path: root/libfshelp/rlock-tweak.c

/*
   Copyright (C) 2001, 2014-2019 Free Software Foundation

   Written by Neal H Walfield <neal@cs.uml.edu>

   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.  If not, see <http://www.gnu.org/licenses/>.  */

#include "fshelp.h"
#include "rlock.h"

#include <assert.h>
#include <stdlib.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <hurd.h>
#include <hurd/process.h>

static inline long overlap (loff_t start, loff_t len, struct rlock_list *l)
{
  return ((len == 0 && l->len == 0)
	  || (len == 0 && l->start + l->len > start)
	  || (l->len == 0 && start + len > l->start)
	  || (l->start + l->len > start && start + len > l->start));
}

error_t
fshelp_rlock_tweak (struct rlock_box *box, pthread_mutex_t *mutex,
		    struct rlock_peropen *po, int open_mode,
		    loff_t obj_size, loff_t cur_pointer, int cmd,
		    struct flock64 *lock, mach_port_t rendezvous)
{
  inline struct rlock_list *
  gen_lock (loff_t start, loff_t len, int type)
    {
      struct rlock_list *l = malloc (sizeof (struct rlock_list));
      if (! l)
        return NULL;

      rlock_list_init (po, l);
      l->start = start;
      l->len = len;
      l->type = type;

      list_link (po, po->locks, l);
      list_link (node, &box->locks, l);
      return l;
    }

  inline void
  rele_lock (struct rlock_list *l, int wake_waiters)
    {
      list_unlink (po, l);
      list_unlink (node, l);

      if (wake_waiters && l->waiting)
	pthread_cond_broadcast (&l->wait);

      pthread_cond_destroy(&l->wait);
      free (l);
    }

  error_t
  unlock_region (loff_t start, loff_t len)
    {
      struct rlock_list *l;

      for (l = *po->locks; l; l = l->po.next)
	{
	  if (l->len != 0 && l->start + l->len <= start)
	    /* We start after the locked region ends.  */
	    {
	      continue;
	    }
	  else if (len != 0 && start + len <= l->start)
	    /* We end before this region starts.  Since we are sorted,
	       we are done.  */
	    {
	      return 0;
	    }
	  else if (start <= l->start
		   && (len == 0
		       || (l->len != 0
			   && l->start + l->len <= start + len)))
	    /* We wrap the locked region; consume it.  */
	    {
	      rele_lock (l, 1);
	      continue;
	    }
	  else if (start <= l->start
		   && (l->len == 0
		       || (l->start < start + len)))
	    /* The locked region is having its head unlocked.  */
	    {
	      assert (len != 0);
	      assert (l->len == 0 || start + len < l->start + l->len);

	      if (l->len != 0)
		l->len -= start + len - l->start;
	      l->start = start + len;

	      if (l->waiting)
		{
		  l->waiting = 0;
		  pthread_cond_broadcast (&l->wait);
		}
	    }
	  else if (l->start < start
		   && ((start < l->start + l->len
		        && (len == 0 || l->start + l->len <= start + len))
		       || (len == 0 && l->len == 0)))
	    /* The locked region needs its tail unlocked.  */
	    {
	      assert (len == 0
		      || (l->len != 0 && l->start + l->len <= start + len));

	      l->len = start - l->start;

	      if (l->waiting)
		{
		  l->waiting = 0;
		  pthread_cond_broadcast (&l->wait);
		}

	      continue;
	    }
	  else if (l->start < start
		   && (l->len == 0
		       || (len != 0
			   && start + len < l->start + l->len)))
	    /* The locked region wraps us (absolutely); crave out the
	       middle.  */
	    {
	      struct rlock_list *upper_half;

	      assert (len != 0);

	      upper_half = gen_lock (start + len,
				     l->len
				       ? l->start + l->len - (start + len)
				       : 0,
				     l->type);
	      if (! upper_half)
		return ENOMEM;

	      l->len = start - l->start;

	      return 0;
	    }
	  else if (start < l->start
		   && len != 0
		   && start + len <= l->start)
	    /* The locked region starts after our end.  */
	    {
	      return 0;
	    }
	  else
	    assert (! "Impossible!");
	}

      return 0;
    }

  inline struct rlock_list *
  find_conflict (loff_t start, loff_t len, int type)
    {
      struct rlock_list *l;

      for (l = box->locks; l; l = l->node.next)
	{
	  if (po->locks == l->po_id)
	    continue;

