Re: [PATCH] xfs: fix up inode32/64 (re)mount handling

Eric Sandeen
2016-02-18T05:51:49Z

On 2/17/16 11:46 PM, Eric Sandeen wrote:
> On 2/17/16 12:30 PM, Brian Foster wrote:
>> On Tue, Feb 16, 2016 at 10:47:49PM -0600, Eric Sandeen wrote:
>>> inode32/inode64 allocator behavior with respect to mount,
>>> remount and growfs is a little tricky.
>>>
>>> The inode32 mount option should only enable the inode32
>>> allocator heuristics if the filesystem is large enough
>>> for 64-bit inodes to exist. Today, it has this behavior
>>> on the initial mount, but a remount with inode32
>>> unconditionally changes the allocation heuristics, even
>>> for a small fs.
>>>
>>> Also, an inode32 mounted small filesystem should transition
>>> to the inode32 allocator if the filesystem is subsequently
>>> grown to a sufficient size. Today that does not happen.
>>>
>>> This patch consolidates xfs_set_inode32 and xfs_set_inode64
>>> into a single new function, and moves the "is the maximum inode
>>> number big enough to matter" test into that function, so
>>> it doesn't rely on the caller to get it right - which
>>> remount did not do, previously.
>>>
>>> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
>>> ---
>>>
>>> Note, this goes after my token-parsing patch for mount.
>
> ...
>
>>> @@ -607,54 +619,48 @@ xfs_set_inode32(struct xfs_mount *mp, xfs_agnumber_t agcount)
>>> max_metadata = agcount;
>>> }
>>>
>>> + /* Get the last possible inode in the filesystem */
>>> agino = XFS_OFFBNO_TO_AGINO(mp, sbp->sb_agblocks - 1, 0);
>>> + ino = XFS_AGINO_TO_INO(mp, agcount - 1, agino);
>>> +
>>> + /*
>>> + * If user asked for no more than 32-bit inodes, and the fs is
>>> + * sufficiently large, set XFS_MOUNT_32BITINODES if we must alter
>>> + * the allocator to accommodate the request.
>>> + */
>>> + if ((mp->m_flags & XFS_MOUNT_SMALL_INUMS) && ino > XFS_MAXINUMBER_32)
>>> + mp->m_flags |= XFS_MOUNT_32BITINODES;
>>> + else
>>> + mp->m_flags &= ~XFS_MOUNT_32BITINODES;
>>
>> In the current code, we call into xfs_set_inode64() if
>> XFS_MOUNT_SMALL_INUMS is not set or it is, but the largest inode is
>> within XFS_MAXINUMBER_32. In that latter case, xfs_set_inode64() does:
>>
>> mp->m_flags &= ~(XFS_MOUNT_32BITINODES |
>> XFS_MOUNT_SMALL_INUMS);
>>
>> ... which I think means we want to clear XFS_MOUNT_SMALL_INUMS along
>> with XFS_MOUNT_32BITINODES here, yes? The rest looks fine to me:
>
> I don't think so; that was a bug, AFAICT.
>
> XFS_MOUNT_32BITINODES means that inode32 was specified at mount

Ugh; I had that backwards.

*XFS_MOUNT_SMALL_INUMS* means that inode32 was specified at mount time.
For the reasons I stated, *that* flag should never be cleared. It
signifies a specified mount option, which does not go away just because
the filesystem is currently small.

Maybe we need clearer flag names :/

-Eric

> time, i.e. the user wants no more than 32-bit inodes for the
> duration of this mount.
>
> So this is actually a bugfix for the 2nd item mentioned above:
>
>>> Also, an inode32 mounted small filesystem should transition
>>> to the inode32 allocator if the filesystem is subsequently
>>> grown to a sufficient size. Today that does not happen.
>
>> Reviewed-by: Brian Foster <bfoster@redhat.com>
>
> Thanks,
> -Eric