From: Karel Zak <kzak@redhat.com>
Date: Mon, 27 Apr 2009 12:33:22 +0000 (+0200)
Subject: blkid: use /sys/block/dm-<N>/dm/name
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6f52b6e9ae8a02285cab0e19bffc2f599e97f517;p=util-linux

blkid: use /sys/block/dm-<N>/dm/name

The Linux kernel (since 2.6.29, patch 784aae735d9b0bba3f8b9faef4c8b30df3bf0128)
exports the real DM device names in /sys/block/<ptname>/dm/name.

The sysfs based solution is nicer and faster than scan for devno in
/dev/mapper/.

CC: Milan Broz <mbroz@redhat.com>
Signed-off-by: Karel Zak <kzak@redhat.com>
---

diff --git a/libs/blkid/src/devname.c b/libs/blkid/src/devname.c
index d2f53330..ef686f4b 100644
--- a/libs/blkid/src/devname.c
+++ b/libs/blkid/src/devname.c
@@ -152,6 +152,30 @@ static int is_dm_leaf(const char *devname)
 	return ret;
 }
 
+/*
+ * 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.
  */
@@ -183,7 +207,9 @@ static void probe_one(blkid_cache cache, const char *ptname,
 	 * to standard /dev/mapper/<name>.
 	 */
 	if (!strncmp(ptname, "dm-", 3) && isdigit(ptname[3])) {
-		blkid__scan_dir("/dev/mapper", devno, 0, &devname);
+		devname = get_dm_name(ptname);
+		if (!devname)
+			blkid__scan_dir("/dev/mapper", devno, 0, &devname);
 		if (devname)
 			goto get_dev;
 	}