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Date:   Wed, 20 Jul 2022 05:46:01 +0000
From:   Arseniy Krasnov <AVKrasnov@...rdevices.ru>
To:     Stefano Garzarella <sgarzare@...hat.com>
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 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
poll()). May be i can remove "SRVSENT" as sleep is enough.

> 

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