Re: [PATCH 1/2] io_uring: ensure recv and recvmsg handle MSG_WAITALL correctly

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.