[Xen-devel] [PATCH] linux/blktap2: use blk_rq_map_sg() here too

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

Just like in blkfront, not doing so can cause the maximum number of
segments check to trigger.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- head-2009-05-29.orig/drivers/xen/blktap2/blktap.h   2009-05-29 
10:25:53.000000000 +0200
+++ head-2009-05-29/drivers/xen/blktap2/blktap.h        2009-05-29 
16:25:25.000000000 +0200
@@ -4,6 +4,7 @@
 #include <linux/fs.h>
 #include <linux/poll.h>
 #include <linux/cdev.h>
+#include <linux/scatterlist.h>
 #include <xen/blkif.h>
 #include <xen/gnttab.h>
 
@@ -174,6 +175,7 @@ struct blktap {
 
        int                            pending_cnt;
        struct blktap_request         *pending_requests[MAX_PENDING_REQS];
+       struct scatterlist             sg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
 
        wait_queue_head_t              wq;
        struct list_head               deferred_queue;
--- head-2009-05-29.orig/drivers/xen/blktap2/device.c   2009-05-29 
10:25:53.000000000 +0200
+++ head-2009-05-29/drivers/xen/blktap2/device.c        2009-05-29 
16:30:25.000000000 +0200
@@ -569,11 +569,10 @@ blktap_device_process_request(struct blk
                              struct blktap_request *request,
                              struct request *req)
 {
-       struct bio *bio;
        struct page *page;
-       struct bio_vec *bvec;
-       int idx, usr_idx, err;
+       int i, usr_idx, err;
        struct blktap_ring *ring;
+       struct scatterlist *sg;
        struct blktap_grant_table table;
        unsigned int fsect, lsect, nr_sects;
        unsigned long offset, uvaddr, kvaddr;
@@ -600,43 +599,39 @@ blktap_device_process_request(struct blk
 
        nr_sects = 0;
        request->nr_pages = 0;
-       blkif_req.nr_segments = 0;
-       rq_for_each_bio(bio, req) {
-               bio_for_each_segment(bvec, bio, idx) {
-                       BUG_ON(blkif_req.nr_segments ==
-                              BLKIF_MAX_SEGMENTS_PER_REQUEST);
-
-                       fsect     = bvec->bv_offset >> 9;
-                       lsect     = fsect + (bvec->bv_len >> 9) - 1;
-                       nr_sects += bvec->bv_len >> 9;
+       blkif_req.nr_segments = blk_rq_map_sg(req->q, req, tap->sg);
+       BUG_ON(blkif_req.nr_segments > BLKIF_MAX_SEGMENTS_PER_REQUEST);
+       for (i = 0; i < blkif_req.nr_segments; ++i) {
+                       sg = tap->sg + i;
+                       fsect = sg->offset >> 9;
+                       lsect = fsect + (sg->length >> 9) - 1;
+                       nr_sects += sg->length >> 9;
 
-                       blkif_req.seg[blkif_req.nr_segments] =
+                       blkif_req.seg[i] =
                                (struct blkif_request_segment) {
                                .gref       = 0,
                                .first_sect = fsect,
                                .last_sect  = lsect };
 
-                       if (PageBlkback(bvec->bv_page)) {
+                       if (PageBlkback(sg->page)) {
                                /* foreign page -- use xen */
                                if (blktap_prep_foreign(tap,
                                                        request,
                                                        &blkif_req,
-                                                       blkif_req.nr_segments,
-                                                       bvec->bv_page,
+                                                       i,
+                                                       sg->page,
                                                        &table))
                                        goto out;
                        } else {
                                /* do it the old fashioned way */
                                blktap_map(tap,
                                           request,
-                                          blkif_req.nr_segments,
-                                          bvec->bv_page);
+                                          i,
+                                          sg->page);
                        }
 
-                       uvaddr = MMAP_VADDR(ring->user_vstart,
-                                           usr_idx, blkif_req.nr_segments);
-                       kvaddr = request_to_kaddr(request,
-                                                 blkif_req.nr_segments);
+                       uvaddr = MMAP_VADDR(ring->user_vstart, usr_idx, i);
+                       kvaddr = request_to_kaddr(request, i);
                        offset = (uvaddr - ring->vma->vm_start) >> PAGE_SHIFT;
                        page   = pfn_to_page(__pa(kvaddr) >> PAGE_SHIFT);
                        ring->foreign_map.map[offset] = page;
@@ -646,12 +641,10 @@ blktap_device_process_request(struct blk
                              uvaddr, page, __pa(kvaddr) >> PAGE_SHIFT);
                        BTDBG("offset: 0x%08lx, pending_req: %p, seg: %d, "
                              "page: %p, kvaddr: 0x%08lx, uvaddr: 0x%08lx\n",
-                             offset, request, blkif_req.nr_segments,
+                             offset, request, i,
                              page, kvaddr, uvaddr);
 
-                       blkif_req.nr_segments++;
                        request->nr_pages++;
-               }
        }
 
        if (blktap_map_foreign(tap, request, &blkif_req, &table))




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