libposix: drafted SIGCHLD management

sys/include/posix.h

@@ -221,6 +221,10 @@ extern int libposix_define_signal(PosixSignals signal, int code);
 
 extern int libposix_define_realtime_signals(int sigrtmin, int sigrtmax);
 
+/* Enable SIGCHLD emulation
+ */
+extern int libposix_emulate_SIGCHLD(void);
+
 /* Define of WCONTINUED, WNOHANG and WUNTRACED bit flags.
  *
  * Note that WCONTINUED and WUNTRACED are not yet supported by libposix

sys/src/lib/posix/build.json

@@ -17,6 +17,7 @@
 			"memory.c",
 			"others.c",
 			"processes.c",
+			"sigchlds.c",
 			"signals.c"
 		]
 	}

sys/src/lib/posix/initlib.c

@@ -40,6 +40,7 @@ libposix_init(int argc, char *argv[], PosixInit init)
 	extern unsigned char *__signals_to_code_map;
 	extern unsigned char *__code_to_signal_map;
 	extern int *__handling_external_signal;
+	extern int *__libposix_sigchld_target_pid;
 
 	WaitList *wait_list;
 	int status;
@@ -47,6 +48,7 @@ libposix_init(int argc, char *argv[], PosixInit init)
 	unsigned char signals_to_code[256];
 	unsigned char code_to_signal[256];
 	int handling_signal;
+	int sigchld_target_pid;
 
 	assert(__initialized == 0);
 
@@ -62,9 +64,11 @@ libposix_init(int argc, char *argv[], PosixInit init)
 	memset(signals_to_code, 0, sizeof(signals_to_code));
 	memset(code_to_signal, 0, sizeof(code_to_signal));
 	handling_signal = 0;
+	sigchld_target_pid = 0;
 	__signals_to_code_map = signals_to_code;
 	__code_to_signal_map = code_to_signal;
 	__handling_external_signal = &handling_signal;
+	__libposix_sigchld_target_pid = &sigchld_target_pid;
 	if(!atnotify(__libposix_note_handler, 1))
 		sysfatal("libposix: atnotify");
 

sys/src/lib/posix/internal.h

@@ -39,5 +39,5 @@ extern int __libposix_note_handler(void *ureg, char *note);
 
 extern void __libposix_free_wait_list(void);
 
-
+extern void __libposix_setup_new_process(void);
 

sys/src/lib/posix/processes.c

@@ -28,6 +28,25 @@ static int __libposix_wnohang;
 
 #define __POSIX_SIGNAL_PREFIX_LEN (sizeof(__POSIX_SIGNAL_PREFIX)-1)
 
+static int
+fork_without_sigchld(int *errnop)
+{
+	int pid = fork();
+
+	if(pid == 0)
+		__libposix_setup_new_process();
+	return pid;
+}
+
+int (*__libposix_fork)(int *errnop) = fork_without_sigchld;
+
+void
+__libposix_setup_new_process(void)
+{
+	/* reset wait list for the child */
+	*__libposix_wait_list = nil;
+}
+
 void
 __libposix_free_wait_list(void)
 {
@@ -110,13 +129,7 @@ POSIX_getppid(int *errnop)
 int
 POSIX_fork(int *errnop)
 {
-	int pid = fork();
-
-	if(pid == 0){
-		/* reset wait list for the child */
-		*__libposix_wait_list = nil;
-	}
-	return pid;
+	return __libposix_fork(errnop);
 }
 
