Hi Thomas, On Thu, May 15, 2014 at 1:34 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > On Wed, 14 May 2014, Carlos O'Donell wrote: > >> On 05/14/2014 03:03 PM, Michael Kerrisk (man-pages) wrote: >> >> 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(). (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*".) >> >> I fully agree with Michael here. >> >> The futex() syscall was never exposed to userspace specifically because >> it was an interface we did not want to support forever with a stable ABI. >> The futex() syscall is an implementation detail that is shared between >> the kernel and the writers of core runtimes for Linux. > > Nonsense. > > If we change that interface (aside of adding functionality or some new > error return) it would break the world and some more, simply because > out of the blue glibc-2.xx would stop to work on linux-3.yy. > > Aside of that the futex syscall is used as a bare interface without > any glibc interaction: > > - It's handy to implement user space wait queues > > - It's (ab)used in very interesting ways by data base apps > > - It's (ab)used by some Java monstrosities. Thanks for the education about user-space uses of futexes. I was unaware. > Nothing you care about and you really don't want to see the gory > details, but you have to accept that there is an universe which is > happy to deal with the raw syscalls instead of going through some ill > defined posix interfaces. And that universe would love to have your documentation of FUTEX_WAKE_BITSET and FUTEX_WAIT_BITSET ;-), Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
