block: honour BlockLimits in bdrv_co_do_write_zeroes
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/block.c b/block.c
index 3759582..b4194da 100644
--- a/block.c
+++ b/block.c
@@ -2711,33 +2711,66 @@
BDRV_REQ_COPY_ON_READ);
}
+/* if no limit is specified in the BlockLimits use a default
+ * of 32768 512-byte sectors (16 MiB) per request.
+ */
+#define MAX_WRITE_ZEROES_DEFAULT 32768
+
static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs,
int64_t sector_num, int nb_sectors, BdrvRequestFlags flags)
{
BlockDriver *drv = bs->drv;
QEMUIOVector qiov;
- struct iovec iov;
- int ret;
+ struct iovec iov = {0};
+ int ret = 0;
- /* TODO Emulate only part of misaligned requests instead of letting block
- * drivers return -ENOTSUP and emulate everything */
+ int max_write_zeroes = bs->bl.max_write_zeroes ?
+ bs->bl.max_write_zeroes : MAX_WRITE_ZEROES_DEFAULT;
- /* First try the efficient write zeroes operation */
- if (drv->bdrv_co_write_zeroes) {
- ret = drv->bdrv_co_write_zeroes(bs, sector_num, nb_sectors, flags);
- if (ret != -ENOTSUP) {
- return ret;
+ while (nb_sectors > 0 && !ret) {
+ int num = nb_sectors;
+
+ /* align request */
+ if (bs->bl.write_zeroes_alignment &&
+ num >= bs->bl.write_zeroes_alignment &&
+ sector_num % bs->bl.write_zeroes_alignment) {
+ if (num > bs->bl.write_zeroes_alignment) {
+ num = bs->bl.write_zeroes_alignment;
+ }
+ num -= sector_num % bs->bl.write_zeroes_alignment;
}
+
+ /* limit request size */
+ if (num > max_write_zeroes) {
+ num = max_write_zeroes;
+ }
+
+ ret = -ENOTSUP;
+ /* First try the efficient write zeroes operation */
+ if (drv->bdrv_co_write_zeroes) {
+ ret = drv->bdrv_co_write_zeroes(bs, sector_num, num, flags);
+ }
+
+ if (ret == -ENOTSUP) {
+ /* Fall back to bounce buffer if write zeroes is unsupported */
+ iov.iov_len = num * BDRV_SECTOR_SIZE;
+ if (iov.iov_base == NULL) {
+ /* allocate bounce buffer only once and ensure that it
+ * is big enough for this and all future requests.
+ */
+ size_t bufsize = num <= nb_sectors ? num : max_write_zeroes;
+ iov.iov_base = qemu_blockalign(bs, bufsize * BDRV_SECTOR_SIZE);
+ memset(iov.iov_base, 0, bufsize * BDRV_SECTOR_SIZE);
+ }
+ qemu_iovec_init_external(&qiov, &iov, 1);
+
+ ret = drv->bdrv_co_writev(bs, sector_num, num, &qiov);
+ }
+
+ sector_num += num;
+ nb_sectors -= num;
}
- /* Fall back to bounce buffer if write zeroes is unsupported */
- iov.iov_len = nb_sectors * BDRV_SECTOR_SIZE;
- iov.iov_base = qemu_blockalign(bs, iov.iov_len);
- memset(iov.iov_base, 0, iov.iov_len);
- qemu_iovec_init_external(&qiov, &iov, 1);
-
- ret = drv->bdrv_co_writev(bs, sector_num, nb_sectors, &qiov);
-
qemu_vfree(iov.iov_base);
return ret;
}
