Date: Mon, 11 Jul 2011 17:22:33 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Petr Salinger <Petr.Salinger@seznam.cz> Cc: freebsd-hackers@freebsd.org, Robert Millan <rmh@debian.org>, current@freebsd.org Subject: Re: [PATCH] Improve LinuxThreads compatibility in rfork() Message-ID: <20110711142232.GU43872@deviant.kiev.zoral.com.ua> In-Reply-To: <alpine.LRH.2.02.1107111556000.7134@sci.felk.cvut.cz> References: <CAOfDtXMe_pkBdAFpUdvzmfs38Re=nw_YBz4w0Va0naEcuak7iw@mail.gmail.com> <20110711123332.GS43872@deviant.kiev.zoral.com.ua> <alpine.LRH.2.02.1107111455230.7134@sci.felk.cvut.cz> <20110711133342.GT43872@deviant.kiev.zoral.com.ua> <alpine.LRH.2.02.1107111556000.7134@sci.felk.cvut.cz>
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[-- Attachment #1 --] On Mon, Jul 11, 2011 at 04:23:36PM +0200, Petr Salinger wrote: > >>>Can you, please, describe the reasoning behind the > >>>>+ if (sig == SIGCHLD) sig = 0; > >>>line ? > >> > >>The main reason is backward compatibility. > >>The original FreeBSD code allows only to select between > >>SIGUSR1 or SIGCHLD signals. > >> > >>The our extension changes meaning of RFLINUXTHPN to select signal based on > >>bits 24-30 of passed flags instead of using SIGUSR1 every time. > >> > >>When the passed "signal" number is zero, it should behave identically > >>on plain FreeBSD and in our environment, therefore SIGUSR1 is selected. > >>The assumption is (have been) that (yet) undefined bits are zero. > >>That way we are backward compatible with original FreeBSD. > >> > >>We still need an alternative way to select "none signal is sent" > >>after child exit (under linux #0 is used). > >> > >>The SIGCHLD can be "selected" (also on original FreeBSD) by not specifying > >>RFLINUXTHPN, therefore combination of RFLINUXTHPN and passed "signal" > >>number SIGCHLD is (have been) used for "none signal". > >> > >>BTW, the opposite side is in > >> > >>http://anonscm.debian.org/viewvc/glibc-bsd/trunk/glibc-ports/kfreebsd/clone.c?view=markup > > > >I shall state that the sig == SIGCHLD case is ugly. Having the separate > >flag "do not send signal to the parent" would be much less clumsy. > >What are the requirements for the ABI stability for Debian/kFreeBSD ? > >Can this be fixed now, or is it too late ? > > It should be backward compatible with one previous version. > > What about in long term this: > > RFLINUXTHPN bit will be renamed and will have meaning > "select signal based on bits 24-30 of passed flags" > > - zero would mean "no signal" > - SIGCHLD would mean undefined > - SIGUSR1 would mean SIGUSR1 > > It is ABI/API breakage under original FreeBSD. > The question is how frequently RFLINUXTHPN is used under native FreeBSD > and its port collection. RFLINUXPTH was used by the linuxthreads port, that was popular in the time of FreeBSD 4.x and may be 5.x to run mysql. I will object against this breakage. > > And under "Debian GNU/kFreeBSD COMPAT" or 8-COMPAT > - SIGCHLD would mean "no signal" We never user COMPAT to _change_ the meaning of something, only to exclude some functionality, like syscall. > > We do not use SIGUSR1 currently, the eglibc side can detect whether > it runs under new-enough kernel and decide whether use 0 or SIGCHLD > for "no signal". > > The kernel side would be something like: > > if (flags & RFLINUXTHPN) > { > p2->p_sigparent = RFTHPNSIGNUM(flags); > #if COMPAT8 > if (p2->p_sigparent == SIGCHLD) > p2->p_sigparent = 0; > #endif > } No, this is even uglier, and see the note about compat. BTW, it seems that our rfork(2) ignores unknown flags. This should be fixed, might be in the same patch. [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (FreeBSD) iEYEARECAAYFAk4bBygACgkQC3+MBN1Mb4jK3wCfUDTbE+y2thPnkLBRDkRLq53a wWQAnjkr4O8ngWU0FTCHpzsmnMbLAl1Q =yDiE -----END PGP SIGNATURE-----
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