Re: [PATCH 2/2] btrfs: fix root leak printk to use %lld instead of %llu

[David Sterba <dsterba@suse.cz>]

On Fri, Jul 24, 2020 at 08:40:17AM +0800, Qu Wenruo wrote:
> 
> 
> On 2020/7/23 下午10:20, David Sterba wrote:
> > On Wed, Jul 22, 2020 at 12:07:22PM -0400, Josef Bacik wrote:
> >> I'm a actual human being so am incapable of converting u64 to s64 in my
> >> head, use %lld so we can see the negative number in order to identify
> >> which of our special roots we leaked.
> >>
> >> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> >> ---
> >>  fs/btrfs/disk-io.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> >> index f1fdbdd44c02..cc4081a1c7f9 100644
> >> --- a/fs/btrfs/disk-io.c
> >> +++ b/fs/btrfs/disk-io.c
> >> @@ -1508,7 +1508,7 @@ void btrfs_check_leaked_roots(struct btrfs_fs_info *fs_info)
> >>  	while (!list_empty(&fs_info->allocated_roots)) {
> >>  		root = list_first_entry(&fs_info->allocated_roots,
> >>  					struct btrfs_root, leak_list);
> >> -		btrfs_err(fs_info, "leaked root %llu-%llu refcount %d",
> >> +		btrfs_err(fs_info, "leaked root %lld-%llu refcount %d",
> > 
> > But this is wrong in another way, roots with high numbers will appear as
> > negative numbers.
> > 
> 
> Nope. We won't have that many roots.
> 
> In fact, for subvolumes, the highest id is only 2 ^ 48, an special limit
> introduced for qgroup.

It's not a hard limit and certainly can have subvolumes with numbers
that high. That qgoups interpret the qgroup in some way is not a
limitation on subvolumes. We'll have to start reusing the subvolume ids
eventually, with qgroups we can on.

Also the negativer numbers start to appear with 2^32 so that's still
below the percieved limit of 2^48.

> So we won't have high enough subvolume ids to be negative, but only
> special trees.

For the internal trees we eg. have pretty-printer in progs so kernel can
reuse that.