Re: [PATCH 4/4] xfs: apply rt extent alignment constraints to cow extsize hint

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, May 12, 2021 at 06:02:04PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> Even though reflink and copy-on-write aren't supported on the realtime
> volume, if we ever turn that on, we'd still be constrained to the same
> rt extent alignment requirements because cow involves remapping, and
> we can only allocate and free in rtextsize units on the realtime volume.
> 
> At the moment there aren't any filesystems with rt and reflink in the
> wild, so this is should be a zero-risk change.
> 
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>

Self NAK; one cannot set a nonzero cowextsize hint on a non-reflink
filesystem, and outside of djwong-dev, reflink on realtime isn't
supported either.  I guess I got too enthusiastic when I was
redistributing patches. :(

--D

> ---
>  fs/xfs/libxfs/xfs_inode_buf.c |   13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> 
> diff --git a/fs/xfs/libxfs/xfs_inode_buf.c b/fs/xfs/libxfs/xfs_inode_buf.c
> index 25261dd73290..704faf806e46 100644
> --- a/fs/xfs/libxfs/xfs_inode_buf.c
> +++ b/fs/xfs/libxfs/xfs_inode_buf.c
> @@ -628,14 +628,21 @@ xfs_inode_validate_cowextsize(
>  	uint16_t			flags,
>  	uint64_t			flags2)
>  {
> -	bool				rt_flag;
> +	bool				rt_flag, rtinherit_flag;
>  	bool				hint_flag;
>  	uint32_t			cowextsize_bytes;
> +	uint32_t			blocksize_bytes;
>  
>  	rt_flag = (flags & XFS_DIFLAG_REALTIME);
> +	rtinherit_flag = (flags & XFS_DIFLAG_RTINHERIT);
>  	hint_flag = (flags2 & XFS_DIFLAG2_COWEXTSIZE);
>  	cowextsize_bytes = XFS_FSB_TO_B(mp, cowextsize);
>  
> +	if (rt_flag || (rtinherit_flag && hint_flag))
> +		blocksize_bytes = XFS_FSB_TO_B(mp, mp->m_sb.sb_rextsize);
> +	else
> +		blocksize_bytes = mp->m_sb.sb_blocksize;
> +
>  	if (hint_flag && !xfs_sb_version_hasreflink(&mp->m_sb))
>  		return __this_address;
>  
> @@ -652,13 +659,13 @@ xfs_inode_validate_cowextsize(
>  	if (hint_flag && rt_flag)
>  		return __this_address;
>  
> -	if (cowextsize_bytes % mp->m_sb.sb_blocksize)
> +	if (cowextsize_bytes % blocksize_bytes)
>  		return __this_address;
>  
>  	if (cowextsize > MAXEXTLEN)
>  		return __this_address;
>  
> -	if (cowextsize > mp->m_sb.sb_agblocks / 2)
> +	if (!rt_flag && cowextsize > mp->m_sb.sb_agblocks / 2)
>  		return __this_address;
>  
>  	return NULL;
>