[MEH] fs: make generic_fillattr() tail-callable and utilize it in ext2/ext4

Commit Message

Mateusz Guzik April 1, 2025, 4:18 p.m. UTC

Unfortunately the other filesystems I checked make adjustments after
their own call to generic_fillattr() and consequently can't benefit.

Signed-off-by: Mateusz Guzik <[e-mail]>
---

There are weird slowdowns on fstat, this is a byproduct of trying to
straighten out the fast path.

Not benchmarked, but I did confirm the compiler jmps out to the routine
instead of emitting a call which is the right thing to do here.

that said I'm not going to argue, but I like to see this out of the way.

there are nasty things which need to be addressed separately

 fs/ext2/inode.c    | 3 +--
 fs/ext4/inode.c    | 3 +--
 fs/stat.c          | 6 +++++-
 include/linux/fs.h | 2 +-
 4 files changed, 8 insertions(+), 6 deletions(-)

Patch

diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
index 30f8201c155f..cf1f89922207 100644
--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -1629,8 +1629,7 @@  int ext2_getattr(struct mnt_idmap *idmap, const struct path *path,
 			STATX_ATTR_IMMUTABLE |
 			STATX_ATTR_NODUMP);
 
-	generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
-	return 0;
+	return generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
 }
 
 int ext2_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 1dc09ed5d403..3edd6e60dd9b 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5687,8 +5687,7 @@  int ext4_getattr(struct mnt_idmap *idmap, const struct path *path,
 				  STATX_ATTR_NODUMP |
 				  STATX_ATTR_VERITY);
 
-	generic_fillattr(idmap, request_mask, inode, stat);
-	return 0;
+	return generic_fillattr(idmap, request_mask, inode, stat);
 }
 
 int ext4_file_getattr(struct mnt_idmap *idmap,
diff --git a/fs/stat.c b/fs/stat.c
index f13308bfdc98..581a95376e70 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -78,8 +78,11 @@  EXPORT_SYMBOL(fill_mg_cmtime);
  * take care to map the inode according to @idmap before filling in the
  * uid and gid filds. On non-idmapped mounts or if permission checking is to be
  * performed on the raw inode simply pass @nop_mnt_idmap.
+ *
+ * The routine always succeeds. We make it return a value so that consumers can
+ * tail-call it.
  */
-void generic_fillattr(struct mnt_idmap *idmap, u32 request_mask,
+int generic_fillattr(struct mnt_idmap *idmap, u32 request_mask,
 		      struct inode *inode, struct kstat *stat)
 {
 	vfsuid_t vfsuid = i_uid_into_vfsuid(idmap, inode);
@@ -110,6 +113,7 @@  void generic_fillattr(struct mnt_idmap *idmap, u32 request_mask,
 		stat->change_cookie = inode_query_iversion(inode);
 	}
 
+	return 0;
 }
 EXPORT_SYMBOL(generic_fillattr);
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 016b0fe1536e..754893d8d2a8 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3471,7 +3471,7 @@  extern int page_symlink(struct inode *inode, const char *symname, int len);
 extern const struct inode_operations page_symlink_inode_operations;
 extern void kfree_link(void *);
 void fill_mg_cmtime(struct kstat *stat, u32 request_mask, struct inode *inode);
-void generic_fillattr(struct mnt_idmap *, u32, struct inode *, struct kstat *);
+int generic_fillattr(struct mnt_idmap *, u32, struct inode *, struct kstat *);
 void generic_fill_statx_attr(struct inode *inode, struct kstat *stat);
 void generic_fill_statx_atomic_writes(struct kstat *stat,
 				      unsigned int unit_min,