Messages in this thread Patch in this message | | | Date | Fri, 06 Feb 2009 13:16:11 -0800 | From | Jeremy Fitzhardinge <> | Subject | [PATCH] xen/blkfront: use blk_rq_map_sg to generate ring entries |
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From: Jens Axboe <jens.axboe@oracle.com>
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.
[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> --- 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 @@ 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; @@ -204,12 +206,11 @@ 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; @@ -238,12 +239,13 @@ 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); @@ -254,16 +256,12 @@ 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++; @@ -622,6 +620,8 @@ 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);
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