From 4ee5eaf4516a60f8ef64d3c246c64c6be0cf8c3a Mon Sep 17 00:00:00 2001 From: Kiyoshi Ueda Date: Thu, 18 Sep 2008 10:46:13 -0400 Subject: [PATCH] block: add a queue flag for request stacking support This patch adds a queue flag to indicate the block device can be used for request stacking. Request stacking drivers need to stack their devices on top of only devices of which q->request_fn is functional. Since bio stacking drivers (e.g. md, loop) basically initialize their queue using blk_alloc_queue() and don't set q->request_fn, the check of (q->request_fn == NULL) looks enough for that purpose. However, dm will become both types of stacking driver (bio-based and request-based). And dm will always set q->request_fn even if the dm device is bio-based of which q->request_fn is not functional actually. So we need something else to distinguish the type of the device. Adding a queue flag is a solution for that. The reason why dm always sets q->request_fn is to keep the compatibility of dm user-space tools. Currently, all dm user-space tools are using bio-based dm without specifying the type of the dm device they use. To use request-based dm without changing such tools, the kernel must decide the type of the dm device automatically. The automatic type decision can't be done at the device creation time and needs to be deferred until such tools load a mapping table, since the actual type is decided by dm target type included in the mapping table. So a dm device has to be initialized using blk_init_queue() so that we can load either type of table. Then, all queue stuffs are set (e.g. q->request_fn) and we have no element to distinguish that it is bio-based or request-based, even after a table is loaded and the type of the device is decided. By the way, some stuffs of the queue (e.g. request_list, elevator) are needless when the dm device is used as bio-based. But the memory size is not so large (about 20[KB] per queue on ia64), so I hope the memory loss can be acceptable for bio-based dm users. Signed-off-by: Kiyoshi Ueda Signed-off-by: Jun'ichi Nomura Signed-off-by: Jens Axboe --- block/blk-core.c | 3 ++- include/linux/blkdev.h | 3 +++ 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/block/blk-core.c b/block/blk-core.c index b8ffbfe85ca4..fa212348c4c9 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -574,7 +574,8 @@ blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id) q->request_fn = rfn; q->prep_rq_fn = NULL; q->unplug_fn = generic_unplug_device; - q->queue_flags = (1 << QUEUE_FLAG_CLUSTER); + q->queue_flags = (1 << QUEUE_FLAG_CLUSTER | + 1 << QUEUE_FLAG_STACKABLE); q->queue_lock = lock; blk_queue_segment_boundary(q, 0xffffffff); diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 964c246bc271..86f77ef127f4 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -441,6 +441,7 @@ struct request_queue #define QUEUE_FLAG_NOMERGES 10 /* disable merge attempts */ #define QUEUE_FLAG_SAME_COMP 11 /* force complete on same CPU */ #define QUEUE_FLAG_FAIL_IO 12 /* fake timeout */ +#define QUEUE_FLAG_STACKABLE 13 /* supports request stacking */ static inline int queue_is_locked(struct request_queue *q) { @@ -547,6 +548,8 @@ enum { #define blk_queue_stopped(q) test_bit(QUEUE_FLAG_STOPPED, &(q)->queue_flags) #define blk_queue_nomerges(q) test_bit(QUEUE_FLAG_NOMERGES, &(q)->queue_flags) #define blk_queue_flushing(q) ((q)->ordseq) +#define blk_queue_stackable(q) \ + test_bit(QUEUE_FLAG_STACKABLE, &(q)->queue_flags) #define blk_fs_request(rq) ((rq)->cmd_type == REQ_TYPE_FS) #define blk_pc_request(rq) ((rq)->cmd_type == REQ_TYPE_BLOCK_PC)