btrfs: use btrfs_dev_name() helper to handle missing devices better

[BUG]
If dev-replace failed to re-construct its data/metadata, the kernel
message would be incorrect for the missing device:

 BTRFS info (device dm-1): dev_replace from <missing disk> (devid 2) to /dev/mapper/test-scratch2 started
 BTRFS error (device dm-1): failed to rebuild valid logical 38862848 for dev (efault)

Note the above "dev (efault)" of the second line.
While the first line is properly reporting "<missing disk>".

[CAUSE]
Although dev-replace is using btrfs_dev_name(), the heavy lifting work
is still done by scrub (scrub is reused by both dev-replace and regular
scrub).

Unfortunately scrub code never uses btrfs_dev_name() helper, as it's
only declared locally inside dev-replace.c.

[FIX]
Fix the output by:

- Move the btrfs_dev_name() helper to volumes.h

- Use btrfs_dev_name() to replace open-coded rcu_str_deref() calls
  Only zoned code is not touched, as I'm not familiar with degraded
  zoned code.

- Constify return value and parameter

Now the output looks pretty sane:

 BTRFS info (device dm-1): dev_replace from <missing disk> (devid 2) to /dev/mapper/test-scratch2 started
 BTRFS error (device dm-1): failed to rebuild valid logical 38862848 for dev <missing disk>

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 3 insertions, 12 deletions

diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 9c4a8649a0f4..78696d331639 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -18,7 +18,6 @@
 #include "volumes.h"
 #include "async-thread.h"
 #include "check-integrity.h"
-#include "rcu-string.h"
 #include "dev-replace.h"
 #include "sysfs.h"
 #include "zoned.h"
@@ -451,14 +450,6 @@ out:
 	return ret;
 }
 
-static char* btrfs_dev_name(struct btrfs_device *device)
-{
-	if (!device || test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state))
-		return "<missing disk>";
-	else
-		return rcu_str_deref(device->name);
-}
-
 static int mark_block_group_to_copy(struct btrfs_fs_info *fs_info,
 				    struct btrfs_device *src_dev)
 {
@@ -674,7 +665,7 @@ static int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
 		      "dev_replace from %s (devid %llu) to %s started",
 		      btrfs_dev_name(src_device),
 		      src_device->devid,
-		      rcu_str_deref(tgt_device->name));
+		      btrfs_dev_name(tgt_device));
 
 	/*
 	 * from now on, the writes to the srcdev are all duplicated to
@@ -933,7 +924,7 @@ static int btrfs_dev_replace_finishing(struct btrfs_fs_info *fs_info,
 				 "btrfs_scrub_dev(%s, %llu, %s) failed %d",
 				 btrfs_dev_name(src_device),
 				 src_device->devid,
-				 rcu_str_deref(tgt_device->name), scrub_ret);
+				 btrfs_dev_name(tgt_device), scrub_ret);
 error:
 		up_write(&dev_replace->rwsem);
 		mutex_unlock(&fs_info->chunk_mutex);
@@ -951,7 +942,7 @@ error:
 			  "dev_replace from %s (devid %llu) to %s finished",
 			  btrfs_dev_name(src_device),
 			  src_device->devid,
-			  rcu_str_deref(tgt_device->name));
+			  btrfs_dev_name(tgt_device));
 	clear_bit(BTRFS_DEV_STATE_REPLACE_TGT, &tgt_device->dev_state);
 	tgt_device->devid = src_device->devid;
 	src_device->devid = BTRFS_DEV_REPLACE_DEVID;