Re: [Qemu-block] [Qemu-devel] [PATCH RFC 2/2] tests/virtio-blk: add test for WRITE_ZEROES command

[Stefano Garzarella]

On Fri, Jan 25, 2019 at 07:07:35AM +0100, Thomas Huth wrote:
> On 2019-01-25 07:01, Thomas Huth wrote:
> > On 2019-01-24 18:23, Stefano Garzarella wrote:
> >> If the WRITE_ZEROES feature is enabled, we check this
> >> command in the test_basic().
> >>
> >> Signed-off-by: Stefano Garzarella <address@hidden>
> >> ---
> >>  tests/virtio-blk-test.c | 63 +++++++++++++++++++++++++++++++++++++++++
> >>  1 file changed, 63 insertions(+)
> >>
> >> diff --git a/tests/virtio-blk-test.c b/tests/virtio-blk-test.c
> >> index 04c608764b..8cabbcb85a 100644
> >> --- a/tests/virtio-blk-test.c
> >> +++ b/tests/virtio-blk-test.c
> >> @@ -231,6 +231,69 @@ static void test_basic(QVirtioDevice *dev, 
> >> QGuestAllocator *alloc,
> >>  
> >>      guest_free(alloc, req_addr);
> >>  
> >> +    if (features & (1u << VIRTIO_BLK_F_WRITE_ZEROES)) {
> >> +        struct virtio_blk_discard_write_zeroes *dwz_hdr;
> >> +        void *expected;
> >> +
> >> +        /*
> >> +         * WRITE_ZEROES request on the same sector of previous test where
> >> +         * we wrote "TEST".
> >> +         */
> >> +        req.type = VIRTIO_BLK_T_WRITE_ZEROES;
> >> +        req.data = g_malloc0(512);
> > 
> > Wouldn't it be more interesting to do a memset(req.data, 0xaa, 512) or
> > something similar here, to see whether zeroes or 0xaa is written?
> 
> Ah, never mind, I thought req.data would be a sector buffer here, but
> looking at the lines below, it apparently is something different.
> 
> Why do you allocate 512 bytes here? I'd rather expect
> g_malloc0(sizeof(struct virtio_blk_discard_write_zeroes)) here. ... and
> then you could also use a local "struct virtio_blk_discard_write_zeroes
> dwz_hdr" variable instead of a pointer, and drop the g_malloc0() completely?
> 

Hi Thomas,
it was my initial implementation, but on the first test I discovered
that virtio_blk_request() has an assert on the data_size and it requires
a multiple of 512 bytes.
Then I looked at the virtio-spec #1, and it seems that data should be
multiple of 512 bytes also if it contains the struct
virtio_blk_discard_write_zeroes. (I'm not sure)

Anyway I tried to allocate only the space for that struct, commented the
assert and the test works well.

How do you suggest to proceed?


[1](https://github.com/oasis-tcs/virtio-spec/blob/master/content.tex#L3944)


Thanks,
Stefano