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From 35538bdb46122fdf90ca869df29869b8aeaefa09 Mon Sep 17 00:00:00 2001
From: Stefan Hajnoczi <stefanha@redhat.com>
Date: Tue, 25 Mar 2014 14:23:42 +0100
Subject: [PATCH 35/49] dmg: drop broken bdrv_pread() loop

RH-Author: Kevin Wolf <kwolf@redhat.com>
Message-id: <1395753835-7591-36-git-send-email-kwolf@redhat.com>
Patchwork-id: n/a
O-Subject: [virt-devel] [EMBARGOED RHEL-7.0 qemu-kvm PATCH 35/48] dmg: drop broken bdrv_pread() loop
Bugzilla: 1066691
RH-Acked-by: Jeff Cody <jcody@redhat.com>
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>

From: Stefan Hajnoczi <stefanha@redhat.com>

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1066691
Upstream status: Series embargoed

It is not necessary to check errno for EINTR and the block layer does
not produce short reads. Therefore we can drop the loop that attempts
to read a compressed chunk.

The loop is buggy because it incorrectly adds the transferred bytes
twice:

do {
ret = bdrv_pread(...);
i += ret;
} while (ret >= 0 && ret + i < s->lengths[chunk]);

Luckily we can drop the loop completely and perform a single
bdrv_pread().

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/dmg.c |   15 ++-------------
 1 files changed, 2 insertions(+), 13 deletions(-)

diff --git a/block/dmg.c b/block/dmg.c
index f4f3e8e..1cc5426 100644
--- a/block/dmg.c
+++ b/block/dmg.c
@@ -298,21 +298,10 @@ static inline int dmg_read_chunk(BlockDriverState *bs, int sector_num)
         s->current_chunk = s->n_chunks;
         switch (s->types[chunk]) {
         case 0x80000005: { /* zlib compressed */
-            int i;
-
             /* we need to buffer, because only the chunk as whole can be
              * inflated. */
-            i = 0;
-            do {
-                ret = bdrv_pread(bs->file, s->offsets[chunk] + i,
-                                 s->compressed_chunk + i,
-                                 s->lengths[chunk] - i);
-                if (ret < 0 && errno == EINTR) {
-                    ret = 0;
-                }
-                i += ret;
-            } while (ret >= 0 && ret + i < s->lengths[chunk]);
-
+            ret = bdrv_pread(bs->file, s->offsets[chunk],
+                             s->compressed_chunk, s->lengths[chunk]);
             if (ret != s->lengths[chunk]) {
                 return -1;
             }
-- 
1.7.1