Re: [PATCH 4/4] xfs: XFS_DIFLAG2_DAX limited by PAGE_SIZE

[Eric Sandeen <sandeen@sandeen.net>]

On 2/14/16 11:22 PM, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> If the block size of a filesystem is not at least PAGE_SIZEd, then
> at this point in time DAX cannot be used due to the fact we can't
> guarantee extents are page sized or aligned without further work.
> Hence disallow setting the DAX flag on an inode if the block size is
> too small. Also, be defensive and check the block size when reading
> an inode in off disk.
> 
> In future, we want to allow DAX to work on any filesystem, so this
> is temporary while we sort of the correct conbination of extent size
> hints and allocation alignment configurations needed to guarantee
> page sized and aligned extent allocation for DAX enabled files.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/xfs/xfs_ioctl.c | 12 ++++++++----
>  fs/xfs/xfs_iops.c  |  1 +
>  2 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index a870d16..8e9cd3c 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1080,11 +1080,15 @@ xfs_ioctl_setattr_dax_invalidate(
>  
>  	/*
>  	 * It is only valid to set the DAX flag on regular files and
> -	 * directories. On directories it serves as an inherit hint.
> +	 * directories on filesystems where the block size is at least the page
                                                              ^^^^^^^^
> +	 * size. On directories it serves as an inherit hint.
>  	 */
> -	if ((fa->fsx_xflags & FS_XFLAG_DAX) &&
> -	    !(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode)))
> -		return -EINVAL;
> +	if (fa->fsx_xflags & FS_XFLAG_DAX) {
> +		if (!(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode)))
> +			return -EINVAL;
> +		if (ip->i_mount->m_sb.sb_blocksize != PAGE_SIZE)
                                                   ^^

So which is it, at least PAGE_SIZE or == PAGE_SIZE?

> +			return -EINVAL;
> +	}
>  
>  	/* If the DAX state is not changing, we have nothing to do here. */
>  	if ((fa->fsx_xflags & FS_XFLAG_DAX) && IS_DAX(inode))
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index 9c984a0..fb7dc61 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -1186,6 +1186,7 @@ xfs_diflags_to_iflags(
>  	if (flags & XFS_DIFLAG_NOATIME)
>  		inode->i_flags |= S_NOATIME;
>  	if (S_ISREG(inode->i_mode) &&
> +	    ip->i_mount->m_sb.sb_blocksize == PAGE_SIZE &&
>  	    (ip->i_mount->m_flags & XFS_MOUNT_DAX ||
>  	     ip->i_d.di_flags2 & XFS_DIFLAG2_DAX))
>  		inode->i_flags |= S_DAX;

Is it possible to get mounted with XFS_MOUNT_DAX if blocksize != PAGE_SIZE?
If so, should it be?  This seems like a strange place to catch this mismatch.

-Eric

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