[PATCH v2] xfs: compile out v4 support if disabled

Christoph Hellwig
2024-03-25T03:13:25Z

Add a few strategic IS_ENABLED statements to let the compiler eliminate
unused code when CONFIG_XFS_SUPPORT_V4 is disabled.

This saves multiple kilobytes of .text in my .config:

$ size xfs.o.*
text data bss dec hex filename
1363633 294836 592 1659061 1950b5 xfs.o.new
1371453 294868 592 1666913 196f61 xfs.o.old

Signed-off-by: Christoph Hellwig <hch@lst.de>
---

Changes since v1:
- compile out the right bits, and more of them

fs/xfs/xfs_mount.h | 40 +++++++++++++++++++++++++++++++---------
fs/xfs/xfs_super.c | 22 +++++++++++++---------
2 files changed, 44 insertions(+), 18 deletions(-)

diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 0e8d7779c0a561..85e327bf05041f 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -337,19 +337,10 @@ static inline void xfs_add_ ## name (struct xfs_mount *mp) \
__XFS_ADD_FEAT(attr, ATTR)
__XFS_HAS_FEAT(nlink, NLINK)
__XFS_ADD_FEAT(quota, QUOTA)
-__XFS_HAS_FEAT(align, ALIGN)
__XFS_HAS_FEAT(dalign, DALIGN)
-__XFS_HAS_FEAT(logv2, LOGV2)
__XFS_HAS_FEAT(sector, SECTOR)
-__XFS_HAS_FEAT(extflg, EXTFLG)
__XFS_HAS_FEAT(asciici, ASCIICI)
-__XFS_HAS_FEAT(lazysbcount, LAZYSBCOUNT)
-__XFS_ADD_FEAT(attr2, ATTR2)
__XFS_HAS_FEAT(parent, PARENT)
-__XFS_ADD_FEAT(projid32, PROJID32)
-__XFS_HAS_FEAT(crc, CRC)
-__XFS_HAS_FEAT(v3inodes, V3INODES)
-__XFS_HAS_FEAT(pquotino, PQUOTINO)
__XFS_HAS_FEAT(ftype, FTYPE)
__XFS_HAS_FEAT(finobt, FINOBT)
__XFS_HAS_FEAT(rmapbt, RMAPBT)
@@ -362,6 +353,37 @@ __XFS_HAS_FEAT(bigtime, BIGTIME)
__XFS_HAS_FEAT(needsrepair, NEEDSREPAIR)
__XFS_HAS_FEAT(large_extent_counts, NREXT64)

+/*
+ * Some features are always on for v5 file systems, allow the compiler to
+ * eliminiate dead code when building without v4 support.
+ */
+#define __XFS_HAS_V4_FEAT(name, NAME) \
+static inline bool xfs_has_ ## name (struct xfs_mount *mp) \
+{ \
+ return !IS_ENABLED(CONFIG_XFS_SUPPORT_V4) || \
+ (mp->m_features & XFS_FEAT_ ## NAME); \
+}
+
+#define __XFS_ADD_V4_FEAT(name, NAME) \
+ __XFS_HAS_V4_FEAT(name, NAME); \
+static inline void xfs_add_ ## name (struct xfs_mount *mp) \
+{ \
+ if (IS_ENABLED(CONFIG_XFS_SUPPORT_V4)) { \
+ mp->m_features |= XFS_FEAT_ ## NAME; \
+ xfs_sb_version_add ## name(&mp->m_sb); \
+ } \
+}
+
+__XFS_HAS_V4_FEAT(align, ALIGN)
+__XFS_HAS_V4_FEAT(logv2, LOGV2)
+__XFS_HAS_V4_FEAT(extflg, EXTFLG)
+__XFS_HAS_V4_FEAT(lazysbcount, LAZYSBCOUNT)
+__XFS_ADD_V4_FEAT(attr2, ATTR2)
+__XFS_ADD_V4_FEAT(projid32, PROJID32)
+__XFS_HAS_V4_FEAT(v3inodes, V3INODES)
+__XFS_HAS_V4_FEAT(crc, CRC)
+__XFS_HAS_V4_FEAT(pquotino, PQUOTINO)
+
/*
* Mount features
*
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 71732457583370..f325a2d1b3a902 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1589,17 +1589,21 @@ xfs_fs_fill_super(
if (error)
goto out_free_sb;

- /* V4 support is undergoing deprecation. */
- if (!xfs_has_crc(mp)) {
-#ifdef CONFIG_XFS_SUPPORT_V4
+ /*
+ * V4 support is undergoing deprecation.
+ *
+ * Note: this has to use an open coded m_features check as xfs_has_crc
+ * always returns false for !CONFIG_XFS_SUPPORT_V4.
+ */
+ if (!(mp->m_features & XFS_FEAT_CRC)) {
+ if (!IS_ENABLED(CONFIG_XFS_SUPPORT_V4)) {
+ xfs_warn(mp,
+ "Deprecated V4 format (crc=0) not supported by kernel.");
+ error = -EINVAL;
+ goto out_free_sb;
+ }
xfs_warn_once(mp,
"Deprecated V4 format (crc=0) will not be supported after September 2030.");
-#else
- xfs_warn(mp,
- "Deprecated V4 format (crc=0) not supported by kernel.");
- error = -EINVAL;
- goto out_free_sb;
-#endif
}

/* ASCII case insensitivity is undergoing deprecation. */
--
2.39.2