
+extern const struct setting ip_setting __setting ( SETTING_IPv4 );
+extern const struct setting netmask_setting __setting ( SETTING_IPv4 );
+extern const struct setting gateway_setting __setting ( SETTING_IPv4 );
+extern const struct setting dns_setting __setting ( SETTING_IPv4_EXTRA );
+extern const struct setting hostname_setting __setting ( SETTING_HOST );
+extern const struct setting domain_setting __setting ( SETTING_IPv4_EXTRA );
+extern const struct setting filename_setting __setting ( SETTING_BOOT );
+extern const struct setting root_path_setting __setting ( SETTING_SANBOOT );
+extern const struct setting username_setting __setting ( SETTING_AUTH );
+extern const struct setting password_setting __setting ( SETTING_AUTH );
+extern const struct setting priority_setting __setting ( SETTING_MISC );
+extern const struct setting uuid_setting __setting ( SETTING_HOST );
+extern const struct setting next_server_setting __setting ( SETTING_BOOT );
+extern const struct setting mac_setting __setting ( SETTING_NETDEV );
+extern const struct setting busid_setting __setting ( SETTING_NETDEV );
+extern const struct setting user_class_setting __setting ( SETTING_HOST_EXTRA );
 
 /**
  * Initialise a settings block
@@ -418,7 +435,7 @@ extern struct setting user_class_setting __setting ( SETTING_HOST_EXTRA );
 static inline void settings_init ( struct settings *settings,
 				   struct settings_operations *op,
 				   struct refcnt *refcnt,
-				   struct settings_scope *default_scope ) {
+				   const struct settings_scope *default_scope ){
 	INIT_LIST_HEAD ( &settings->siblings );
 	INIT_LIST_HEAD ( &settings->children );
 	settings->op = op;
@@ -447,20 +464,21 @@ static inline void generic_settings_init ( struct generic_settings *generics,
  * @ret rc		Return status code
  */
 static inline int delete_setting ( struct settings *settings,
-				   struct setting *setting ) {
+				   const struct setting *setting ) {
 	return store_setting ( settings, setting, NULL, 0 );
 }
 
 /**
- * Check existence of setting
+ * Check existence of predefined setting
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
  * @ret exists		Setting exists
  */
 static inline int setting_exists ( struct settings *settings,
-				   struct setting *setting ) {
-	return ( fetch_setting_len ( settings, setting ) >= 0 );
+				   const struct setting *setting ) {
+	return ( fetch_setting ( settings, setting, NULL, NULL,
+				 NULL, 0 ) >= 0 );
 }
 
 #endif /* _IPXE_SETTINGS_H */
diff --git a/src/interface/efi/efi_snp_hii.c b/src/interface/efi/efi_snp_hii.c
index 9ea15a623..61954b632 100644
--- a/src/interface/efi/efi_snp_hii.c
+++ b/src/interface/efi/efi_snp_hii.c
@@ -276,7 +276,9 @@ static int efi_snp_hii_fetch ( struct efi_snp_device *snpdev,
 			       const char *key, const char *value,
 			       wchar_t **results, int *have_setting ) {
 	struct settings *settings = efi_snp_hii_settings ( snpdev );
+	struct settings *origin;
 	struct setting *setting;
+	struct setting fetched;
 	int len;
 	char *buf;
 	char *encoded;
@@ -311,7 +313,8 @@ static int efi_snp_hii_fetch ( struct efi_snp_device *snpdev,
 	if ( setting_exists ( settings, setting ) ) {
 
 		/* Calculate formatted length */
-		len = fetchf_setting ( settings, setting, NULL, 0 );
+		len = fetchf_setting ( settings, setting, &origin, &fetched,
+				       NULL, 0 );
 		if ( len < 0 ) {
 			rc = len;
 			DBGC ( snpdev, "SNPDEV %p could not fetch %s: %s\n",
@@ -328,7 +331,8 @@ static int efi_snp_hii_fetch ( struct efi_snp_device *snpdev,
 		encoded = ( buf + len + 1 /* NUL */ );
 
 		/* Format value */
-		fetchf_setting ( settings, setting, buf, ( len + 1 /* NUL */ ));
+		fetchf_setting ( origin, &fetched, NULL, NULL, buf,
+				 ( len + 1 /* NUL */ ) );
 		for ( i = 0 ; i < len ; i++ ) {
 			sprintf ( ( encoded + ( 4 * i ) ), "%04x",
 				  *( ( uint8_t * ) buf + i ) );
diff --git a/src/interface/smbios/smbios_settings.c b/src/interface/smbios/smbios_settings.c
index ecd3f1d97..9995bd751 100644
--- a/src/interface/smbios/smbios_settings.c
+++ b/src/interface/smbios/smbios_settings.c
@@ -28,7 +28,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #include <ipxe/smbios.h>
 
 /** SMBIOS settings scope */
-static struct settings_scope smbios_settings_scope;
+static const struct settings_scope smbios_settings_scope;
 
 /**
  * Construct SMBIOS raw-data tag
@@ -63,7 +63,7 @@ static struct settings_scope smbios_settings_scope;
  * @ret applies		Setting applies within this settings block
  */
 static int smbios_applies ( struct settings *settings __unused,
-			    struct setting *setting ) {
+			    const struct setting *setting ) {
 
 	return ( setting->scope == &smbios_settings_scope );
 }
@@ -188,7 +188,7 @@ struct init_fn smbios_init_fn __init_fn ( INIT_NORMAL ) = {
 };
 
 /** UUID setting obtained via SMBIOS */
-struct setting uuid_setting __setting ( SETTING_HOST ) = {
+const struct setting uuid_setting __setting ( SETTING_HOST ) = {
 	.name = "uuid",
 	.description = "UUID",
 	.tag = SMBIOS_RAW_TAG ( SMBIOS_TYPE_SYSTEM_INFORMATION,
@@ -198,7 +198,7 @@ struct setting uuid_setting __setting ( SETTING_HOST ) = {
 };
 
