[cpio] Split out bzImage initrd CPIO header construction

iPXE will construct CPIO headers for images that have a non-empty
command line, thereby allowing raw images (without CPIO headers) to be
injected into a dynamically constructed initrd.  This feature is
currently implemented within the BIOS-only bzImage format support.

Split out the CPIO header construction logic to allow for reuse in
other contexts such as in a UEFI build.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/x86/image/bzimage.c

@@ -326,32 +326,6 @@ static void bzimage_set_cmdline ( struct image *image,
 	DBGC ( image, "bzImage %p command line \"%s\"\n", image, cmdline );
 }
 
-/**
- * Parse standalone image command line for cpio parameters
- *
- * @v image		bzImage file
- * @v cpio		CPIO header
- * @v cmdline		Command line
- */
-static void bzimage_parse_cpio_cmdline ( struct image *image,
-					 struct cpio_header *cpio,
-					 const char *cmdline ) {
-	char *arg;
-	char *end;
-	unsigned int mode;
-
-	/* Look for "mode=" */
-	if ( ( arg = strstr ( cmdline, "mode=" ) ) ) {
-		arg += 5;
-		mode = strtoul ( arg, &end, 8 /* Octal for file mode */ );
-		if ( *end && ( *end != ' ' ) ) {
-			DBGC ( image, "bzImage %p strange \"mode=\""
-			       "terminator '%c'\n", image, *end );
-		}
-		cpio_set_field ( cpio->c_mode, ( 0100000 | mode ) );
-	}
-}
-
 /**
  * Align initrd length
  *
@@ -374,11 +348,9 @@ static inline size_t bzimage_align ( size_t len ) {
 static size_t bzimage_load_initrd ( struct image *image,
 				    struct image *initrd,
 				    userptr_t address ) {
-	char *filename = initrd->cmdline;
+	const char *filename = cpio_name ( initrd );
-	char *cmdline;
 	struct cpio_header cpio;
 	size_t offset;
-	size_t name_len;
 	size_t pad_len;
 
 	/* Do not include kernel image itself as an initrd */
@@ -386,25 +358,7 @@ static size_t bzimage_load_initrd ( struct image *image,
 		return 0;
 
 	/* Create cpio header for non-prebuilt images */
-	if ( filename && filename[0] ) {
+	offset = cpio_header ( initrd, &cpio );
-		cmdline = strchr ( filename, ' ' );
-		name_len = ( ( cmdline ? ( ( size_t ) ( cmdline - filename ) )
-			       : strlen ( filename ) ) + 1 /* NUL */ );
-		memset ( &cpio, '0', sizeof ( cpio ) );
-		memcpy ( cpio.c_magic, CPIO_MAGIC, sizeof ( cpio.c_magic ) );
-		cpio_set_field ( cpio.c_mode, 0100644 );
-		cpio_set_field ( cpio.c_nlink, 1 );
-		cpio_set_field ( cpio.c_filesize, initrd->len );
-		cpio_set_field ( cpio.c_namesize, name_len );
-		if ( cmdline ) {
-			bzimage_parse_cpio_cmdline ( image, &cpio,
-						     ( cmdline + 1 /* ' ' */ ));
-		}
-		offset = ( ( sizeof ( cpio ) + name_len + 0x03 ) & ~0x03 );
-	} else {
-		offset = 0;
-		name_len = 0;
-	}
 
 	/* Copy in initrd image body (and cpio header if applicable) */
 	if ( address ) {
@@ -413,7 +367,7 @@ static size_t bzimage_load_initrd ( struct image *image,
 			memset_user ( address, 0, 0, offset );
 			copy_to_user ( address, 0, &cpio, sizeof ( cpio ) );
 			copy_to_user ( address, sizeof ( cpio ), filename,
-				       ( name_len - 1 /* NUL (or space) */ ) );
+				       cpio_name_len ( initrd ) );
 		}
 		DBGC ( image, "bzImage %p initrd %p [%#08lx,%#08lx,%#08lx)"
 		       "%s%s\n", image, initrd, user_to_phys ( address, 0 ),

src/arch/x86/image/initrd.c

@@ -29,6 +29,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #include <ipxe/uaccess.h>
 #include <ipxe/init.h>
 #include <ipxe/memblock.h>
+#include <ipxe/cpio.h>
 
 /** @file
  *

src/arch/x86/include/initrd.h

@@ -11,13 +11,6 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 #include <ipxe/uaccess.h>
 
