Is it OK to poll() a device file descriptor

[Elazar Leibovich]

Try to open /dev/null, and then to poll the file descriptor. Neither in the
man page nor in the standard I see anything preventing you to poll on
/dev/null, yet, it does not work on Mac OS X. You get a POLLNVAL.

Run the following:

https://gist.github.com/elazarl/5805848

#include <stdio.h>
#include <poll.h>

#include <fcntl.h>

int main() {
    int fd = open("/dev/null", O_WRONLY);
    struct pollfd pollfds = { fd, POLLOUT, 0 };
    if (fd < 0) {
        perror("open");
        return 1;
    }
    if (poll(&pollfds, 1, -1) < 0) {
        perror("poll");
        return 2;
    }
    if (pollfds.revents == POLLNVAL) {
        puts("huh? why poll({/dev/null, POLLOUT, 0}, 1) returns POLLNVAL?");
    }
    if (pollfds.revents == POLLOUT) {
        puts("working as expected");
    }
    return 0;
}

Is there anything I'm missing? Or is it a real vaguely implemented
corner of the standard.
If it is, I'll be glad to see a list of supported/unsupported platforms,
as well as list of other corner cases (for instance, POLLHUP may or
may be received on EOF).
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