From: Keir Fraser <keir.fraser@citrix.com>
Date: Thu, 17 Dec 2009 06:27:56 +0000 (+0000)
Subject: Request re-coalescing for qcow disks. qcow driver had the habit of breaking each
X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~12855
X-Git-Url: https://dgit.raspbian.org/%22http://www.example.com/cgi/%22/%22http:/www.example.com/cgi/%22?a=commitdiff_plain;h=5db8a5259c8d4bba3d99761785f2444c6b3dd5ef;p=xen.git

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@citrix.com>
---

diff --git a/tools/blktap2/drivers/block-qcow.c b/tools/blktap2/drivers/block-qcow.c
index e0590ae59b..13d6c324ea 100644
--- a/tools/blktap2/drivers/block-qcow.c
+++ b/tools/blktap2/drivers/block-qcow.c
@@ -1035,6 +1035,17 @@ void tdqcow_queue_read(td_driver_t *driver, td_request_t treq)
 		}
 		
 		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;