Nir Soffer <nir...@gmail.com> writes:
> If read-zeroes is not set, we did not report BDRV_BLOCK_DATA or
> BDRV_BLOCK_ZERO. This is not consistent with other drivers and can
> confuse users or other programs:
>
> % qemu-img map --output json "json:{'driver': 'raw', 'file': {'driver':
> 'null-co', 'size': '1g'}}"
> [{ "start": 0, "length": 1073741824, "depth": 0, "present": false,
> "zero": false, "data": false, "compressed": false}]
>
> % qemu-nbd "json:{'driver': 'raw', 'file': {'driver': 'null-co', 'size':
> '1g'}}" &
>
> % nbdinfo --map nbd://127.0.0.1
> 0 1073741824 1 hole
>
> With this change we report DATA in this case:
>
> % ./qemu-img map --output json "json:{'driver': 'raw', 'file': {'driver':
> 'null-co', 'size': '1g'}}"
> [{ "start": 0, "length": 1073741824, "depth": 0, "present": true, "zero":
> false, "data": true, "compressed": false, "offset": 0}]
>
> % ./qemu-nbd "json:{'driver': 'raw', 'file': {'driver': 'null-co',
> 'size': '1g'}}" &
>
> % nbdinfo --map nbd://127.0.0.1
> 0 1073741824 0 data
>
> Signed-off-by: Nir Soffer <nir...@gmail.com>
> ---
> block/null.c | 4 +---
> qapi/block-core.json | 5 +++--
> 2 files changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/block/null.c b/block/null.c
> index dc0b1fdbd9..7ba87bd9a9 100644
> --- a/block/null.c
> +++ b/block/null.c
> @@ -239,9 +239,7 @@ static int coroutine_fn
> null_co_block_status(BlockDriverState *bs,
> *map = offset;
> *file = bs;
>
> - if (s->read_zeroes) {
> - ret |= BDRV_BLOCK_ZERO;
> - }
> + ret |= s->read_zeroes ? BDRV_BLOCK_ZERO : BDRV_BLOCK_DATA;
> return ret;
> }
>
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index b1937780e1..7c95c9e36a 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -3293,8 +3293,9 @@
> # requests. Default to zero which completes requests immediately.
> # (Since 2.4)
> #
> -# @read-zeroes: if true, reads from the device produce zeroes; if
> -# false, the buffer is left unchanged.
> +# @read-zeroes: if true, emulate a sparse image, and reads from the
> +# device produce zeroes; if false, emulate an allocated image but
> +# reads from the device leave the buffer unchanged.
> # (default: false; since: 4.1)
> #
> # Since: 2.9
Possibly dumb question: how is this doc change related to the code fix?
Suggest to split the sentence for easier reading:
# @read-zeroes: If true, emulate a sparse image, and reads from the
# device produce zeroes. If false, emulate an allocated image,
# but reads from the device leave the buffer unchanged.
