block: Add bdrv_(p)write_sync
Add new functions that write and flush the written data to disk immediately.
This is what needs to be used for image format metadata to maintain integrity
for cache=... modes that don't use O_DSYNC. (Actually, we only need barriers,
and therefore the functions are defined as such, but flushes is what is
implemented in this patch - we can try to change that later)
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block.c b/block.c
index 3fc2969..e71a771 100644
--- a/block.c
+++ b/block.c
@@ -1010,6 +1010,43 @@
return count1;
}
+/*
+ * Writes to the file and ensures that no writes are reordered across this
+ * request (acts as a barrier)
+ *
+ * Returns 0 on success, -errno in error cases.
+ */
+int bdrv_pwrite_sync(BlockDriverState *bs, int64_t offset,
+ const void *buf, int count)
+{
+ int ret;
+
+ ret = bdrv_pwrite(bs, offset, buf, count);
+ if (ret < 0) {
+ return ret;
+ }
+
+ /* No flush needed for cache=writethrough, it uses O_DSYNC */
+ if ((bs->open_flags & BDRV_O_CACHE_MASK) != 0) {
+ bdrv_flush(bs);
+ }
+
+ return 0;
+}
+
+/*
+ * Writes to the file and ensures that no writes are reordered across this
+ * request (acts as a barrier)
+ *
+ * Returns 0 on success, -errno in error cases.
+ */
+int bdrv_write_sync(BlockDriverState *bs, int64_t sector_num,
+ const uint8_t *buf, int nb_sectors)
+{
+ return bdrv_pwrite_sync(bs, BDRV_SECTOR_SIZE * sector_num,
+ buf, BDRV_SECTOR_SIZE * nb_sectors);
+}
+
/**
* Truncate file to 'offset' bytes (needed only for file protocols)
*/
