Re: [PATCH v3 08/21] xfs: Introduce FORCEALIGN inode flag

[John Garry]

On 12/06/2024 03:10, Long Li wrote:
> On Mon, Apr 29, 2024 at 05:47:33PM +0000, John Garry wrote:
> > From: "Darrick J. Wong"<djwong@xxxxxxxxxx>
> >
> > Add a new inode flag to require that all file data extent mappings must
> > be aligned (both the file offset range and the allocated space itself)
> > to the extent size hint.  Having a separate COW extent size hint is no
> > longer allowed.
> >
> > The goal here is to enable sysadmins and users to mandate that all space
> > mappings in a file must have a startoff/blockcount that are aligned to
> > (say) a 2MB alignment and that the startblock/blockcount will follow the
> > same alignment.
> >
> > jpg: Enforce extsize is a power-of-2 and aligned with afgsize + stripe
> >       alignment for forcealign
> > Signed-off-by: "Darrick J. Wong"<djwong@xxxxxxxxxx>
> > Co-developed-by: John Garry<john.g.garry@xxxxxxxxxx>
> > Signed-off-by: John Garry<john.g.garry@xxxxxxxxxx>
> > ---
> >   fs/xfs/libxfs/xfs_format.h    |  6 ++++-
> >   fs/xfs/libxfs/xfs_inode_buf.c | 50 +++++++++++++++++++++++++++++++++++
> >   fs/xfs/libxfs/xfs_inode_buf.h |  3 +++
> >   fs/xfs/libxfs/xfs_sb.c        |  2 ++
> >   fs/xfs/xfs_inode.c            | 12 +++++++++
> >   fs/xfs/xfs_inode.h            |  2 +-
> >   fs/xfs/xfs_ioctl.c            | 34 +++++++++++++++++++++++-
> >   fs/xfs/xfs_mount.h            |  2 ++
> >   fs/xfs/xfs_super.c            |  4 +++
> >   include/uapi/linux/fs.h       |  2 ++
> >   10 files changed, 114 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
> > index 2b2f9050fbfb..4dd295b047f8 100644
> > --- a/fs/xfs/libxfs/xfs_format.h
> > +++ b/fs/xfs/libxfs/xfs_format.h
> > @@ -353,6 +353,7 @@ xfs_sb_has_compat_feature(
> >   #define XFS_SB_FEAT_RO_COMPAT_RMAPBT   (1 << 1)		/* reverse map btree */
> >   #define XFS_SB_FEAT_RO_COMPAT_REFLINK  (1 << 2)		/* reflinked files */
> >   #define XFS_SB_FEAT_RO_COMPAT_INOBTCNT (1 << 3)		/* inobt block counts */
> > +#define XFS_SB_FEAT_RO_COMPAT_FORCEALIGN (1 << 30)	/* aligned file data extents */
>   
> Hi, John
>
> You know I've been using and testing your atomic writes patch series recently,
> and I'm particularly interested in the changes to the on-disk format. I noticed
> that XFS_SB_FEAT_RO_COMPAT_FORCEALIGN uses bit 30 instead of bit 4, which would
> be the next available bit in sequence.
>
> I'm wondering if using bit 30 is just a temporary solution to avoid conflicts,
> and if the plan is to eventually use bits sequentially, for example, using bit 4?
> I'm looking forward to your explanation.

I really don't know. I'm looking through the history and it has been 
like that this the start of my source control records.

Maybe it was a copy-and-paste error from XFS_FEAT_FORCEALIGN, whose 
value has changed since.

Anyway, I'll ask a bit more internally, and I'll look to change to (1 << 
4) if ok.

Thanks,
John