Re: accept() improvements for rt signals

From: Alessandro Sala (a.sala@mclink.it)
Date: Sun Mar 05 2000 - 05:49:51 EST

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    Hello,

    Julian Anastasov wrote:
    >
    > Hello,
    >
    > On Tue, 22 Feb 2000, Stephen C. Tweedie wrote:
    >
    > > Hi,
    > >
    > > On Tue, 22 Feb 2000 17:38:45 +0200 (EET), Julian Anastasov
    > > <uli@linux.tu-varna.acad.bg> said:
    > >
    > > > Is there a known problem with O_NONBLOCK|O_ASYNC listening
    > > > sockets (2.2.15pre7 UP) ? I receive unexpected SIGIO after accept()
    > > > using such listening socket.
    > >
    >
    > After adding some debugging in the kernel I found that
    > send_sig_info() returns EPERM and send_sigio() fallbacks to
    > SIGIO delivery using "send_sig(SIGIO, p, 1);". I have stopped to
    > search the exact values used in the EPERM checking because I found
    > this posting from Alessandro Sala <a.sala@mclink.it> on 06-DEC-1999
    > with the subject:
    > "PROBLEM: Asynchronous I/O with realtime signals erroneously sends SIGIO".
    >
    > http://kernelnotes.org/lnxlists/linux-kernel/lk_9912_01/msg01206.html
    > http://marc.theaimsgroup.com/?l=linux-kernel&m=94451812209885&w=2
    >
    > The problem is described very well and I think I have
    > the same one. send_sigio() must pass the perm checking in
    > send_sig_info(). I didn't checked the corresponding 2.3 code. This

    I checked 2.3.34 and it seems the problem is still there: the perm
    checking code in send_sig_info() is the same as 2.2.x, SI_SIGIO still
    has a negative value, and the macro SI_FROMUSER(siptr) is still
    defined as (siptr)->si_code <= 0.

    If you need to use realtime signals with F_SETSIG, I suggest you
    apply the workaround I suggested in my posting: replace
    the definition of SI_FROMUSER in asm-i386/siginfo.h with

    #define SI_FROMUSER(siptr) ((siptr)->si_code <= 0 && \
                                      (siptr)->si_code >= SI_QUEUE)

    I'am using this and I've had no problems so far, but I realize
    it's only a workaround: I'd like someone commented about my proposed
    solution: changing the definition of SI_SIGIO, SI_ASYNCIO, SI_MESGQ
    and SI_TIMER to positive values. I think this would solve the problem
    and would make the realtime signals more compliant with The Single Unix
    specification.

    bye,
    Alessandro 

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