On Wed, Mar 23, 2022 at 10:14 PM Pavel Begunkov asml.silence@gmail.com wrote:
On 3/23/22 15:39, Jens Axboe wrote:
We currently don't attempt to get the full asked for length even if MSG_WAITALL is set, if we get a partial receive. If we do see a partial receive, then just note how many bytes we did and return -EAGAIN to get it retried.
The iov is advanced appropriately for the vector based case, and we manually bump the buffer and remainder for the non-vector case.
How datagrams work with MSG_WAITALL? I highly doubt it coalesces 2+ packets to satisfy the length requirement (e.g. because it may move the address back into the userspace). I'm mainly afraid about breaking io_uring users who are using the flag just to fail links when there is not enough data in a packet.
-- Pavel Begunkov
Pavel:
Datagrams have message boundaries and the MSG_WAITALL flag does not make sense there. I believe it is ignored by receive code on daragram sockets. MSG_WAITALL makes sends only on stream sockets, like TCP. The manual page says "This flag has no effect for datagram sockets.".