1 files changed, 25 insertions, 0 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 4ec8305fe078..e14f8bd4b310 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4297,6 +4297,31 @@ static void block_rsv_add_bytes(struct btrfs_block_rsv *block_rsv,
         spin_unlock(&block_rsv->lock);
 }
 
+int btrfs_cond_migrate_bytes(struct btrfs_fs_info *fs_info,
+                             struct btrfs_block_rsv *dest, u64 num_bytes,
+                             int min_factor)
+{
+        struct btrfs_block_rsv *global_rsv = &fs_info->global_block_rsv;
+        u64 min_bytes;
+
+        if (global_rsv->space_info != dest->space_info)
+                return -ENOSPC;
+
+        spin_lock(&global_rsv->lock);
+        min_bytes = div_factor(global_rsv->size, min_factor);
+        if (global_rsv->reserved < min_bytes + num_bytes) {
+                spin_unlock(&global_rsv->lock);
+                return -ENOSPC;
+        }
+        global_rsv->reserved -= num_bytes;
+        if (global_rsv->reserved < global_rsv->size)
+                global_rsv->full = 0;
+        spin_unlock(&global_rsv->lock);
+
+        block_rsv_add_bytes(dest, num_bytes, 1);
+        return 0;
+}
+
 static void block_rsv_release_bytes(struct btrfs_fs_info *fs_info,
                                     struct btrfs_block_rsv *block_rsv,
                                     struct btrfs_block_rsv *dest, u64 num_bytes)