Fixed device path canonicalization for use by devmapper (basilinya)

For some reason, when the monted device is "/dev/mapper/*", a record
in the form "/dev/dm-*" ends up in /etc/mtab and the device cannot be
unmounted.

The reason is unclear, the /dev/mapper name is not a symlink, and the
function doing the name change is not known. No detailed feedback from
the users having met the issue.

The patch changes the name back to the /dev/mapper name after realpath()
is called, and, if there is an actual change, both the name passed to
ntfs-3g and the one passed to fuse and mount are logged in the hope
of getting a clue about what is happening.

But ntfs-3g is probably not the right place for a fix.

include/ntfs-3g/Makefile.am

@@ -29,6 +29,7 @@ headers = \
 	ntfstime.h	\
 	object_id.h	\
 	param.h	\
+	realpath.h	\
 	reparse.h	\
 	runlist.h	\
 	security.h	\

include/ntfs-3g/param.h

@@ -63,6 +63,11 @@ enum {
 
 #define XATTRMAPPINGFILE ".NTFS-3G/XattrMapping" /* default mapping file */
 
+/*
+ *		Parameters for path canonicalization
+ */
+
+#define MAPPERNAMELTH 256
 
 /*
  *		Permission checking modes for high level and low level

include/ntfs-3g/realpath.h

@@ -0,0 +1,24 @@
+/*
+ * realpath.h - realpath() aware of device mapper
+ */
+
+#ifndef REALPATH_H
+#define REALPATH_H
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#ifdef HAVE_REALPATH
+#define ntfs_realpath realpath
+#else
+extern char *ntfs_realpath(const char *path, char *resolved_path);
+#endif
+
+#ifdef linux
+extern char *ntfs_realpath_canonicalize(const char *path, char *resolved_path);
+#else
+#define ntfs_realpath_canonicalize ntfs_realpath
+#endif
+
+#endif /* REALPATH_H */

libntfs-3g/Makefile.am

@@ -36,6 +36,7 @@ libntfs_3g_la_SOURCES =	\
 	misc.c 		\
 	mst.c 		\
 	object_id.c 	\
+	realpath.c	\
 	reparse.c 	\
 	runlist.c 	\
 	security.c 	\

libntfs-3g/realpath.c

@@ -0,0 +1,103 @@
+/*
+ * realpath.c - realpath() aware of device mapper
+ * Originated from the util-linux project.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+#ifdef HAVE_LIMITS_H
+#include <limits.h>
+#endif
+#ifdef HAVE_CTYPE_H
+#include <ctype.h>
+#endif
+
+#include "param.h"
+#include "realpath.h"
+
+/* If there is no realpath() on the system, provide a dummy one. */
+#ifndef HAVE_REALPATH
+char *ntfs_realpath(const char *path, char *resolved_path)
+{
+       strncpy(resolved_path, path, PATH_MAX);
+       resolved_path[PATH_MAX] = '\0';
+       return resolved_path;
+}
+#endif
+
+
+#ifdef linux
+
+/*
+ * Converts private "dm-N" names to "/dev/mapper/<name>"
+ *
+ * Since 2.6.29 (patch 784aae735d9b0bba3f8b9faef4c8b30df3bf0128) kernel sysfs
+ * provides the real DM device names in /sys/block/<ptname>/dm/name
+ */
+static char *
+canonicalize_dm_name(const char *ptname, char *canonical)
+{
+	FILE	*f;
+	size_t	sz;
+	char	path[MAPPERNAMELTH + 24];
+	char	name[MAPPERNAMELTH + 16];
+	char	*res = NULL;
+
+	snprintf(path, sizeof(path), "/sys/block/%s/dm/name", ptname);
+	if (!(f = fopen(path, "r")))
+		return NULL;
+
+	/* read "<name>\n" from sysfs */
+	if (fgets(name, sizeof(name), f) && (sz = strlen(name)) > 1) {
+		name[sz - 1] = '\0';
+		snprintf(path, sizeof(path), "/dev/mapper/%s", name);
+		res = strcpy(canonical, path);
+	}
+	fclose(f);
+	return res;
+}
+
+/*
+ *		Canonicalize a device path
+ *
+ *	Workaround from "basinilya" for fixing device mapper paths.
+ *
+ *  Background (Phillip Susi, 2011-04-09)
+ *	- ntfs-3g canonicalizes the device name so that if you mount with
+ *	  /dev/mapper/foo, the device name listed in mtab is /dev/dm-n,
+ *	  so you can not umount /dev/mapper/foo
+ *	- umount won't even recognize and translate /dev/dm-n to the mount
+ *	  point, apparently because of the '-' involved. Editing mtab and
+ *	  removing the '-' allows you to umount /dev/dmn successfully.
+ *
+ *	This code restores the devmapper name after canonicalization,
+ *	until a proper fix is implemented.
+ */
+
+char *ntfs_realpath_canonicalize(const char *path, char *canonical)
+{
+	char *p;
+
+	if (path == NULL)
+		return NULL;
+
+	if (!ntfs_realpath(path, canonical))
+		return NULL;
+
+	p = strrchr(canonical, '/');
+	if (p && strncmp(p, "/dm-", 4) == 0 && isdigit(*(p + 4))) {
+		p = canonicalize_dm_name(p+1, canonical);
+		if (p)
+			return p;
+	}
+
+	return canonical;
+}
+
+#endif

libntfs-3g/volume.c

@@ -67,6 +67,7 @@
 #include "dir.h"
 #include "logging.h"
 #include "cache.h"
+#include "realpath.h"
 #include "misc.h"
 
 const char *ntfs_home = 
@@ -1359,18 +1360,6 @@ int ntfs_umount(ntfs_volume *vol, const BOOL force __attribute__((unused)))
 
