On 5/14/14, 13:56, "Davidlohr Bueso" <davidlohr@xxxxxx> wrote: >On Wed, 2014-05-14 at 21:03 +0200, Michael Kerrisk (man-pages) wrote: >> Hi Darren, >> >> On Wed, May 14, 2014 at 6:18 PM, Darren Hart <dvhart@xxxxxxxxxxxxxxx> >>wrote: >> > On 5/14/14, 3:35, "Michael Kerrisk (man-pages)" >><mtk.manpages@xxxxxxxxx> >> > wrote: >> > >> >>[So, some futex recent discussions remind me I should make this >>request] >> >> >> >>Hello all (especially those in the To:, namely Thomas, Darren, Ingo, >> >>Jakub), >> >> >> >>The futex man pages: >> >>http://man7.org/linux/man-pages/man2/futex.2.html >> >>http://man7.org/linux/man-pages/man7/futex.7.html >> >>are currently in a sorry state. I'm by no means convinced that all of >>the >> >>futex operations described there are explained fully and correctly. >>And >> >>probably not all error cases for each operation are properly >>documented. >> >>I'd be very happy if some folk could review those pages and send me >> >>corrections (Git: >> >>http://git.kernel.org/pub/scm/docs/man-pages/man-pages). >> >> >> >>But worse, a number of futex operations remain undocumented in >>futex(2) >> >>(see the list below). >> >> >> >>I am aware of Documentation/pi-futex.txt and >> >>Documentation/futex-requeue-pi.txt. However, both of those documents >> >>are rather thin on details / explain what certain FUTEX_* operations >>are >> >>used for rather than what they do / focus on the implementation, >>rather >> >>than the semantics. >> >> >> >>What I would like is that the futex(2) page documenta each one of >> >>these operations with a focus on the semantics in a way that might be >> >>useful to writers of library functions or those who simply wish to >> >>better understand (from a user-space perspective) what futexes are >> >>and how they are used. However, I don't have the knowledge to do >> >>this well in any reasonable time. >> >> >> >>Would the folk in the To: list (or anyone else who is knowledgeable) >> >>be willing to write patches >> >>(Git: http://git.kernel.org/pub/scm/docs/man-pages/man-pages ) >> >>or just supply me with some raw text that documents these currently >> >>undocumented futex operations, in the manner suggested? >> > >> > Yes, I'll be glad to help. >> >> Thanks! >> >> > However, unless I'm sorely mistaken, the larger problem is that glibc >> > removed the futex() call entirely, so these man pages don't describe >> >> I don't think futex() ever was in glibc--that's by design, and >> completely understandable: no user-space application would want to >> directly use futex(). > >That's actually not quite true. There are plenty of software efforts out >there that use futex calls directly to implement userspace serialization >mechanisms as an alternative to the bulky sysv semaphores. I worked >closely with an in-memory DB project that makes heavy use of them. Not >everyone can simply rely on pthreads. Userspace RCU from Mattieu Desnoyers / Efficios uses it as well - or did. > >> (BTW, I mispoke in my earlier mail when I said I >> wanted documentation suitable for "writers of library functions" -- I >> meant suitable for "writers of *C library*".) > >While kind of beyond the scope of documentation like manpages, I would >very much welcome this! The internet is full of >misleading/false/stupid/incomplete references to futexes and how to use >them. Having a best practises helps the kernel directly avoiding users >from misusing them. Agreed. -- Darren Hart Open Source Technology Center darren.hart@xxxxxxxxx Intel Corporation -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