 /** Other SMBIOS predefined settings */
-struct setting smbios_predefined_settings[] __setting ( SETTING_HOST_EXTRA ) = {
+const struct setting smbios_predefined_settings[] __setting ( SETTING_HOST_EXTRA ) = {
 	{
 		.name = "manufacturer",
 		.description = "Manufacturer",
diff --git a/src/net/80211/net80211.c b/src/net/80211/net80211.c
index 3893f652c..db4dc1168 100644
--- a/src/net/80211/net80211.c
+++ b/src/net/80211/net80211.c
@@ -204,7 +204,7 @@ struct settings_applicator net80211_applicator __settings_applicator = {
  * If this is blank, we scan for all networks and use the one with the
  * greatest signal strength.
  */
-struct setting net80211_ssid_setting __setting ( SETTING_NETDEV_EXTRA ) = {
+const struct setting net80211_ssid_setting __setting ( SETTING_NETDEV_EXTRA ) = {
 	.name = "ssid",
 	.description = "Wireless SSID",
 	.type = &setting_type_string,
@@ -216,7 +216,7 @@ struct setting net80211_ssid_setting __setting ( SETTING_NETDEV_EXTRA ) = {
  * active scan (send probe packets). If this setting is nonzero, an
  * active scan on the 2.4GHz band will be used to associate.
  */
-struct setting net80211_active_setting __setting ( SETTING_NETDEV_EXTRA ) = {
+const struct setting net80211_active_setting __setting ( SETTING_NETDEV_EXTRA ) = {
 	.name = "active-scan",
 	.description = "Actively scan for wireless networks",
 	.type = &setting_type_int8,
@@ -228,7 +228,7 @@ struct setting net80211_active_setting __setting ( SETTING_NETDEV_EXTRA ) = {
  * normal iPXE method for entering hex settings; an ASCII string of
  * hex characters will not behave as expected.
  */
-struct setting net80211_key_setting __setting ( SETTING_NETDEV_EXTRA ) = {
+const struct setting net80211_key_setting __setting ( SETTING_NETDEV_EXTRA ) = {
 	.name = "key",
 	.description = "Wireless encryption key",
 	.type = &setting_type_string,
diff --git a/src/net/80211/wep.c b/src/net/80211/wep.c
index 37b27f71a..e22ac8998 100644
--- a/src/net/80211/wep.c
+++ b/src/net/80211/wep.c
@@ -236,8 +236,8 @@ static int trivial_init ( struct net80211_device *dev )
 	     dev->associating->crypto == NET80211_CRYPT_NONE )
 		return 0;	/* no crypto? OK. */
 
-	len = fetch_setting ( netdev_settings ( dev->netdev ),
-			      &net80211_key_setting, key, WEP_MAX_KEY );
+	len = fetch_raw_setting ( netdev_settings ( dev->netdev ),
+				  &net80211_key_setting, key, WEP_MAX_KEY );
 
 	if ( len <= 0 ) {
 		DBGC ( dev, "802.11 %p cannot do WEP without a key\n", dev );
@@ -278,8 +278,8 @@ static int trivial_change_key ( struct net80211_device *dev )
 	if ( ! dev->crypto || ( dev->crypto->init != wep_init ) )
 		change ^= 1;
 
-	len = fetch_setting ( netdev_settings ( dev->netdev ),
-			      &net80211_key_setting, key, WEP_MAX_KEY );
+	len = fetch_raw_setting ( netdev_settings ( dev->netdev ),
+				  &net80211_key_setting, key, WEP_MAX_KEY );
 	if ( len <= 0 )
 		change ^= 1;
 
diff --git a/src/net/dhcppkt.c b/src/net/dhcppkt.c
index 3722c09e1..a9a6d3a94 100644
--- a/src/net/dhcppkt.c
+++ b/src/net/dhcppkt.c
@@ -226,7 +226,7 @@ int dhcppkt_fetch ( struct dhcp_packet *dhcppkt, unsigned int tag,
  * @ret applies		Setting applies within this settings block
  */
 static int dhcppkt_settings_applies ( struct settings *settings,
-				      struct setting *setting ) {
+				      const struct setting *setting ) {
 	struct dhcp_packet *dhcppkt =
 		container_of ( settings, struct dhcp_packet, settings );
 
@@ -244,7 +244,7 @@ static int dhcppkt_settings_applies ( struct settings *settings,
  * @ret rc		Return status code
  */
 static int dhcppkt_settings_store ( struct settings *settings,
-				    struct setting *setting,
+				    const struct setting *setting,
 				    const void *data, size_t len ) {
 	struct dhcp_packet *dhcppkt =
 		container_of ( settings, struct dhcp_packet, settings );
diff --git a/src/net/fakedhcp.c b/src/net/fakedhcp.c
index d67501ed3..3dec88b11 100644
--- a/src/net/fakedhcp.c
+++ b/src/net/fakedhcp.c
@@ -49,8 +49,8 @@ static int copy_encap_settings ( struct dhcp_packet *dest,
 	struct setting setting = { .name = "" };
 	unsigned int subtag;
 	unsigned int tag;
+	void *data;
 	int len;
-	int check_len;
 	int rc;
 
 	for ( subtag = DHCP_MIN_OPTION; subtag <= DHCP_MAX_OPTION; subtag++ ) {
@@ -66,17 +66,11 @@ static int copy_encap_settings ( struct dhcp_packet *dest,
 		default:
 			/* Copy setting, if present */
 			setting.tag = tag;
-			len = fetch_setting_len ( source, &setting );
-			if ( len < 0 )
-				break;
-			{
-				char buf[len];
-
-				check_len = fetch_setting ( source, &setting,
-							    buf, sizeof (buf));
-				assert ( check_len == len );
-				if ( ( rc = dhcppkt_store ( dest, tag, buf,
-							    sizeof(buf) )) !=0)
+			len = fetch_raw_setting_copy ( source, &setting, &data);
+			if ( len >= 0 ) {
+				rc = dhcppkt_store ( dest, tag, data, len );
+				free ( data );
+				if ( rc != 0 )
 					return rc;
 			}
 			break;
diff --git a/src/net/ipv4.c b/src/net/ipv4.c
index 438fe9ac5..f0a2e4d65 100644
--- a/src/net/ipv4.c
+++ b/src/net/ipv4.c
@@ -591,7 +591,7 @@ struct sockaddr_converter ipv4_sockaddr_converter __sockaddr_converter = {
  */
 
 /** IPv4 address setting */
-struct setting ip_setting __setting ( SETTING_IPv4 ) = {
+const struct setting ip_setting __setting ( SETTING_IPv4 ) = {
 	.name = "ip",
 	.description = "IP address",
 	.tag = DHCP_EB_YIADDR,
@@ -599,7 +599,7 @@ struct setting ip_setting __setting ( SETTING_IPv4 ) = {
 };
 
