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.
And under "Debian GNU/kFreeBSD COMPAT" or 8-COMPAT
- SIGCHLD would mean "no signal"
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
}
Petr
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