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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>
This commit is contained in:
Qu Wenruo 2023-11-02 07:54:50 +10:30 committed by Greg Kroah-Hartman
parent 0ad7d59e79
commit 3f26d9b257
2 changed files with 5 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
fs/btrfs/disk-io.c
View File

@ -3493,6 +3493,7 @@ 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

5
fs/btrfs/super.c
View File

@ -391,7 +391,10 @@ 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 {