btrfs-progs: Add delayed refs infrastructure

This commit pulls those portions of the kernel implementation of
delayed refs which are necessary to have them working in user-space.
I've done the following modifications:

1. Replaced all kmem_cache_alloc calls to kmalloc.

2. Removed all locking-related code, since we are single threaded in
   userspace.

3. Removed code which deals with data refs - delayed refs in user space
   are going to be used only for cowonly trees.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Makefile

@@ -116,7 +116,8 @@ objects = ctree.o disk-io.o kernel-lib/radix-tree.o extent-tree.o print-tree.o \
 	  qgroup.o free-space-cache.o kernel-lib/list_sort.o props.o \
 	  kernel-shared/ulist.o qgroup-verify.o backref.o string-table.o task-utils.o \
 	  inode.o file.o find-root.o free-space-tree.o help.o send-dump.o \
-	  fsfeatures.o kernel-lib/tables.o kernel-lib/raid56.o transaction.o
+	  fsfeatures.o kernel-lib/tables.o kernel-lib/raid56.o transaction.o \
+	  delayed-ref.o
 cmds_objects = cmds-subvolume.o cmds-filesystem.o cmds-device.o cmds-scrub.o \
 	       cmds-inspect.o cmds-balance.o cmds-send.o cmds-receive.o \
 	       cmds-quota.o cmds-qgroup.o cmds-replace.o check/main.o \

ctree.h

@@ -2790,4 +2790,7 @@ int btrfs_punch_hole(struct btrfs_trans_handle *trans,
 int btrfs_read_file(struct btrfs_root *root, u64 ino, u64 start, int len,
 		    char *dest);
 
+/* extent-tree.c */
+int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans, unsigned long nr);
+
 #endif