How to send messages in PM server Minix - c

Question

So I'm trying to create a new system call on PM server. My question is, how can I send some kind of message to function.
in IPC server all I had to do is add my system call to the list, because all functions there were defined as (*func)(message *)
(...)/servers/ipc/main.c
static struct {
int type;
int (*func)(message *);
int reply; /* whether the reply action is passed through */
} ipc_calls[] = {
(...)
{ IPC_MYNEWSIGNAL, do_something, 1 },
};
but in PM in table.c functions are defined as
(...)/servers/pm/table.c
int (* const call_vec[NR_PM_CALLS])(void) = {
(...)
CALL(PM_GETSYSINFO) = do_getsysinfo
}
and if I try to pass function with signature
int do_something(message *m)
I will get error:
Incompatible pointer types: initializing int (*const)(void) with int (message *)
What is the correct way to create signal on PM server if I need to receive some kind of information?

Answer 1

As far as I understood from the question, you want to receive arguments inside the syscall handler. Let's take as an example the library function clock_settime from libc.
int clock_settime(clockid_t clock_id, const struct timespec *ts)
{
message m;
memset(&m, 0, sizeof(m));
m.m_lc_pm_time.clk_id = clock_id;
m.m_lc_pm_time.now = 1; /* set time immediately. don't use adjtime() method. */
m.m_lc_pm_time.sec = ts->tv_sec;
m.m_lc_pm_time.nsec = ts->tv_nsec;
if (_syscall(PM_PROC_NR, PM_CLOCK_SETTIME, &m) < 0)
return -1;
return 0;
}
As you can see it writes the args inside message struct and passes to _syscall. OK, now have a look at syscall handler for PM_CLOCK_SETTIME which is mounted in table.c.
int do_gettime()
{
clock_t ticks, realtime, clock;
time_t boottime;
int s;
if ( (s=getuptime(&ticks, &realtime, &boottime)) != OK)
panic("do_time couldn't get uptime: %d", s);
switch (m_in.m_lc_pm_time.clk_id) {
case CLOCK_REALTIME:
clock = realtime;
break;
case CLOCK_MONOTONIC:
clock = ticks;
break;
default:
return EINVAL; /* invalid/unsupported clock_id */
}
mp->mp_reply.m_pm_lc_time.sec = boottime + (clock / system_hz);
mp->mp_reply.m_pm_lc_time.nsec =
(uint32_t) ((clock % system_hz) * 1000000000ULL / system_hz);
return(OK);
}
It becomes clear that the argument is a global variable named m_in. A little bit more search shows that it comes from glo.h
/* The parameters of the call are kept here. */
EXTERN message m_in; /* the incoming message itself is kept here. */
I suppose that MINIX will handle setting and accessing the global variable, so you don't need to explicitly write to it.
Have a look at point 7 Passing a parameter to a system call here. To understand how to compile the kernel correctly refer to this post.