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From 56adc601b22b81ae4c681af6b13f38e560f16867 Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Wed, 11 Dec 2013 19:50:32 +0100
Subject: [PATCH 04/37] block: Inherit opt_transfer_length
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Message-id: <1392117622-28812-5-git-send-email-kwolf@redhat.com>
Patchwork-id: 57169
O-Subject: [RHEL-7.0 qemu-kvm PATCH v2 04/37] block: Inherit opt_transfer_length
Bugzilla: 748906
RH-Acked-by: Laszlo Ersek <lersek@redhat.com>
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Max Reitz <mreitz@redhat.com>

When there is a format driver between the backend, it's not guaranteed
that exposing the opt_transfer_length for the format driver results in
the optimal requests (because of fragmentation etc.), but it can't make
things worse, so let's just do it.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: BenoƮt Canet <benoit@irqsave.net>
(cherry picked from commit 466ad822deef3a03757d505218a52993c5d56b5d)

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)
---
 block.c |   20 +++++++++++++++++++-
 1 files changed, 19 insertions(+), 1 deletions(-)

diff --git a/block.c b/block.c
index 26eebcc..8b36d05 100644
--- a/block.c
+++ b/block.c
@@ -452,7 +452,25 @@ static int bdrv_refresh_limits(BlockDriverState *bs)
 
     memset(&bs->bl, 0, sizeof(bs->bl));
 
-    if (drv && drv->bdrv_refresh_limits) {
+    if (!drv) {
+        return 0;
+    }
+
+    /* Take some limits from the children as a default */
+    if (bs->file) {
+        bdrv_refresh_limits(bs->file);
+        bs->bl.opt_transfer_length = bs->file->bl.opt_transfer_length;
+    }
+
+    if (bs->backing_hd) {
+        bdrv_refresh_limits(bs->backing_hd);
+        bs->bl.opt_transfer_length =
+            MAX(bs->bl.opt_transfer_length,
+                bs->backing_hd->bl.opt_transfer_length);
+    }
+
+    /* Then let the driver override it */
+    if (drv->bdrv_refresh_limits) {
         return drv->bdrv_refresh_limits(bs);
     }
 
-- 
1.7.1