[PATCH] Improve LinuxThreads compatibility in rfork()

[Kostik Belousov]

On Tue, Jul 12, 2011 at 11:16:28AM +0200, Petr Salinger wrote:
> >>Seems this interface be acceptable ?
> >
> >Looks good to me.
> 
> The proposed code changes are in the attached patch.
> 
> Proposed wording of addition into RFORK(2):

Below is the patch I intend to commit after you retest it.
I added the checks for validity of the flags, and some rewording to the
manual page.

diff --git a/lib/libc/sys/rfork.2 b/lib/libc/sys/rfork.2
index f1ae14b..993fd1b 100644
--- a/lib/libc/sys/rfork.2
+++ b/lib/libc/sys/rfork.2
@@ -5,7 +5,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd March 15, 2011
+.Dd July 12, 2011
 .Dt RFORK 2
 .Os
 .Sh NAME
@@ -84,6 +84,16 @@ Note that a lot of code will not run correctly in such an environment.
 .It Dv RFSIGSHARE
 If set, the kernel will force sharing the sigacts structure between the
 child and the parent.
+.It Dv RFTSIGZMB
+If set, the kernel will deliver a specified signal to the parent
+upon the child exit, instead of default SIGCHILD.
+The signal number
+.Dv signum
+is specified by oring the
+.Dv RFTSIGFLAGS(signum)
+expression into
+.Fa flags .
+Specifying signal number 0 disables signal delivery upon the child exit.
 .It Dv RFLINUXTHPN
 If set, the kernel will return SIGUSR1 instead of SIGCHILD upon thread
 exit for the child.
@@ -164,6 +174,8 @@ would be exceeded (see
 Both the RFFDG and the RFCFDG flags were specified.
 .It Bq Er EINVAL
 Any flags not listed above were specified.
+.It Bq Er EINVAL
+An invalid signal number was specified.
 .It Bq Er ENOMEM
 There is insufficient swap space for the new process.
 .El
diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
index a8abd8e..9d3e22d 100644
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -476,7 +476,10 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
 		sigacts_copy(newsigacts, p1->p_sigacts);
 		p2->p_sigacts = newsigacts;
 	}
-	if (flags & RFLINUXTHPN) 
+
+	if (flags & RFTSIGZMB)
+	        p2->p_sigparent = RFTSIGNUM(flags);
+	else if (flags & RFLINUXTHPN)
 	        p2->p_sigparent = SIGUSR1;
 	else
 	        p2->p_sigparent = SIGCHLD;
@@ -719,10 +722,22 @@ fork1(struct thread *td, int flags, int pages, struct proc **procp)
 	static int curfail;
 	static struct timeval lastfail;
 
+	/* Check for the undefined or unimplemented flags. */
+	if ((flags & ~(RFFLAGS | RFTSIGFLAGS(RFTSIGMASK))) != 0)
+		return (EINVAL);
+
+	/* Signal value requires RFTSIGZMB. */
+	if ((flags & RFTSIGFLAGS(RFTSIGMASK)) != 0 && (flags & RFTSIGZMB) == 0)
+		return (EINVAL);
+
 	/* Can't copy and clear. */
 	if ((flags & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
 		return (EINVAL);
 
+	/* Check the validity of the signal number. */
+	if ((flags & RFTSIGZMB) != 0 && (u_int)RFTSIGNUM(flags) > _SIG_MAXSIG)
+		return (EINVAL);
+
 	p1 = td->td_proc;
 
 	/*
diff --git a/sys/sys/unistd.h b/sys/sys/unistd.h
index 378308d..9d56a3a 100644
--- a/sys/sys/unistd.h
+++ b/sys/sys/unistd.h
@@ -180,8 +180,16 @@
 #define	RFLINUXTHPN	(1<<16)	/* do linux clone exit parent notification */
 #define	RFSTOPPED	(1<<17)	/* leave child in a stopped state */
 #define	RFHIGHPID	(1<<18)	/* use a pid higher than 10 (idleproc) */
+#define	RFTSIGZMB	(1<<19)	/* select signal for exit parent notification */
+#define	RFTSIGSHIFT	20	/* selected signal number is in bits 20-27  */
+#define	RFTSIGMASK	0xFF
+#define	RFTSIGNUM(flags)	(((flags) >> RFTSIGSHIFT) & RFTSIGMASK)
+#define	RFTSIGFLAGS(signum)	((signum) << RFTSIGSHIFT)
 #define	RFPPWAIT	(1<<31)	/* parent sleeps until child exits (vfork) */
 #define	RFKERNELONLY	(RFSTOPPED | RFHIGHPID | RFPPWAIT)
+#define	RFFLAGS		(RFFDG | RFPROC | RFMEM | RFNOWAIT | RFCFDG | \
+    RFTHREAD | RFSIGSHARE | RFLINUXTHPN | RFSTOPPED | RFHIGHPID | RFTSIGZMB | \
+    RFPPWAIT)
 
 #endif /* __BSD_VISIBLE */
 
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