Re: [RFC PATCH v1 3/3] vsock_test: POLLIN + SO_RCVLOWAT test.

[Stefano Garzarella]

On Wed, Jul 20, 2022 at 05:46:01AM +0000, Arseniy Krasnov wrote:
> On 19.07.2022 15:52, Stefano Garzarella wrote:
> > On Mon, Jul 18, 2022 at 08:19:06AM +0000, Arseniy Krasnov wrote:
> > > This adds test to check, that when poll() returns POLLIN and
> > > POLLRDNORM bits, next read call won't block.
> > >
> > > Signed-off-by: Arseniy Krasnov <AVKrasnov@xxxxxxxxxxxxxx>
> > > ---
> > > tools/testing/vsock/vsock_test.c | 90 ++++++++++++++++++++++++++++++++
> > > 1 file changed, 90 insertions(+)
> > >
> > > diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
> > > index dc577461afc2..8e394443eaf6 100644
> > > --- a/tools/testing/vsock/vsock_test.c
> > > +++ b/tools/testing/vsock/vsock_test.c
> > > @@ -18,6 +18,7 @@
> > > #include <sys/socket.h>
> > > #include <time.h>
> > > #include <sys/mman.h>
> > > +#include <poll.h>
> > >
> > > #include "timeout.h"
> > > #include "control.h"
> > > @@ -596,6 +597,90 @@ static void test_seqpacket_invalid_rec_buffer_server(const struct test_opts *opt
> > >     close(fd);
> > > }
> > >
> > > +static void test_stream_poll_rcvlowat_server(const struct test_opts *opts)
> > > +{
> > > +#define RCVLOWAT_BUF_SIZE 128
> > > +    int fd;
> > > +    int i;
> > > +
> > > +    fd = vsock_stream_accept(VMADDR_CID_ANY, 1234, NULL);
> > > +    if (fd < 0) {
> > > +        perror("accept");
> > > +        exit(EXIT_FAILURE);
> > > +    }
> > > +
> > > +    /* Send 1 byte. */
> > > +    send_byte(fd, 1, 0);
> > > +
> > > +    control_writeln("SRVSENT");
> > > +
> > > +    /* Just empirically delay value. */
> > > +    sleep(4);
> >
> > Why we need this sleep()?
> Purpose of sleep() is to move client in state, when it has 1 byte of rx data
> and poll() won't wake. For example:
> client:                        server:
> waits for "SRVSENT"
>                               send 1 byte
>                               send "SRVSENT"
> poll()
>                               sleep
> ...
> poll sleeps
> ...
>                               send rest of data
> poll wake up
>
> I think, without sleep there is chance, that client enters poll() when whole
> data from server is already received, thus test will be useless(it just tests

Right, I see (maybe add a comment in the test).

> poll()). May be i can remove "SRVSENT" as sleep is enough.

I think it's fine.

An alternative could be to use the `timeout` of poll():

client:                        server:
waits for "SRVSENT"
                               send 1 byte
                               send "SRVSENT"
poll(, timeout = 1 * 1000)
                               wait for "CLNSENT"
poll should return 0
send "CLNSENT"

poll(, timeout = 10 * 1000)
...
poll sleeps
...
                               send rest of data
poll wake up


I don't have a strong opinion, also your version seems fine, just an 
alternative ;-)

Maybe in your version you can add a 10 sec timeout to poll, to avoid 
that the test stuck for some reason (failing if the timeout is reached).

Thanks,
Stefano