btrfs: simplify generation check in btrfs_get_dentry

Callers that pass non-zero generation always want to perform the
generation check, we can simply encode that in one parameter and drop
check_generation. Add function documentation.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/export.c

@@ -57,9 +57,20 @@ static int btrfs_encode_fh(struct inode *inode, u32 *fh, int *max_len,
 	return type;
 }
 
+/*
+ * Read dentry of inode with @objectid from filesystem root @root_objectid.
+ *
+ * @sb:             the filesystem super block
+ * @objectid:       inode objectid
+ * @root_objectid:  object id of the subvolume root where to look up the inode
+ * @generation:     optional, if not zero, verify that the found inode
+ *                  generation matches
+ *
+ * Return dentry alias for the inode, otherwise an error. In case the
+ * generation does not match return ESTALE.
+ */
 struct dentry *btrfs_get_dentry(struct super_block *sb, u64 objectid,
-				u64 root_objectid, u64 generation,
-				int check_generation)
+				u64 root_objectid, u64 generation)
 {
 	struct btrfs_fs_info *fs_info = btrfs_sb(sb);
 	struct btrfs_root *root;
@@ -77,7 +88,7 @@ struct dentry *btrfs_get_dentry(struct super_block *sb, u64 objectid,
 	if (IS_ERR(inode))
 		return ERR_CAST(inode);
 
-	if (check_generation && generation != inode->i_generation) {
+	if (generation != 0 && generation != inode->i_generation) {
 		iput(inode);
 		return ERR_PTR(-ESTALE);
 	}
@@ -106,7 +117,7 @@ static struct dentry *btrfs_fh_to_parent(struct super_block *sb, struct fid *fh,
 	objectid = fid->parent_objectid;
 	generation = fid->parent_gen;
 
-	return btrfs_get_dentry(sb, objectid, root_objectid, generation, 1);
+	return btrfs_get_dentry(sb, objectid, root_objectid, generation);
 }
 
 static struct dentry *btrfs_fh_to_dentry(struct super_block *sb, struct fid *fh,
@@ -128,7 +139,7 @@ static struct dentry *btrfs_fh_to_dentry(struct super_block *sb, struct fid *fh,
 	root_objectid = fid->root_objectid;
 	generation = fid->gen;
 
-	return btrfs_get_dentry(sb, objectid, root_objectid, generation, 1);
+	return btrfs_get_dentry(sb, objectid, root_objectid, generation);
 }
 
 struct dentry *btrfs_get_parent(struct dentry *child)
@@ -188,7 +199,7 @@ struct dentry *btrfs_get_parent(struct dentry *child)
 
 	if (found_key.type == BTRFS_ROOT_BACKREF_KEY) {
 		return btrfs_get_dentry(fs_info->sb, key.objectid,
-					found_key.offset, 0, 0);
+					found_key.offset, 0);
 	}
 
 	return d_obtain_alias(btrfs_iget(fs_info->sb, key.objectid, root));

fs/btrfs/export.h

@@ -19,8 +19,7 @@ struct btrfs_fid {
 } __attribute__ ((packed));
 
 struct dentry *btrfs_get_dentry(struct super_block *sb, u64 objectid,
-				u64 root_objectid, u64 generation,
-				int check_generation);
+				u64 root_objectid, u64 generation);
 struct dentry *btrfs_get_parent(struct dentry *child);
 
 #endif

fs/btrfs/ioctl.c

@@ -3274,7 +3274,7 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
 
 			dentry = btrfs_get_dentry(fs_info->sb,
 					BTRFS_FIRST_FREE_OBJECTID,
-					vol_args2->subvolid, 0, 0);
+					vol_args2->subvolid, 0);
 			if (IS_ERR(dentry)) {
 				err = PTR_ERR(dentry);
 				goto out_drop_write;