Add device-mapper support to the blkid library

On systems where is multi-path storage device is problem with duplicated
filesystems. The solution is select "the best" device. This is possible
by device-mapper library.

Short quotation from RH bugzilla:

With my patch, all dm devices remains in libblkid cache.

Only the top level dm devices are given high priority
and more appropriate node names (i.e. /dev/mapper/*) are used.

For example, if we have linear mapped dm device "ov1" over
dm device "disk1p3" which is multipath mapped to /dev/sdd3 and /dev/sdh3:
  # dmsetup.static ls --tree
  ov1 (253:5) <-- /dev/mapper/ov1 or /dev/dm-5
   `-disk1p3 (253:4) <-- /dev/mapper/disk1p3 or /dev/dm-4
      `-disk1 (253:0)
         |- (8:112) <-- /dev/sdh
         `- (8:48) <-- /dev/sdd

Original version of blkid will show:
  # ./orig/blkid -t LABEL=mpdisk1p3 -l
  /dev/sdd3: LABEL="mpdisk1p3" ... TYPE="ext3"

With my patch, blkid will show:
  # ./deptree/blkid -t LABEL=mpdisk1p3 -l
  /dev/mapper/ov1: LABEL="mpdisk1p3" ... TYPE="ext3"

In blkid cache, all devices are listed:

  # ./orig/blkid -t LABEL=mpdisk1p3
  /dev/sdd3: LABEL="mpdisk1p3" ... TYPE="ext3"
  /dev/sdh3: LABEL="mpdisk1p3" ... TYPE="ext3"
  /dev/dm-4: LABEL="mpdisk1p3" ... TYPE="ext3"
  /dev/dm-5: LABEL="mpdisk1p3" ... TYPE="ext3"

  # ./deptree/blkid -t LABEL=mpdisk1p3
  /dev/mapper/ov1: LABEL="mpdisk1p3" ... TYPE="ext3"
  /dev/sdd3: LABEL="mpdisk1p3" ... TYPE="ext3"
  /dev/sdh3: LABEL="mpdisk1p3" ... TYPE="ext3"
  /dev/dm-4: LABEL="mpdisk1p3" ... TYPE="ext3"

For more details see discussion on:
https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=156324

Addresses Red Hat Bug: #156324

Signed-off-by: Karel Zak <kzak@redhat.com>
Signed-off-by: Peter Jones <pjones@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 166 insertions, 0 deletions

diff --git a/lib/blkid/devname.c b/lib/blkid/devname.c
index 3b1ad89b..0a13c477 100644
--- a/lib/blkid/devname.c
+++ b/lib/blkid/devname.c
@@ -11,6 +11,8 @@
  * %End-Header%
  */
 
+#define _GNU_SOURCE 1
+
 #include <stdio.h>
 #include <string.h>
 #if HAVE_UNISTD_H
@@ -35,6 +37,10 @@
 
 #include "blkidP.h"
 
+#ifdef HAVE_DEVMAPPER
+#include <libdevmapper.h>
+#endif
+
 /*
  * Find a dev struct in the cache by device name, if available.
  *
@@ -75,6 +81,10 @@ blkid_dev blkid_get_dev(blkid_cache cache, const char *devname, int flags)
 	return dev;
 }
 
+#ifdef HAVE_DEVMAPPER
+static int dm_device_is_leaf(const dev_t dev);
+#endif
+
 /*
  * Probe a single block device to add to the device cache.
  */
@@ -90,6 +100,10 @@ static void probe_one(blkid_cache cache, const char *ptname,
 	list_for_each(p, &cache->bic_devs) {
 		blkid_dev tmp = list_entry(p, struct blkid_struct_dev,
 					   bid_devs);
+#ifdef HAVE_DEVMAPPER
+		if (!dm_device_is_leaf(devno))
+			continue;
+#endif
 		if (tmp->bid_devno == devno) {
 			if (only_if_new)
 				return;
@@ -137,6 +151,155 @@ set_pri:
 	return;
 }
 