 /** IPv4 subnet mask setting */
-struct setting netmask_setting __setting ( SETTING_IPv4 ) = {
+const struct setting netmask_setting __setting ( SETTING_IPv4 ) = {
 	.name = "netmask",
 	.description = "Subnet mask",
 	.tag = DHCP_SUBNET_MASK,
@@ -607,7 +607,7 @@ struct setting netmask_setting __setting ( SETTING_IPv4 ) = {
 };
 
 /** Default gateway setting */
-struct setting gateway_setting __setting ( SETTING_IPv4 ) = {
+const struct setting gateway_setting __setting ( SETTING_IPv4 ) = {
 	.name = "gateway",
 	.description = "Default gateway",
 	.tag = DHCP_ROUTERS,
diff --git a/src/net/ipv6.c b/src/net/ipv6.c
index b4f33f0d0..68a0c89bf 100644
--- a/src/net/ipv6.c
+++ b/src/net/ipv6.c
@@ -954,7 +954,7 @@ struct sockaddr_converter ipv6_sockaddr_converter __sockaddr_converter = {
  * @v len		Length of buffer
  * @ret len		Length of raw value, or negative error
  */
-static int parse_ipv6_setting ( struct setting_type *type __unused,
+static int parse_ipv6_setting ( const struct setting_type *type __unused,
 				const char *value, void *buf, size_t len ) {
 	struct in6_addr ipv6;
 	int rc;
@@ -981,7 +981,7 @@ static int parse_ipv6_setting ( struct setting_type *type __unused,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_ipv6_setting ( struct setting_type *type __unused,
+static int format_ipv6_setting ( const struct setting_type *type __unused,
 				 const void *raw, size_t raw_len, char *buf,
 				 size_t len ) {
 	const struct in6_addr *ipv6 = raw;
@@ -992,7 +992,7 @@ static int format_ipv6_setting ( struct setting_type *type __unused,
 }
 
 /** An IPv6 address setting type */
-struct setting_type setting_type_ipv6 __setting_type = {
+const struct setting_type setting_type_ipv6 __setting_type = {
 	.name = "ipv6",
 	.parse = parse_ipv6_setting,
 	.format = format_ipv6_setting,
diff --git a/src/net/netdev_settings.c b/src/net/netdev_settings.c
index 994e0506f..cfadd9e4e 100644
--- a/src/net/netdev_settings.c
+++ b/src/net/netdev_settings.c
@@ -36,27 +36,27 @@ FILE_LICENCE ( GPL2_OR_LATER );
  */
 
 /** Network device predefined settings */
-struct setting mac_setting __setting ( SETTING_NETDEV ) = {
+const struct setting mac_setting __setting ( SETTING_NETDEV ) = {
 	.name = "mac",
 	.description = "MAC address",
 	.type = &setting_type_hex,
 };
-struct setting bustype_setting __setting ( SETTING_NETDEV ) = {
+const struct setting bustype_setting __setting ( SETTING_NETDEV ) = {
 	.name = "bustype",
 	.description = "Bus type",
 	.type = &setting_type_string,
 };
-struct setting busloc_setting __setting ( SETTING_NETDEV ) = {
+const struct setting busloc_setting __setting ( SETTING_NETDEV ) = {
 	.name = "busloc",
 	.description = "Bus location",
 	.type = &setting_type_uint32,
 };
-struct setting busid_setting __setting ( SETTING_NETDEV ) = {
+const struct setting busid_setting __setting ( SETTING_NETDEV ) = {
 	.name = "busid",
 	.description = "Bus ID",
 	.type = &setting_type_hex,
 };
-struct setting chip_setting __setting ( SETTING_NETDEV ) = {
+const struct setting chip_setting __setting ( SETTING_NETDEV ) = {
 	.name = "chip",
 	.description = "Chip",
 	.type = &setting_type_string,
@@ -194,7 +194,7 @@ static int netdev_fetch_chip ( struct net_device *netdev, void *data,
 /** A network device setting operation */
 struct netdev_setting_operation {
 	/** Setting */
-	struct setting *setting;
+	const struct setting *setting;
 	/** Store setting (or NULL if not supported)
 	 *
 	 * @v netdev		Network device
@@ -232,7 +232,8 @@ static struct netdev_setting_operation netdev_setting_operations[] = {
  * @v len		Length of setting data
  * @ret rc		Return status code
  */
-static int netdev_store ( struct settings *settings, struct setting *setting,
+static int netdev_store ( struct settings *settings,
+			  const struct setting *setting,
 			  const void *data, size_t len ) {
 	struct net_device *netdev = container_of ( settings, struct net_device,
 						   settings.settings );
diff --git a/src/net/tcp/iscsi.c b/src/net/tcp/iscsi.c
index c9daf1ff4..197069cc3 100644
--- a/src/net/tcp/iscsi.c
+++ b/src/net/tcp/iscsi.c
@@ -1860,7 +1860,7 @@ enum iscsi_root_path_component {
 };
 
 /** iSCSI initiator IQN setting */
-struct setting initiator_iqn_setting __setting ( SETTING_SANBOOT_EXTRA ) = {
+const struct setting initiator_iqn_setting __setting ( SETTING_SANBOOT_EXTRA ) = {
 	.name = "initiator-iqn",
 	.description = "iSCSI initiator name",
 	.tag = DHCP_ISCSI_INITIATOR_IQN,
@@ -1868,7 +1868,7 @@ struct setting initiator_iqn_setting __setting ( SETTING_SANBOOT_EXTRA ) = {
 };
 
 /** iSCSI reverse username setting */
-struct setting reverse_username_setting __setting ( SETTING_AUTH_EXTRA ) = {
+const struct setting reverse_username_setting __setting ( SETTING_AUTH_EXTRA ) = {
 	.name = "reverse-username",
 	.description = "Reverse user name",
 	.tag = DHCP_EB_REVERSE_USERNAME,
@@ -1876,7 +1876,7 @@ struct setting reverse_username_setting __setting ( SETTING_AUTH_EXTRA ) = {
 };
 
