libblkid: use partno for partitions mapped by DM

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

1 files changed, 44 insertions, 4 deletions

diff --git a/shlibs/blkid/src/partitions/partitions.c b/shlibs/blkid/src/partitions/partitions.c
index 060461d27..76cb21d40 100644
--- a/shlibs/blkid/src/partitions/partitions.c
+++ b/shlibs/blkid/src/partitions/partitions.c
@@ -892,20 +892,60 @@ blkid_partition blkid_partlist_devno_to_partition(blkid_partlist ls, dev_t devno
 {
 	struct sysfs_cxt sysfs;
 	uint64_t start, size;
-	int i, rc;
+	int i, rc, partno = 0;
 
 	if (sysfs_init(&sysfs, devno, NULL))
 		return NULL;
 
-	rc = sysfs_read_u64(&sysfs, "start", &start);
-	if (!rc)
-		rc = sysfs_read_u64(&sysfs, "size", &size);
+	rc = sysfs_read_u64(&sysfs, "size", &size);
+	if (!rc) {
+		rc = sysfs_read_u64(&sysfs, "start", &start);
+		if (rc) {
+			/* try to get partition number from DM uuid.
+			 */
+			char *uuid = sysfs_strdup(&sysfs, "dm/uuid");
+			char *tmp = uuid;
+			char *prefix = uuid ? strsep(&tmp, "-") : NULL;
+
+			if (prefix && strncasecmp(prefix, "part", 4) == 0) {
+				char *end = NULL;
+
+				partno = strtol(prefix + 4, &end, 10);
+				if (prefix == end || (end && *end))
+					partno = 0;
+				else
+					rc = 0;		/* success */
+			}
+			free(uuid);
+		}
+	}
 
 	sysfs_deinit(&sysfs);
 
 	if (rc)
 		return NULL;
 
+	if (partno) {
+		/*
+		 * Partition mapped by kpartx does not provide "start" offset
+		 * in /sys, but if we know partno and size of the partition
+		 * that we can probably make the releation bettween the device
+		 * and an entry in partition table.
+		 */
+		 for (i = 0; i < ls->nparts; i++) {
+			 blkid_partition par = &ls->parts[i];
+
+			 if (partno != blkid_partition_get_partno(par))
+				 continue;
+
+			 if (size == blkid_partition_get_size(par) ||
+			     (blkid_partition_is_extended(par) && size <= 1024))
+				 return par;
+
+		 }
+		 return NULL;
+	}
+
 	for (i = 0; i < ls->nparts; i++) {
 		blkid_partition par = &ls->parts[i];