Date: Wed, 21 Feb 2018 11:29:24 +0800 From: Julian Elischer <julian@freebsd.org> To: Stefan Blachmann <sblachmann@gmail.com>, Eitan Adler <lists@eitanadler.com> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: Marking select(2) as restrict Message-ID: <01800d65-ec8d-2337-5459-803b5e2fbe0e@freebsd.org> In-Reply-To: <CACc-My27BA-VAuNmqD1Eah%2BusUwWA8PUxyux1HxehZrqE8G%2BZA@mail.gmail.com> References: <CAF6rxg=h_oMiUu7P=GAOQf_OySQM2w31hg6Kas%2B3jeEM3qq_Cg@mail.gmail.com> <CAF6rxgnt9c0n8i-nHQwoKGbZKF2hM5AZqEJnz0CLo26XOO4_sg@mail.gmail.com> <CACc-My27BA-VAuNmqD1Eah%2BusUwWA8PUxyux1HxehZrqE8G%2BZA@mail.gmail.com>
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On 21/2/18 9:52 am, Stefan Blachmann wrote: > As the last C standard I know is ANSI, I was curious and read what > restrict does (https://en.wikipedia.org/wiki/Restrict). > > To understand more about select() I read in the Linux tutorial > (http://man7.org/linux/man-pages/man2/select_tut.2.html) . > The section "Select Law" looks like that things could break easy. > > Personally (in particular because I don't know the matter) I would be > afraid that making select pointers restrict could cause hard-to debug > misbehavior of a few programs that are already working borderline > (linux ports etc). > > But as said, this is my unqualified guess. > And, few, almost no documents on select show it as restrict. > > Always following Posix isn't necessarily good, as many don't care about it. > For example, with 11.0 the default Posix conform SHM setting was > changed to non-Posix-compliant, because posix conformity caused just > too many people troubles. > And, maybe the gain would be little anyway? > > Just my worthless 2 cents. > Have a good day @hackers :) > Stefan > > > On 2/21/18, Eitan Adler <lists@eitanadler.com> wrote: >> I filed a request for a slightly modified version of this patch to be >> exp-run. I'm planning on committing unless there is significant >> fallout or objections on this list. >> >> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225981 >> >> On 15 February 2018 at 00:10, Eitan Adler <lists@eitanadler.com> wrote: >>> Hi all, >>> >>> POSIX requires that the fd_set arguments in select(2) be marked as >>> restrict. This patch attempts to implement that. >>> >>> (a) Am I missing anything? >>> (b) Anything in particular to watch out for? >>> (c) Assuming an exp-run passes any reason not to commit? >>> >>> >>> Index: lib/libc/sys/select.2 >>> =================================================================== >>> --- lib/libc/sys/select.2 (revision 329296) >>> +++ lib/libc/sys/select.2 (working copy) >>> @@ -39,7 +39,7 @@ >>> .Sh SYNOPSIS >>> .In sys/select.h >>> .Ft int >>> -.Fn select "int nfds" "fd_set *readfds" "fd_set *writefds" "fd_set >>> *exceptfds" "struct timeval *timeout" >>> +.Fn select "int nfds" "fd_set * restrict readfds" "fd_set * restrict >>> writefds" "fd_set * restrict exceptfds" "struct timeval *timeout" >>> .Fn FD_SET fd &fdset >>> .Fn FD_CLR fd &fdset >>> .Fn FD_ISSET fd &fdset >>> Index: lib/libc/sys/select.c >>> =================================================================== >>> --- lib/libc/sys/select.c (revision 329296) >>> +++ lib/libc/sys/select.c (working copy) >>> @@ -41,7 +41,7 @@ __weak_reference(__sys_select, __select); >>> >>> #pragma weak select >>> int >>> -select(int n, fd_set *rs, fd_set *ws, fd_set *es, struct timeval *t) >>> +select(int n, fd_set * restrict rs, fd_set * restrict ws, fd_set * >>> restrict es, struct timeval *t) >>> { >>> >>> return (((int (*)(int, fd_set *, fd_set *, fd_set *, struct timeval *)) >>> Index: sys/sys/select.h >>> =================================================================== >>> --- sys/sys/select.h (revision 329296) >>> +++ sys/sys/select.h (working copy) >>> @@ -101,8 +101,7 @@ int pselect(int, fd_set *__restrict, fd_set *__res >>> const struct timespec *__restrict, const sigset_t *__restrict); >>> #ifndef _SELECT_DECLARED >>> #define _SELECT_DECLARED >>> -/* XXX missing restrict type-qualifier */ >>> -int select(int, fd_set *, fd_set *, fd_set *, struct timeval *); >>> +int select(int, fd_set *__restrict, fd_set *__restrict, fd_set >>> *__restrict, struct timeval *); >>> #endif >>> __END_DECLS >>> #endif /* !_KERNEL */ >>> >>> >>> -- >>> Eitan Adler >> >> >> -- >> Eitan Adler >> _______________________________________________ >> freebsd-hackers@freebsd.org mailing list >> https://lists.freebsd.org/mailman/listinfo/freebsd-hackers >> To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org" >> > _______________________________________________ > freebsd-hackers@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org" >
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