+#ifdef HAVE_DEVMAPPER
+/* 
+ * device-mapper support 
+ */
+static int dm_device_has_dep(const dev_t dev, const char *name)
+{
+	struct dm_task *task;
+	struct dm_deps *deps;
+	struct dm_info info;
+	int i;
+
+	task = dm_task_create(DM_DEVICE_DEPS);
+	if (!task)
+		return 0;
+
+	dm_task_set_name(task, name);
+	dm_task_run(task);
+	dm_task_get_info(task, &info);
+
+	if (!info.exists) {
+		dm_task_destroy(task);
+		return 0;
+	}
+
+	deps = dm_task_get_deps(task);
+	if (!deps || deps->count == 0) {
+		dm_task_destroy(task);
+		return 0;
+	}
+
+	for (i = 0; i < deps->count; i++) {
+		dev_t dep_dev = deps->device[i];
+
+		if (dev == dep_dev) {
+			dm_task_destroy(task);
+			return 1;
+		}
+	}
+
+	dm_task_destroy(task);
+	return 0;
+}
+
+static int dm_device_is_leaf(const dev_t dev)
+{
+	struct dm_task *task;
+	struct dm_names *names;
+	unsigned int next = 0;
+	int n, ret = 1;
+
+	task = dm_task_create(DM_DEVICE_LIST);
+	if (!task)
+		return 1;
+
+	dm_task_run(task);
+	names = dm_task_get_names(task);
+	if (!names || !names->dev) {
+		dm_task_destroy(task);
+		return 1;
+	}
+
+	n = 0;
+	do {
+		names = (void *)names + next;
+
+		if (dm_device_has_dep(dev, names->name))
+			ret = 0;
+
+		next = names->next;
+	} while (next);
+
+	dm_task_destroy(task);
+
+	return ret;
+}
+
+static dev_t dm_get_devno(const char *name)
+{
+	struct dm_task *task;
+	struct dm_info info;
+	dev_t ret = 0;
+
+	task = dm_task_create(DM_DEVICE_INFO);
+	if (!task)
+		return ret;
+
+	dm_task_set_name(task, name);
+	dm_task_run(task);
+	dm_task_get_info(task, &info);
+
+	if (!info.exists) {
+		dm_task_destroy(task);
+		return ret;
+	}
+
+	ret = makedev(info.major, info.minor);
+
+	dm_task_destroy(task);
+	
+	return ret;
+}
+
+static void dm_probe_all(blkid_cache cache, int only_if_new)
+{
+	struct dm_task *task;
+	struct dm_names *names;
+	unsigned int next = 0;
+	int n;
+
+	task = dm_task_create(DM_DEVICE_LIST);
+	if (!task)
+		return;
+
+	dm_task_run(task);
+	names = dm_task_get_names(task);
+	if (!names || !names->dev) {
+		dm_task_destroy(task);
+		return;
+	}
+
+	n = 0;
+	do {
+		int rc;
+		char *device = NULL;
+		dev_t dev = 0;
+
+		names = (void *)names + next;
+
+		rc = asprintf(&device, "/dev/mapper/%s", names->name);
+		if (rc < 0)
+			goto try_next;
+
+		dev = dm_get_devno(names->name);
+		if (dev == 0)
+			goto try_next;
+
+		if (!dm_device_is_leaf(dev)) 
+			goto try_next;
+
+		probe_one(cache, device, dev, BLKID_PRI_DM, only_if_new);
+
+try_next:
+		next = names->next;
+	} while (next);
+
+	dm_task_destroy(task);
+}
+#endif /* HAVE_DEVMAPPER */
+
 #define PROC_PARTITIONS "/proc/partitions"
 #define VG_DIR		"/proc/lvm/VGs"
 
@@ -290,6 +453,9 @@ static int probe_all(blkid_cache cache, int only_if_new)
 		return 0;
 
 	blkid_read_cache(cache);
+#ifdef HAVE_DEVMAPPER
+	dm_probe_all(cache, only_if_new);
+#endif
 	evms_probe_all(cache, only_if_new);
 #ifdef VG_DIR
 	lvm_probe_all(cache, only_if_new);