 /** iSCSI reverse password setting */
-struct setting reverse_password_setting __setting ( SETTING_AUTH_EXTRA ) = {
+const struct setting reverse_password_setting __setting ( SETTING_AUTH_EXTRA ) = {
 	.name = "reverse-password",
 	.description = "Reverse password",
 	.tag = DHCP_EB_REVERSE_PASSWORD,
@@ -1947,46 +1947,23 @@ static int iscsi_fetch_settings ( struct iscsi_session *iscsi ) {
 	/* Fetch relevant settings.  Don't worry about freeing on
 	 * error, since iscsi_free() will take care of that anyway.
 	 */
-	if ( ( len = fetch_string_setting_copy ( NULL, &username_setting,
-					  &iscsi->initiator_username ) ) < 0 ) {
-		DBGC ( iscsi, "iSCSI %p could not fetch username: %s\n",
-		       iscsi, strerror ( len ) );
-		return len;
-	}
-	if ( ( len = fetch_string_setting_copy ( NULL, &password_setting,
-					  &iscsi->initiator_password ) ) < 0 ) {
-		DBGC ( iscsi, "iSCSI %p could not fetch password: %s\n",
-		       iscsi, strerror ( len ) );
-		return len;
-	}
-	if ( ( len = fetch_string_setting_copy( NULL, &reverse_username_setting,
-					     &iscsi->target_username ) ) < 0 ) {
-		DBGC ( iscsi, "iSCSI %p could not fetch reverse username: %s\n",
-		       iscsi, strerror ( len ) );
-		return len;
-	}
-	if ( ( len = fetch_string_setting_copy( NULL, &reverse_password_setting,
-					     &iscsi->target_password ) ) < 0 ) {
-		DBGC ( iscsi, "iSCSI %p could not fetch reverse password: %s\n",
-		       iscsi, strerror ( len ) );
-		return len;
-	}
+	fetch_string_setting_copy ( NULL, &username_setting,
+				    &iscsi->initiator_username );
+	fetch_string_setting_copy ( NULL, &password_setting,
+				    &iscsi->initiator_password );
+	fetch_string_setting_copy ( NULL, &reverse_username_setting,
+				    &iscsi->target_username );
+	fetch_string_setting_copy ( NULL, &reverse_password_setting,
+				    &iscsi->target_password );
 
-	/* Find a suitable initiator name */
-	if ( ( len = fetch_string_setting_copy ( NULL, &initiator_iqn_setting,
-					       &iscsi->initiator_iqn ) ) < 0 ) {
-		DBGC ( iscsi, "iSCSI %p could not fetch initiator IQN: %s\n",
-		       iscsi, strerror ( len ) );
-		return len;
-	}
+	/* Use explicit initiator IQN if provided */
+	fetch_string_setting_copy ( NULL, &initiator_iqn_setting,
+				    &iscsi->initiator_iqn );
 	if ( iscsi->initiator_iqn )
 		return 0;
-	if ( ( len = fetch_string_setting_copy ( NULL, &hostname_setting,
-						&hostname ) ) < 0 ) {
-		DBGC ( iscsi, "iSCSI %p could not fetch hostname: %s\n",
-		       iscsi, strerror ( len ) );
-		return len;
-	}
+
+	/* Otherwise, try to construct an initiator IQN from the hostname */
+	fetch_string_setting_copy ( NULL, &hostname_setting, &hostname );
 	if ( hostname ) {
 		len = asprintf ( &iscsi->initiator_iqn,
 				 ISCSI_DEFAULT_IQN_PREFIX ":%s", hostname );
@@ -1999,6 +1976,8 @@ static int iscsi_fetch_settings ( struct iscsi_session *iscsi ) {
 		assert ( iscsi->initiator_iqn );
 		return 0;
 	}
+
+	/* Otherwise, try to construct an initiator IQN from the UUID */
 	if ( ( len = fetch_uuid_setting ( NULL, &uuid_setting, &uuid ) ) < 0 ) {
 		DBGC ( iscsi, "iSCSI %p has no suitable initiator IQN\n",
 		       iscsi );
diff --git a/src/net/tcp/oncrpc.c b/src/net/tcp/oncrpc.c
index 819d31794..0a3b38580 100644
--- a/src/net/tcp/oncrpc.c
+++ b/src/net/tcp/oncrpc.c
@@ -58,14 +58,14 @@ struct oncrpc_cred oncrpc_auth_none = {
 	.length = 0
 };
 
-struct setting uid_setting __setting ( SETTING_AUTH ) = {
+const struct setting uid_setting __setting ( SETTING_AUTH ) = {
 	.name        = "uid",
 	.description = "User ID",
 	.tag         = DHCP_EB_UID,
 	.type        = &setting_type_uint32
 };
 
-struct setting gid_setting __setting ( SETTING_AUTH ) = {
+const struct setting gid_setting __setting ( SETTING_AUTH ) = {
 	.name        = "gid",
 	.description = "Group ID",
 	.tag         = DHCP_EB_GID,
diff --git a/src/net/tcp/syslogs.c b/src/net/tcp/syslogs.c
index bcda8b45c..503ed177a 100644
--- a/src/net/tcp/syslogs.c
+++ b/src/net/tcp/syslogs.c
@@ -190,7 +190,7 @@ struct console_driver syslogs_console __console_driver = {
  */
 
 /** Encrypted syslog server setting */
-struct setting syslogs_setting __setting ( SETTING_MISC ) = {
+const struct setting syslogs_setting __setting ( SETTING_MISC ) = {
 	.name = "syslogs",
 	.description = "Encrypted syslog server",
 	.tag = DHCP_EB_SYSLOGS_SERVER,
@@ -206,15 +206,10 @@ static int apply_syslogs_settings ( void ) {
 	static char *old_server;
 	char *server;
 	struct interface *socket;
-	int len;
 	int rc;
 
 	/* Fetch log server */
-	len = fetch_string_setting_copy ( NULL, &syslogs_setting, &server );
-	if ( len < 0 ) {
-		rc = len;
-		goto err_fetch_server;
-	}
+	fetch_string_setting_copy ( NULL, &syslogs_setting, &server );
 
 	/* Do nothing unless log server has changed */
 	if ( ( ( server == NULL ) && ( old_server == NULL ) ) ||
@@ -266,7 +261,6 @@ static int apply_syslogs_settings ( void ) {
  out_no_server:
  out_no_change:
 	free ( server );
- err_fetch_server:
 	return rc;
 }
 
diff --git a/src/net/udp/dhcp.c b/src/net/udp/dhcp.c
index 66bcc83ae..3163f39c7 100644
--- a/src/net/udp/dhcp.c
+++ b/src/net/udp/dhcp.c
@@ -92,7 +92,7 @@ static uint8_t dhcp_request_options_data[] = {
 };
 
 /** DHCP server address setting */
-struct setting dhcp_server_setting __setting ( SETTING_MISC ) = {
+const struct setting dhcp_server_setting __setting ( SETTING_MISC ) = {
 	.name = "dhcp-server",
 	.description = "DHCP server",
 	.tag = DHCP_SERVER_IDENTIFIER,
@@ -975,6 +975,7 @@ int dhcp_create_request ( struct dhcp_packet *dhcppkt,
 	uint8_t *dhcp_features;
 	size_t dhcp_features_len;
 	size_t ll_addr_len;
+	void *user_class;
 	ssize_t len;
 	int rc;
 
