dm: add BLK_FEAT_WRITE_ZEROES_UNMAP support

Set the BLK_FEAT_WRITE_ZEROES_UNMAP feature on stacking queue limits by
default. This feature shall be disabled if any underlying device does
not support it.

Signed-off-by: Zhang Yi <[email protected]>
Reviewed-by: Benjamin Marzinski <[email protected]>

Author: zhangyi089

drivers/md/dm-table.c

@@ -599,7 +599,8 @@ int dm_split_args(int *argc, char ***argvp, char *input)
 static void dm_set_stacking_limits(struct queue_limits *limits)
 {
 	blk_set_stacking_limits(limits);
-	limits->features |= BLK_FEAT_IO_STAT | BLK_FEAT_NOWAIT | BLK_FEAT_POLL;
+	limits->features |= BLK_FEAT_IO_STAT | BLK_FEAT_NOWAIT | BLK_FEAT_POLL |
+			    BLK_FEAT_WRITE_ZEROES_UNMAP;
 }
 
 /*
@@ -1851,8 +1852,10 @@ int dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 		limits->discard_alignment = 0;
 	}
 
-	if (!dm_table_supports_write_zeroes(t))
+	if (!dm_table_supports_write_zeroes(t)) {
 		limits->max_write_zeroes_sectors = 0;
+		limits->features &= ~BLK_FEAT_WRITE_ZEROES_UNMAP;
+	}
 
 	if (!dm_table_supports_secure_erase(t))
 		limits->max_secure_erase_sectors = 0;

drivers/md/dm.c

@@ -1096,6 +1096,7 @@ void disable_write_zeroes(struct mapped_device *md)
 
 	/* device doesn't really support WRITE ZEROES, disable it */
 	limits->max_write_zeroes_sectors = 0;
+	limits->features &= ~BLK_FEAT_WRITE_ZEROES_UNMAP;
 }
 
 static bool swap_bios_limit(struct dm_target *ti, struct bio *bio)