bcache: export backing_dev_uuid via sysfs

When there are multiple bcache devices, after a reboot the name of
bcache devices may change (e.g. current /dev/bcache1 was /dev/bcache0
before reboot). Therefore we need the backing device UUID (sb.uuid) to
identify each bcache device.

Backing device uuid can be found by program bcache-super-show, but
directly exporting backing_dev_uuid by sysfs file
/sys/block/bcache<?>/bcache/backing_dev_uuid is a much simpler method.

With backing_dev_uuid, and partition uuids from /dev/disk/by-partuuid/,
now we can identify each bcache device and its partitions conveniently.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
index b9166ee027fa..9be27b26d300 100644
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c
@@ -68,6 +68,7 @@ read_attribute(btree_written);
 read_attribute(metadata_written);
 read_attribute(active_journal_entries);
 read_attribute(backing_dev_name);
+read_attribute(backing_dev_uuid);
 
 sysfs_time_stats_attribute(btree_gc,    sec, ms);
 sysfs_time_stats_attribute(btree_split, sec, us);
@@ -250,6 +251,13 @@ SHOW(__bch_cached_dev)
                 return strlen(buf);
         }
 
+        if (attr == &sysfs_backing_dev_uuid) {
+                /* convert binary uuid into 36-byte string plus '\0' */
+                snprintf(buf, 36+1, "%pU", dc->sb.uuid);
+                strcat(buf, "\n");
+                return strlen(buf);
+        }
+
 #undef var
         return 0;
 }
@@ -460,6 +468,7 @@ static struct attribute *bch_cached_dev_files[] = {
         &sysfs_bypass_torture_test,
 #endif
         &sysfs_backing_dev_name,
+        &sysfs_backing_dev_uuid,
         NULL
 };
 KTYPE(bch_cached_dev);