On Wed, May 14, 2014 at 02:03:13PM -0700, Darren Hart wrote: > 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. It still does. ;-) Thanx, Paul > >> (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
