Re: [PATCH 3/3] xfs: respect the stable writes flag on the RT device

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On Tue, Oct 24, 2023 at 08:44:16AM +0200, Christoph Hellwig wrote:
> Update the per-folio stable writes flag dependening on which device an
> inode resides on.
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
>  fs/xfs/xfs_inode.h | 8 ++++++++
>  fs/xfs/xfs_ioctl.c | 9 +++++++++
>  fs/xfs/xfs_iops.c  | 7 +++++++
>  3 files changed, 24 insertions(+)
> 
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index 0c5bdb91152e1c..682959c8f78cb0 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -561,6 +561,14 @@ 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);
>  
> +static inline void xfs_update_stable_writes(struct xfs_inode *ip)
> +{
> +	if (bdev_stable_writes(xfs_inode_buftarg(ip)->bt_bdev))
> +		mapping_set_stable_writes(VFS_I(ip)->i_mapping);
> +	else
> +		mapping_clear_stable_writes(VFS_I(ip)->i_mapping);
> +}
> +
>  /*
>   * When setting up a newly allocated inode, we need to call
>   * xfs_finish_inode_setup() once the inode is fully instantiated at
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 55bb01173cde8c..67bf613b3c86bc 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1147,6 +1147,15 @@ xfs_ioctl_setattr_xflags(
>  	ip->i_diflags2 = i_flags2;
>  
>  	xfs_diflags_to_iflags(ip, false);
> +
> +	/*
> +	 * Make the stable writes flag match that of the device the inode
> +	 * resides on when flipping the RT flag.
> +	 */
> +	if (S_ISREG(VFS_I(ip)->i_mode) &&
> +	    XFS_IS_REALTIME_INODE(ip) != (fa->fsx_xflags & FS_XFLAG_REALTIME))
> +		xfs_update_stable_writes(ip);

Hmm.  Won't the masking operation here result in the if test comparing 0
or FS_XFLAG_REALTIME to 0 or 1?

Oh.  FS_XFLAG_REALTIME == 1, so that's not an issue in this one case.
That's a bit subtle though, I'd have preferred

	    XFS_IS_REALTIME_INODE(ip) != !!(fa->fsx_xflags & FS_XFLAG_REALTIME))

to make it more obvious that the if test isn't comparing apples to
oranges.

> +
>  	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 2b3b05c28e9e48..b8ec045708c318 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -1298,6 +1298,13 @@ xfs_setup_inode(
>  	gfp_mask = mapping_gfp_mask(inode->i_mapping);
>  	mapping_set_gfp_mask(inode->i_mapping, (gfp_mask & ~(__GFP_FS)));
>  
> +	/*
> +	 * For real-time inodes update the stable write flags to that of the RT
> +	 * device instead of the data device.
> +	 */
> +	if (S_ISREG(inode->i_mode) && XFS_IS_REALTIME_INODE(ip))
> +		xfs_update_stable_writes(ip);

I wonder if xfs_update_stable_writes should become an empty function for
the CONFIG_XFS_RT=n case, to avoid the atomic flags update?

(The extra code is probably not worth the microoptimization.)

With the !! nit addressed,
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>

--D

> +
>  	/*
>  	 * If there is no attribute fork no ACL can exist on this inode,
>  	 * and it can't have any file capabilities attached to it either.
> -- 
> 2.39.2
> 



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