Hello,

I've found another issue with blkback handling of flush operations, it
was incorrectly setting one of the bio parameters when using a block
device as backend. The attached patch fixes it, and also includes a
small fix to correctly set the operation when writing the response on
the ring (all responses written by FreeBSD blkback were of type
BLKIF_OP_READ, because nreq->operation was not set).
>From b6cd715b2a2fcff0321ccaafe9740082f15b5943 Mon Sep 17 00:00:00 2001
From: Roger Pau Monne <roger....@citrix.com>
Date: Wed, 4 Sep 2013 18:33:22 +0200
Subject: [PATCH] xen-blkback: fix incorrect handling of flush for block
 devices

When issuing a flush operation to a block device (from
xbb_dispatch_dev), bio->bio_caller1 was incorrectly set to
xbb_xen_req, when the bio callback (xbb_bio_done) specifically
expects bio_caller1 to be of type xbb_xen_reqlist.

Also set the request operation to match the one on the request from
the ring, so that when we write the reply the operation matches.
---
 sys/dev/xen/blkback/blkback.c |    7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/sys/dev/xen/blkback/blkback.c b/sys/dev/xen/blkback/blkback.c
index fa9a744..58b53e7 100644
--- a/sys/dev/xen/blkback/blkback.c
+++ b/sys/dev/xen/blkback/blkback.c
@@ -1240,6 +1240,7 @@ xbb_get_resources(struct xbb_softc *xbb, struct 
xbb_xen_reqlist **reqlist,
        nreq->reqlist = *reqlist;
        nreq->req_ring_idx = ring_idx;
        nreq->id = ring_req->id;
+       nreq->operation = ring_req->operation;
 
        if (xbb->abi != BLKIF_PROTOCOL_NATIVE) {
                bcopy(ring_req, &nreq->ring_req_storage, sizeof(*ring_req));
@@ -2062,7 +2063,6 @@ xbb_dispatch_dev(struct xbb_softc *xbb, struct 
xbb_xen_reqlist *reqlist,
 {
        struct xbb_dev_data *dev_data;
        struct bio          *bios[XBB_MAX_SEGMENTS_PER_REQLIST];
-       struct xbb_xen_req  *nreq;
        off_t                bio_offset;
        struct bio          *bio;
        struct xbb_sg       *xbb_sg;
@@ -2080,7 +2080,6 @@ xbb_dispatch_dev(struct xbb_softc *xbb, struct 
xbb_xen_reqlist *reqlist,
        bio_idx    = 0;
 
        if (operation == BIO_FLUSH) {
-               nreq = STAILQ_FIRST(&reqlist->contig_req_list);
                bio = g_new_bio();
                if (unlikely(bio == NULL)) {
                        DPRINTF("Unable to allocate bio for BIO_FLUSH\n");
@@ -2094,10 +2093,10 @@ xbb_dispatch_dev(struct xbb_softc *xbb, struct 
xbb_xen_reqlist *reqlist,
                bio->bio_offset  = 0;
                bio->bio_data    = 0;
                bio->bio_done    = xbb_bio_done;
-               bio->bio_caller1 = nreq;
+               bio->bio_caller1 = reqlist;
                bio->bio_pblkno  = 0;
 
-               nreq->pendcnt    = 1;
+               reqlist->pendcnt = 1;
 
                SDT_PROBE1(xbb, kernel, xbb_dispatch_dev, flush,
                           device_get_unit(xbb->dev));
-- 
1.7.7.5 (Apple Git-26)

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