[Xen-changelog] Fix blkback request notification holdoff. req_cons must be

[Xen patchbot -unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID 8754277cec01d26b7174a3ef8644ef557f42ed26
# Parent  4c588e255c8595f0502a56555a68379f8fcb034d
Fix blkback request notification holdoff. req_cons must be
updated before make_response() is called. This fixes attaching
ramdisk-backed vbds to a blkfront.

Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>

diff -r 4c588e255c85 -r 8754277cec01 
linux-2.6-xen-sparse/drivers/xen/blkback/blkback.c
--- a/linux-2.6-xen-sparse/drivers/xen/blkback/blkback.c        Sat Dec  3 
10:00:03 2005
+++ b/linux-2.6-xen-sparse/drivers/xen/blkback/blkback.c        Sat Dec  3 
10:41:49 2005
@@ -296,22 +296,23 @@
 {
        blkif_back_ring_t *blk_ring = &blkif->blk_ring;
        blkif_request_t *req;
-       RING_IDX i, rp;
+       RING_IDX rc, rp;
        int more_to_do = 0;
 
+       rc = blk_ring->req_cons;
        rp = blk_ring->sring->req_prod;
        rmb(); /* Ensure we see queued requests up to 'rp'. */
 
-       for (i = blk_ring->req_cons; 
-            (i != rp) && !RING_REQUEST_CONS_OVERFLOW(blk_ring, i);
-            i++) {
+       while ((rc != rp) && !RING_REQUEST_CONS_OVERFLOW(blk_ring, rc)) {
                if ((max_to_do-- == 0) ||
                    (NR_PENDING_REQS == MAX_PENDING_REQS)) {
                        more_to_do = 1;
                        break;
                }
-        
-               req = RING_GET_REQUEST(blk_ring, i);
+
+               req = RING_GET_REQUEST(blk_ring, rc);
+               blk_ring->req_cons = ++rc; /* before make_response() */
+
                switch (req->operation) {
                case BLKIF_OP_READ:
                case BLKIF_OP_WRITE:
@@ -327,7 +328,6 @@
                }
        }
 
-       blk_ring->req_cons = i;
        return more_to_do;
 }
 

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