While creating a subvolume/snapshot, we don't use inode cache to allocate
an inode id for the root dir ".", so inode cache doesn't mark that id as
used, and when we create a new file, it'll be unhappy and throw out
-EEXIST.

Reviewed-by: Miao Xie <[email protected]>
Signed-off-by: Liu Bo <[email protected]>
---
 fs/btrfs/inode-map.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/inode-map.c b/fs/btrfs/inode-map.c
index b7fb1a8..77cb72a 100644
--- a/fs/btrfs/inode-map.c
+++ b/fs/btrfs/inode-map.c
@@ -532,6 +532,16 @@ static int btrfs_find_highest_objectid(struct btrfs_root 
*root, u64 *objectid)
        struct btrfs_key search_key;
        struct btrfs_key found_key;
        int slot;
+       u64 min_objectid;
+
+       /*
+        * For fs/file tree, FIRST_FREE_OBJECTID is reserved for
+        * root dir "."
+        */
+       if (is_fstree(root->root_key.objectid))
+               min_objectid = BTRFS_FIRST_FREE_OBJECTID;
+       else
+               min_objectid = BTRFS_FIRST_FREE_OBJECTID - 1;
 
        path = btrfs_alloc_path();
        if (!path)
@@ -548,10 +558,9 @@ static int btrfs_find_highest_objectid(struct btrfs_root 
*root, u64 *objectid)
                slot = path->slots[0] - 1;
                l = path->nodes[0];
                btrfs_item_key_to_cpu(l, &found_key, slot);
-               *objectid = max_t(u64, found_key.objectid,
-                                 BTRFS_FIRST_FREE_OBJECTID - 1);
+               *objectid = max_t(u64, found_key.objectid, min_objectid);
        } else {
-               *objectid = BTRFS_FIRST_FREE_OBJECTID - 1;
+               *objectid = min_objectid;
        }
        ret = 0;
 error:
-- 
1.8.2.1

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