@@ -985,7 +986,7 @@ int dhcp_create_request ( struct dhcp_packet *dhcppkt,
 					 data, max_len ) ) != 0 ) {
 		DBG ( "DHCP could not create DHCP packet: %s\n",
 		      strerror ( rc ) );
-		return rc;
+		goto err_create_packet;
 	}
 
 	/* Set client IP address */
@@ -998,17 +999,17 @@ int dhcp_create_request ( struct dhcp_packet *dhcppkt,
 				    dhcp_features_len ) ) != 0 ) {
 		DBG ( "DHCP could not set features list option: %s\n",
 		      strerror ( rc ) );
-		return rc;
+		goto err_store_features;
 	}
 
 	/* Add options to identify the network device */
-	fetch_setting ( &netdev->settings.settings, &busid_setting, &dhcp_desc,
-		sizeof ( dhcp_desc ) );
+	fetch_raw_setting ( netdev_settings ( netdev ), &busid_setting,
+			    &dhcp_desc, sizeof ( dhcp_desc ) );
 	if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_EB_BUS_ID, &dhcp_desc,
 				    sizeof ( dhcp_desc ) ) ) != 0 ) {
 		DBG ( "DHCP could not set bus ID option: %s\n",
 		      strerror ( rc ) );
-		return rc;
+		goto err_store_busid;
 	}
 
 	/* Add DHCP client identifier.  Required for Infiniband, and
@@ -1022,7 +1023,7 @@ int dhcp_create_request ( struct dhcp_packet *dhcppkt,
 				    ( ll_addr_len + 1 ) ) ) != 0 ) {
 		DBG ( "DHCP could not set client ID: %s\n",
 		      strerror ( rc ) );
-		return rc;
+		goto err_store_client_id;
 	}
 
 	/* Add client UUID, if we have one.  Required for PXE.  The
@@ -1039,25 +1040,29 @@ int dhcp_create_request ( struct dhcp_packet *dhcppkt,
 					    sizeof ( client_uuid ) ) ) != 0 ) {
 			DBG ( "DHCP could not set client UUID: %s\n",
 			      strerror ( rc ) );
-			return rc;
+			goto err_store_client_uuid;
 		}
 	}
 
 	/* Add user class, if we have one. */
-	if ( ( len = fetch_setting_len ( NULL, &user_class_setting ) ) >= 0 ) {
-		char user_class[len];
-		fetch_setting ( NULL, &user_class_setting, user_class,
-				sizeof ( user_class ) );
+	if ( ( len = fetch_raw_setting_copy ( NULL, &user_class_setting,
+					      &user_class ) ) >= 0 ) {
 		if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_USER_CLASS_ID,
-					    &user_class,
-					    sizeof ( user_class ) ) ) != 0 ) {
+					    user_class, len ) ) != 0 ) {
 			DBG ( "DHCP could not set user class: %s\n",
 			      strerror ( rc ) );
-			return rc;
+			goto err_store_user_class;
 		}
 	}
 
-	return 0;
+ err_store_user_class:
+	free ( user_class );
+ err_store_client_uuid:
+ err_store_client_id:
+ err_store_busid:
+ err_store_features:
+ err_create_packet:
+	return rc;
 }
 
 /****************************************************************************
@@ -1384,7 +1389,8 @@ int start_pxebs ( struct interface *job, struct net_device *netdev,
 	int rc;
 
 	/* Get upper bound for PXE boot server IP address list */
-	pxebs_list_len = fetch_setting_len ( NULL, &pxe_boot_servers_setting );
+	pxebs_list_len = fetch_raw_setting ( NULL, &pxe_boot_servers_setting,
+					     NULL, 0 );
 	if ( pxebs_list_len < 0 )
 		pxebs_list_len = 0;
 
@@ -1422,8 +1428,8 @@ int start_pxebs ( struct interface *job, struct net_device *netdev,
 	if ( pxebs_list_len ) {
 		uint8_t buf[pxebs_list_len];
 
-		fetch_setting ( NULL, &pxe_boot_servers_setting,
-				buf, sizeof ( buf ) );
+		fetch_raw_setting ( NULL, &pxe_boot_servers_setting,
+				    buf, sizeof ( buf ) );
 		pxebs_list ( dhcp, buf, sizeof ( buf ), ip );
 	}
 	if ( ! dhcp->pxe_attempt->s_addr ) {
diff --git a/src/net/udp/dhcpv6.c b/src/net/udp/dhcpv6.c
index 42d11194f..7bed83d92 100644
--- a/src/net/udp/dhcpv6.c
+++ b/src/net/udp/dhcpv6.c
@@ -256,7 +256,7 @@ static int dhcpv6_iaaddr ( struct dhcpv6_option_list *options, uint32_t iaid,
  */
 
 /** DHCPv6 settings scope */
-static struct settings_scope dhcpv6_settings_scope;
+static const struct settings_scope dhcpv6_settings_scope;
 
 /** A DHCPv6 settings block */
 struct dhcpv6_settings {
@@ -276,7 +276,7 @@ struct dhcpv6_settings {
  * @ret applies		Setting applies within this settings block
  */
 static int dhcpv6_applies ( struct settings *settings __unused,
-			    struct setting *setting ) {
+			    const struct setting *setting ) {
 
 	return ( setting->scope == &dhcpv6_settings_scope );
 }
@@ -543,7 +543,7 @@ static size_t dhcpv6_user_class ( void *data, size_t len ) {
 	int actual_len;
 
 	/* Fetch user-class setting, if defined */
-	actual_len = fetch_setting ( NULL, &user_class_setting, data, len );
+	actual_len = fetch_raw_setting ( NULL, &user_class_setting, data, len );
 	if ( actual_len >= 0 )
 		return actual_len;
 
diff --git a/src/net/udp/dns.c b/src/net/udp/dns.c
index 45f0f07c1..447da8afd 100644
--- a/src/net/udp/dns.c
+++ b/src/net/udp/dns.c
@@ -594,7 +594,7 @@ struct resolver dns_resolver __resolver ( RESOLV_NORMAL ) = {
  */
 
 /** DNS server setting */
-struct setting dns_setting __setting ( SETTING_IPv4_EXTRA ) = {
+const struct setting dns_setting __setting ( SETTING_IPv4_EXTRA ) = {
 	.name = "dns",
 	.description = "DNS server",
 	.tag = DHCP_DNS_SERVERS,
@@ -622,11 +622,7 @@ static int apply_dns_settings ( void ) {
 