 int

sys/src/lib/posix/sigchlds.c

@@ -0,0 +1,188 @@
+/*
+ * This file is part of Jehanne.
+ *
+ * Copyright (C) 2017 Giacomo Tesio <giacomo@tesio.it>
+ *
+ * This is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3 of the License.
+ *
+ * Jehanne is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Jehanne.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <u.h>
+#include <lib9.h>
+#include <posix.h>
+#include "internal.h"
+
+/* rendezvous points */
+extern unsigned char *__signals_to_code_map;
+extern unsigned char *__code_to_signal_map;
+
+/* pointer to the pid to forward notes to */
+int *__libposix_sigchld_target_pid;
+
+#define CHILD_READY(pid) ((long)rendezvous(&__signals_to_code_map, (void*)(~(pid))))
+#define C2P_READY(pid) ((long)rendezvous(&__code_to_signal_map, (void*)(~(pid))))
+
+static void
+release_inherited_resources(void)
+{
+	notify(nil);
+	rfork(RFCNAMEG|RFCENVG|RFNOTEG|RFCFDG);
+	bind("#P", "/proc", MREPL);
+	rfork(RFNOMNT);
+}
+
+static void
+forwarding_note_handler(void *ureg, char *note)
+{
+	postnote(PNPROC, *__libposix_sigchld_target_pid, note);
+	noted(NCONT);
+}
+
+static void
+forward_wait_msg(int sigchld_receiver, char *name)
+{
+	int n;
+	char buf[512], err[ERRMAX], note[512], *fld[5];
+
+	snprint(buf, sizeof(buf), "/proc/%d/args", getpid());
+	n = open(buf, OWRITE);
+	write(n, name, strlen(name)+1);
+	close(n);
+
+	n = 0;
+WaitInterrupted:
+	n = await(buf, sizeof buf-1);
+	if(n < 0){
+		rerrstr(err, ERRMAX);
+		if(strstr(err, "no living children") == nil)
+			goto WaitInterrupted;
+		snprint(note, sizeof(note), "%s: %r", name);
+		if(sigchld_receiver)
+			postnote(PNPROC, sigchld_receiver, note);
+		exits(note);
+	}
+	buf[n] = '\0';
+	if(jehanne_tokenize(buf, fld, nelem(fld)) != nelem(fld)){
+		snprint(note, sizeof(note), "%s: couldn't parse wait message", name);
+		if(sigchld_receiver)
+			postnote(PNPROC, sigchld_receiver, note);
+		exits(note);
+	}
+	snprint(note, sizeof(note), __POSIX_SIGNAL_PREFIX " %d", __signals_to_code_map[PosixSIGCHLD]);
+	if(sigchld_receiver){
+		postnote(PNPROC, sigchld_receiver, note);
+	}
+	exits(fld[4]);
+}
+
+
+static int
+fork_with_sigchld(int *errnop)
+{
+	int father = getpid();
+	int p2c;
+	long c2p = -1, child = -1;
+	char proxy_name[256];
+
+	/* Father here:
+	 * - create P2C
+	 * - wait for C2P to be ready
+	 * - register P2C in children list
+	 * - return P2C pid
+	 */
+	switch(p2c = rfork(RFPROC|RFMEM)){
+	case -1:
+		return -1;
+	case 0:
+		/* P2C here:
+		 * - create C2P
+		 * - wait for the child pid
+		 * - release all inherited resources
+		 * - install forwarding_note_handler
+		 * - send to father the C2P pid
+		 * - start waiting for the child
+		 */
+		switch(c2p = rfork(RFPROC|RFMEM)){
+		case -1:
+			while(C2P_READY(-2) == -1)
+				;
+			exits("rfork (c2p)");
+		case 0:
+			/* C2P here:
+			 * - create child
+			 * - release all inherited resources
+			 * - install forwarding_note_handler
+			 * - send to P2C the child pid
+			 * - start forwarding notes to the father
+			 */
+			switch(child = fork()){
+			case -1:
+				while(CHILD_READY(-2) == -1)
+					;
+				exits("rfork (child)");
+			case 0:
+				/* Beloved child here
+				 */
+				__libposix_setup_new_process();
+				return 0;
+			default:
+				release_inherited_resources();
+				*__libposix_sigchld_target_pid = father;
+				notify(forwarding_note_handler);
+				snprint(proxy_name, sizeof(proxy_name), "libposix signal proxy %d < %d", father, child);
+				while(CHILD_READY(child) == -1)
+					;
+				forward_wait_msg(father, proxy_name);
+			}
+		default:
+			while((child = CHILD_READY(-3)) == -1)
+				;
+			child = ~child;
+			if(child < 0){
+				while(C2P_READY(-2) == -1)
+					;
+				waitpid();
+				exits("rfork (child)");
+			}
+			release_inherited_resources();
+			*__libposix_sigchld_target_pid = child;
+			notify(forwarding_note_handler);
+			snprint(proxy_name, sizeof(proxy_name), "libposix signal proxy %d > %d", father, child);
+			while(C2P_READY(c2p) == -1)
+				;
+			forward_wait_msg(0, proxy_name);
+		}
+	default:
+		while((c2p = C2P_READY(-3)) == -1)
+			;
+		c2p = ~c2p;
+		if(c2p < 0){
+			waitpid();
+			return -1;
+		}
+		break;
+	}
+
+	/* TODO: register p2c among known children so that kill can
+	 * handle them properly.
+	 */
+
+	return p2c;
+}
+
+int
+libposix_emulate_SIGCHLD(void)
+{
+	extern int (*__libposix_fork)(int *errnop);
+	__libposix_fork = fork_with_sigchld;
+	return 1;
+}

sys/src/lib/posix/signals.c

@@ -161,7 +161,7 @@ terminated_by_signal(int sig)
 	exits(buf);
 }
 
-static int
+int
 send_control_msg(int pid, char *msg)
 {
 	int fd, n;