[PATCH] btrfs: re-instantiate the removed BTRFS_SUBVOL_CREATE_ASYNC definition

[Eugene Syromiatnikov <esyr@redhat.com>]

The commit 9c1036fdb1d1ff1b ("btrfs: Remove BTRFS_SUBVOL_CREATE_ASYNC
support") breaks strace build with the kernel headers from git:

    btrfs.c: In function "btrfs_test_subvol_ioctls":
    btrfs.c:531:23: error: "BTRFS_SUBVOL_CREATE_ASYNC" undeclared (first use
    in this function)
       vol_args_v2.flags = BTRFS_SUBVOL_CREATE_ASYNC;

Moreover, it is improper to break UAPI anyway.

Restore the macro definition and put it under "#ifndef __KERNEL__"
in order to prevent inadvertent in-kernel usage.

Fixes: 9c1036fdb1d1ff1b ("btrfs: Remove BTRFS_SUBVOL_CREATE_ASYNC support")
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
---
 include/uapi/linux/btrfs.h | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index 8134924..e6b6cb0f 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -36,12 +36,10 @@ struct btrfs_ioctl_vol_args {
 #define BTRFS_DEVICE_PATH_NAME_MAX	1024
 #define BTRFS_SUBVOL_NAME_MAX 		4039
 
-/*
- * Deprecated since 5.7:
- *
- * BTRFS_SUBVOL_CREATE_ASYNC	(1ULL << 0)
- */
-
+#ifndef __KERNEL__
+/* Deprecated since 5.7 */
+# define BTRFS_SUBVOL_CREATE_ASYNC	(1ULL << 0)
+#endif
 #define BTRFS_SUBVOL_RDONLY		(1ULL << 1)
 #define BTRFS_SUBVOL_QGROUP_INHERIT	(1ULL << 2)
 
-- 
2.1.4