In message <[EMAIL PROTECTED]>
so spake Alexander Farber (alexander.farber):
> In the file /usr/src/lib/libc/gen/daemon.c
>
> if (!noclose && (fd = open(_PATH_DEVNULL, O_RDWR, 0)) != -1) {
> (void)dup2(fd, STDIN_FILENO);
> (void)dup2(fd, STDOUT_FILENO);
> (void)dup2(fd, STDERR_FILENO);
> if (fd > 2)
> (void)close (fd);
> }
>
> is same as:
>
> if (!noclose && (fd = open(_PATH_DEVNULL, O_RDWR, 0)) != -1) {
> (void)dup2(fd, 0);
> (void)dup2(fd, 1);
> (void)dup2(fd, 2);
> if (fd > 2)
> (void)close (fd);
> }
>
> right?
Right.
> What is this last check (fd > 2) needed for? Isn't fd always > 2,
> because the first 3 are already taken by the STDxxx streams at the
> program start?
Nope. There is no guarantee that fds 0-2 are open when a program
starts. In that case, fd will fall in the range 0-2 and without
the check we can close one of the descriptors 0-2.
Bonus trivia: There's also no guarantee that argc > 0 when a program
starts. Lots of programs make bad assumptions...
- todd
