setpgid: support changing between process groups and doing it for other processes

kernel-src/sys/syscalls/setpid.c

@@ -12,10 +12,45 @@ syscallret_t syscall_setsid(context_t *) {
 
 syscallret_t syscall_setpgid(context_t *, pid_t pid, pid_t pgid) {
 	syscallret_t ret;
-	__assert(pid == 0 || pid == _cpu()->thread->proc->pid);
-	__assert(pgid == 0 || pgid == _cpu()->thread->proc->pid);
 
-	ret.errno = jobctl_newgroup(_cpu()->thread->proc);
-	ret.ret = ret.errno ? -1 : _cpu()->thread->proc->pid;
+	proc_t *proc = NULL;
+	if (pid == 0) {
+		proc = _cpu()->thread->proc;
+		PROC_HOLD(proc);
+	} else {
+		proc = sched_getprocfrompid(pid);
+	}
+
+	if (proc == NULL) {
+		ret.errno = ESRCH;
+		return ret;
+	}
+
+	proc_t *pgrp = NULL;
+	if (pgid == 0) {
+		pgrp = _cpu()->thread->proc;
+		PROC_HOLD(pgrp);
+	} else {
+		pgrp = sched_getprocfrompid(pgid);
+	}
+
+	if (pgrp == NULL) {
+		PROC_RELEASE(proc);
+		ret.errno = EPERM;
+		return ret;
+	}
+
+	if (pgid == pid || pgid == 0) {
+		// create new group for process
+		ret.errno = jobctl_newgroup(proc);
+	} else {
+		// switch process group
+		ret.errno = jobctl_changegroup(proc, pgrp);
+	}
+
+	PROC_RELEASE(pgrp);
+	PROC_RELEASE(proc);
+
+	ret.ret = ret.errno ? -1 : 0;
 	return ret;
 }