mount: and libblkid: covert /dev/dm-N to /dev/mapper/<name>

 * mount(8) uses private device-mapper names in mtab

 * libblkid returns private device-mapper names when evaluate udev
   /dev/disk-by symlinks.

 * on systems where DM is fully integrated with udev the /dev/mapper/<name>
   files are symlinks to /dev/dm-N. It means we need a special care to hide
   private device-mapper names.

Signed-off-by: Karel Zak <kzak@redhat.com>

3 files changed, 47 insertions, 29 deletions

diff --git a/include/canonicalize.h b/include/canonicalize.h
index b04510c7..f26df18c 100644
--- a/include/canonicalize.h
+++ b/include/canonicalize.h
@@ -4,5 +4,6 @@
 #include "c.h"	/* for PATH_MAX */
 
 extern char *canonicalize_path(const char *path);
+extern char *canonicalize_dm_name(const char *ptname);
 
 #endif /* CANONICALIZE_H */
diff --git a/lib/canonicalize.c b/lib/canonicalize.c
index b888fbb8..e54cf0c0 100644
--- a/lib/canonicalize.c
+++ b/lib/canonicalize.c
@@ -20,6 +20,9 @@
  *
  * TODO: use canonicalize_file_name() when exist in glibc
  */
+#include <stdio.h>
+#include <string.h>
+#include <ctype.h>
 #include <unistd.h>
 #include <string.h>
 #include <errno.h>
@@ -136,17 +139,54 @@ myrealpath(const char *path, char *resolved_path, int maxreslth) {
 	return NULL;
 }
 
+/*
+ * 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
+ */
 char *
-canonicalize_path(const char *path) {
+canonicalize_dm_name(const char *ptname)
+{
+	FILE	*f;
+	size_t	sz;
+	char	path[256], name[256], *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 = strdup(path);
+	}
+	fclose(f);
+	return res;
+}
+
+char *
+canonicalize_path(const char *path)
+{
 	char canonical[PATH_MAX+2];
+	char *p;
 
 	if (path == NULL)
 		return NULL;
 
-	if (myrealpath (path, canonical, PATH_MAX+1))
-		return strdup(canonical);
+	if (!myrealpath(path, canonical, PATH_MAX+1))
+		return strdup(path);
+
+
+	p = strrchr(canonical, '/');
+	if (p && strncmp(p, "/dm-", 4) == 0 && isdigit(*(p + 4))) {
+		p = canonicalize_dm_name(p+1);
+		if (p)
+			return p;
+	}
 
-	return strdup(path);
+	return strdup(canonical);
 }
 
 
diff --git a/shlibs/blkid/src/devname.c b/shlibs/blkid/src/devname.c
index fe0d1b33..d048c722 100644
--- a/shlibs/blkid/src/devname.c
+++ b/shlibs/blkid/src/devname.c
@@ -38,6 +38,7 @@
 #include <time.h>
 
 #include "blkidP.h"
+#include "canonicalize.h"		/* $(top_srcdir)/include */
 
 /*
  * Find a dev struct in the cache by device name, if available.
@@ -153,30 +154,6 @@ static int is_dm_leaf(const char *devname)
 }
 
 /*
- * Since 2.6.29 (patch 784aae735d9b0bba3f8b9faef4c8b30df3bf0128) kernel sysfs
- * provides the real DM device names in /sys/block/<ptname>/dm/name
- */
-static char *get_dm_name(const char *ptname)
-{
-	FILE	*f;
-	size_t	sz;
-	char	path[256], name[256], *res = NULL;
-
-	snprintf(path, sizeof(path), "/sys/block/%s/dm/name", ptname);
-	if ((f = fopen(path, "r")) == NULL)
-		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 = blkid_strdup(path);
-	}
-	fclose(f);
-	return res;
-}
-
-/*
  * Probe a single block device to add to the device cache.
  */
 static void probe_one(blkid_cache cache, const char *ptname,
@@ -207,7 +184,7 @@ static void probe_one(blkid_cache cache, const char *ptname,
 	 * to standard /dev/mapper/<name>.
 	 */
 	if (!strncmp(ptname, "dm-", 3) && isdigit(ptname[3])) {
-		devname = get_dm_name(ptname);
+		devname = canonicalize_dm_name(ptname);
 		if (!devname)
 			blkid__scan_dir("/dev/mapper", devno, 0, &devname);
 		if (devname)