[Xen-changelog] [xen-unstable] Request re-coalescing for qcow disks. qcow driver had the habit of breaking each

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

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1261031276 0
# Node ID 180d46ac70d3b3572277dc2223d42cbd04dab632
# Parent  51d1fec19ad44a882def905df7559f4be7f91d92
Request re-coalescing for qcow disks. qcow driver had the habit of breaking each
(4K) block read into 8 (512 bytes) sector reads. This is inefficient, but also
prevents sharing detector from working, as it is based on page-size reads.

Signed-off-by: Grzegorz Milos <Grzegorz.Milos@xxxxxxxxxx>
---
 tools/blktap2/drivers/block-qcow.c |   11 +++++++++++
 1 files changed, 11 insertions(+)

diff -r 51d1fec19ad4 -r 180d46ac70d3 tools/blktap2/drivers/block-qcow.c
--- a/tools/blktap2/drivers/block-qcow.c        Thu Dec 17 06:27:56 2009 +0000
+++ b/tools/blktap2/drivers/block-qcow.c        Thu Dec 17 06:27:56 2009 +0000
@@ -1035,6 +1035,17 @@ void tdqcow_queue_read(td_driver_t *driv
                }
                
                if(!cluster_offset) {
+            int i;
+            /* Forward entire request if possible. */
+            for(i=0; i<nb_sectors; i++)
+                if(get_cluster_offset(s, (sector+i) << 9, 0, 0, 0, 0))
+                    goto coalesce_failed;
+            treq.buf  = buf;
+            treq.sec  = sector;
+            treq.secs = nb_sectors;
+                       td_forward_request(treq);
+            return;
+coalesce_failed:            
                        treq.buf  = buf;
                        treq.sec  = sector;
                        treq.secs = n;

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