On 10/17/18 5:49 PM, Eric Sandeen wrote:
>
>
> On 10/17/18 5:30 PM, Darrick J. Wong wrote:
>> On Wed, Oct 17, 2018 at 05:20:56PM -0500, Eric Sandeen wrote:
>>> Today we reject this flag on an already-reflinked inode, but we really
>>> need to reject it for any inode on a reflink-capable filesystem until
>>> reflink+dax is supported.
>>>
>>> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
>>> ---
>>>
>>> (um, do we need to catch this when reading from disk as well? If we
>>> found a dax-flagged inode on a reflinked fs, then what would we do with it?)
>>
>> Ignore the DAX flag. See xfs_inode_supports_dax.
>
> Oh, ok.
>
> Hohum, by that measure shouldn't we allow mount -o dax on reflink filesystems,
> and just ignore/reject dax behavior on actually reflinked inodes?
>
>>> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
>>> index 0ef5ece5634c..63d579c652f2 100644
>>> --- a/fs/xfs/xfs_ioctl.c
>>> +++ b/fs/xfs/xfs_ioctl.c
>>> @@ -1031,8 +1031,9 @@ xfs_ioctl_setattr_xflags(
>>> if ((fa->fsx_xflags & FS_XFLAG_REALTIME) && xfs_is_reflink_inode(ip))
>>> ip->i_d.di_flags2 &= ~XFS_DIFLAG2_REFLINK;
>>>
>>> - /* Don't allow us to set DAX mode for a reflinked file for now. */
>>> - if ((fa->fsx_xflags & FS_XFLAG_DAX) && xfs_is_reflink_inode(ip))
>>> + /* Don't allow us to set DAX mode on a reflink filesystem for now. */
>>> + if ((fa->fsx_xflags & FS_XFLAG_DAX) &&
>>> + xfs_sb_version_hasreflink(&ip->i_mount->m_sb))
>>> return -EINVAL;
>>
>> Not sure we need this, since DAX always loses to REFLINK, whether it's
>> at inode loading time or if someone's trying to set it in the ioctl.
>
> loses to a reflinked /inode/ but not to a reflink-capable fs, like
> mount does.
>
>> Ofc it's hard to say what the behavior should be since the dax iflag
>> semantics are poorly defined (it's been more or less advisory this whole
>> time)...
>>
>> ...but I gather you're sending this patch because you don't like this
>> wishy washy "ok you change this flag but it doesn't tell you if that had
>> any effect and there's no way to find out either" behavior? :)
>
> Just aiming for some semblance of consistency. Today we have:
>
> mount -o dax + xfs_sb_version_hasreflink =>
> ignore mount option, disable dax for all inodes regardless of reflinked status
>
> chattr +x + xfs_sb_version_hasreflink =>
> inode is dax until it gets reflinked, then it's ignored
>
> right?
>
> (and what happens if we have a daxified inode that gets reflinked later?)
Bit 15 (0x8000) - XFS_XFLAG_DAX
If the filesystem lives on directly accessible persistent mem‐
ory, reads and writes to this file will go straight to the per‐
sistent memory, bypassing the page cache. A file cannot be
reflinked and have the XFS_XFLAG_DAX set at the same time.
That is to say that DAX files cannot share blocks.
# xfs_io -c "lsattr" /mnt/test/dax
--------------x- /mnt/test/dax
# cp --reflink=always /mnt/test/dax /mnt/test/reflink
# xfs_io -c "lsattr" /mnt/test/reflink
---------------- /mnt/test/reflink
# xfs_bmap -v /mnt/test/dax /mnt/test/reflink
/mnt/test/dax:
EXT: FILE-OFFSET BLOCK-RANGE AG AG-OFFSET TOTAL
0: [0..7]: 104..111 0 (104..111) 8 100000
/mnt/test/reflink:
EXT: FILE-OFFSET BLOCK-RANGE AG AG-OFFSET TOTAL
0: [0..7]: 104..111 0 (104..111) 8 100000
# xfs_io -c "lsattr" /mnt/test/dax
--------------x- /mnt/test/dax
