Re: [PATCH 03/15] xfs: create a log incompat flag for atomic file mapping exchanges

[Dave Chinner <david@fromorbit.com>]

On Tue, Mar 26, 2024 at 06:53:36PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> Create a log incompat flag so that we only attempt to process file
> mapping exchange log items if the filesystem supports it, and a geometry
> flag to advertise support if it's present or could be present.
> 
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/libxfs/xfs_format.h |   13 +++++++++++++
>  fs/xfs/libxfs/xfs_fs.h     |    3 +++
>  fs/xfs/libxfs/xfs_sb.c     |    3 +++
>  fs/xfs/xfs_exchrange.c     |   31 +++++++++++++++++++++++++++++++
>  fs/xfs/xfs_exchrange.h     |    2 ++
>  5 files changed, 52 insertions(+)
> 
> 
> diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
> index 2b2f9050fbfbb..753adde56a2d0 100644
> --- a/fs/xfs/libxfs/xfs_format.h
> +++ b/fs/xfs/libxfs/xfs_format.h
> @@ -391,6 +391,12 @@ xfs_sb_has_incompat_feature(
>  }
>  
>  #define XFS_SB_FEAT_INCOMPAT_LOG_XATTRS   (1 << 0)	/* Delayed Attributes */
> +
> +/*
> + * Log contains file mapping exchange log intent items which are not otherwise
> + * protected by an INCOMPAT/RO_COMPAT feature flag.
> + */
> +#define XFS_SB_FEAT_INCOMPAT_LOG_EXCHMAPS (1 << 1)
>  #define XFS_SB_FEAT_INCOMPAT_LOG_ALL \
>  	(XFS_SB_FEAT_INCOMPAT_LOG_XATTRS)
>  #define XFS_SB_FEAT_INCOMPAT_LOG_UNKNOWN	~XFS_SB_FEAT_INCOMPAT_LOG_ALL
> @@ -423,6 +429,13 @@ static inline bool xfs_sb_version_haslogxattrs(struct xfs_sb *sbp)
>  		 XFS_SB_FEAT_INCOMPAT_LOG_XATTRS);
>  }
>  
> +static inline bool xfs_sb_version_haslogexchmaps(struct xfs_sb *sbp)
> +{
> +	return xfs_sb_is_v5(sbp) &&
> +		(sbp->sb_features_log_incompat &
> +		 XFS_SB_FEAT_INCOMPAT_LOG_EXCHMAPS);
> +}
> +
>  static inline bool
>  xfs_is_quota_inode(struct xfs_sb *sbp, xfs_ino_t ino)
>  {
> diff --git a/fs/xfs/libxfs/xfs_fs.h b/fs/xfs/libxfs/xfs_fs.h
> index 8a1e30cf4dc88..ea07fb7b89722 100644
> --- a/fs/xfs/libxfs/xfs_fs.h
> +++ b/fs/xfs/libxfs/xfs_fs.h
> @@ -240,6 +240,9 @@ typedef struct xfs_fsop_resblks {
>  #define XFS_FSOP_GEOM_FLAGS_INOBTCNT	(1 << 22) /* inobt btree counter */
>  #define XFS_FSOP_GEOM_FLAGS_NREXT64	(1 << 23) /* large extent counters */
>  
> +/* file range exchange available to userspace */
> +#define XFS_FSOP_GEOM_FLAGS_EXCHANGE_RANGE	(1 << 24)
> +
>  /*
>   * Minimum and maximum sizes need for growth checks.
>   *
> diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
> index d991eec054368..c2d86faeee61b 100644
> --- a/fs/xfs/libxfs/xfs_sb.c
> +++ b/fs/xfs/libxfs/xfs_sb.c
> @@ -26,6 +26,7 @@
>  #include "xfs_health.h"
>  #include "xfs_ag.h"
>  #include "xfs_rtbitmap.h"
> +#include "xfs_exchrange.h"
>  
>  /*
>   * Physical superblock buffer manipulations. Shared with libxfs in userspace.
> @@ -1258,6 +1259,8 @@ xfs_fs_geometry(
>  	}
>  	if (xfs_has_large_extent_counts(mp))
>  		geo->flags |= XFS_FSOP_GEOM_FLAGS_NREXT64;
> +	if (xfs_exchrange_possible(mp))
> +		geo->flags |= XFS_FSOP_GEOM_FLAGS_EXCHANGE_RANGE;
>  	geo->rtsectsize = sbp->sb_blocksize;
>  	geo->dirblocksize = xfs_dir2_dirblock_bytes(sbp);
>  
> diff --git a/fs/xfs/xfs_exchrange.c b/fs/xfs/xfs_exchrange.c
> index a575e26ae1a58..620cf1eb7464b 100644
> --- a/fs/xfs/xfs_exchrange.c
> +++ b/fs/xfs/xfs_exchrange.c
> @@ -15,6 +15,37 @@
>  #include "xfs_exchrange.h"
>  #include <linux/fsnotify.h>
>  
> +/*
> + * If the filesystem has relatively new features enabled, we're willing to
> + * upgrade the filesystem to have the EXCHMAPS log incompat feature.
> + * Technically we could do this with any V5 filesystem, but let's not deal
> + * with really old kernels.
> + */

Please document tnis in the commit message - this decision needs to
be seen by anyone reading the commit history rather than the code...

-Dave.
-- 
Dave Chinner
david@fromorbit.com