Date: Mon, 22 Mar 1999 22:28:35 +0000 (GMT) From: Brian Feldman <green@unixhelp.org> To: "Richard Seaman, Jr." <dick@tar.com> Cc: Peter Wemm <peter@netplex.com.au>, Matthew Dillon <dillon@apollo.backplane.com>, "John S. Dyson" <dyson@iquest.net>, freebsd-current@FreeBSD.ORG Subject: Re: rfork() Message-ID: <Pine.BSF.4.05.9903222227380.14721-100000@zone.syracuse.net> In-Reply-To: <19990322082601.L32029@tar.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Mon, 22 Mar 1999, Richard Seaman, Jr. wrote: > On Mon, Mar 22, 1999 at 11:34:25AM +0800, Peter Wemm wrote: > > > Doing clone() in libc that calls rfork(2) and doing all the stack setup > > should be pretty easy.. (Richard has done it already, yes?) > > Its in package at http://lt.tar.com/linuxthreads.tar.gz . If anyone wants > to grab it out of there an put it into shape to commit it, be my guest. > > > On the other > > hand, the linux emulator needs it so there's a counter-argument for making > > it a proper syscall outright. Leaving the rfork(2) stuff unmolested and at > > least resembling it's plan9 origins probably has some merit - adding extra > > arguments would mess that up. > > I) clone syscall > --------------------- > The linux emulator needs (and has) a clone syscall: > > int linux_clone(int flags, void *stack) > > The value of an exit signal is passed in the lower 8 bits of the flags argument, > the linux counterparts to the FreeBSD RF* flags are passed in the balance > of the flags argument. > > I haven't seen or heard of a linux app that calls the clone syscall directly. > I know of two "apps", linuxthreads and the linux version of WINE, that call > the linux glibc version of clone (see below), which is a wrapper for the > syscall. > > The only thing that the linux syscall does, that can't be done easily in > FreeBSD using rfork and an appropriate wrapper to rfork, is pass in the > exit signal. rfork does have a flag to set an exit signal of SIGUSR1, but > it does not conveniently take a parameter to set it more flexibly. OTOH, > the only FreeBSD app I know of that actually sets an exit signal other > that the default SIGCHLD, is the linuxthreads port noted above. > > I'm not sure there is really a need for a "clone" syscall at this point, > but if you wanted it, you could just copy the linux_clone code in > linux_misc.c . You would have to decide if you want the flags parameter > to take the linux flags values, or FreeBSD flags (the emulator has > to take the linux values, obviously). > > My vote: don't bother with a syscall until there's a demonstrated need. > > II) clone in libc > ----------------- > Linux glibc has a clone call wrapper for the clone syscall, defined as: > > int clone (int (*fn) (void *arg), void *stack, int flags, void *arg) > > The stack and flags are passed directly to the clone syscall, and > the fn(arg) is the user function the cloned process should execute. > > Its easy enough to implement this in FreeBSD as a wrapper for rfork. > If you want to facilitate porting linux code, you would want the > flags argument to take linux flags, which would then be translated > into their FreeBSD counterparts before rfork is call. This is what > the code in the linuxthreads port does, and you are welcome to commit > it. > > The only issue here is whether people need to port linux code that > calls clone directly. As noted above, the only code I know of that > calls clone directly is WINE and linuxthreads. All the rest of the > code uses pthread_create, which only indirectly calls clone. > > My vote: I haven't seen the need, but if there is one, lets do it. > > III) libc rfork wrapper > ----------------------- > > It probably would be nice to have a libc rfork wrapper that grafts a > stack and a user function onto the rfork'd child process. But, it > should probably take FreeBSD flags, and there's no reason to > call it "clone". John Dyson's thr_fork is one such implementation. > Luoqi Chen posted another variation to either -hackers or -current > maybe 6-9 months ago. Matt Dillon just posted yet another variation. > Or, the linuxthreads port has a variation of the clone call that > has the same API as the linux clone call, but takes FreeBSD flags > (see clone.S). > > My vote: its worth doing, but not a top priority. The main issue > is to decide what interface would be most convenient. Its not a > top priority since the code already exists for those (rare) cases > where someone really needs it. And, lets not call it "clone". Let's call it "rfork() with one extra argument" instead then :) I don't see why this is a bad thing. Full backward compatibility is maintained, and it would be easy to implement. > > -- > Richard Seaman, Jr. email: dick@tar.com > 5182 N. Maple Lane phone: 414-367-5450 > Chenequa WI 53058 fax: 414-367-5852 > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-current" in the body of the message > Brian Feldman _ __ ___ ___ ___ green@unixhelp.org _ __ ___ | _ ) __| \ http://www.freebsd.org/ _ __ ___ ____ | _ \__ \ |) | FreeBSD: The Power to Serve! _ __ ___ ____ _____ |___/___/___/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?Pine.BSF.4.05.9903222227380.14721-100000>