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

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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

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