linux-kernel - Re: [PATCH v5 7/7] xfs: Support setting FMODE_CAN_ATOMIC

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Message-ID: <20240822204407.GU865349@frogsfrogsfrogs>
Date: Thu, 22 Aug 2024 13:44:07 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: John Garry <john.g.garry@...cle.com>
Cc: axboe@...nel.dk, brauner@...nel.org, viro@...iv.linux.org.uk,
	jack@...e.cz, chandan.babu@...cle.com, dchinner@...hat.com,
	hch@....de, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, hare@...e.de,
	martin.petersen@...cle.com, catherine.hoang@...cle.com,
	kbusch@...nel.org
Subject: Re: [PATCH v5 7/7] xfs: Support setting FMODE_CAN_ATOMIC_WRITE

On Thu, Aug 22, 2024 at 07:04:02PM +0100, John Garry wrote:
> On 21/08/2024 18:11, Darrick J. Wong wrote:
> > On Sat, Aug 17, 2024 at 09:48:00AM +0000, John Garry wrote:
> > > For when an inode is enabled for atomic writes, set FMODE_CAN_ATOMIC_WRITE
> > > flag. Only direct IO is currently supported, so check for that also.
> > > 
> > > We rely on the block layer to reject atomic writes which exceed the bdev
> > > request_queue limits, so don't bother checking any such thing here.
> > > 
> > > Signed-off-by: John Garry <john.g.garry@...cle.com>
> > > ---
> > >   fs/xfs/xfs_file.c | 14 ++++++++++++++
> > >   1 file changed, 14 insertions(+)
> > > 
> > > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> > > index 9b6530a4eb4a..3489d478809e 100644
> > > --- a/fs/xfs/xfs_file.c
> > > +++ b/fs/xfs/xfs_file.c
> > > @@ -1149,6 +1149,18 @@ xfs_file_remap_range(
> > >   	return remapped > 0 ? remapped : ret;
> > >   }
> > > +static bool xfs_file_open_can_atomicwrite(
> > > +	struct inode		*inode,
> > > +	struct file		*file)
> > > +{
> > > +	struct xfs_inode	*ip = XFS_I(inode);
> > > +
> > > +	if (!(file->f_flags & O_DIRECT))
> > > +		return false;
> > > +
> > > +	return xfs_inode_has_atomicwrites(ip);
> > 
> > ...and here too.  I do like the shift to having an incore flag that
> > controls whether you get untorn write support or not.
> 
> Do you mean that add a new member to xfs_inode to record this? If yes, it
> sounds ok, but we need to maintain consistency (of that member) whenever
> anything which can affect it changes, which is always a bit painful.

I actually meant something more like:

static bool
xfs_file_open_can_atomicwrite(
	struct file		*file,
	struct inode		*inode)
{
	struct xfs_inode	*ip = XFS_I(inode);
	struct xfs_mount	*mp = ip->i_mount;
	struct xfs_buftarg	*target = xfs_inode_buftarg(ip);

	if (!(file->f_flags & O_DIRECT))
		return false;
	if (!xfs_inode_has_atomicwrites(ip))
		return false;
	if (mp->m_dalign && (mp->m_dalign % ip->i_extsize))
		return false;
	if (mp->m_swidth && (mp->m_swidth % ip->i_extsize))
		return false;
	if (mp->m_sb.sb_blocksize < target->bt_bdev_awu_min)
		return false;
	if (xfs_inode_alloc_unitsize(ip) > target->bt_bdev_awu_max)
		return false;
	return true;
}

--D

> John
>