btrfs: add allocator_hint for no allocation preferred

This is useful where you want to prevent new allocations of chunks on a
disk which is going to be removed from the pool anyways, e.g. due to
bad blocks or because it's slow.

Signed-off-by: Kai Krakow <kai@kaishome.de>

Author: kakra

fs/btrfs/volumes.c

@@ -195,6 +195,7 @@ static const char alloc_hint_map[BTRFS_DEV_ALLOCATION_MASK_COUNT] = {
 	[BTRFS_DEV_ALLOCATION_PREFERRED_DATA] = 0,
 	[BTRFS_DEV_ALLOCATION_PREFERRED_METADATA] = 1,
 	[BTRFS_DEV_ALLOCATION_METADATA_ONLY] = 2,
+	[BTRFS_DEV_ALLOCATION_PREFERRED_NONE] = 99,
 	/* the other values are set to 0 */
 };
 #endif
@@ -5362,7 +5363,10 @@ static int gather_device_info(struct btrfs_fs_devices *fs_devices,
 			 * sort also by hint (metadata hint
 			 * higher priority)
 			 */
-			devices_info[ndevs].alloc_hint = alloc_hint_map[hint];
+			if (hint == BTRFS_DEV_ALLOCATION_PREFERRED_NONE)
+				devices_info[ndevs].alloc_hint = -alloc_hint_map[hint];
+			else
+				devices_info[ndevs].alloc_hint = alloc_hint_map[hint];
 		}
 #endif
 

include/uapi/linux/btrfs_tree.h

@@ -591,6 +591,8 @@ struct btrfs_node {
 #define BTRFS_DEV_ALLOCATION_METADATA_ONLY	(2ULL)
 /* only data chunk allowed */
 #define BTRFS_DEV_ALLOCATION_DATA_ONLY		(3ULL)
+/* avoid chunk allocation if possible */
+#define BTRFS_DEV_ALLOCATION_PREFERRED_NONE	(4ULL)
 /* 5..7 are unused values */
 
 #endif