/*
   Copyright (C) 1993, 1994 Free Software Foundation

This file is part of the GNU Hurd.

The GNU Hurd is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

The GNU Hurd 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 General Public License
along with the GNU Hurd; see the file COPYING.  If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */

/* Written by Michael I. Bushnell.  */

#include "fshelp.h"

error_t
fshelp_acquire_lock (struct lock_box *box, int *user, struct mutex *mut,
		     int flags)
{
  if (!(flags & (LOCK_UN | LOCK_EX | LOCK_SH)))
    return 0;
  
  if ((flags & LOCK_UN)
      && (flags & (LOCK_SH | LOCK_EX)))
    return EINVAL;
  
  if (flags & LOCK_EX)
    flags &= ~LOCK_SH;
  
  /* flags now contains exactly one of LOCK_UN, LOCK_SH, or LOCK_EX.  */

  if (flags & LOCK_UN)
    {
      if (*user & LOCK_UN)
	return EBADF;
      assert (*user == box->type);
      assert (*user == LOCK_SH || *user == LOCK_EX);
      if (*user == LOCK_SH)
	{
	  if (!--box->shcount)
	    box->lock_type == LOCK_UN;
	}
      else if (*user == LOCK_EX)
	box->lock_type == LOCK_UN;
      
      if (box->lock_type == LOCK_UN && box->waiting)
	{
	  box->waiting = 0;
	  condition_broadcast (&box->wait);
	}
      *user = LOCK_UN;
    }
  else
    {
      /* If we have an exclusive lock, release it. */
      if (*user == LOCK_EX)
	{
	  *user = LOCK_UN;
	  box->type = LOCK_UN;
	  if (box->waiting)
	    {
	      box->waiting = 0;
	      condition_broadcast (&box->wait);
	    }
	}
      
      /* If there is an exclusive lock, wait for it to end. */
      while (lock->type == LOCK_EX)
	{
	  if (flags & LOCK_NB)
	    return EWOULDBLOCK;
	  box->waiting = 1;
	  condition_wait (&box->wait, mut);
	}

      /* If we have a shared lock, release it. */
      if (*user == LOCK_SH)
	{
	  *user = LOCK_UN;
	  if (!--box->shcount)
	    {
	      box->type = LOCK_UN;
	      if (box->waiting)
		{
		  box->waiting = 0;
		  condition_broadcast (&box->wait);
		}
	    }
	}
      
      assert ((flags & LOCK_SH) || (flags & LOCK_EX));
      if (flags & LOCK_SH)
	{
	  assert (box->type != LOCK_EX);
	  *user = LOCK_SH;
	  box->type = LOCK_SH;
	  box->shcount++;
	}
      else if (flags & LOCK_EX)
	{
	  /* Wait for any shared locks to finish. */
	  while (box->type == LOCK_SH)
	    {
	      if (flags & LOCK_NB)
		return EWOULDBLOCK;
	      else
		{
		  box->waiting = 1;
		  condition_wait (&box->wait, mut);
		}
	    }
	  box->type = LOCK_EX;
	  *user = LOCK_EX;
	}
    }
  return 0;
}