[Qemu-devel] [PATCH 03/27] block/parallels: switch to bdrv_read

["Denis V. Lunev" <den@openvz.org>]

From: Roman Kagan <rkagan@parallels.com>

Switch the .bdrv_read method implementation from using bdrv_pread() to
bdrv_read() on the underlying file, since the latter is subject to i/o
throttling while the former is not.

Besides, since bdrv_read() operates in sectors rather than bytes, adjust
the helper functions to do so too.

Signed-off-by: Roman Kagan <rkagan@parallels.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
---
 block/parallels.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/block/parallels.c b/block/parallels.c
index dca0df6..baefd3e 100644
--- a/block/parallels.c
+++ b/block/parallels.c
@@ -146,9 +146,8 @@ fail:
     return ret;
 }
 
-static int64_t seek_to_sector(BlockDriverState *bs, int64_t sector_num)
+static int64_t seek_to_sector(BDRVParallelsState *s, int64_t sector_num)
 {
-    BDRVParallelsState *s = bs->opaque;
     uint32_t index, offset;
 
     index = sector_num / s->tracks;
@@ -157,24 +156,27 @@ static int64_t seek_to_sector(BlockDriverState *bs, int64_t sector_num)
     /* not allocated */
     if ((index >= s->catalog_size) || (s->catalog_bitmap[index] == 0))
         return -1;
-    return
-        ((uint64_t)s->catalog_bitmap[index] * s->off_multiplier + offset) * 512;
+    return (uint64_t)s->catalog_bitmap[index] * s->off_multiplier + offset;
 }
 
 static int parallels_read(BlockDriverState *bs, int64_t sector_num,
                     uint8_t *buf, int nb_sectors)
 {
+    BDRVParallelsState *s = bs->opaque;
+
     while (nb_sectors > 0) {
-        int64_t position = seek_to_sector(bs, sector_num);
+        int64_t position = seek_to_sector(s, sector_num);
         if (position >= 0) {
-            if (bdrv_pread(bs->file, position, buf, 512) != 512)
-                return -1;
+            int ret = bdrv_read(bs->file, position, buf, 1);
+            if (ret < 0) {
+                return ret;
+            }
         } else {
-            memset(buf, 0, 512);
+            memset(buf, 0, BDRV_SECTOR_SIZE);
         }
         nb_sectors--;
         sector_num++;
-        buf += 512;
+        buf += BDRV_SECTOR_SIZE;
     }
     return 0;
 }
-- 
1.9.1