Re: detect valid fd

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

On Tue, Sep 16, 2014 at 12:51:24AM +0100, Justin Cormack wrote:
> On Tue, Sep 16, 2014 at 12:20 AM, Patrick Welche <prlw1%cam.ac.uk@localhost> 
> wrote:
> > Given a filedescriptor, how can you tell that it is valid and has been
> > opened?
> >
> > In the attached simple program, a file and a directory are opened
> > (with CLOEXEC set). I then call fcntl(fd, F_GETFD) on the range
> > fd = [3..15].  fd = {3,4} correspond to the open file and directory.
> > Why don't I get fcntl(4):
> >
> >      [EBADF]            fildes is not a valid open file descriptor.
> >
> > for fd = [5..15], but only for some of them?
> >
> > $ ./cloexec
> > fd  3 testfile.txt flags = 0x1 (0x1)
> > fd  4 testdir flags = 0x1 (0x1)
> > fd  3's flags = 0x1 (0x1)
> > fd  4's flags = 0x1 (0x1)
> > fd  5's flags = 0x0 (0x0)
> > fd  6's flags = 0x0 (0x0)
> > fd  7's flags = 0x0 (0x0)
> > fd  8's flags = 0x0 (0x0)
> > fd  9's flags = 0x0 (0x0)
> > fd 10's flags = 0x0 (0x0)
> > cloexec: fcntl 11: Bad file descriptor
> > cloexec: fcntl 12: Bad file descriptor
> > fd 13's flags = 0x0 (0x0)
> > fd 14's flags = 0x0 (0x0)
> > cloexec: fcntl 15: Bad file descriptor
> 
> I get
> 
> fd  3 testfile.txt flags = 0x1 (0x1)
> fd  4 testdir flags = 0x1 (0x1)
> fd  3's flags = 0x1 (0x1)
> fd  4's flags = 0x1 (0x1)
> cloexec: fcntl 5: Bad file descriptor
> cloexec: fcntl 6: Bad file descriptor
> cloexec: fcntl 7: Bad file descriptor
> cloexec: fcntl 8: Bad file descriptor
> cloexec: fcntl 9: Bad file descriptor
> cloexec: fcntl 10: Bad file descriptor
> cloexec: fcntl 11: Bad file descriptor
> cloexec: fcntl 12: Bad file descriptor
> cloexec: fcntl 13: Bad file descriptor
> cloexec: fcntl 14: Bad file descriptor
> cloexec: fcntl 15: Bad file descriptor
> 
> Which looks fine, on netbsd6.1.4 and 7-pre, both on amd64.
> 
> What NetBSD version are you testing on?

So for both of you, things look correct!

This is on Sunday's NetBSD 7.99.1 amd64, but this is an old problem for
me...

Cheers,

Patrick