Messages in this thread | | | Date | Fri, 3 Dec 2021 16:19:28 +0000 | Subject | Re: [RFC 00/12] io_uring zerocopy send | From | Pavel Begunkov <> |
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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.
>> 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;
-- Pavel Begunkov
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