 	/* Get local domain DHCP option */
 	free ( localdomain );
-	if ( ( len = fetch_string_setting_copy ( NULL, &domain_setting,
-						 &localdomain ) ) < 0 ) {
-		DBG ( "DNS could not fetch local domain: %s\n",
-		      strerror ( len ) );
-	}
+	fetch_string_setting_copy ( NULL, &domain_setting, &localdomain );
 	if ( localdomain )
 		DBG ( "DNS local domain %s\n", localdomain );
 
diff --git a/src/net/udp/syslog.c b/src/net/udp/syslog.c
index 4210083d2..6554ab9bf 100644
--- a/src/net/udp/syslog.c
+++ b/src/net/udp/syslog.c
@@ -188,7 +188,7 @@ struct console_driver syslog_console __console_driver = {
  */
 
 /** Syslog server setting */
-struct setting syslog_setting __setting ( SETTING_MISC ) = {
+const struct setting syslog_setting __setting ( SETTING_MISC ) = {
 	.name = "syslog",
 	.description = "Syslog server",
 	.tag = DHCP_LOG_SERVERS,
@@ -209,17 +209,9 @@ static int apply_syslog_settings ( void ) {
 
 	/* Fetch hostname and domain name */
 	free ( syslog_hostname );
-	if ( ( len = fetch_string_setting_copy ( NULL, &hostname_setting,
-						 &syslog_hostname ) ) < 0 ) {
-		rc = len;
-		DBG ( "SYSLOG could not fetch hostname: %s\n", strerror ( rc ));
-	}
+	fetch_string_setting_copy ( NULL, &hostname_setting, &syslog_hostname );
 	free ( syslog_domain );
-	if ( ( len = fetch_string_setting_copy ( NULL, &domain_setting,
-						 &syslog_domain ) ) < 0 ) {
-		rc = len;
-		DBG ( "SYSLOG could not fetch domain: %s\n", strerror ( rc ) );
-	}
+	fetch_string_setting_copy ( NULL, &domain_setting, &syslog_domain );
 
 	/* Fetch log server */
 	syslog_console.disabled = CONSOLE_DISABLED;
diff --git a/src/net/validator.c b/src/net/validator.c
index d61cb92f4..56eebe3d6 100644
--- a/src/net/validator.c
+++ b/src/net/validator.c
@@ -121,7 +121,7 @@ static struct interface_descriptor validator_job_desc =
  */
 
 /** Cross-signed certificate source setting */
-struct setting crosscert_setting __setting ( SETTING_CRYPTO ) = {
+const struct setting crosscert_setting __setting ( SETTING_CRYPTO ) = {
 	.name = "crosscert",
 	.description = "Cross-signed certificate source",
 	.tag = DHCP_EB_CROSS_CERT,
@@ -232,14 +232,7 @@ static int validator_start_download ( struct validator *validator,
 	int rc;
 
 	/* Determine cross-signed certificate source */
-	len = fetch_string_setting_copy ( NULL, &crosscert_setting,
-					  &crosscert_copy );
-	if ( len < 0 ) {
-		rc = len;
-		DBGC ( validator, "VALIDATOR %p could not fetch crosscert "
-		       "setting: %s\n", validator, strerror ( rc ) );
-		goto err_fetch_crosscert;
-	}
+	fetch_string_setting_copy ( NULL, &crosscert_setting, &crosscert_copy );
 	crosscert = ( crosscert_copy ? crosscert_copy : crosscert_default );
 
 	/* Allocate URI string */
@@ -279,7 +272,6 @@ static int validator_start_download ( struct validator *validator,
 	free ( uri_string );
  err_alloc_uri_string:
 	free ( crosscert_copy );
- err_fetch_crosscert:
 	return rc;
 }
 
diff --git a/src/tests/settings_test.c b/src/tests/settings_test.c
index 1be2cc323..5da31b4ce 100644
--- a/src/tests/settings_test.c
+++ b/src/tests/settings_test.c
@@ -38,26 +38,26 @@ FILE_LICENCE ( GPL2_OR_LATER );
 /**
  * Report a formatted-store test result
  *
- * @v settings		Settings block
- * @v setting		Setting
- * @v formatted		Formatted value
- * @v raw_array		Expected raw value
+ * @v _settings		Settings block
+ * @v _setting		Setting
+ * @v _formatted	Formatted value
+ * @v _raw_array	Expected raw value
  */
-#define storef_ok( settings, setting, formatted, raw_array ) do {	\
-	const uint8_t expected[] = raw_array;				\
+#define storef_ok( _settings, _setting, _formatted, _raw_array ) do {	\
+	const uint8_t expected[] = _raw_array;				\
 	uint8_t actual[ sizeof ( expected ) ];				\
 	int len;							\
 									\
-	ok ( storef_setting ( settings, setting, formatted ) == 0 );	\
-	len = fetch_setting ( settings, setting, actual,		\
+	ok ( storef_setting ( _settings, _setting, _formatted ) == 0 );	\
+	len = fetch_setting ( _settings, _setting, NULL, NULL, actual,	\
 			      sizeof ( actual ) );			\
 	if ( len >= 0 ) {						\
-		DBGC ( settings, "Stored %s \"%s\", got:\n",		\
-		       (setting)->type->name, formatted );		\
-		DBGC_HDA ( settings, 0, actual, len );			\
+		DBGC ( _settings, "Stored %s \"%s\", got:\n",		\
+		       (_setting)->type->name, _formatted );		\
+		DBGC_HDA ( _settings, 0, actual, len );			\
 	} else {							\
-		DBGC ( settings, "Stored %s \"%s\", got error %s\n",	\
-		       (setting)->type->name, formatted,		\
+		DBGC ( _settings, "Stored %s \"%s\", got error %s\n",	\
+		       (_setting)->type->name, _formatted,		\
 		       strerror ( len ) );				\
 	}								\
 	ok ( len == ( int ) sizeof ( actual ) );			\
@@ -67,52 +67,52 @@ FILE_LICENCE ( GPL2_OR_LATER );
 /**
  * Report a formatted-fetch test result
  *
- * @v settings		Settings block
- * @v setting		Setting
- * @v raw_array		Raw value
- * @v formatted		Expected formatted value
+ * @v _settings		Settings block
+ * @v _setting		Setting
+ * @v _raw_array	Raw value
+ * @v _formatted	Expected formatted value
  */
-#define fetchf_ok( settings, setting, raw_array, formatted ) do {	\
-	const uint8_t raw[] = raw_array;				\
-	char actual[ strlen ( formatted ) + 1 ];			\
+#define fetchf_ok( _settings, _setting, _raw_array, _formatted ) do {	\
+	const uint8_t raw[] = _raw_array;				\
+	char actual[ strlen ( _formatted ) + 1 ];			\
 	int len;							\
 									\
-	ok ( store_setting ( settings, setting, raw,			\
+	ok ( store_setting ( _settings, _setting, raw,			\
 			     sizeof ( raw ) ) == 0 );			\
-	len = fetchf_setting ( settings, setting, actual,		\
+	len = fetchf_setting ( _settings, _setting, NULL, NULL, actual,	\
 			       sizeof ( actual ) );			\
-	DBGC ( settings, "Fetched %s \"%s\" from:\n",			\
-	       (setting)->type->name, actual );				\
-	DBGC_HDA ( settings, 0, raw, sizeof ( raw ) );			\
+	DBGC ( _settings, "Fetched %s \"%s\" from:\n",			\
+	       (_setting)->type->name, actual );			\
+	DBGC_HDA ( _settings, 0, raw, sizeof ( raw ) );			\
 	ok ( len == ( int ) ( sizeof ( actual ) - 1 ) );		\
-	ok ( strcmp ( actual, formatted ) == 0 );			\
+	ok ( strcmp ( actual, _formatted ) == 0 );			\
 	} while ( 0 )
 
