f2fs: Enable negative dentries on case-insensitive lookup

Instead of invalidating negative dentries during case-insensitive
lookups, mark them as such and let them be added to the dcache.
d_ci_revalidate is able to properly filter them out if necessary based
on the dentry casefold flag.

Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
---
Changes since v5:
  - Use IS_CASEFOLDED directly (eric)
Changes since v4:
  - Use helper to decide if should set dentry flag.

Changes since v2:
  - Move dentry flag set closer to fscrypt code (Eric)

fs/f2fs/namei.c

@@ -533,6 +533,10 @@ static struct dentry *f2fs_lookup(struct inode *dir, struct dentry *dentry,
 
 	err = f2fs_prepare_lookup(dir, dentry, &fname);
 	generic_set_encrypted_ci_d_ops(dentry);
+
+	if (IS_CASEFOLDED(dir))
+		d_set_casefolded_name(dentry);
+
 	if (err == -ENOENT)
 		goto out_splice;
 	if (err)
@@ -578,17 +582,6 @@ static struct dentry *f2fs_lookup(struct inode *dir, struct dentry *dentry,
 		goto out_iput;
 	}
 out_splice:
-#if IS_ENABLED(CONFIG_UNICODE)
-	if (!inode && IS_CASEFOLDED(dir)) {
-		/* Eventually we want to call d_add_ci(dentry, NULL)
-		 * for negative dentries in the encoding case as
-		 * well.  For now, prevent the negative dentry
-		 * from being cached.
-		 */
-		trace_f2fs_lookup_end(dir, dentry, ino, err);
-		return NULL;
-	}
-#endif
 	new = d_splice_alias(inode, dentry);
 	trace_f2fs_lookup_end(dir, !IS_ERR_OR_NULL(new) ? new : dentry,
 				ino, IS_ERR(new) ? PTR_ERR(new) : err);
@@ -641,16 +634,6 @@ static int f2fs_unlink(struct inode *dir, struct dentry *dentry)
 	f2fs_delete_entry(de, page, dir, inode);
 	f2fs_unlock_op(sbi);
 
-#if IS_ENABLED(CONFIG_UNICODE)
-	/* VFS negative dentries are incompatible with Encoding and
-	 * Case-insensitiveness. Eventually we'll want avoid
-	 * invalidating the dentries here, alongside with returning the
-	 * negative dentries at f2fs_lookup(), when it is better
-	 * supported by the VFS for the CI case.
-	 */
-	if (IS_CASEFOLDED(dir))
-		d_invalidate(dentry);
-#endif
 	if (IS_DIRSYNC(dir))
 		f2fs_sync_fs(sbi->sb, 1);
 fail: