linux-ext4 - Re: [PATCH V7 5/9] fs/xfs: Create function xfs_inode_enable

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Date:   Mon, 13 Apr 2020 12:39:28 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     linux-kernel@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        Jeff Moyer <jmoyer@...hat.com>, linux-ext4@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH V7 5/9] fs/xfs: Create function xfs_inode_enable_dax()

On Mon, Apr 13, 2020 at 08:52:51AM -0700, Darrick J. Wong wrote:
> On Sun, Apr 12, 2020 at 10:40:42PM -0700, ira.weiny@...el.com wrote:
> > From: Ira Weiny <ira.weiny@...el.com>
> > 
> > xfs_inode_supports_dax() should reflect if the inode can support DAX not
> > that it is enabled for DAX.
> > 
> > Change the use of xfs_inode_supports_dax() to reflect only if the inode
> > and underlying storage support dax.
> > 
> > Add a new function xfs_inode_enable_dax() which reflects if the inode
> > should be enabled for DAX.
> > 
> > Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> > 
> > ---
> > Changes from v6:
> > 	Change enable checks to be sequential logic.
> > 	Update for 2 bit tri-state option.
> > 	Make 'static' consistent.
> > 	Don't set S_DAX if !CONFIG_FS_DAX
> > 
> > Changes from v5:
> > 	Update to reflect the new tri-state mount option
> > 
> > Changes from v3:
> > 	Update functions and names to be more clear
> > 	Update commit message
> > 	Merge with
> > 		'fs/xfs: Clean up DAX support check'
> > 		don't allow IS_DAX() on a directory
> > 		use STATIC macro for static
> > 		make xfs_inode_supports_dax() static
> > ---
> >  fs/xfs/xfs_iops.c | 34 +++++++++++++++++++++++++++++-----
> >  1 file changed, 29 insertions(+), 5 deletions(-)
> > 
> > diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> > index 81f2f93caec0..37bd15b55878 100644
> > --- a/fs/xfs/xfs_iops.c
> > +++ b/fs/xfs/xfs_iops.c
> > @@ -1244,12 +1244,11 @@ xfs_inode_supports_dax(
> >  	struct xfs_mount	*mp = ip->i_mount;
> >  
> >  	/* Only supported on non-reflinked files. */
> > -	if (!S_ISREG(VFS_I(ip)->i_mode) || xfs_is_reflink_inode(ip))
> > +	if (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))
> > +	/* Only supported on regular files. */
> > +	if (!S_ISREG(VFS_I(ip)->i_mode))
> >  		return false;
> 
> Why separate the !S_ISREG and the is_reflink_inode checks?
> 
> The part about "Change the use of xfs_inode_supports_dax() to reflect
> only if the inode and underlying storage support dax" would be a lot
> more straightforward if this hunk only removed the DIFLAG2_DAX check.

Yes I could see that.  But for me the separate checks were more clear.  FWIW,
Dave requested a similar pattern for xfs_inode_enable_dax()[*] and I think I
agree with him.

So I'm inclined to keep the checks like this.

Thanks for the reviews!
Ira

[*] https://lore.kernel.org/lkml/20200408000533.GG24067@dread.disaster.area/

> 
> The rest of the patch looks ok.
> 
> --D
> 
> >  
> >  	/* Block size must match page size */
> > @@ -1260,6 +1259,31 @@ xfs_inode_supports_dax(
> >  	return xfs_inode_buftarg(ip)->bt_daxdev != NULL;
> >  }
> >  
> > +#ifdef CONFIG_FS_DAX
> > +static bool
> > +xfs_inode_enable_dax(
> > +	struct xfs_inode *ip)
> > +{
> > +	if (ip->i_mount->m_flags & XFS_MOUNT_NODAX)
> > +		return false;
> > +	if (!xfs_inode_supports_dax(ip))
> > +		return false;
> > +	if (ip->i_mount->m_flags & XFS_MOUNT_DAX)
> > +		return true;
> > +	if (ip->i_d.di_flags2 & XFS_DIFLAG2_DAX)
> > +		return true;
> > +	return false;
> > +}
> > +#else /* !CONFIG_FS_DAX */
> > +static bool
> > +xfs_inode_enable_dax(
> > +	struct xfs_inode *ip)
> > +{
> > +	return false;
> > +}
> > +#endif /* CONFIG_FS_DAX */
> > +
> > +
> >  STATIC void
> >  xfs_diflags_to_iflags(
> >  	struct inode		*inode,
> > @@ -1278,7 +1302,7 @@ xfs_diflags_to_iflags(
> >  		inode->i_flags |= S_SYNC;
> >  	if (flags & XFS_DIFLAG_NOATIME)
> >  		inode->i_flags |= S_NOATIME;
> > -	if (xfs_inode_supports_dax(ip))
> > +	if (xfs_inode_enable_dax(ip))
> >  		inode->i_flags |= S_DAX;
> >  }
> >  
> > -- 
> > 2.25.1
> >