On Fri, Apr 6, 2012 at 12:23 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote: > On 04/06/2012 02:54 AM, Alexey Dobriyan wrote: >> >> Without proc knowledge about fdtable is gathered linearly and still unreliable. >> With nextfd(2), even procful environments could lose several failure branches. >> And they can keep old dumb fd++ or smart /proc/self/fd loops for a change. >> > > Incidentally, if we were to create a system call for this -- which I so > far see no reason for -- I would make it return a select-style bitmask > of file descriptors in use, not a "next fd" which would require a system > call per iteration. I know the reason. fcntl(F_NEXT) is one of a proposal of next SUS enhancement. http://austingroupbugs.net/view.php?id=149 nextfd() has a semantics of F_NEXT. Next, why shoundn't we implement fcntl(F_NEXT) in our kernel? I think we have two reason. 1) As linus pointed out, linux specific "flags" argument may be useful. 2) The name of F_NEXT is not fixed yet. another url of the austin says it is FD_NEXT. So, we can't choose right name yet. Moreover, A meanings of 3rd argument of F_NEXT haven't been fixed. I dont think following #ifdef is insane. but glibc also can provide correct F_NEXT when next SUS is published. #ifdef FOO #define NEXTFD(fd) nextfd(fd, flags) #else #define NEXTFD(fd) fcntl(fd, F_NEXT, O_FDWR) #endif In short, kernel developer don't care any standard at all. but application programmer usually care it. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
