[Qemu-devel] [5859] Write table offset and size in one syscall (Gleb Natapov)

[Anthony Liguori]

Revision: 5859
          http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=5859
Author:   aliguori
Date:     2008-12-02 20:10:14 +0000 (Tue, 02 Dec 2008)

Log Message:
-----------
Write table offset and size in one syscall (Gleb Natapov)

Otherwise if VM is killed between two writes data may be lost.
But if offset and size fields are at the same disk block one
write should update them both simultaneously.

Signed-off-by: Gleb Natapov <address@hidden>
Signed-off-by: Anthony Liguori <address@hidden>

Modified Paths:
--------------
    trunk/block-qcow2.c

Modified: trunk/block-qcow2.c
===================================================================
--- trunk/block-qcow2.c 2008-12-02 20:08:04 UTC (rev 5858)
+++ trunk/block-qcow2.c 2008-12-02 20:10:14 UTC (rev 5859)
@@ -429,8 +429,7 @@
     int new_l1_size, new_l1_size2, ret, i;
     uint64_t *new_l1_table;
     uint64_t new_l1_table_offset;
-    uint64_t data64;
-    uint32_t data32;
+    uint8_t data[12];
 
     new_l1_size = s->l1_size;
     if (min_size <= new_l1_size)
@@ -460,14 +459,11 @@
         new_l1_table[i] = be64_to_cpu(new_l1_table[i]);
 
     /* set new table */
-    data64 = cpu_to_be64(new_l1_table_offset);
-    if (bdrv_pwrite(s->hd, offsetof(QCowHeader, l1_table_offset),
-                    &data64, sizeof(data64)) != sizeof(data64))
+    cpu_to_be32w((uint32_t*)data, new_l1_size);
+    cpu_to_be64w((uint64_t*)(data + 4), new_l1_table_offset);
+    if (bdrv_pwrite(s->hd, offsetof(QCowHeader, l1_size), data,
+                sizeof(data)) != sizeof(data))
         goto fail;
-    data32 = cpu_to_be32(new_l1_size);
-    if (bdrv_pwrite(s->hd, offsetof(QCowHeader, l1_size),
-                    &data32, sizeof(data32)) != sizeof(data32))
-        goto fail;
     qemu_free(s->l1_table);
     free_clusters(bs, s->l1_table_offset, s->l1_size * sizeof(uint64_t));
     s->l1_table_offset = new_l1_table_offset;
@@ -2281,8 +2277,7 @@
     int new_table_size, new_table_size2, refcount_table_clusters, i, ret;
     uint64_t *new_table;
     int64_t table_offset;
-    uint64_t data64;
-    uint32_t data32;
+    uint8_t data[12];
     int old_table_size;
     int64_t old_table_offset;
 
@@ -2321,14 +2316,11 @@
     for(i = 0; i < s->refcount_table_size; i++)
         be64_to_cpus(&new_table[i]);
 
-    data64 = cpu_to_be64(table_offset);
+    cpu_to_be64w((uint64_t*)data, table_offset);
+    cpu_to_be32w((uint32_t*)(data + 8), refcount_table_clusters);
     if (bdrv_pwrite(s->hd, offsetof(QCowHeader, refcount_table_offset),
-                    &data64, sizeof(data64)) != sizeof(data64))
+                    data, sizeof(data)) != sizeof(data))
         goto fail;
-    data32 = cpu_to_be32(refcount_table_clusters);
-    if (bdrv_pwrite(s->hd, offsetof(QCowHeader, refcount_table_clusters),
-                    &data32, sizeof(data32)) != sizeof(data32))
-        goto fail;
     qemu_free(s->refcount_table);
     old_table_offset = s->refcount_table_offset;
     old_table_size = s->refcount_table_size;