From: Lu Fengqi <lufq.f...@cn.fujitsu.com>

Introduce the function check_shared_data_backref() to check the
referencer of a given shared data backref.

Signed-off-by: Lu Fengqi <lufq.f...@cn.fujitsu.com>
Signed-off-by: Qu Wenruo <quwen...@cn.fujitsu.com>
---
 cmds-check.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/cmds-check.c b/cmds-check.c
index 6b59397..18325f9 100644
--- a/cmds-check.c
+++ b/cmds-check.c
@@ -9028,6 +9028,50 @@ out:
        return 0;
 }
 
+/*
+ * Check if the referencer of a shared data backref exists
+ */
+static int check_shared_data_backref(struct btrfs_fs_info *fs_info,
+                                    u64 parent, u64 bytenr)
+{
+       struct extent_buffer *eb;
+       struct btrfs_key key;
+       struct btrfs_file_extent_item *fi;
+       u32 nodesize = btrfs_super_nodesize(fs_info->super_copy);
+       u32 nr;
+       int found_parent = 0;
+       int i;
+
+       eb = read_tree_block_fs_info(fs_info, parent, nodesize, 0);
+       if (!extent_buffer_uptodate(eb))
+               goto out;
+
+       nr = btrfs_header_nritems(eb);
+       for (i = 0; i < nr; i++) {
+               btrfs_item_key_to_cpu(eb, &key, i);
+               if (key.type != BTRFS_EXTENT_DATA_KEY)
+                       continue;
+
+               fi = btrfs_item_ptr(eb, i, struct btrfs_file_extent_item);
+               if (btrfs_file_extent_type(eb, fi) == BTRFS_FILE_EXTENT_INLINE)
+                       continue;
+
+               if (btrfs_file_extent_disk_bytenr(eb, fi) == bytenr) {
+                       found_parent = 1;
+                       break;
+               }
+       }
+
+out:
+       free_extent_buffer(eb);
+       if (!found_parent) {
+               error("Shared extent %llu referencer lost(parent: %llu)",
+                     bytenr, parent);
+               return REFERENCER_MISSING;
+       }
+       return 0;
+}
+
 static int btrfs_fsck_reinit_root(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root, int overwrite)
 {
-- 
2.8.2



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