[patch 73/96] xen/blkfront: use blk_rq_map_sg to generate ring entries

Greg KH
2009-03-14T00:44:34Z

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2.6.27-stable review patch. If anyone has any objections, please let us know.

------------------

From: Jens Axboe <jens.axboe@oracle.com>

commit 9e973e64ac6dc504e6447d52193d4fff1a670156 upstream.

On occasion, the request will apparently have more segments than we
fit into the ring. Jens says:

> The second problem is that the block layer then appears to create one
> too many segments, but from the dump it has rq->nr_phys_segments ==
> BLKIF_MAX_SEGMENTS_PER_REQUEST. I suspect the latter is due to
> xen-blkfront not handling the merging on its own. It should check that
> the new page doesn't form part of the previous page. The
> rq_for_each_segment() iterates all single bits in the request, not dma
> segments. The "easiest" way to do this is to call blk_rq_map_sg() and
> then iterate the mapped sg list. That will give you what you are
> looking for.

> Here's a test patch, compiles but otherwise untested. I spent more
> time figuring out how to enable XEN than to code it up, so YMMV!
> Probably the sg list wants to be put inside the ring and only
> initialized on allocation, then you can get rid of the sg on stack and
> sg_init_table() loop call in the function. I'll leave that, and the
> testing, to you.

[Moved sg array into info structure, and initialize once. -J]

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Sven Köhler <sven.koehler@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/block/xen-blkfront.c | 30 +++++++++++++++---------------
1 file changed, 15 insertions(+), 15 deletions(-)

--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -40,6 +40,7 @@
#include <linux/hdreg.h>
#include <linux/cdrom.h>
#include <linux/module.h>
+#include <linux/scatterlist.h>

#include <xen/xenbus.h>
#include <xen/grant_table.h>
@@ -82,6 +83,7 @@ struct blkfront_info
enum blkif_state connected;
int ring_ref;
struct blkif_front_ring ring;
+ struct scatterlist sg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
unsigned int evtchn, irq;
struct request_queue *rq;
struct work_struct work;
@@ -203,12 +205,11 @@ static int blkif_queue_request(struct re
struct blkfront_info *info = req->rq_disk->private_data;
unsigned long buffer_mfn;
struct blkif_request *ring_req;
- struct req_iterator iter;
- struct bio_vec *bvec;
unsigned long id;
unsigned int fsect, lsect;
- int ref;
+ int i, ref;
grant_ref_t gref_head;
+ struct scatterlist *sg;

if (unlikely(info->connected != BLKIF_STATE_CONNECTED))
return 1;
@@ -237,12 +238,13 @@ static int blkif_queue_request(struct re
if (blk_barrier_rq(req))
ring_req->operation = BLKIF_OP_WRITE_BARRIER;

- ring_req->nr_segments = 0;
- rq_for_each_segment(bvec, req, iter) {
- BUG_ON(ring_req->nr_segments == BLKIF_MAX_SEGMENTS_PER_REQUEST);
- buffer_mfn = pfn_to_mfn(page_to_pfn(bvec->bv_page));
- fsect = bvec->bv_offset >> 9;
- lsect = fsect + (bvec->bv_len >> 9) - 1;
+ ring_req->nr_segments = blk_rq_map_sg(req->q, req, info->sg);
+ BUG_ON(ring_req->nr_segments > BLKIF_MAX_SEGMENTS_PER_REQUEST);
+
+ for_each_sg(info->sg, sg, ring_req->nr_segments, i) {
+ buffer_mfn = pfn_to_mfn(page_to_pfn(sg_page(sg)));
+ fsect = sg->offset >> 9;
+ lsect = fsect + (sg->length >> 9) - 1;
/* install a grant reference. */
ref = gnttab_claim_grant_reference(&gref_head);
BUG_ON(ref == -ENOSPC);
@@ -253,16 +255,12 @@ static int blkif_queue_request(struct re
buffer_mfn,
rq_data_dir(req) );

- info->shadow[id].frame[ring_req->nr_segments] =
- mfn_to_pfn(buffer_mfn);
-
- ring_req->seg[ring_req->nr_segments] =
+ info->shadow[id].frame[i] = mfn_to_pfn(buffer_mfn);
+ ring_req->seg[i] =
(struct blkif_request_segment) {
.gref = ref,
.first_sect = fsect,
.last_sect = lsect };
-
- ring_req->nr_segments++;
}

info->ring.req_prod_pvt++;
@@ -592,6 +590,8 @@ static int setup_blkring(struct xenbus_d
SHARED_RING_INIT(sring);
FRONT_RING_INIT(&info->ring, sring, PAGE_SIZE);

+ sg_init_table(info->sg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
+
err = xenbus_grant_ring(dev, virt_to_mfn(info->ring.sring));
if (err < 0) {
free_page((unsigned long)sring);