On Wed, Jan 12, 2022 at 3:17 PM dormando <dormando@xxxxxxxxx> wrote: > > Hey, > > Been integrating io_uring in my stack which has been going well-ish. > Wondering if you folks have seen implementations of client libraries that > feel clean and user friendly? libev: http://cvs.schmorp.de/libev/ has an io_uring backend: http://cvs.schmorp.de/libev/ev_iouring.c?view=markup > > IE: with poll/select/epoll/kqueue most client libraries (like libcurl) > implement functions like "client_send_data(ctx, etc)", which returns > -WANT_READ/-WANT_WRITE/etc and an fd if it needs more data to move > forward. With the syscalls themselves externalized in io_uring I'm > struggling to come up with abstractions I like and haven't found much > public on a googlin'. Do any public ones exist yet? > > On implementing networked servers, it feels natural to do a core loop > like: > > while (1) { > io_uring_submit_and_wait(&t->ring, 1); > > uint32_t head = 0; > uint32_t count = 0; > > io_uring_for_each_cqe(&t->ring, head, cqe) { > > event *pe = io_uring_cqe_get_data(cqe); > pe->callback(pe->udata, cqe); > > count++; > } > io_uring_cq_advance(&t->ring, count); > } > > ... but A) you can run out of SQE's if they're generated from within > callbacks()'s (retries, get further data, writes after reads, etc). > B) Run out of CQE's with IORING_FEAT_NODROP and can no longer free up > SQE's > > So this loop doesn't work under pressure :) > > I see that qemu's implementation walks an object queue, which calls > io_uring_submit() if SQE's are exhausted. I don't recall it trying to do > anything if submit returns EBUSY because of CQE exhaustion? I've not found > other merged code implementing non-toy network servers and most examples > are rewrites of CLI tooling which are much more constrained problems. Have > I missed anything? > > I can make this work but a lot of solutions are double walking lists > (fetch all CQE's into an array, advance them, then process), or not being > able to take advantage of any of the batching API's. Hoping the > community's got some better examples to untwist my brain a bit :) > > For now I have things working but want to do a cleanup pass before making > my clients/server bits public facing. > > Thanks! > -Dormando
