Messages in this thread | | | Date | Fri, 10 Oct 2008 15:19:31 +0200 (CEST) | From | Bodo Eggert <> | Subject | Re: dup2() vs dup3() inconsistency when |
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On Fri, 10 Oct 2008, Michael Kerrisk wrote: > On Fri, Oct 10, 2008 at 1:42 PM, Bodo Eggert <7eggert@gmx.de> wrote: > > Michael Kerrisk <mtk.manpages@googlemail.com> wrote: > > > >> Well, as long as we are fixing the dup3() interface in the way that Al > >> and Ulrich have suggested, what about another fix: > >> > >> give an error if newfd is already open, thus forcing the user to do an > >> explicit close > >> > >> ? > >> > >> This silent close in dup2() is an implementation blemish. Why not eliminate > >> it? > > > > I think it might be usefull: > > Thread B does some logging to fd 42 > > Thread A switches the logfile by creating a new file, writing a header and > > then does dup3(fd, 42, O_WRONLY|O_APPEND|O_CLOEXEC); close(fd); > > I don't know the details of the kernel locks here, so perhaps this is > a naive question: but, as things stand is there not the potential for > some nasty race if one thread is writing to fd 42 at the same time as > another thread does a dup2(fd, 42)?
I strongly hope there would not be any ...
> > (Off cause this is not yet implemented, O_RDONLY would give some problems, > > O_CLOEXEC alone might be better done while open()ing the file, ... but you > > get the idea.) > > > > > > BTW: I think dup3(fd, -1, flags) should use the file descriptor dup() would > > return. Or should there be a dupf(fd, flags) syscall instead? > > If one did this, maybe it would be better to have an extra flag that > said: "use the first free file descriptor >= newfd", thus giving the > more general functionality like fcntl(F_DUPFD).
I think you are right. I thought about something similar, too, but was distracted enough to not think about the connection. -- Funny quotes: 10. Nothing is fool proof to a talented fool.
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