Date: Mon, 13 Sep 2021 13:43:18 -0700 From: John Baldwin <jhb@FreeBSD.org> To: Michael Tuexen <michael.tuexen@macmic.franken.de> Cc: Mark Johnston <markj@FreeBSD.org>, "src-committers@freebsd.org" <src-committers@FreeBSD.org>, "dev-commits-src-all@freebsd.org" <dev-commits-src-all@FreeBSD.org>, "dev-commits-src-main@freebsd.org" <dev-commits-src-main@FreeBSD.org> Subject: Re: git: b864b67a0d19 - main - socket: Do not include control messages in FIONREAD return value Message-ID: <4ae85e22-a95f-5046-fe7d-40f2cc881c82@FreeBSD.org> In-Reply-To: <BFB7C96E-CB33-4EB8-804C-E9AACC4BCAB7@macmic.franken.de> References: <202109122039.18CKdpwW094531@gitrepo.freebsd.org> <270ac6c6-1fdf-879a-cbea-ef43200ef12a@FreeBSD.org> <BFB7C96E-CB33-4EB8-804C-E9AACC4BCAB7@macmic.franken.de>
next in thread | previous in thread | raw e-mail | index | archive | help
On 9/13/21 12:25 PM, Michael Tuexen wrote: >> On 13. Sep 2021, at 18:29, John Baldwin <jhb@freebsd.org> wrote: >> >> On 9/12/21 1:39 PM, Mark Johnston wrote: >>> The branch main has been updated by markj: >>> URL: https://cgit.FreeBSD.org/src/commit/?id=b864b67a0d197f59ecf6698940600956ceee2cae >>> commit b864b67a0d197f59ecf6698940600956ceee2cae >>> Author: Mark Johnston <markj@FreeBSD.org> >>> AuthorDate: 2021-09-12 20:05:49 +0000 >>> Commit: Mark Johnston <markj@FreeBSD.org> >>> CommitDate: 2021-09-12 20:39:44 +0000 >>> socket: Do not include control messages in FIONREAD return value >>> Some system software expects to be able to read at least the number of >>> bytes returned by FIONREAD. When control messages are counted in this >>> return value, this assumption is violated. Follow Linux and OpenBSD >>> here (as well as our own kevent(EVFILT_READ)) and only return the number >>> of data bytes available. >>> Reported by: avg >>> MFC after: 2 weeks >> >> In a somewhat similar vein, it would be nice to eventually have new ioctls >> to know how much data and control are available in the next message for >> datagram-oriented sockets. Right now if you are working with a datagram >> socket with variable-sized messages there's no good way to know how big the >> next message is (to resize a read buffer) as FIONREAD can count multiple >> messages. There's also no way at all to cope with control messages aside >> from retrying with some naive algorithm like doubling the size if MSG_CTRUNC >> is set, but that also requires always using MSG_PEEK so that you always >> end up reading a message at least twice. > That still requires two system calls. In SCTP, there is a CMSG you can > receive with a messages, which contains the metadata of the next message > you will receive. > So it might be an idea to define a CMSG containing the length of the next > message (if available). We could at least just have a single ioctl that returns a struct with two members (data length and control length) perhaps to get it back down to just 1 syscall similar to FIONREAD. -- John Baldwin
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?4ae85e22-a95f-5046-fe7d-40f2cc881c82>