kern/149857: [kqueue] kqueue not reporting EOF under certain circumstances

Konstantin Belousov kostikbel at gmail.com
Tue Jul 10 14:03:17 UTC 2012


On Tue, Jul 10, 2012 at 03:16:45PM +0300, Volodymyr Kostyrko wrote:
> Hi all.
> 
> http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/149857
> 
> This PR is rather old. I just had submitted new test case, now in plain c.
> 
> It doesn't work exactly like python version, but the result is the same:
> 
> > clang test.c
> > cat test.c | ./a.out
> -1 916 0 0 0
> -1 0 32768 0 0
> > ./a.out < test.c
> -1 916 0 0 0
> <- and here we have a complete hang in [kqread].

And what is your expectation ?

The vnode filter never returns EOF when current file position at the end
of file. It is documented that read filter returns when file offset if not
at the end of file, thats all. In fact, EV_EOF is returned on forced unmount.
I do not see a bug in kqueue.

On the other hand, your C code has at least two things that I cannot
understand. First, EV_EOF is output flag, it makes absolutely no sense
to set it in command. Second, it is mistery for me what do you check with
		if (kev.flags >> 15 == 1) {
test.
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