infect: Place sigchild handler on ictx

To track victim health state criu sets up the sigchild handler.
So will have to do the compel, but the ability to request for
own handler would be required.
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/include/parasite-syscall.h

@@ -29,6 +29,8 @@ struct thread_ctx {
 struct infect_ctx {
 	int	*p_sock;
 	unsigned long		flags;			/* fine-tune (e.g. faults) */
+
+	void (*child_handler)(int, siginfo_t *, void *);	/* hander for SIGCHLD deaths */
 };
 
 #define INFECT_NO_MEMFD		0x1	/* don't use memfd() */

criu/parasite-syscall.c

@@ -411,10 +411,10 @@ static void sigchld_handler(int signal, siginfo_t *siginfo, void *data)
 	exit(1);
 }
 
-static int setup_child_handler()
+static int setup_child_handler(struct parasite_ctl *ctl)
 {
 	struct sigaction sa = {
-		.sa_sigaction	= sigchld_handler,
+		.sa_sigaction	= ctl->ictx.child_handler,
 		.sa_flags	= SA_SIGINFO | SA_RESTART,
 	};
 
@@ -524,7 +524,7 @@ static int parasite_init_daemon(struct parasite_ctl *ctl)
 		goto err;
 
 	/* after this we can catch parasite errors in chld handler */
-	if (setup_child_handler())
+	if (setup_child_handler(ctl))
 		goto err;
 
 	regs = ctl->orig.regs;
@@ -1480,6 +1480,7 @@ struct parasite_ctl *parasite_infect_seized(pid_t pid, struct pstree_item *item,
 	if (!ctl)
 		return NULL;
 
+	ctl->ictx.child_handler = sigchld_handler;
 	ctl->ictx.p_sock = &dmpi(item)->netns->net.seqsk;
 
 	if (fault_injected(FI_NO_MEMFD))