[RFC PATCH v2 3/8] btrfs-progs: sub list: Add helper function which checks the permission for tree search ioctl

["Misono, Tomohiro" <misono.tomohiro@jp.fujitsu.com>]

This is a preparetion work to allow normal user to call
"subvolume list/show".

Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
---
 btrfs-list.c | 33 +++++++++++++++++++++++++++++++++
 btrfs-list.h |  1 +
 2 files changed, 34 insertions(+)

diff --git a/btrfs-list.c b/btrfs-list.c
index 50e5ce5f..88689a9d 100644
--- a/btrfs-list.c
+++ b/btrfs-list.c
@@ -958,6 +958,39 @@ out:
 	return 0;
 }
 
+/*
+ * Check the permission for tree search ioctl by searching a key
+ * which alwasys exists
+ */
+int check_perm_for_tree_search(int fd)
+{
+	struct btrfs_ioctl_search_args args;
+	struct btrfs_ioctl_search_key *sk = &args.key;
+	int ret;
+
+	memset(&args, 0, sizeof(args));
+	sk->tree_id = BTRFS_ROOT_TREE_OBJECTID;
+	sk->min_objectid = BTRFS_EXTENT_TREE_OBJECTID;
+	sk->max_objectid = BTRFS_EXTENT_TREE_OBJECTID;
+	sk->min_type = BTRFS_ROOT_ITEM_KEY;
+	sk->max_type = BTRFS_ROOT_ITEM_KEY;
+	sk->min_offset = 0;
+	sk->max_offset = (u64)-1;
+	sk->min_transid = 0;
+	sk->max_transid = (u64)-1;
+	sk->nr_items = 1;
+	ret = ioctl(fd, BTRFS_IOC_TREE_SEARCH, &args);
+
+	if (!ret)
+		ret = 1;
+	else if (ret < 0 && errno == EPERM)
+		ret = 0;
+	else
+		ret = -errno;
+
+	return ret;
+}
+
 static int list_subvol_search(int fd, struct root_lookup *root_lookup)
 {
 	int ret;
diff --git a/btrfs-list.h b/btrfs-list.h
index 6e5fc778..6225311d 100644
--- a/btrfs-list.h
+++ b/btrfs-list.h
@@ -176,5 +176,6 @@ char *btrfs_list_path_for_root(int fd, u64 root);
 int btrfs_list_get_path_rootid(int fd, u64 *treeid);
 int btrfs_get_subvol(int fd, struct root_info *the_ri);
 int btrfs_get_toplevel_subvol(int fd, struct root_info *the_ri);
+int check_perm_for_tree_search(int fd);
 
 #endif
-- 
2.14.3