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Date:   Wed, 20 Jul 2022 10:56:49 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Arseniy Krasnov <AVKrasnov@...rdevices.ru>
Cc:     "David S. Miller" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Krasnov Arseniy <oxffffaa@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        kernel <kernel@...rdevices.ru>
Subject: Re: [RFC PATCH v1 3/3] vsock_test: POLLIN + SO_RCVLOWAT test.

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@...rdevices.ru>
>>> ---
>>> 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

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