block/parallels: read parallels image header and BAT into single buffer

This metadata cache would allow to properly batch BAT updates to disk
in next patches. These updates will be properly aligned to avoid
read-modify-write transactions on block level.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Roman Kagan <rkagan@parallels.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Roman Kagan <rkagan@parallels.com>
Message-id: 1430207220-24458-18-git-send-email-den@openvz.org
CC: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 17 insertions, 7 deletions

diff --git a/block/parallels.c b/block/parallels.c
index 431adf1..f8a9981 100644
--- a/block/parallels.c
+++ b/block/parallels.c
@@ -61,6 +61,8 @@ typedef struct BDRVParallelsState {
      */
     CoMutex lock;
 
+    ParallelsHeader *header;
+    uint32_t header_size;
     uint32_t *bat_bitmap;
     unsigned int bat_size;
 
@@ -91,7 +93,7 @@ static int parallels_open(BlockDriverState *bs, QDict *options, int flags,
 {
     BDRVParallelsState *s = bs->opaque;
     ParallelsHeader ph;
-    int ret;
+    int ret, size;
 
     ret = bdrv_pread(bs->file, 0, &ph, sizeof(ph));
     if (ret < 0) {
@@ -130,17 +132,25 @@ static int parallels_open(BlockDriverState *bs, QDict *options, int flags,
         ret = -EFBIG;
         goto fail;
     }
-    s->bat_bitmap = g_try_new(uint32_t, s->bat_size);
-    if (s->bat_size && s->bat_bitmap == NULL) {
+
+    size = sizeof(ParallelsHeader) + sizeof(uint32_t) * s->bat_size;
+    s->header_size = ROUND_UP(size, bdrv_opt_mem_align(bs->file));
+    s->header = qemu_try_blockalign(bs->file, s->header_size);
+    if (s->header == NULL) {
         ret = -ENOMEM;
         goto fail;
     }
+    if (le32_to_cpu(ph.data_off) < s->header_size) {
+        /* there is not enough unused space to fit to block align between BAT
+           and actual data. We can't avoid read-modify-write... */
+        s->header_size = size;
+    }
 
-    ret = bdrv_pread(bs->file, sizeof(ParallelsHeader),
-                     s->bat_bitmap, s->bat_size * sizeof(uint32_t));
+    ret = bdrv_pread(bs->file, 0, s->header, s->header_size);
     if (ret < 0) {
         goto fail;
     }
+    s->bat_bitmap = (uint32_t *)(s->header + 1);
 
     s->has_truncate = bdrv_has_zero_init(bs->file) &&
                       bdrv_truncate(bs->file, bdrv_getlength(bs->file)) == 0;
@@ -152,7 +162,7 @@ fail_format:
     error_setg(errp, "Image not in Parallels format");
     ret = -EINVAL;
 fail:
-    g_free(s->bat_bitmap);
+    qemu_vfree(s->header);
     return ret;
 }
 
@@ -400,7 +410,7 @@ exit:
 static void parallels_close(BlockDriverState *bs)
 {
     BDRVParallelsState *s = bs->opaque;
-    g_free(s->bat_bitmap);
+    qemu_vfree(s->header);
 }
 
 static QemuOptsList parallels_create_opts = {