[PATCH 5/5] xfs: rearrange xfs_da_args a bit to use less space

Darrick J. Wong
2024-04-16T01:22:24Z

A few notes about struct xfs_da_args:

The XFS_ATTR_* flags only go up as far as XFS_ATTR_INCOMPLETE, which
means that attr_filter could be a u8 field.

The XATTR_* flags only have two values, which means that xattr_flags
could be shrunk to a u8.

I've reduced the number of XFS_DA_OP_* flags down to the point where
op_flags would also fit into a u8.

filetype has 7 bytes of slack after it, which is wasteful.

namelen will never be greater than MAXNAMELEN, which is 256. This field
could be reduced to a short.

Rearrange the fields in xfs_da_args to waste less space. This reduces
the structure size from 136 bytes to 128. Later when we add extra
fields to support parent pointer replacement, this will only bloat the
structure to 144 bytes, instead of 168.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
fs/xfs/libxfs/xfs_da_btree.h | 20 +++++++++++---------
1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_da_btree.h b/fs/xfs/libxfs/xfs_da_btree.h
index 706b529a81feb..17cef594b5bbb 100644
--- a/fs/xfs/libxfs/xfs_da_btree.h
+++ b/fs/xfs/libxfs/xfs_da_btree.h
@@ -54,16 +54,20 @@ enum xfs_dacmp {
*/
typedef struct xfs_da_args {
struct xfs_da_geometry *geo; /* da block geometry */
- const uint8_t *name; /* string (maybe not NULL terminated) */
- int namelen; /* length of string (maybe no NULL) */
- uint8_t filetype; /* filetype of inode for directories */
+ const uint8_t *name; /* string (maybe not NULL terminated) */
void *value; /* set of bytes (maybe contain NULLs) */
- int valuelen; /* length of value */
- unsigned int attr_filter; /* XFS_ATTR_{ROOT,SECURE,INCOMPLETE} */
- xfs_dahash_t hashval; /* hash value of name */
- xfs_ino_t inumber; /* input/output inode number */
struct xfs_inode *dp; /* directory inode to manipulate */
struct xfs_trans *trans; /* current trans (changes over time) */
+
+ xfs_ino_t inumber; /* input/output inode number */
+ xfs_ino_t owner; /* inode that owns the dir/attr data */
+
+ int valuelen; /* length of value */
+ uint8_t filetype; /* filetype of inode for directories */
+ uint8_t op_flags; /* operation flags */
+ uint8_t attr_filter; /* XFS_ATTR_{ROOT,SECURE,INCOMPLETE} */
+ short namelen; /* length of string (maybe no NULL) */
+ xfs_dahash_t hashval; /* hash value of name */
xfs_extlen_t total; /* total blocks needed, for 1st bmap */
int whichfork; /* data or attribute fork */
xfs_dablk_t blkno; /* blkno of attr leaf of interest */
@@ -76,9 +80,7 @@ typedef struct xfs_da_args {
xfs_dablk_t rmtblkno2; /* remote attr value starting blkno */
int rmtblkcnt2; /* remote attr value block count */
int rmtvaluelen2; /* remote attr value length in bytes */
- uint32_t op_flags; /* operation flags */
enum xfs_dacmp cmpresult; /* name compare result for lookups */
- xfs_ino_t owner; /* inode that owns the dir/attr data */
} xfs_da_args_t;

/*