Re: [PATCH net v4 2/3] vsock/test: fix MSG_PEEK handling in recv_buf()

[Stefano Garzarella]

On Wed, Apr 15, 2026 at 05:09:29PM +0200, Luigi Leonardi wrote:
> `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@xxxxxxxxxx>
> Signed-off-by: Luigi Leonardi <leonardi@xxxxxxxxxx>
> ---
> tools/testing/vsock/util.c       | 15 +++++++++++++++
> tools/testing/vsock/vsock_test.c | 13 +------------
> 2 files changed, 16 insertions(+), 12 deletions(-)

Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>