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vsock/test: fix MSG_PEEK handling in recv_buf()

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`recv_buf` does not handle the MSG_PEEK flag correctly: it keeps calling
`recv` until all requested bytes are available or an error occurs.

The problem is how it calculates the number of bytes read: MSG_PEEK
doesn't consume any bytes and will re-read the same bytes from the buffer
head, so summing the return value every time is wrong.

Moreover, MSG_PEEK doesn't consume the bytes in the buffer, so if more
bytes are requested than are available, the loop will never terminate,
because `recv` will never return EOF. For this reason, we need to compare
the number of bytes read with the number of bytes expected.

Add a check: if the MSG_PEEK flag is present, update the byte counter and
break out of the loop only after at least the expected number of bytes
have been received; otherwise, retry after a short delay to avoid
consuming too many CPU cycles.

This allows us to simplify the `test_stream_credit_update_test` by
reusing `recv_buf`, like some other tests already do.

Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Luigi Leonardi <leonardi@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://patch.msgid.link/20260415-fix_peek-v4-2-8207e872759e@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Luigi Leonardi
2026-04-15 17:09:29 +02:00
committed by Jakub Kicinski
parent 080f22f5d3
commit a3f77afbf6
2 changed files with 16 additions and 12 deletions
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15
tools/testing/vsock/util.c
View File

@@ -381,7 +381,13 @@ void send_buf(int fd, const void *buf, size_t len, int flags,
}
}
#define RECV_PEEK_RETRY_USEC (10 * 1000)
/* Receive bytes in a buffer and check the return value.
*
* When MSG_PEEK is set, recv() is retried until it returns at least
* expected_ret bytes. The function returns on error, EOF, or timeout
* as usual.
*
* expected_ret:
* <0 Negative errno (for testing errors)
@@ -403,6 +409,15 @@ void recv_buf(int fd, void *buf, size_t len, int flags, ssize_t expected_ret)
if (ret <= 0)
break;
if (flags & MSG_PEEK) {
if (ret >= expected_ret) {
nread = ret;
break;
}
timeout_usleep(RECV_PEEK_RETRY_USEC);
continue;
}
nread += ret;
} while (nread < len);
timeout_end();

13
tools/testing/vsock/vsock_test.c
View File

@@ -1500,18 +1500,7 @@ static void test_stream_credit_update_test(const struct test_opts *opts,
}
/* Wait until there will be 128KB of data in rx queue. */
while (1) {
ssize_t res;
res = recv(fd, buf, buf_size, MSG_PEEK);
if (res == buf_size)
break;
if (res <= 0) {
fprintf(stderr, "unexpected 'recv()' return: %zi\n", res);
exit(EXIT_FAILURE);
}
}
recv_buf(fd, buf, buf_size, MSG_PEEK, buf_size);
/* There is 128KB of data in the socket's rx queue, dequeue first
* 64KB, credit update is sent if 'low_rx_bytes_test' == true.