Fix regression introduced by r6824

The changes introduced by r6824 broke a subtle, and admittedly obscure, aspect
of the block API.  While bdrv_{pread,pwrite} return the number of bytes read
or written upon success, bdrv_{read,write} returns a zero upon success.

When using bdrv_pread for bdrv_read, special care must be taken to handle this
case.

This fixes certain guest images (notably linux-0.2 provided on the qemu
website).
Reported-by: Nmalc <av1474@comtv.ru>
Reported-by: NHerve Poussineau <hpoussin@reactos.org>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>



git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6828 c046a42c-6fe2-441c-8c8c-71466251a162

block-raw-posix.c

@@ -361,7 +361,12 @@ static int raw_pread(BlockDriverState *bs, int64_t offset,
 static int raw_read(BlockDriverState *bs, int64_t sector_num,
                     uint8_t *buf, int nb_sectors)
 {
-    return raw_pread(bs, sector_num * 512, buf, (uint64_t)nb_sectors * 512);
+    int ret;
+
+    ret = raw_pread(bs, sector_num * 512, buf, nb_sectors * 512);
+    if (ret == (nb_sectors * 512))
+        ret = 0;
+    return ret;
 }
 
 /*
@@ -445,7 +450,11 @@ static int raw_pwrite(BlockDriverState *bs, int64_t offset,
 static int raw_write(BlockDriverState *bs, int64_t sector_num,
                      const uint8_t *buf, int nb_sectors)
 {
-    return raw_pwrite(bs, sector_num * 512, buf, (uint64_t)nb_sectors * 512);
+    int ret;
+    ret = raw_pwrite(bs, sector_num * 512, buf, nb_sectors * 512);
+    if (ret == (nb_sectors * 512))
+        ret = 0;
+    return ret;
 }
 
 #ifdef CONFIG_AIO

block-raw-win32.c

@@ -145,6 +145,8 @@ static int raw_read(BlockDriverState *bs, int64_t sector_num,
 #endif
             return ret_count;
     }
+    if (ret_count == count)
+        ret_count = 0;
     return ret_count;
 }
 
@@ -171,6 +173,8 @@ static int raw_write(BlockDriverState *bs, int64_t sector_num,
 #endif
             return ret_count;
     }
+    if (ret_count == count)
+        ret_count = 0;
     return ret_count;
 }