Re: bpf/pcap are weird

• Previous message: Robert Watson: "Re: adding crypto support to GENERIC"
• Maybe in reply to: Brian Fundakowski Feldman: "bpf/pcap are weird"
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Date: Fri, 21 Nov 2003 01:27:41 -0800
To: Bruce Evans <bde@zeta.org.au>

> > bpfpoll() is reported to be broken; see PR 36219.
>
> Yes, that's the PR that indicated that "select()"/"poll()" don't, in
> fact, work correctly with timeouts.
>
> That was fixed in 4.5...
>
> > Rev.1.113 of bpf.c may have disturbed this.
>
> ...but might have been re-broken.
>
> > It removed the comment which said that
> > bpf_ready() doesn't acually imitate resultof(FIONREAD) != 0.
>
> ...and it also removed the check for "d->bd_state == BPF_TIMED_OUT" that
> made "select()"/"poll()" work with timeouts.

I didn't read the code fully - no, it didn't. Revision 1.113 changed

        if (events & (POLLIN | POLLRDNORM)) {
                /*
                 * An imitation of the FIONREAD ioctl code.
                 * XXX not quite. An exact imitation:
                 * if (d->b_slen != 0 ||
                 * (d->bd_hbuf != NULL && d->bd_hlen != 0)
                 */
                if (d->bd_hlen != 0 ||
                    ((d->bd_immediate || d->bd_state == BPF_TIMED_OUT) &&
                    d->bd_slen != 0))
                        revents |= events & (POLLIN | POLLRDNORM);
                else {
                        selrecord(td, &d->bd_sel);
                        /* Start the read timeout if necessary. */
                        if (d->bd_rtout > 0 && d->bd_state == BPF_IDLE) {
                                callout_reset(&d->bd_callout, d->bd_rtout,
                                    bpf_timed_out, d);
                                d->bd_state = BPF_WAITING;
                        }
                }
        }

to

        if (events & (POLLIN | POLLRDNORM)) {
                if (bpf_ready(d))
                        revents |= events & (POLLIN | POLLRDNORM);
                else {
                        selrecord(td, &d->bd_sel);
                        /* Start the read timeout if necessary. */
                        if (d->bd_rtout > 0 && d->bd_state == BPF_IDLE) {
                                callout_reset(&d->bd_callout, d->bd_rtout,
                                    bpf_timed_out, d);
                                d->bd_state = BPF_WAITING;
                        }
                }
        }

but revision 1.23 of "bpfdesc.h" introduce a macro "bpf_ready(bd)" that
does

        #define bpf_ready(bd) \
                ((bd)->bd_hlen != 0 || \
                 (((bd)->bd_immediate || (bd)->bd_state == BPF_TIMED_OUT) && \
                  (bd)->bd_slen != 0))

so the actual "bpf_poll()" code doesn't change.

Revision 1.23 was MFC'ed to the 4.x branch in revision 1.14.2.3, which
is in 4.9.

(Also, the problem I mentioned with FreeBSD 4.4 not supporting the
workaround for "select()" not working is in FreeBSD 4.3 as well.)
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• Previous message: Robert Watson: "Re: adding crypto support to GENERIC"
• Maybe in reply to: Brian Fundakowski Feldman: "bpf/pcap are weird"
• Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]