Re: [PATCH V7 6/9] fs/xfs: Combine xfs_diflags_to_linux() and xfs_diflags_to_iflags()

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Sun, Apr 12, 2020 at 10:40:43PM -0700, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
> 
> The functionality in xfs_diflags_to_linux() and xfs_diflags_to_iflags() are
> nearly identical.  The only difference is that *_to_linux() is called after
> inode setup and disallows changing the DAX flag.
> 
> Combining them can be done with a flag which indicates if this is the initial
> setup to allow the DAX flag to be properly set only at init time.
> 
> So remove xfs_diflags_to_linux() and call the modified xfs_diflags_to_iflags()
> directly.
> 
> While we are here simplify xfs_diflags_to_iflags() to take struct xfs_inode and
> use xfs_ip2xflags() to ensure future diflags are included correctly.
> 
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> 
> ---
> Changes from V6:
> 	Move unrelated hunk to previous patch.
> 	Change logic for better code generation.
> 
> Changes from V5:
> 	The functions are no longer identical so we can only combine
> 	them rather than deleting one completely.  This is reflected in
> 	the new init parameter.
> ---
>  fs/xfs/xfs_inode.h |  1 +
>  fs/xfs/xfs_ioctl.c | 33 +--------------------------------
>  fs/xfs/xfs_iops.c  | 42 +++++++++++++++++++++++-------------------
>  3 files changed, 25 insertions(+), 51 deletions(-)
> 
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index 492e53992fa9..e76ed9ca17f7 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -466,6 +466,7 @@ int	xfs_break_layouts(struct inode *inode, uint *iolock,
>  /* from xfs_iops.c */
>  extern void xfs_setup_inode(struct xfs_inode *ip);
>  extern void xfs_setup_iops(struct xfs_inode *ip);
> +extern void xfs_diflags_to_iflags(struct xfs_inode *ip, bool init);
>  
>  /*
>   * When setting up a newly allocated inode, we need to call
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index d42de92cb283..c6cd92ef4a05 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1100,37 +1100,6 @@ xfs_flags2diflags2(
>  	return di_flags2;
>  }
>  
> -STATIC void
> -xfs_diflags_to_linux(
> -	struct xfs_inode	*ip)
> -{
> -	struct inode		*inode = VFS_I(ip);
> -	unsigned int		xflags = xfs_ip2xflags(ip);
> -
> -	if (xflags & FS_XFLAG_IMMUTABLE)
> -		inode->i_flags |= S_IMMUTABLE;
> -	else
> -		inode->i_flags &= ~S_IMMUTABLE;
> -	if (xflags & FS_XFLAG_APPEND)
> -		inode->i_flags |= S_APPEND;
> -	else
> -		inode->i_flags &= ~S_APPEND;
> -	if (xflags & FS_XFLAG_SYNC)
> -		inode->i_flags |= S_SYNC;
> -	else
> -		inode->i_flags &= ~S_SYNC;
> -	if (xflags & FS_XFLAG_NOATIME)
> -		inode->i_flags |= S_NOATIME;
> -	else
> -		inode->i_flags &= ~S_NOATIME;
> -#if 0	/* disabled until the flag switching races are sorted out */
> -	if (xflags & FS_XFLAG_DAX)
> -		inode->i_flags |= S_DAX;
> -	else
> -		inode->i_flags &= ~S_DAX;
> -#endif
> -}
> -
>  static int
>  xfs_ioctl_setattr_xflags(
>  	struct xfs_trans	*tp,
> @@ -1168,7 +1137,7 @@ xfs_ioctl_setattr_xflags(
>  	ip->i_d.di_flags = xfs_flags2diflags(ip, fa->fsx_xflags);
>  	ip->i_d.di_flags2 = di_flags2;
>  
> -	xfs_diflags_to_linux(ip);
> +	xfs_diflags_to_iflags(ip, false);
>  	xfs_trans_ichgtime(tp, ip, XFS_ICHGTIME_CHG);
>  	xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
>  	XFS_STATS_INC(mp, xs_ig_attrchg);
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index 37bd15b55878..856ad823e754 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -1284,26 +1284,30 @@ xfs_inode_enable_dax(
>  #endif /* CONFIG_FS_DAX */
>  
>  
> -STATIC void
> +void
>  xfs_diflags_to_iflags(
> -	struct inode		*inode,
> -	struct xfs_inode	*ip)
> +	struct xfs_inode	*ip,
> +	bool init)
>  {
> -	uint16_t		flags = ip->i_d.di_flags;
> -
> -	inode->i_flags &= ~(S_IMMUTABLE | S_APPEND | S_SYNC |
> -			    S_NOATIME | S_DAX);
> -
> -	if (flags & XFS_DIFLAG_IMMUTABLE)
> -		inode->i_flags |= S_IMMUTABLE;
> -	if (flags & XFS_DIFLAG_APPEND)
> -		inode->i_flags |= S_APPEND;
> -	if (flags & XFS_DIFLAG_SYNC)
> -		inode->i_flags |= S_SYNC;
> -	if (flags & XFS_DIFLAG_NOATIME)
> -		inode->i_flags |= S_NOATIME;
> -	if (xfs_inode_enable_dax(ip))
> -		inode->i_flags |= S_DAX;
> +	struct inode            *inode = VFS_I(ip);
> +	unsigned int            xflags = xfs_ip2xflags(ip);
> +	unsigned int            flags = 0;
> +
> +	ASSERT(!(IS_DAX(inode) && init));
> +
> +	if (xflags & FS_XFLAG_IMMUTABLE)
> +		flags |= S_IMMUTABLE;
> +	if (xflags & FS_XFLAG_APPEND)
> +		flags |= S_APPEND;
> +	if (xflags & FS_XFLAG_SYNC)
> +		flags |= S_SYNC;
> +	if (xflags & FS_XFLAG_NOATIME)
> +		flags |= S_NOATIME;
> +	if (init && xfs_inode_enable_dax(ip))
> +		flags |= S_DAX;
> +
> +	inode->i_flags &= ~(S_IMMUTABLE | S_APPEND | S_SYNC | S_NOATIME);

I noticed that S_DAX drops out of the mask out operation here, which of
course resulted in an eyebrow-raise because the other four flags are
always set to whatever we just computed. :)

Then I realized that yes, this is intentional since we can't change
S_DAX on the fly, and that S_DAX is never set i_flags on an inode that's
being initialized so we don't need to mask off S_DAX ever.

Could we add a comment here to remind the reader that S_DAX is a bit
special?

/*
 * S_DAX can only be set during inode initialization and is never set by
 * the VFS, so we cannot mask off S_DAX in i_flags.
 */

With that added,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> +	inode->i_flags |= flags;
>  }
>  
>  /*
> @@ -1332,7 +1336,7 @@ xfs_setup_inode(
>  	inode->i_gid    = xfs_gid_to_kgid(ip->i_d.di_gid);
>  
>  	i_size_write(inode, ip->i_d.di_size);
> -	xfs_diflags_to_iflags(inode, ip);
> +	xfs_diflags_to_iflags(ip, true);
>  
>  	if (S_ISDIR(inode->i_mode)) {
>  		/*
> -- 
> 2.25.1
>