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

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(-)

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.

On Tue, Feb 11, 2020 at 04:47:48PM +1100, Dave Chinner wrote:
> On Sat, Feb 08, 2020 at 11:34:36AM -0800, ira.weiny@intel.com wrote:
> > From: Ira Weiny <ira.weiny@intel.com>
> > 

[snip]

> >  
> > +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. :)

Sure...  I'm particularly bad as well...

FWIW I don't see how xfs_inode_mount_is_dax() is worse, I rather think that is
pretty clear but I'm not going to quibble over names because I know I'm rubbish
at it and I'm certainly not enough of a FS person to make them clear...  ;-)

> 
> > +
> > +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:

Well just to defend myself a little bit.  My thought was:

"When setting i_flags, should I use dax?"

> 
> 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;
> }

Anyway, I'm good with this.

Changed for V4.

Thanks!
Ira

> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com