btrfs: add dmesg output for first mount and last unmount of a filesystem

commit 2db313205f8b96eea467691917138d646bb50aef upstream.

There is a feature request to add dmesg output when unmounting a btrfs.
There are several alternative methods to do the same thing, but with
their own problems:

- Use eBPF to watch btrfs_put_super()/open_ctree()
  Not end user friendly, they have to dip their head into the source
  code.

- Watch for directory /sys/fs/<uuid>/
  This is way more simple, but still requires some simple device -> uuid
  lookups.  And a script needs to use inotify to watch /sys/fs/.

Compared to all these, directly outputting the information into dmesg
would be the most simple one, with both device and UUID included.

And since we're here, also add the output when mounting a filesystem for
the first time for parity. A more fine grained monitoring of subvolume
mounts should be done by another layer, like audit.

Now mounting a btrfs with all default mkfs options would look like this:

  [81.906566] BTRFS info (device dm-8): first mount of filesystem 633b5c16-afe3-4b79-b195-138fe145e4f2
  [81.907494] BTRFS info (device dm-8): using crc32c (crc32c-intel) checksum algorithm
  [81.908258] BTRFS info (device dm-8): using free space tree
  [81.912644] BTRFS info (device dm-8): auto enabling async discard
  [81.913277] BTRFS info (device dm-8): checking UUID tree
  [91.668256] BTRFS info (device dm-8): last unmount of filesystem 633b5c16-afe3-4b79-b195-138fe145e4f2

CC: stable@vger.kernel.org # 5.4+
Link: https://github.com/kdave/btrfs-progs/issues/689
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index f0654fe80b34691ecc23a7752ed7a9dc5c974059..24d10b541a135873e84a563d0a062205a122ba6b 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3204,6 +3204,7 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
                goto fail_alloc;
        }
 
+       btrfs_info(fs_info, "first mount of filesystem %pU", disk_super->fsid);
        /*
         * Verify the type first, if that or the checksum value are
         * corrupted, we'll find out

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 2fd0ee0e6e9310c4a713b0b6cf45526c67d575f7..718119e3830db735d46ab9e45e98ed04d59c6f9c 100644 (file)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -337,7 +337,10 @@ void __btrfs_panic(struct btrfs_fs_info *fs_info, const char *function,
 
 static void btrfs_put_super(struct super_block *sb)
 {
-       close_ctree(btrfs_sb(sb));
+       struct btrfs_fs_info *fs_info = btrfs_sb(sb);
+
+       btrfs_info(fs_info, "last unmount of filesystem %pU", fs_info->fs_devices->fsid);
+       close_ctree(fs_info);
 }
 
 enum {