Re: [PATCH 0/2] libblkid: add FSSIZE with XFS implementation

[Karel Zak <kzak@redhat.com>]

On Mon, Apr 25, 2022 at 10:38:02AM -0500, Eric Sandeen wrote:
> On 4/25/22 8:43 AM, Karel Zak wrote:
> > 
> >  Thanks Andrey,
> > 
> > the code looks good.
> > 
> > On Thu, Apr 21, 2022 at 03:09:44PM +0200, Andrey Albershteyn wrote:
> >> I had a look into other fs, like ext4 and btrfs, to implement FSSIZE
> >> for them, but I think I don't have enough expertize to do that as
> >> they have not so trivial metadata overhead calculation :)
> > 
> > But it would be nice to have ext4 and btrfs too. Maybe Eric can help
> > you :-)
> > 
> >     Karel
> 
> For ext4 something like e2fsprogs does is probably ok:
> 
> static __u64 e2p_free_blocks_count(struct ext2_super_block *super)
> {
>         return super->s_free_blocks_count |
>                 (ext2fs_has_feature_64bit(super) ?
>                 (__u64) super->s_free_blocks_hi << 32 : 0);
> }
> 
> though I wonder if a little documentation on the intent of the flag is
> in order; ext4 can return "df" in different ways (see the minixdf and
> bsddf mount options.)
> 
> I think best effort seems fine here, and reporting the same number
> as the ext4 utilities do should be fine.

Yes, that's good enough.

> As for btrfs - I'm really not sure what this should return on a
> multi-device filesystem?

Hmm ... good point. I guess the right answer is return nothing,
because we really don't want any complicated fs-specific logic in
libblkid.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com