	  if ((l->type == F_WRLCK || type == F_WRLCK)
	      && overlap (start, len, l))
	    return l;
	}

      return NULL;
    }

  inline error_t
  merge_in (loff_t start, loff_t len, int type)
    {
      struct rlock_list *l;

      for (l = *po->locks; l; l = l->po.next)
	{
	  if (l->start <= start
	      && (l->len == 0
		  || (len != 0
		      && start + len <= l->start + l->len)))
	    /* Our start and end fall between the locked region
	       (i.e. we are wrapped).  */
	    {
	      struct rlock_list *head = NULL;
	      struct rlock_list *tail = NULL;

	      if (type == l->type || type == F_RDLCK)
		return 0;

	      assert (type == F_WRLCK && l->type == F_RDLCK);

	      if (l->start < start)
	        /* We need to split the head off.  */
		{
		  head = gen_lock (l->start, start - l->start, F_RDLCK);
		  if (! head)
		    return ENOMEM;
		}

	      if ((l->len == 0 && len != 0)
		  || start + len < l->start + l->len)
		/* We need to split the tail off.  */
	        {
		  tail = gen_lock (start + len,
				   l->len
				     ? l->start + l->len - (start + len)
				     : 0,
				   F_RDLCK);
		  if (! tail)
		    {
		      if (head)
			rele_lock (head, 0);
		      return ENOMEM;
		    }
		}

	      if (head)
		{
		  loff_t shift = start - l->start;

		  if (l->len != 0)
		    l->len -= shift;
		  l->start += shift;
		}

	      if (tail)
	        l->len = tail->start - l->start;

	      if (! tail)
		/* There is a chance we can merge some more.  */
	        {
		  start = l->start;
		  len = l->len;

		  rele_lock (l, 1);
		  continue;
		}
	      else
	        {
	          l->type = F_WRLCK;
		  return 0;
		}
	    }
	  else if (start <= l->start
		   && (len == 0
		       || (l->len != 0
			   && l->start + l->len <= start + len)))
	    /* We fully wrap the locked region.  */
	    {
	      struct rlock_list *head;

	      if (type == l->type || type == F_WRLCK)
		{
		  rele_lock (l, 1);
		  /* Try to merge more.  */
		  continue;
		}

	      assert (type == F_RDLCK && l->type == F_WRLCK);

	      if (start < l->start)
		/* Generate our head.  */
		{
		  head = gen_lock (start, l->start - start, F_RDLCK);
		  if (! head)
		    return ENOMEM;
		}
	      else
		head = NULL;

	      if (l->len != 0
		  && (len == 0 || l->start + l->len < start + len))
		/* We have a tail, try to merge it also.  */
		{
		  if (len != 0)
		    len = start + len - (l->start + l->len);
		  start = l->start + l->len;

		  continue;
		}
	      else
		/* Our end is silently consumed.  */
	        {
		  /* If we do not have a tail, we must have had a head
		     (if not, the first case would have caught us).  */
		  assert (head);
	          return 0;
		}
	    }
	  else if (l->start < start && start <= l->start + l->len
		   && (len == 0 || start + len > l->start + l->len))
	    /* Our start falls within the locked region or exactly one
	       byte after it and our end falls beyond it.  We know that
	       we cannot consume the entire region.  */
	    {
	      assert (l->len != 0);

	      if (type == l->type)
		/* Merge the two areas.  */
		{
		  if (len != 0)
		    len += start - l->start;
		  start = l->start;

		  rele_lock (l, 1);

		  /* Try to merge in more.  */
		  continue;
		}
	      else if (start == l->start + l->len)
		  /* We fall just after the locked region (there is no
		     intersection) and we are not the same type.  */
		{
		  /* The is nothing to do except continue the search.  */
		  continue;
		}
	      else if (type == F_WRLCK)
		/* We comsume the intersection.  */
		{
		  assert (l->type == F_RDLCK);

		  l->len -= l->start + l->len - start;

		  /* Don't create the lock now; we might be able to
		     consume more locks.  */
		  continue;
		}
	      else
		/* We are dominated; the locked region comsumes the
		   intersection.  */
		{
		  loff_t common = l->start + l->len - start;

		  assert (type == F_RDLCK);
		  assert (l->type == F_WRLCK);

		  start += common;
		  if (len != 0)
		    len -= common;