 /**
  * Report a numeric-store test result
  *
- * @v settings		Settings block
- * @v setting		Setting
- * @v numeric		Numeric value
- * @v raw_array		Expected raw value
+ * @v _settings		Settings block
+ * @v _setting		Setting
+ * @v _numeric		Numeric value
+ * @v _raw_array	Expected raw value
  */
-#define storen_ok( settings, setting, numeric, raw_array ) do {		\
-	const uint8_t expected[] = raw_array;				\
+#define storen_ok( _settings, _setting, _numeric, _raw_array ) do {	\
+	const uint8_t expected[] = _raw_array;				\
 	uint8_t actual[ sizeof ( expected ) ];				\
 	int len;							\
 									\
-	ok ( storen_setting ( settings, setting, numeric ) == 0 );	\
-	len = fetch_setting ( settings, setting, actual,		\
+	ok ( storen_setting ( _settings, _setting, _numeric ) == 0 );	\
+	len = fetch_setting ( _settings, _setting, NULL, NULL, actual,	\
 			      sizeof ( actual ) );			\
 	if ( len >= 0 ) {						\
-		DBGC ( settings, "Stored %s %#lx, got:\n",		\
-		       (setting)->type->name,				\
-		       ( unsigned long ) numeric );			\
-		DBGC_HDA ( settings, 0, actual, len );			\
+		DBGC ( _settings, "Stored %s %#lx, got:\n",		\
+		       (_setting)->type->name,				\
+		       ( unsigned long ) _numeric );			\
+		DBGC_HDA ( _settings, 0, actual, len );			\
 	} else {							\
-		DBGC ( settings, "Stored %s %#lx, got error %s\n",	\
-		       (setting)->type->name,				\
-		       ( unsigned long ) numeric, strerror ( len ) );	\
+		DBGC ( _settings, "Stored %s %#lx, got error %s\n",	\
+		       (_setting)->type->name,				\
+		       ( unsigned long ) _numeric, strerror ( len ) );	\
 	}								\
 	ok ( len == ( int ) sizeof ( actual ) );			\
 	ok ( memcmp ( actual, expected, sizeof ( actual ) ) == 0 );	\
@@ -121,22 +121,23 @@ FILE_LICENCE ( GPL2_OR_LATER );
 /**
  * Report a numeric-fetch test result
  *
- * @v settings		Settings block
- * @v setting		Setting
- * @v raw_array		Raw array
- * @v numeric		Expected numeric value
+ * @v _settings		Settings block
+ * @v _setting		Setting
+ * @v _raw_array	Raw array
+ * @v _numeric		Expected numeric value
  */
-#define fetchn_ok( settings, setting, raw_array, numeric ) do {		\
-	const uint8_t raw[] = raw_array;				\
+#define fetchn_ok( _settings, _setting, _raw_array, _numeric ) do {	\
+	const uint8_t raw[] = _raw_array;				\
 	unsigned long actual;						\
 									\
-	ok ( store_setting ( settings, setting, raw,			\
+	ok ( store_setting ( _settings, _setting, raw,			\
 			     sizeof ( raw ) ) == 0 );			\
-	ok ( fetchn_setting ( settings, setting, &actual ) == 0 );	\
-	DBGC ( settings, "Fetched %s %#lx from:\n",			\
-	       (setting)->type->name, actual );				\
-	DBGC_HDA ( settings, 0, raw, sizeof ( raw ) );			\
-	ok ( actual == ( unsigned long ) numeric );			\
+	ok ( fetchn_setting ( _settings, _setting, NULL, NULL,		\
+			      &actual ) == 0 );				\
+	DBGC ( _settings, "Fetched %s %#lx from:\n",			\
+	       (_setting)->type->name, actual );			\
+	DBGC_HDA ( _settings, 0, raw, sizeof ( raw ) );			\
+	ok ( actual == ( unsigned long ) _numeric );			\
 	} while ( 0 )
 
 /** Test generic settings block */
diff --git a/src/usr/autoboot.c b/src/usr/autoboot.c
index 6d6419d63..a29f8c17c 100644
--- a/src/usr/autoboot.c
+++ b/src/usr/autoboot.c
@@ -59,7 +59,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #define CYAN	"\033[36m"
 
 /** The "scriptlet" setting */
-struct setting scriptlet_setting __setting ( SETTING_MISC ) = {
+const struct setting scriptlet_setting __setting ( SETTING_MISC ) = {
 	.name = "scriptlet",
 	.description = "Boot scriptlet",
 	.tag = DHCP_EB_SCRIPTLET,
@@ -119,7 +119,7 @@ static struct uri * parse_next_server_and_filename ( struct in_addr next_server,
 }
 
 /** The "keep-san" setting */
-struct setting keep_san_setting __setting ( SETTING_SANBOOT_EXTRA ) = {
+const struct setting keep_san_setting __setting ( SETTING_SANBOOT_EXTRA ) = {
 	.name = "keep-san",
 	.description = "Preserve SAN connection",
 	.tag = DHCP_EB_KEEP_SAN,
@@ -127,7 +127,7 @@ struct setting keep_san_setting __setting ( SETTING_SANBOOT_EXTRA ) = {
 };
 
