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, 2 insertions, 2 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 7a9e697d9931..bed74a3ff574 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1228,7 +1228,7 @@ static noinline int btrfs_ioctl_resize(struct file *file,
 	if (ret == 0 && new_size != old_size)
 		btrfs_info_in_rcu(fs_info,
 			"resize device %s (devid %llu) from %llu to %llu",
-			rcu_str_deref(device->name), device->devid,
+			btrfs_dev_name(device), device->devid,
 			old_size, new_size);
 out_finish:
 	btrfs_exclop_finish(fs_info);
@@ -2860,7 +2860,7 @@ static long btrfs_ioctl_dev_info(struct btrfs_fs_info *fs_info,
 	di_args->total_bytes = btrfs_device_get_total_bytes(dev);
 	memcpy(di_args->uuid, dev->uuid, sizeof(di_args->uuid));
 	if (dev->name) {
-		strncpy(di_args->path, rcu_str_deref(dev->name),
+		strncpy(di_args->path, btrfs_dev_name(dev),
 				sizeof(di_args->path) - 1);
 		di_args->path[sizeof(di_args->path) - 1] = 0;
 	} else {