[v3] snapshot: use local variable to bdrv_pwrite_sync L1 table

Use local variable to bdrv_pwrite_sync L1 table,
needless to make conversion of cached L1 table between
big-endian and host style.

Signed-off-by: Zhang Haoyu <zhanghy@sangfor.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
---
v2 -> v3:
 - replace g_try_malloc0 with qemu_try_blockalign
 - copy the latest local L1 table back to s->l1_table
   after successfully bdrv_pwrite_sync L1 table

v1 -> v2:
 - remove the superflous assignment, l1_table = NULL;
 - replace 512 with BDRV_SECTOR_SIZE, and align_offset with ROUND_UP
 - remove needless check of if (l1_table) before g_free(l1_table)

 block/qcow2-refcount.c | 25 +++++++++----------------
 1 file changed, 9 insertions(+), 16 deletions(-)

>Use local variable to bdrv_pwrite_sync L1 table,
>needless to make conversion of cached L1 table between
>big-endian and host style.
>
>Signed-off-by: Zhang Haoyu <zhanghy@sangfor.com>
>Reviewed-by: Max Reitz <mreitz@redhat.com>
>---
>v2 -> v3:
> - replace g_try_malloc0 with qemu_try_blockalign
> - copy the latest local L1 table back to s->l1_table
>   after successfully bdrv_pwrite_sync L1 table
>
>v1 -> v2:
> - remove the superflous assignment, l1_table = NULL;
> - replace 512 with BDRV_SECTOR_SIZE, and align_offset with ROUND_UP
> - remove needless check of if (l1_table) before g_free(l1_table)
>
> block/qcow2-refcount.c | 25 +++++++++----------------
> 1 file changed, 9 insertions(+), 16 deletions(-)
>
>diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
>index 2bcaaf9..bceadce 100644
>--- a/block/qcow2-refcount.c
>+++ b/block/qcow2-refcount.c
>@@ -881,14 +881,17 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
> {
>     BDRVQcowState *s = bs->opaque;
>     uint64_t *l1_table, *l2_table, l2_offset, offset, l1_size2;
>-    bool l1_allocated = false;
>     int64_t old_offset, old_l2_offset;
>     int i, j, l1_modified = 0, nb_csectors, refcount;
>     int ret;
> 
>     l2_table = NULL;
>-    l1_table = NULL;
>     l1_size2 = l1_size * sizeof(uint64_t);
>+    l1_table = qemu_try_blockalign(bs->file, l1_size2);
>+    if (l1_size2 && l1_table == NULL) {
>+        ret = -ENOMEM;
>+        goto fail;
>+    }
> 
>     s->cache_discards = true;
> 
>@@ -896,13 +899,6 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
>      * l1_table_offset when it is the current s->l1_table_offset! Be careful
>      * when changing this! */
>     if (l1_table_offset != s->l1_table_offset) {
>-        l1_table = g_try_malloc0(align_offset(l1_size2, 512));
>-        if (l1_size2 && l1_table == NULL) {
>-            ret = -ENOMEM;
>-            goto fail;
>-        }
>-        l1_allocated = true;
>-
>         ret = bdrv_pread(bs->file, l1_table_offset, l1_table, l1_size2);
>         if (ret < 0) {
>             goto fail;
>@@ -912,8 +908,7 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
>             be64_to_cpus(&l1_table[i]);
>     } else {
>         assert(l1_size == s->l1_size);
>-        l1_table = s->l1_table;
>-        l1_allocated = false;
>+        memcpy(l1_table, s->l1_table, l1_size2);
>     }
> 
>     for(i = 0; i < l1_size; i++) {
>@@ -1055,13 +1050,11 @@ fail:
>         }
> 
>         ret = bdrv_pwrite_sync(bs->file, l1_table_offset, l1_table, l1_size2);
>-
>-        for (i = 0; i < l1_size; i++) {
>-            be64_to_cpus(&l1_table[i]);
>+        if (ret == 0) {
>+            memcpy(s->l1_table, l1_table, l1_size2);
I made a mistake, big-endian l1 table was copied back to s->l1_table.
>         }
>     }
>-    if (l1_allocated)
>-        g_free(l1_table);
>+    g_free(l1_table);
>     return ret;
> }
> 
>-- 
>1.7.12.4