/* Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <sysdep.h>
#include <errno.h>
#include <unistd.h>
#include <stdarg.h>
#include <sys/syscall.h>
#include <parlib/arch/atomic.h>
#include <ros/procdata.h>

/* This is a simple ev_q that ultimately triggers notif_pending on vcore 0 (due
 * to the IPI) and makes sure the process wakes up.
 *
 * This works for any bit messages, even if the process hasn't done any set up
 * yet, since the memory for the mbox is allocted by the kernel (procdata). */
struct event_mbox __simple_evbitmap = { .type = EV_MBOX_BITMAP, };
struct event_queue __ros_scp_simple_evq =
                  { .ev_mbox = &__simple_evbitmap,
                    .ev_flags = EVENT_WAKEUP | EVENT_IPI,
                    .ev_alert_pending = FALSE,
                    .ev_vcore = 0,
                    .ev_handler = 0 };

/* Helper, from u/p/event.c.  Keep it in sync.  (don't want to move this into
 * glibc yet). */
static bool register_evq(struct syscall *sysc, struct event_queue *ev_q)
{
	int old_flags;
	sysc->ev_q = ev_q;
	wrmb();	/* don't let that write pass any future reads (flags) */
	/* Try and set the SC_UEVENT flag (so the kernel knows to look at ev_q)
	 */
	do {
		/* no cmb() needed, the atomic_read will reread flags */
		old_flags = atomic_read(&sysc->flags);
		/* Spin if the kernel is mucking with syscall flags */
		while (old_flags & SC_K_LOCK)
			old_flags = atomic_read(&sysc->flags);
		/* If the kernel finishes while we are trying to sign up for an
		 * event, we need to bail out */
		if (old_flags & (SC_DONE | SC_PROGRESS)) {
			/* not necessary, but might help with bugs */
			sysc->ev_q = 0;
			return FALSE;
		}
	} while (!atomic_cas(&sysc->flags, old_flags, old_flags | SC_UEVENT));
	return TRUE;
}

/* Glibc initial blockon, usable before parlib code can init things (or if it
 * never can, like for RTLD).  As processes initialize further, they will use
 * different functions.
 *
 * In essence, we're in vcore context already.  For one, this function could be
 * called from a full SCP in vcore context.  For early processes, we are not
 * vcctx_ready.  Either way, we don't need to worry about the kernel forcing us
 * into vcore context and otherwise clearing notif_pending.  For those curious,
 * the old race was that the kernel sets notif pending after we register, then
 * we drop into VC ctx, clear notif pending, and yield. */
void __ros_early_syscall_blockon(struct syscall *sysc)
{
	/* For early SCPs, notif_pending will probably be false anyways.  For
	 * SCPs in VC ctx, it might be set.  Regardless, when we pop back up,
	 * notif_pending will be set (for a full SCP in VC ctx). */
	__procdata.vcore_preempt_data[0].notif_pending = FALSE;
	/* order register after clearing notif_pending, handled by register_evq
	 */
	/* Ask for a SYSCALL event when the sysc is done.  We don't need a
	 * handler, we just need the kernel to restart us from proc_yield.  If
	 * register fails, we're already done. */
	if (register_evq(sysc, &__ros_scp_simple_evq)) {
		/* Sending false for now - we want to signal proc code that we
		 * want to wait (piggybacking on the MCP meaning of this
		 * variable).  If notif_pending is set, the kernel will
		 * immediately return us. */
		__ros_syscall_noerrno(SYS_proc_yield, FALSE, 0, 0, 0, 0, 0);
	}
	/* For early SCPs, the kernel turns off notif_pending for us.  For SCPs
	 * in vcore context that blocked (should be rare!), it'll still be set.
	 * Other VC ctx code must handle it later. (could have coalesced notifs)
	 */
}

/* Function pointer for the blockon function.  MCPs need to switch to the parlib
 * blockon before becoming an MCP.  Default is the glibc SCP handler */
void (*ros_syscall_blockon)(struct syscall *sysc) = __ros_early_syscall_blockon;

/* Issue a single syscall and block into the 2LS until it completes */
static inline void __ros_syscall_sync(struct syscall *sysc)
{
	/* There is only one syscall in the syscall array when we want to do it
	 * synchronously */
	__ros_arch_syscall((long)sysc, 1);
	/* Don't proceed til we are done */
	while (!(atomic_read(&sysc->flags) & SC_DONE))
		ros_syscall_blockon(sysc);
	/* Need to wait til it is unlocked.  It's not really done until SC_DONE
	 * & !SC_K_LOCK. */
	while (atomic_read(&sysc->flags) & SC_K_LOCK)
		cpu_relax();
}
void ros_syscall_sync(struct syscall *sysc) {
	__ros_syscall_sync(sysc);
}
libc_hidden_def(ros_syscall_sync)

/* TODO: make variants of __ros_syscall() based on the number of args (0 - 6) */
/* These are simple synchronous system calls, built on top of the kernel's async
 * interface.  This version makes no assumptions about errno.  You usually don't
 * want this. */
static inline struct syscall
__ros_syscall_inline(unsigned int _num, long _a0, long _a1, long _a2, long _a3,
                     long _a4, long _a5)
{
	struct syscall sysc = {0};
	sysc.num = _num;
	sysc.ev_q = 0;
	sysc.arg0 = _a0;
	sysc.arg1 = _a1;
	sysc.arg2 = _a2;
	sysc.arg3 = _a3;
	sysc.arg4 = _a4;
	sysc.arg5 = _a5;
	__ros_syscall_sync(&sysc);
	return sysc;
}

long __ros_syscall_noerrno(unsigned int _num, long _a0, long _a1, long _a2,
                           long _a3, long _a4, long _a5)
{
	struct syscall sysc = __ros_syscall_inline(_num, _a0, _a1, _a2, _a3,
	                                           _a4, _a5);
	return sysc.retval;
}
libc_hidden_def(__ros_syscall_noerrno)

/* This version knows about errno and will handle it. */
long __ros_syscall_errno(unsigned int _num, long _a0, long _a1, long _a2,
                         long _a3, long _a4, long _a5)
{
	struct syscall sysc = __ros_syscall_inline(_num, _a0, _a1, _a2, _a3,
	                                           _a4, _a5);

	/* Consider calling syscall_retval_is_error() */
	if (__builtin_expect(sysc.err, 0)) {
		errno = sysc.err;
		memcpy(errstr(), sysc.errstr, MAX_ERRSTR_LEN);
	}
	return sysc.retval;
}
libc_hidden_def(__ros_syscall_errno)

long int syscall(long int num, ...)
{
	va_list vl;
	va_start(vl, num);
	long int a0 = va_arg(vl, long int);
	long int a1 = va_arg(vl, long int);
	long int a2 = va_arg(vl, long int);
	long int a3 = va_arg(vl, long int);
	long int a4 = va_arg(vl, long int);
	long int a5 = va_arg(vl, long int);
	va_end(vl);
	
	return ros_syscall(num, a0, a1, a2, a3, a4, a5);
}