-/** Minimum alignment for initrds
- *
- * Some versions of Linux complain about initrds that are not
- * page-aligned.
- */
-#define INITRD_ALIGN 4096
-
 /** Minimum free space required to reshuffle initrds
  *
  * Chosen to avoid absurdly long reshuffling times

src/core/cpio.c

@@ -30,6 +30,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  */
 
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 #include <ipxe/cpio.h>
 
@@ -45,3 +46,87 @@ void cpio_set_field ( char *field, unsigned long value ) {
 	snprintf ( buf, sizeof ( buf ), "%08lx", value );
 	memcpy ( field, buf, 8 );
 }
+
+/**
+ * Get CPIO image filename
+ *
+ * @v image		Image
+ * @ret len		CPIO filename length (0 for no filename)
+ */
+size_t cpio_name_len ( struct image *image ) {
+	const char *name = cpio_name ( image );
+	char *sep;
+	size_t len;
+
+	/* Check for existence of CPIO filename */
+	if ( ! name )
+		return 0;
+
+	/* Locate separator (if any) */
+	sep = strchr ( name, ' ' );
+	len = ( sep ? ( ( size_t ) ( sep - name ) ) : strlen ( name ) );
+
+	return len;
+}
+
+/**
+ * Parse CPIO image parameters
+ *
+ * @v image		Image
+ * @v cpio		CPIO header to fill in
+ */
+static void cpio_parse_cmdline ( struct image *image,
+				 struct cpio_header *cpio ) {
+	const char *cmdline;
+	char *arg;
+	char *end;
+	unsigned int mode;
+
+	/* Skip image filename */
+	cmdline = ( cpio_name ( image ) + cpio_name_len ( image ) );
+
+	/* Look for "mode=" */
+	if ( ( arg = strstr ( cmdline, "mode=" ) ) ) {
+		arg += 5;
+		mode = strtoul ( arg, &end, 8 /* Octal for file mode */ );
+		if ( *end && ( *end != ' ' ) ) {
+			DBGC ( image, "CPIO %p strange \"mode=\" "
+			       "terminator '%c'\n", image, *end );
+		}
+		cpio_set_field ( cpio->c_mode, ( 0100000 | mode ) );
+	}
+}
+
+/**
+ * Construct CPIO header for image, if applicable
+ *
+ * @v image		Image
+ * @v cpio		CPIO header to fill in
+ * @ret len		Length of magic CPIO header (including filename)
+ */
+size_t cpio_header ( struct image *image, struct cpio_header *cpio ) {
+	size_t name_len;
+	size_t len;
+
+	/* Get filename length */
+	name_len = cpio_name_len ( image );
+
+	/* Images with no filename are assumed to already be CPIO archives */
+	if ( ! name_len )
+		return 0;
+
+	/* Construct CPIO header */
+	memset ( cpio, '0', sizeof ( *cpio ) );
+	memcpy ( cpio->c_magic, CPIO_MAGIC, sizeof ( cpio->c_magic ) );
+	cpio_set_field ( cpio->c_mode, 0100644 );
+	cpio_set_field ( cpio->c_nlink, 1 );
+	cpio_set_field ( cpio->c_filesize, image->len );
+	cpio_set_field ( cpio->c_namesize, ( name_len + 1 /* NUL */ ) );
+	cpio_parse_cmdline ( image, cpio );
+
+	/* Calculate total length */
+	len = ( ( sizeof ( *cpio ) + name_len + 1 /* NUL */ + CPIO_ALIGN - 1 )
+		& ~( CPIO_ALIGN - 1 ) );
+
+	return len;
+}

src/include/ipxe/cpio.h

@@ -9,6 +9,8 @@
 
 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
+#include <ipxe/image.h>
+
 /** A CPIO archive header
  *
  * All field are hexadecimal ASCII numbers padded with '0' on the
@@ -48,6 +50,25 @@ struct cpio_header {
 /** CPIO magic */
 #define CPIO_MAGIC "070701"
 
+/** CPIO header length alignment */
+#define CPIO_ALIGN 4
+
+/** Alignment for CPIO archives within an initrd */
+#define INITRD_ALIGN 4096
+
+/**
+ * Get CPIO image name
+ *
+ * @v image		Image
+ * @ret name		Image name (not NUL terminated)
+ */
+static inline __attribute__ (( always_inline )) const char *
+cpio_name ( struct image *image ) {
+	return image->cmdline;
+}
+
 extern void cpio_set_field ( char *field, unsigned long value );
+extern size_t cpio_name_len ( struct image *image );
+extern size_t cpio_header ( struct image *image, struct cpio_header *cpio );
 
 #endif /* _IPXE_CPIO_H */