On Mon, Dec 11, 2023 at 03:56:16PM +0100, Greg Kroah-Hartman wrote: > On Sat, Dec 09, 2023 at 10:28:36AM -0700, Nathan Chancellor wrote: > > On Tue, Dec 05, 2023 at 12:17:31PM +0900, Greg Kroah-Hartman wrote: > > > 5.4-stable review patch. If anyone has any objections, please let me know. > > > > > > ------------------ > > > > > > From: Qu Wenruo <wqu@xxxxxxxx> > > > > > > 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@xxxxxxxxxxxxxxx # 5.4+ > > > Link: https://github.com/kdave/btrfs-progs/issues/689 > > > Reviewed-by: Anand Jain <anand.jain@xxxxxxxxxx> > > > Signed-off-by: Qu Wenruo <wqu@xxxxxxxx> > > > Reviewed-by: David Sterba <dsterba@xxxxxxxx> > > > [ update changelog ] > > > Signed-off-by: David Sterba <dsterba@xxxxxxxx> > > > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > > --- > > > fs/btrfs/disk-io.c | 1 + > > > fs/btrfs/super.c | 5 ++++- > > > 2 files changed, 5 insertions(+), 1 deletion(-) > > > > > > --- a/fs/btrfs/disk-io.c > > > +++ b/fs/btrfs/disk-io.c > > > @@ -2829,6 +2829,7 @@ int open_ctree(struct super_block *sb, > > > goto fail_alloc; > > > } > > > > > > + btrfs_info(fs_info, "first mount of filesystem %pU", disk_super->fsid); > > > > clang tells me this backport does not appear to be correct and will > > likely introduce a null pointer deference: > > > > fs/btrfs/disk-io.c:2832:55: warning: variable 'disk_super' is uninitialized when used here [-Wuninitialized] > > 2832 | btrfs_info(fs_info, "first mount of filesystem %pU", disk_super->fsid); > > | ^~~~~~~~~~ > > fs/btrfs/ctree.h:3002:41: note: expanded from macro 'btrfs_info' > > 3002 | btrfs_printk(fs_info, KERN_INFO fmt, ##args) > > | ^~~~ > > fs/btrfs/disk-io.c:2630:38: note: initialize the variable 'disk_super' to silence this warning > > 2630 | struct btrfs_super_block *disk_super; > > | ^ > > | = NULL > > 1 warning generated. > > Thanks for the notice, I've now reverted this. Thanks. I've verified that this only affects 5.4. The patch is still possible to apply there, the btrfs_info() call would have to be moved after 'disk_super' is initialized. The patch is not that important so reverting is OK for me.
