Re: [PATCH 2/3] design: document the large extent count ondisk format changes

[Chandan Babu R <chandan.babu@oracle.com>]

On Tue, Jan 17, 2023 at 04:45:05 PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
>
> Update the ondisk format documentation to discuss the larger maximum
> extent counts that were added in 2022.
>

Looks good to me.

Reviewed-by: Chandan Babu R <chandan.babu@oracle.com>

-- 
chandan

> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
>  .../allocation_groups.asciidoc                     |    4 +
>  .../XFS_Filesystem_Structure/ondisk_inode.asciidoc |   61 ++++++++++++++++++--
>  2 files changed, 58 insertions(+), 7 deletions(-)
>
>
> diff --git a/design/XFS_Filesystem_Structure/allocation_groups.asciidoc b/design/XFS_Filesystem_Structure/allocation_groups.asciidoc
> index 7ee5d561..c64b4fad 100644
> --- a/design/XFS_Filesystem_Structure/allocation_groups.asciidoc
> +++ b/design/XFS_Filesystem_Structure/allocation_groups.asciidoc
> @@ -454,6 +454,10 @@ xref:Timestamps[timestamps] for more information.
>  The filesystem is not in operable condition, and must be run through
>  xfs_repair before it can be mounted.
>  
> +| +XFS_SB_FEAT_INCOMPAT_NREXT64+ |
> +Large file fork extent counts.  This greatly expands the maximum number of
> +space mappings allowed in data and extended attribute file forks.
> +
>  |=====
>  
>  *sb_features_log_incompat*::
> diff --git a/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc b/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc
> index 1922954e..34c06487 100644
> --- a/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc
> +++ b/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc
> @@ -84,14 +84,41 @@ struct xfs_dinode_core {
>       __uint32_t                di_nlink;
>       __uint16_t                di_projid;
>       __uint16_t                di_projid_hi;
> -     __uint8_t                 di_pad[6];
> -     __uint16_t                di_flushiter;
> +     union {
> +          /* Number of data fork extents if NREXT64 is set */
> +          __be64               di_big_nextents;
> +
> +          /* Padding for V3 inodes without NREXT64 set. */
> +          __be64               di_v3_pad;
> +
> +          /* Padding and inode flush counter for V2 inodes. */
> +          struct {
> +               __u8            di_v2_pad[6];
> +               __be16          di_flushiter;
> +          };
> +     };
>       xfs_timestamp_t           di_atime;
>       xfs_timestamp_t           di_mtime;
>       xfs_timestamp_t           di_ctime;
>       xfs_fsize_t               di_size;
>       xfs_rfsblock_t            di_nblocks;
>       xfs_extlen_t              di_extsize;
> +     union {
> +          /*
> +           * For V2 inodes and V3 inodes without NREXT64 set, this
> +           * is the number of data and attr fork extents.
> +           */
> +          struct {
> +               __be32          di_nextents;
> +               __be16          di_anextents;
> +          } __packed;
> +
> +          /* Number of attr fork extents if NREXT64 is set. */
> +          struct {
> +               __be32          di_big_anextents;
> +               __be16          di_nrext64_pad;
> +          } __packed;
> +     } __packed;
>       xfs_extnum_t              di_nextents;
>       xfs_aextnum_t             di_anextents;
>       __uint8_t                 di_forkoff;
> @@ -162,7 +189,7 @@ When the number exceeds 65535, the inode is converted to v2 and the link count
>  is stored in +di_nlink+.
>  
>  *di_uid*::
> -Specifies the owner's UID of the inode. 
> +Specifies the owner's UID of the inode.
>  
>  *di_gid*::
>  Specifies the owner's GID of the inode.
> @@ -181,10 +208,17 @@ Specifies the high 16 bits of the owner's project ID in v2 inodes, if the
>  +XFS_SB_VERSION2_PROJID32BIT+ feature is set; and zero otherwise.
>  
>  *di_pad[6]*::
> -Reserved, must be zero.
> +Reserved, must be zero.  Only exists for v2 inodes.
>  
>  *di_flushiter*::
> -Incremented on flush.
> +Incremented on flush.  Only exists for v2 inodes.
> +
> +*di_v3_pad*::
> +Must be zero for v3 inodes without the NREXT64 flag set.
> +
> +*di_big_nextents*::
> +Specifies the number of data extents associated with this inode if the NREXT64
> +flag is set.  This allows for up to 2^48^ - 1 extent mappings.
>  
>  *di_atime*::
>  
> @@ -231,10 +265,19 @@ file is written to beyond allocated space, XFS will attempt to allocate
>  additional disk space based on this value.
>  
>  *di_nextents*::
> -Specifies the number of data extents associated with this inode.
> +Specifies the number of data extents associated with this inode if the NREXT64
> +flag is not set.  Supports up to 2^31^ - 1 extents.
>  
>  *di_anextents*::
> -Specifies the number of extended attribute extents associated with this inode.
> +Specifies the number of extended attribute extents associated with this inode
> +if the NREXT64 flag is not set.  Supports up to 2^15^ - 1 extents.
> +
> +*di_big_anextents*::
> +Specifies the number of extended attribute extents associated with this inode
> +if the NREXT64 flag is set.  Supports up to 2^32^ - 1 extents.
> +
> +*di_nrext64_pad*::
> +Must be zero if the NREXT64 flag is set.
>  
>  *di_forkoff*::
>  Specifies the offset into the inode's literal area where the extended attribute
> @@ -336,6 +379,10 @@ This inode shares (or has shared) data blocks with another inode.
>  For files, this is the extent size hint for copy on write operations; see
>  +di_cowextsize+ for details.  For directories, the value in +di_cowextsize+
>  will be copied to all newly created files and directories.
> +| +XFS_DIFLAG2_NREXT64+		|
> +Files with this flag set may have up to (2^48^ - 1) extents mapped to the data
> +fork and up to (2^32^ - 1) extents mapped to the attribute fork.  This flag
> +requires the +XFS_SB_FEAT_INCOMPAT_NREXT64+ feature to be enabled.
>  |=====
>  
>  *di_cowextsize*::