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>

1 files changed, 44 insertions, 4 deletions

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);
 }