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SubjectRe: [PATCH] Fix queued SIGIO
On Tue, 19 Sep 2000, Julian Anastasov wrote:
> On Mon, 18 Sep 2000, Andi Kleen wrote:
>
> > > SI_SIGIO is not generated from kernel. The same is for the
> > > other SI_ consts < 0 not defined with __SI_CODE.
> >
> > Ok, then you have already broken binary compatibility between 2.2 and 2.4
>
> Looking in the old kernels, it seems the binary compatibility
> was broken in 2.3.21 when si_code returns POLL_xxx events just like
> mentioned in "The Single UNIX ® Specification, Version 2",
> xsh/signal.h.html and not SI_SIGIO.
>
> SI_SIGIO in si_code for 2.2 does not return any information
> about the events. I even see that Redhat maintains patch against 2.2
> to backport the POLL_xxx events from 2.3. Not sure after the changes
> in 2.4.0-test1. Anyway, 2.2 looks unusable for me and I don't see other
> way this problem to be fixed. The binary compatibility is impossible
> to exist. The applications can support the both ways: the old SI_SIGIO
> and the new POLL_xxx events (recompiled after test1) in si_code.

because the 2.2 kernels are already "broken" in this regard, i can't see
how binary compatibility between 2.2 and 2.4 could even be an
issue. applications can't use this stuff in 2.2 without at least the
RedHat patch.

unless there's a problem implementing a glibc that runs on both 2.2 and
2.4, perhaps this should be revisited.

also, the test at issue here (from line 363 of kernel/signal.c):

/* If this was sent by a rt mechanism, try again. */
if (info->si_code != SI_USER) {
ret = -EAGAIN;
goto out;
}

has always been unclear as to its intent. it seems like there is
overloading going on here -- if the real intent is to prevent users
without credentials from sending "kernel-only" signals, then that should
be the logic here.

> The next step is somebody to implement event merging and to
> allow receiving of many events with one call. For the next kernels.

we just published a paper in the ALS proceedings describing our
implementation of a new system call similar to sigtimedwait() that
collects many events at once.

- Chuck Lever
--
corporate: <chuckl@netscape.com>
personal: <chucklever@bigfoot.com>

The Linux Scalability project:
http://www.citi.umich.edu/projects/linux-scalability/

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