		  /* There is still a chance that we can consume more
		     locks.  */
		  continue;
		}
	    }
	  else if (start < l->start
		   && (l->len == 0
		       || l->start <= start + len))
	    /* Our start falls before the locked region and our
	       end falls (inclusively) between it or one byte before it.
	       Note, we know that we do not consume the entire locked
	       area.  */
	    {
	      assert (len != 0);
	      assert (l->len == 0 || start + len < l->start + l->len);

	      if (type == l->type)
		/* Merge the two areas.  */
		{
		  if (l->len)
		    l->len += l->start - start;
		  l->start = start;
		  return 0;
		}
	      else if (l->start == start + len)
		/* Our end falls just before the start of the locked
		   region, however, we are not the same type.  Just
		   insert it.  */
		{
		  continue;
		}
	      else if (type == F_WRLCK)
		/* We consume the intersection.  */
		{
		  struct rlock_list *e;
		  loff_t common = start + len - l->start;

		  assert (l->type == F_RDLCK);

		  e = gen_lock (start, len, F_WRLCK);
		  if (! e)
		    return ENOMEM;

		  if (l->len)
		    l->len -= common;
		  l->start += common;

		  return 0;
		}
	      else
		/* The locked region comsumes the intersection.  */
		{
		  struct rlock_list *e;

		  assert (l->type == F_WRLCK);
		  assert (type == F_RDLCK);

		  e = gen_lock (start, l->start - start, F_RDLCK);
		  if (! e)
		    return ENOMEM;

		  return 0;
		}
	    }
	  else if (start < l->start
		   && len != 0
		   && start + len <= l->start)
	    /* We start and end before this locked region.  Therefore,
	       knowing that the list is sorted, the merge is done.  */
	    {
	      break;
	    }
	  else
	    /* We start beyond the end of this locked region.  */
	    {
	      assert (start >= l->start + l->len);
	      assert (l->len != 0);
	      continue;
	    }
	}

      return (gen_lock (start, len, type) ? 0 : ENOMEM);
    }

  struct rlock_list *e;
  loff_t start;
  loff_t len;

  if (rendezvous != MACH_PORT_NULL)
    return EOPNOTSUPP;

  if (cmd != F_GETLK64
      && cmd != F_SETLK64
      && cmd != F_SETLKW64)
    return EOPNOTSUPP;

  if (lock->l_type != F_UNLCK
      && lock->l_type != F_RDLCK
      && lock->l_type != F_WRLCK)
    return EINVAL;

  if (lock->l_type == F_UNLCK)
    {
      if (cmd == F_SETLKW64)
        /* If we are unlocking a region, map F_SETLKW64 to F_SETLK64.  */
        cmd = F_SETLK64;
      else if (cmd == F_GETLK64)
	/* Impossible!  */
	return EINVAL;
    }

  /* From POSIX-1003.1: A request for an exclusive lock shall fail if
     the file descriptor was not opened with write access. */
  if ((cmd == F_SETLK64 || cmd == F_SETLKW64 )
      && lock->l_type == F_WRLCK && !(open_mode & O_WRITE))
    return EBADF;

  switch (lock->l_whence)
    {
    case SEEK_SET:
      start = lock->l_start;
      break;

    case SEEK_CUR:
      start = cur_pointer + lock->l_start;
      break;

    case SEEK_END:
      start = obj_size + lock->l_start;
      break;

    default:
      return EINVAL;
    }

  if (start < 0)
    return EINVAL;

  len = lock->l_len;
  if (len < 0)
    return EINVAL;

  if (cmd == F_SETLK64 && lock->l_type == F_UNLCK)
    return unlock_region (start, len);

retry:
  e = find_conflict (start, len, lock->l_type);

  if (cmd == F_GETLK64)
    {
      if (e)
	{
	  lock->l_type = e->type;
	  lock->l_start = e->start;
	  lock->l_whence = SEEK_SET;
	  lock->l_len = e->len;
	  /* XXX: This will be fixed when the proc_{user,server}_identify
             RPCs are implemented */
	  lock->l_pid = -1;
	  return 0;
	}
      else
	{
	  lock->l_type = F_UNLCK;
	  return 0;
	}
    }
  else
    {
      assert (cmd == F_SETLK64 || cmd == F_SETLKW64);

      if (! e)
	return merge_in (start, len, lock->l_type);
      else
        {
	  if (cmd == F_SETLKW64)
	    {
	      e->waiting = 1;
	      if (pthread_hurd_cond_wait_np (&e->wait, mutex))
	        return EINTR;
	      goto retry;
	    }
	  else
	    return EAGAIN;
	}
    }
}