Re: [PATCH v3 03/12] fs/xfs: Separate functionality of xfs_inode_supports_dax()

Dave Chinner
2020-02-11T05:47:58Z

On Sat, Feb 08, 2020 at 11:34:36AM -0800, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> xfs_inode_supports_dax() should reflect if the inode can support DAX not
> that it is enabled for DAX. Leave that to other helper functions.
>
> Change the caller of xfs_inode_supports_dax() to call
> xfs_inode_use_dax() which reflects new logic to override the effective
> DAX flag with either the mount option or the physical DAX flag.
>
> To make the logic clear create 2 helper functions for the mount and
> physical flag.
>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> ---
> fs/xfs/xfs_iops.c | 32 ++++++++++++++++++++++++++------
> 1 file changed, 26 insertions(+), 6 deletions(-)
>
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index 81f2f93caec0..a7db50d923d4 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -1236,6 +1236,15 @@ static const struct inode_operations xfs_inline_symlink_inode_operations = {
> .update_time = xfs_vn_update_time,
> };
>
> +static bool
> +xfs_inode_mount_is_dax(
> + struct xfs_inode *ip)
> +{
> + struct xfs_mount *mp = ip->i_mount;
> +
> + return (mp->m_flags & XFS_MOUNT_DAX) == XFS_MOUNT_DAX;
> +}
> +
> /* Figure out if this file actually supports DAX. */
> static bool
> xfs_inode_supports_dax(
> @@ -1247,11 +1256,6 @@ xfs_inode_supports_dax(
> if (!S_ISREG(VFS_I(ip)->i_mode) || xfs_is_reflink_inode(ip))
> return false;
>
> - /* DAX mount option or DAX iflag must be set. */
> - if (!(mp->m_flags & XFS_MOUNT_DAX) &&
> - !(ip->i_d.di_flags2 & XFS_DIFLAG2_DAX))
> - return false;
> -
> /* Block size must match page size */
> if (mp->m_sb.sb_blocksize != PAGE_SIZE)
> return false;
> @@ -1260,6 +1264,22 @@ xfs_inode_supports_dax(
> return xfs_inode_buftarg(ip)->bt_daxdev != NULL;
> }
>
> +static bool
> +xfs_inode_is_dax(
> + struct xfs_inode *ip)
> +{
> + return (ip->i_d.di_flags2 & XFS_DIFLAG2_DAX) == XFS_DIFLAG2_DAX;
> +}

I don't think these wrappers add any value at all - the naming of
them is entirely confusing, too. e.g. "inode is dax" doesn't tell me
that it is checking the on disk flags - it doesn't tell me how it is
different to IS_DAX, or why I'd use one versus the other. And then
xfs_inode_mount_is_dax() is just... worse.

Naming is hard. :)

> +
> +static bool
> +xfs_inode_use_dax(
> + struct xfs_inode *ip)
> +{
> + return xfs_inode_supports_dax(ip) &&
> + (xfs_inode_mount_is_dax(ip) ||
> + xfs_inode_is_dax(ip));
> +}

Urk. Naming - we're not "using dax" here, we are checkign to see if
we should enable DAX on this inode. IOWs:

static bool
xfs_inode_enable_dax(
struct xfs_inode *ip)
{
if (!xfs_inode_supports_dax(ip))
return false;

if (ip->i_d.di_flags2 & XFS_DIFLAG2_DAX)
return true;
if (ip->i_mount->m_flags & XFS_MOUNT_DAX)
return true;
return false;
}

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com