storage: Ensure 'qemu-img resize' size arg is a 512 multiple

qemu-img resize will fail with "The new size must be a multiple of 512"
if libvirt doesn't round it first.
This fixes rhbz#951495

Signed-off-by: Christophe Fergeau <cfergeau@redhat.com>

src/internal.h

@@ -339,6 +339,9 @@
 /* divide value by size, rounding up */
 # define VIR_DIV_UP(value, size) (((value) + (size) - 1) / (size))
 
+/* round up value to the closest multiple of size */
+# define VIR_ROUND_UP(value, size) (VIR_DIV_UP(value, size) * (size))
+
 
 # if WITH_DTRACE_PROBES
 #  ifndef LIBVIRT_PROBES_H

src/libvirt.c

@@ -14131,7 +14131,8 @@ error:
  * Changes the capacity of the storage volume @vol to @capacity. The
  * operation will fail if the new capacity requires allocation that would
  * exceed the remaining free space in the parent pool.  The contents of
- * the new capacity will appear as all zero bytes.
+ * the new capacity will appear as all zero bytes. The capacity value will
+ * be rounded to the granularity supported by the hypervisor.
  *
  * Normally, the operation will attempt to affect capacity with a minimum
  * impact on allocation (that is, the default operation favors a sparse

src/storage/storage_backend_fs.c

@@ -1219,6 +1219,10 @@ virStorageBackendFilesystemResizeQemuImg(const char *path,
         return -1;
     }
 
+    /* Round capacity as qemu-img resize errors out on sizes which are not
+     * a multiple of 512 */
+    capacity = VIR_ROUND_UP(capacity, 512);
+
     cmd = virCommandNew(img_tool);
     virCommandAddArgList(cmd, "resize", path, NULL);
     virCommandAddArgFormat(cmd, "%llu", capacity);