On Fri, Dec 3, 2021 at 11:19 AM Pavel Begunkov <asml.silence@xxxxxxxxx> wrote: > > On 12/2/21 21:25, Willem de Bruijn wrote: > >>> What if the ubuf pool can be found from the sk, and the index in that > >>> pool is passed as a cmsg? > >> > >> It looks to me that ubufs are by nature is something that is not > >> tightly bound to a socket (at least for io_uring API in the patchset), > >> it'll be pretty ugly: > >> > >> 1) io_uring'd need to care to register the pool in the socket. Having > >> multiple rings using the same socket would be horrible. It may be that > >> it doesn't make much sense to send in parallel from multiple rings, but > >> a per thread io_uring is a popular solution, and then someone would > >> want to pass a socket from one thread to another and we'd need to support > >> it. > >> > >> 2) And io_uring would also need to unregister it, so the pool would > >> store a list of sockets where it's used, and so referencing sockets > >> and then we need to bind it somehow to io_uring fixed files or > >> register all that for tracking referencing circular dependencies. > >> > >> 3) IIRC, we can't add a cmsg entry from the kernel, right? May be wrong, > >> but if so I don't like exposing basically io_uring's referencing through > >> cmsg. And it sounds io_uring would need to parse cmsg then. > >> > >> > >> A lot of nuances :) I'd really prefer to pass it on per-request basis, > > > > Ok > > > >> it's much cleaner, but still haven't got what's up with msghdr > >> initialisation... > > > > And passing the struct through multiple layers of functions. > > If you refer to ip_make_skb(ubuf) -> __ip_append_data(ubuf), I agree > it's a bit messier, will see what can be done. If you're about > msghdr::msg_ubuf, for me it's more like passing a callback, > which sounds like a normal thing to do. Thanks, I do mean the first. Also, small nit now that it comes up again msghdr::msg_ubuf is not plain C. I would avoid that pseudo C++ notation (in the subject line of 3/12) > > >> Maybe, it's better to add a flags field, which would include > >> "msg_control_is_user : 1" and whether msghdr includes msg_iocb, msg_ubuf, > >> and everything else that may be optional. Does it sound sane? > > > > If sendmsg takes the argument, it will just have to be initialized, I think. > > > > Other functions are not aware of its existence so it can remain > > uninitialized there. > > Got it, need to double check, but looks something like 1/12 should > be as you outlined. > > And if there will be multiple optional fields that have to be > initialised, we would be able to hide all the zeroing under a > single bitmask. E.g. instead of > > msg->field1 = NULL; > ... > msg->fieldN = NULL; > > It may look like > > msg->mask = 0; // HAS_FIELD1 | HAS_FIELDN; Makes sense to me. This patch series only adds one field, so you can leave the optimization for a possible future separate patch series?
