simple_lookup(): just set DCACHE_DONTCACHE

No need to mess with ->d_op at all.  Note that ->d_delete that always
returns 1 is equivalent to having DCACHE_DONTCACHE in ->d_flags.
Later the same thing will be placed into ->s_d_flags of the filesystems
where we want that behaviour for all dentries; then the check in
simple_lookup() will at least get unlikely() slapped on it.

NOTE: there are only two filesystems where
	* simple_lookup() might be called
	* default ->d_op is non-NULL
	* its ->d_delete() doesn't always return 1
If not for those, we could have simple_lookup() just set DCACHE_DONTCACHE
without even looking at ->d_op.  Filesystems in question are btrfs
and tracefs; both have ->d_delete() returning 1 on anything fed to
simple_lookup(), so both would be fine with simple_lookup() setting
DCACHE_DONTCACHE regardless of ->d_op.

IOW, we might want to drop the check for ->d_op in simple_lookup();
it's definitely a separate story, though.

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/libfs.c b/fs/libfs.c
index ab82de070310b0c5ae16ad3ca8852f804af60fa2..19cc1265170886f5fff9577b5440dfd6e403d499 100644 (file)
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -75,9 +75,11 @@ struct dentry *simple_lookup(struct inode *dir, struct dentry *dentry, unsigned
 {
        if (dentry->d_name.len > NAME_MAX)
                return ERR_PTR(-ENAMETOOLONG);
-       if (!dentry->d_op)
-               d_set_d_op(dentry, &simple_dentry_operations);
-
+       if (!dentry->d_op && !(dentry->d_flags & DCACHE_DONTCACHE)) {
+               spin_lock(&dentry->d_lock);
+               dentry->d_flags |= DCACHE_DONTCACHE;
+               spin_unlock(&dentry->d_lock);
+       }
        if (IS_ENABLED(CONFIG_UNICODE) && IS_CASEFOLDED(dir))
                return NULL;