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Subject[PATCH v2] ubd: remove use of blk_rq_map_sg
Date
From: Christoph Hellwig <hch@lst.de>

There is no good reason to create a scatterlist in the ubd driver,
it can just iterate the request directly.

Signed-off-by: Christoph Hellwig <hch@lst.de>
[rw: Folded in improvements as discussed with hch and jens]
Signed-off-by: Richard Weinberger <richard@nod.at>
---
arch/um/drivers/ubd_kern.c | 158 +++++++++++++------------------------
1 file changed, 54 insertions(+), 104 deletions(-)

diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 9cb0cabb4e02..74c002ddc0ce 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -160,12 +160,6 @@ struct ubd {
spinlock_t lock;
};

-struct ubd_pdu {
- struct scatterlist sg[MAX_SG];
- int start_sg, end_sg;
- sector_t rq_pos;
-};
-
#define DEFAULT_COW { \
.file = NULL, \
.fd = -1, \
@@ -197,9 +191,6 @@ static struct proc_dir_entry *proc_ide = NULL;

static blk_status_t ubd_queue_rq(struct blk_mq_hw_ctx *hctx,
const struct blk_mq_queue_data *bd);
-static int ubd_init_request(struct blk_mq_tag_set *set,
- struct request *req, unsigned int hctx_idx,
- unsigned int numa_node);

static void make_proc_ide(void)
{
@@ -895,7 +886,6 @@ static int ubd_disk_register(int major, u64 size, int unit,

static const struct blk_mq_ops ubd_mq_ops = {
.queue_rq = ubd_queue_rq,
- .init_request = ubd_init_request,
};

static int ubd_add(int n, char **error_out)
@@ -918,7 +908,6 @@ static int ubd_add(int n, char **error_out)
ubd_dev->tag_set.queue_depth = 64;
ubd_dev->tag_set.numa_node = NUMA_NO_NODE;
ubd_dev->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
- ubd_dev->tag_set.cmd_size = sizeof(struct ubd_pdu);
ubd_dev->tag_set.driver_data = ubd_dev;
ubd_dev->tag_set.nr_hw_queues = 1;

@@ -1300,123 +1289,84 @@ static void cowify_req(struct io_thread_req *req, unsigned long *bitmap,
req->bitmap_words, bitmap_len);
}

-/* Called with dev->lock held */
-static void prepare_request(struct request *req, struct io_thread_req *io_req,
- unsigned long long offset, int page_offset,
- int len, struct page *page)
+static int ubd_queue_one_vec(struct blk_mq_hw_ctx *hctx, struct request *req,
+ u64 off, struct bio_vec *bvec)
{
- struct gendisk *disk = req->rq_disk;
- struct ubd *ubd_dev = disk->private_data;
-
- io_req->req = req;
- io_req->fds[0] = (ubd_dev->cow.file != NULL) ? ubd_dev->cow.fd :
- ubd_dev->fd;
- io_req->fds[1] = ubd_dev->fd;
- io_req->cow_offset = -1;
- io_req->offset = offset;
- io_req->length = len;
- io_req->error = 0;
- io_req->sector_mask = 0;
-
- io_req->op = (rq_data_dir(req) == READ) ? UBD_READ : UBD_WRITE;
- io_req->offsets[0] = 0;
- io_req->offsets[1] = ubd_dev->cow.data_offset;
- io_req->buffer = page_address(page) + page_offset;
- io_req->sectorsize = 1 << 9;
-
- if(ubd_dev->cow.file != NULL)
- cowify_req(io_req, ubd_dev->cow.bitmap,
- ubd_dev->cow.bitmap_offset, ubd_dev->cow.bitmap_len);
-
-}
+ struct ubd *dev = hctx->queue->queuedata;
+ struct io_thread_req *io_req;
+ int ret;

-/* Called with dev->lock held */
-static void prepare_flush_request(struct request *req,
- struct io_thread_req *io_req)
-{
- struct gendisk *disk = req->rq_disk;
- struct ubd *ubd_dev = disk->private_data;
+ io_req = kmalloc(sizeof(struct io_thread_req), GFP_ATOMIC);
+ if (!io_req)
+ return -ENOMEM;

io_req->req = req;
- io_req->fds[0] = (ubd_dev->cow.file != NULL) ? ubd_dev->cow.fd :
- ubd_dev->fd;
- io_req->op = UBD_FLUSH;
-}
-
-static void submit_request(struct io_thread_req *io_req, struct ubd *dev)
-{
- int n = os_write_file(thread_fd, &io_req,
- sizeof(io_req));
+ if (dev->cow.file)
+ io_req->fds[0] = dev->cow.fd;
+ else
+ io_req->fds[0] = dev->fd;

