libmount: improve mnt_table_next_child_fs()

The function utilizes the struct libmnt_itr to iterate through the mountinfo file
but neglects the direction specified by the iterator. This a bug. The application
must manage the direction, as, for instance, umount(8) requires the children of
the mountpoint in reverse order.

Fixes: https://github.com/util-linux/util-linux/issues/2552
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/libmount/src/tab.c b/libmount/src/tab.c
index 60bef8b2d16b394bb065e0becd6061dfd4b9f6c2..5c2d5c868b84932860ea87fcd012ed0770cd36ed 100644 (file)
--- a/libmount/src/tab.c
+++ b/libmount/src/tab.c
@@ -650,8 +650,8 @@ int mnt_table_get_root_fs(struct libmnt_table *tb, struct libmnt_fs **root)
  * @parent: parental FS
  * @chld: NULL or returns the next child filesystem
  *
- * Note that filesystems are returned in the order of mounting (according to
- * IDs in /proc/self/mountinfo).
+ * Since version 2.40, the filesystems are returned in the order specified by
+ * @itr. In the old versions the derection is always MNT_ITER_FORWARD.
  *
  * Returns: 0 on success, negative number in case of error or 1 at the end of list.
  */
@@ -660,6 +660,7 @@ int mnt_table_next_child_fs(struct libmnt_table *tb, struct libmnt_iter *itr,
 {
        struct libmnt_fs *fs, *chfs = NULL;
        int parent_id, lastchld_id = 0, chld_id = 0;
+       int direction = mnt_iter_get_direction(itr);
 
        if (!tb || !itr || !parent || !is_mountinfo(tb))
                return -EINVAL;
@@ -675,7 +676,7 @@ int mnt_table_next_child_fs(struct libmnt_table *tb, struct libmnt_iter *itr,
                lastchld_id = mnt_fs_get_id(fs);
        }
 
-       mnt_reset_iter(itr, MNT_ITER_FORWARD);
+       mnt_reset_iter(itr, direction);
        while (mnt_table_next_fs(tb, itr, &fs) == 0) {
                int id;
 
@@ -689,10 +690,20 @@ int mnt_table_next_child_fs(struct libmnt_table *tb, struct libmnt_iter *itr,
                if (id == parent_id)
                        continue;
 
-               if ((!lastchld_id || id > lastchld_id) &&
-                   (!chfs || id < chld_id)) {
-                       chfs = fs;
-                       chld_id = id;
+               if (direction == MNT_ITER_FORWARD) {
+                       /* return in the order of mounting */
+                       if ((!lastchld_id || id > lastchld_id) &&
+                           (!chfs || id < chld_id)) {
+                               chfs = fs;
+                               chld_id = id;
+                       }
+               } else {
+                       /* return last child first */
+                       if ((!lastchld_id || id < lastchld_id) &&
+                           (!chfs || id > chld_id)) {
+                               chfs = fs;
+                               chld_id = id;
+                       }
                }
        }