 /** The "skip-san-boot" setting */
-struct setting skip_san_boot_setting __setting ( SETTING_SANBOOT_EXTRA ) = {
+const struct setting skip_san_boot_setting __setting ( SETTING_SANBOOT_EXTRA )={
 	.name = "skip-san-boot",
 	.description = "Do not boot from SAN device",
 	.tag = DHCP_EB_SKIP_SAN_BOOT,
@@ -256,16 +256,15 @@ struct uri * fetch_next_server_and_filename ( struct settings *settings ) {
 	struct uri *uri = NULL;
 	char *filename;
 
-	/* Determine settings block containing the filename, if any */
-	settings = fetch_setting_origin ( settings, &filename_setting );
-
-	/* If we have a filename, fetch it along with next-server */
-	if ( settings ) {
+	/* If we have a filename, fetch it along with the next-server
+	 * setting from the same settings block.
+	 */
+	if ( fetch_setting ( settings, &filename_setting, &settings,
+			     NULL, NULL, 0 ) >= 0 ) {
+		fetch_string_setting_copy ( settings, &filename_setting,
+					    &raw_filename );
 		fetch_ipv4_setting ( settings, &next_server_setting,
 				     &next_server );
-		if ( fetch_string_setting_copy ( settings, &filename_setting,
-						 &raw_filename ) < 0 )
-			goto err_fetch;
 	}
 
 	/* Expand filename setting */
@@ -286,7 +285,6 @@ struct uri * fetch_next_server_and_filename ( struct settings *settings ) {
 	free ( filename );
  err_expand:
 	free ( raw_filename );
- err_fetch:
 	return uri;
 }
 
@@ -297,25 +295,30 @@ struct uri * fetch_next_server_and_filename ( struct settings *settings ) {
  * @ret uri		URI, or NULL on failure
  */
 static struct uri * fetch_root_path ( struct settings *settings ) {
-	char buf[256];
+	struct uri *uri = NULL;
+	char *raw_root_path;
 	char *root_path;
-	struct uri *uri;
 
 	/* Fetch root-path setting */
-	fetch_string_setting ( settings, &root_path_setting,
-			       buf, sizeof ( buf ) );
-	if ( buf[0] )
-		printf ( "Root path: %s\n", buf );
+	fetch_string_setting_copy ( settings, &root_path_setting,
+				    &raw_root_path );
 
 	/* Expand filename setting */
-	root_path = expand_settings ( buf );
+	root_path = expand_settings ( raw_root_path ? raw_root_path : "" );
 	if ( ! root_path )
-		return NULL;
+		goto err_expand;
 
 	/* Parse root path */
+	if ( root_path[0] )
+		printf ( "Root path: %s\n", root_path );
 	uri = parse_uri ( root_path );
+	if ( ! uri )
+		goto err_parse;
 
+ err_parse:
 	free ( root_path );
+ err_expand:
+	free ( raw_root_path );
 	return uri;
 }
 
@@ -331,7 +334,7 @@ static int have_pxe_menu ( void ) {
 		= { .tag = DHCP_PXE_DISCOVERY_CONTROL };
 	struct setting pxe_boot_menu_setting
 		= { .tag = DHCP_PXE_BOOT_MENU };
-	char buf[256];
+	char buf[ 10 /* "PXEClient" + NUL */ ];
 	unsigned int pxe_discovery_control;
 
 	fetch_string_setting ( NULL, &vendor_class_id_setting,
diff --git a/src/usr/nslookup.c b/src/usr/nslookup.c
index b691962ef..66818d11b 100644
--- a/src/usr/nslookup.c
+++ b/src/usr/nslookup.c
@@ -71,7 +71,7 @@ static void nslookup_close ( struct nslookup *nslookup, int rc ) {
 static void nslookup_resolv_done ( struct nslookup *nslookup,
 				   struct sockaddr *sa ) {
 	struct sockaddr_in *sin;
-	struct setting_type *default_type;
+	const struct setting_type *default_type;
 	struct settings *settings;
 	struct setting setting;
 	void *data;
diff --git a/src/usr/pxemenu.c b/src/usr/pxemenu.c
index d50ee6ba9..c5cffd3d4 100644
--- a/src/usr/pxemenu.c
+++ b/src/usr/pxemenu.c
@@ -101,9 +101,9 @@ static int pxe_menu_parse ( struct pxe_menu **menu ) {
 
 	/* Fetch raw menu */
 	memset ( raw_menu, 0, sizeof ( raw_menu ) );
-	if ( ( raw_menu_len = fetch_setting ( NULL, &pxe_boot_menu_setting,
-					      raw_menu,
-					      sizeof ( raw_menu ) ) ) < 0 ) {
+	if ( ( raw_menu_len = fetch_raw_setting ( NULL, &pxe_boot_menu_setting,
+						  raw_menu,
+						  sizeof ( raw_menu ) ) ) < 0 ){
 		rc = raw_menu_len;
 		DBG ( "Could not retrieve raw PXE boot menu: %s\n",
 		      strerror ( rc ) );
@@ -116,8 +116,9 @@ static int pxe_menu_parse ( struct pxe_menu **menu ) {
 	raw_menu_end = ( raw_menu + raw_menu_len );
 
 	/* Fetch raw prompt length */
-	raw_prompt_len = fetch_setting_len ( NULL,
-					     &pxe_boot_menu_prompt_setting );
+	raw_prompt_len =
+		fetch_raw_setting ( NULL, &pxe_boot_menu_prompt_setting,
+				    NULL, 0 );
 	if ( raw_prompt_len < 0 )
 		raw_prompt_len = 0;
 
@@ -168,8 +169,8 @@ static int pxe_menu_parse ( struct pxe_menu **menu ) {
 	if ( raw_prompt_len ) {
 		raw_menu_prompt = ( ( ( void * ) raw_menu_item ) +
 				    1 /* NUL */ );
-		fetch_setting ( NULL, &pxe_boot_menu_prompt_setting,
-				raw_menu_prompt, raw_prompt_len );
+		fetch_raw_setting ( NULL, &pxe_boot_menu_prompt_setting,
+				    raw_menu_prompt, raw_prompt_len );
 		(*menu)->timeout =
 			( ( raw_menu_prompt->timeout == 0xff ) ?
 			  -1 : raw_menu_prompt->timeout );