- if (n != sizeof(io_req)) {
- if (n != -EAGAIN)
- pr_err("write to io thread failed: %d\n", -n);
+ if (req_op(req) == REQ_OP_FLUSH) {
+ io_req->op = UBD_FLUSH;
+ } else {
+ io_req->fds[1] = dev->fd;
+ io_req->cow_offset = -1;
+ io_req->offset = off;
+ io_req->length = bvec->bv_len;
+ io_req->error = 0;
+ io_req->sector_mask = 0;
+
+ io_req->op = rq_data_dir(req) == READ ? UBD_READ : UBD_WRITE;
+ io_req->offsets[0] = 0;
+ io_req->offsets[1] = dev->cow.data_offset;
+ io_req->buffer = page_address(bvec->bv_page) + bvec->bv_offset;
+ io_req->sectorsize = 1 << 9;
+
+ if (dev->cow.file) {
+ cowify_req(io_req, dev->cow.bitmap,
+ dev->cow.bitmap_offset, dev->cow.bitmap_len);
+ }
+ }

- blk_mq_requeue_request(io_req->req, true);
+ ret = os_write_file(thread_fd, &io_req, sizeof(io_req));
+ if (ret != sizeof(io_req)) {
+ if (ret != -EAGAIN)
+ pr_err("write to io thread failed: %d\n", -ret);
kfree(io_req);
}
+
+ return ret;
}

static blk_status_t ubd_queue_rq(struct blk_mq_hw_ctx *hctx,
const struct blk_mq_queue_data *bd)
{
struct request *req = bd->rq;
- struct ubd *dev = hctx->queue->queuedata;
- struct ubd_pdu *pdu = blk_mq_rq_to_pdu(req);
- struct io_thread_req *io_req;
+ int ret = 0;

blk_mq_start_request(req);

- pdu->rq_pos = blk_rq_pos(req);
- pdu->start_sg = 0;
- pdu->end_sg = blk_rq_map_sg(req->q, req, pdu->sg);
-
if (req_op(req) == REQ_OP_FLUSH) {
- io_req = kmalloc(sizeof(struct io_thread_req), GFP_ATOMIC);
- if (io_req == NULL) {
- blk_mq_requeue_request(req, true);
- goto done;
+ ret = ubd_queue_one_vec(hctx, req, 0, NULL);
+ } else {
+ struct req_iterator iter;
+ struct bio_vec bvec;
+ u64 off = (u64)blk_rq_pos(req) << 9;
+
+ rq_for_each_segment(bvec, req, iter) {
+ ret = ubd_queue_one_vec(hctx, req, off, &bvec);
+ if (ret < 0)
+ goto out;
+ off += bvec.bv_len;
}
- prepare_flush_request(req, io_req);
- submit_request(io_req, dev);
-
- goto done;
}
-
- while (pdu->start_sg < pdu->end_sg) {
- struct scatterlist *sg = &pdu->sg[pdu->start_sg];
-
- io_req = kmalloc(sizeof(struct io_thread_req),
- GFP_ATOMIC);
- if (io_req == NULL) {
- blk_mq_requeue_request(req, true);
- goto done;
- }
- prepare_request(req, io_req,
- (unsigned long long)pdu->rq_pos << 9,
- sg->offset, sg->length, sg_page(sg));
-
- submit_request(io_req, dev);
-
- pdu->rq_pos += sg->length >> 9;
- pdu->start_sg++;
+out:
+ if (ret < 0) {
+ blk_mq_requeue_request(req, true);
}
-
-done:
return BLK_STS_OK;
}

-static int ubd_init_request(struct blk_mq_tag_set *set,
- struct request *req, unsigned int hctx_idx,
- unsigned int numa_node)
-{
- struct ubd_pdu *pdu = blk_mq_rq_to_pdu(req);
-
- sg_init_table(pdu->sg, MAX_SG);
-
- return 0;
-}
-
static int ubd_getgeo(struct block_device *bdev, struct hd_geometry *geo)
{
struct ubd *ubd_dev = bdev->bd_disk->private_data;
--
2.19.1
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