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

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: [email protected] # 5.4+
Link: https://github.com/kdave/btrfs-progs/issues/689
Reviewed-by: Anand Jain <[email protected]>
Signed-off-by: Qu Wenruo <[email protected]>
Reviewed-by: David Sterba <[email protected]>
[ update changelog ]
Signed-off-by: David Sterba <[email protected]>

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 401ea09ae4b8ce284c1b07a1d24347159f9821dc..bbcc3df776461f5b6952422c246e65bbcbc1ccc6 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3213,6 +3213,7 @@ 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 6ecf78d09694342f41857f83bbfd7177efeac616..9e1f3dbc80fa5321a42f5130c826710e29cf4e66 100644 (file)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -80,7 +80,10 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data);
 
 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 {