 #ifdef HAVE_MNTENT_H
 
-#ifndef HAVE_REALPATH
-/**
- * realpath - If there is no realpath on the system
- */
-static char *realpath(const char *path, char *resolved_path)
-{
-	strncpy(resolved_path, path, PATH_MAX);
-	resolved_path[PATH_MAX] = '\0';
-	return resolved_path;
-}
-#endif
-
 /**
  * ntfs_mntent_check - desc
  *
@@ -1394,7 +1383,7 @@ static int ntfs_mntent_check(const char *file, unsigned long *mnt_flags)
 		err = errno;
 		goto exit;
 	}
-	if (!realpath(file, real_file)) {
+	if (!ntfs_realpath_canonicalize(file, real_file)) {
 		err = errno;
 		goto exit;
 	}
@@ -1403,7 +1392,7 @@ static int ntfs_mntent_check(const char *file, unsigned long *mnt_flags)
 		goto exit;
 	}
 	while ((mnt = getmntent(f))) {
-		if (!realpath(mnt->mnt_fsname, real_fsname))
+		if (!ntfs_realpath_canonicalize(mnt->mnt_fsname, real_fsname))
 			continue;
 		if (!strcmp(real_file, real_fsname))
 			break;

src/lowntfs-3g.c

@@ -3457,16 +3457,6 @@ static void usage(void)
 			EXEC_NAME, ntfs_home);
 }
 
-#ifndef HAVE_REALPATH
-/* If there is no realpath() on the system, provide a dummy one. */
-static char *realpath(const char *path, char *resolved_path)
-{
-	strncpy(resolved_path, path, PATH_MAX);
-	resolved_path[PATH_MAX] = '\0';
-	return resolved_path;
-}
-#endif
-
 #if defined(linux) || defined(__uClinux__)
 
 static const char *dev_fuse_msg =
@@ -3668,6 +3658,9 @@ static void setup_logging(char *parsed_options)
 	ctx->seccache = (struct PERMISSIONS_CACHE*)NULL;
 
 	ntfs_log_info("Version %s %s %d\n", VERSION, FUSE_TYPE, fuse_version());
+	if (strcmp(opts.arg_device,opts.device))
+		ntfs_log_info("Requested device %s canonicalized as %s\n",
+				opts.arg_device,opts.device);
 	ntfs_log_info("Mounted %s (%s, label \"%s\", NTFS %d.%d)\n",
 			opts.device, (ctx->ro) ? "Read-Only" : "Read-Write",
 			ctx->vol->vol_name, ctx->vol->major_ver,

src/ntfs-3g.c

@@ -3372,16 +3372,6 @@ static void usage(void)
 			EXEC_NAME, ntfs_home);
 }
 
-#ifndef HAVE_REALPATH
-/* If there is no realpath() on the system, provide a dummy one. */
-static char *realpath(const char *path, char *resolved_path)
-{
-	strncpy(resolved_path, path, PATH_MAX);
-	resolved_path[PATH_MAX] = '\0';
-	return resolved_path;
-}
-#endif
-
 #if defined(linux) || defined(__uClinux__)
 
 static const char *dev_fuse_msg =
@@ -3588,6 +3578,9 @@ static void setup_logging(char *parsed_options)
 	ctx->seccache = (struct PERMISSIONS_CACHE*)NULL;
 
 	ntfs_log_info("Version %s %s %d\n", VERSION, FUSE_TYPE, fuse_version());
+	if (strcmp(opts.arg_device,opts.device))
+		ntfs_log_info("Requested device %s canonicalized as %s\n",
+				opts.arg_device,opts.device);
 	ntfs_log_info("Mounted %s (%s, label \"%s\", NTFS %d.%d)\n",
 			opts.device, (ctx->ro) ? "Read-Only" : "Read-Write",
 			ctx->vol->vol_name, ctx->vol->major_ver,

src/ntfs-3g_common.c

@@ -47,6 +47,7 @@
 #include "security.h"
 #include "xattrs.h"
 #include "ntfs-3g_common.h"
+#include "realpath.h"
 #include "misc.h"
 
 const char xattr_ntfs_3g[] = "ntfs-3g.";
@@ -509,7 +510,9 @@ int ntfs_parse_options(struct ntfs_options *popts, void (*usage)(void),
 					return -1;
 				
 				/* Canonicalize device name (mtab, etc) */
-				if (!realpath(optarg, popts->device)) {
+				popts->arg_device = optarg;
+				if (!ntfs_realpath_canonicalize(optarg,
+						popts->device)) {
 					ntfs_log_perror("%s: Failed to access "
 					     "volume '%s'", EXEC_NAME, optarg);
 					free(popts->device);

src/ntfs-3g_common.h

@@ -29,6 +29,7 @@ struct ntfs_options {
         char    *mnt_point;     /* Mount point */    
         char    *options;       /* Mount options */  
         char    *device;        /* Device to mount */
+	char	*arg_device;	/* Device requested in argv */
 } ;
 
 typedef enum {