On Thu, 03/24 23:33, Max Reitz wrote:
> This is optional so that it does not impede the null block driver's
> performance unless this behavior is desired.
>
> Signed-off-by: Max Reitz <mre...@redhat.com>
> ---
> block/null.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/block/null.c b/block/null.c
> index d90165d..a7df386 100644
> --- a/block/null.c
> +++ b/block/null.c
> @@ -14,10 +14,12 @@
> #include "block/block_int.h"
>
> #define NULL_OPT_LATENCY "latency-ns"
> +#define NULL_OPT_ZEROES "read-zeroes"
>
> typedef struct {
> int64_t length;
> int64_t latency_ns;
> + bool read_zeroes;
> } BDRVNullState;
>
> static QemuOptsList runtime_opts = {
> @@ -40,6 +42,11 @@ static QemuOptsList runtime_opts = {
> .help = "nanoseconds (approximated) to wait "
> "before completing request",
> },
> + {
> + .name = NULL_OPT_ZEROES,
> + .type = QEMU_OPT_BOOL,
> + .help = "return zeroes when read",
> + },
> { /* end of list */ }
> },
> };
> @@ -61,6 +68,7 @@ static int null_file_open(BlockDriverState *bs, QDict
> *options, int flags,
> error_setg(errp, "latency-ns is invalid");
> ret = -EINVAL;
> }
> + s->read_zeroes = qemu_opt_get_bool(opts, NULL_OPT_ZEROES, false);
> qemu_opts_del(opts);
> return ret;
> }
> @@ -90,6 +98,12 @@ static coroutine_fn int null_co_readv(BlockDriverState *bs,
> int64_t sector_num, int nb_sectors,
> QEMUIOVector *qiov)
> {
> + BDRVNullState *s = bs->opaque;
> +
> + if (s->read_zeroes) {
> + qemu_iovec_memset(qiov, 0, 0, nb_sectors * BDRV_SECTOR_SIZE);
> + }
> +
> return null_co_common(bs);
> }
>
> @@ -159,6 +173,12 @@ static BlockAIOCB *null_aio_readv(BlockDriverState *bs,
> BlockCompletionFunc *cb,
> void *opaque)
> {
> + BDRVNullState *s = bs->opaque;
> +
> + if (s->read_zeroes) {
> + qemu_iovec_memset(qiov, 0, 0, nb_sectors * BDRV_SECTOR_SIZE);
> + }
> +
> return null_aio_common(bs, cb, opaque);
> }
>
> --
> 2.7.4
>
Acked-by: Fam Zheng <f...@redhat.com>
