path: root/fatfs/pager.c

/* pager.c - Pager for fatfs.
   Copyright (C) 1997, 1999, 2002, 2003 Free Software Foundation, Inc.
   Written by Thomas Bushnell, n/BSG and Marcus Brinkmann.

   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 this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111, USA. */

#include <string.h>
#include <hurd/store.h>
#include "fatfs.h"

/* A ports bucket to hold pager ports.  */
struct port_bucket *pager_bucket;

/* Mapped image of the FAT.  */
void *fat_image;

pthread_spinlock_t node_to_page_lock = PTHREAD_SPINLOCK_INITIALIZER;

#ifdef DONT_CACHE_MEMORY_OBJECTS
#define MAY_CACHE 0
#else
#define MAY_CACHE 1
#endif

#define STAT_INC(field) (void) 0

#define MAX_FREE_PAGE_BUFS 32

static pthread_spinlock_t free_page_bufs_lock = PTHREAD_SPINLOCK_INITIALIZER;
static void *free_page_bufs = 0;
static int num_free_page_bufs = 0;

/* Returns a single page page-aligned buffer.  */
static void *
get_page_buf ()
{
  void *buf;

  pthread_spin_lock (&free_page_bufs_lock);

  buf = free_page_bufs;
  if (buf == 0)
    {
      pthread_spin_unlock (&free_page_bufs_lock);
      buf = mmap (0, vm_page_size, PROT_READ|PROT_WRITE, MAP_ANON, 0, 0);
      if (buf == (void *) -1)
        buf = 0;
    }
  else
    {
      free_page_bufs = *(void **)buf;
      num_free_page_bufs--;
      pthread_spin_unlock (&free_page_bufs_lock);
    }

  return buf;
}

/* Frees a block returned by get_page_buf.  */
static void
free_page_buf (void *buf)
{
  pthread_spin_lock (&free_page_bufs_lock);
  if (num_free_page_bufs < MAX_FREE_PAGE_BUFS)
    {
      *(void **)buf = free_page_bufs;
      free_page_bufs = buf;
      num_free_page_bufs++;
      pthread_spin_unlock (&free_page_bufs_lock);
    }
  else
    {
      pthread_spin_unlock (&free_page_bufs_lock);
      munmap (buf, vm_page_size);
    }
}

/* Find the location on disk of page OFFSET in NODE.  Return the disk
   cluster in CLUSTER. If *LOCK is 0, then it a reader
   lock is acquired on NODE's ALLOC_LOCK before doing anything, and left
   locked after return -- even if an error is returned.  0 on success or an
   error code otherwise is returned.  */
static error_t
find_cluster (struct node *node, vm_offset_t offset,
	      cluster_t *cluster, pthread_rwlock_t **lock)
{
  error_t err;

  if (!*lock)
    {
      *lock = &node->dn->alloc_lock;
      pthread_rwlock_rdlock (*lock);
    }

  if (round_cluster (offset) > node->allocsize)
    return EIO;

  err = fat_getcluster (node, offset >> log2_bytes_per_cluster, 0, cluster);

  return err;
}

/* Read one page for the root dir pager at offset PAGE, into BUF.  This
   may need to select several filesystem sectors to satisfy one page.
   Assumes that fat_type is FAT12 or FAT16, and that vm_page_size is a
   power of two multiple of bytes_per_sector (which happens to be true).
*/
static error_t
root_dir_pager_read_page (vm_offset_t page, void **buf, int *writelock)
{
  error_t err;
  daddr_t addr;
  int overrun = 0;
  size_t read = 0;

  *writelock = 0;

  if (page >= diskfs_root_node->allocsize)
    {
      return EIO;
    }
  
  pthread_rwlock_rdlock (&diskfs_root_node->dn->alloc_lock);

  addr = first_root_dir_byte + page;
  if (page + vm_page_size > diskfs_root_node->allocsize)
    overrun = page + vm_page_size - diskfs_root_node->allocsize;

  err = store_read (store, addr >> store->log2_block_size,
		    vm_page_size, (void **) buf, &read);
  if (!err && read != vm_page_size)
    err = EIO;
  
  pthread_rwlock_unlock (&diskfs_root_node->dn->alloc_lock);

  if (overrun)
    bzero ((void *) *buf + vm_page_size - overrun, overrun);

  return err;
}

/* Read one page for the pager backing NODE at offset PAGE, into BUF.  This
   may need to select only a part of a filesystem block to satisfy one page.
   Assumes that bytes_per_cluster is a power of two multiple of vm_page_size.
*/
static error_t
file_pager_read_small_page (struct node *node, vm_offset_t page,
			    void **buf, int *writelock)
{
  error_t err;
  pthread_rwlock_t *lock = NULL;
  cluster_t cluster;
  size_t read = 0;

  *writelock = 0;

  if (page >= node->allocsize)
    {
      return EIO;
    }

  err = find_cluster (node, page, &cluster, &lock);

  if (!err)
    {
      err = store_read (store,
			FAT_FIRST_CLUSTER_BLOCK(cluster)
			+ ((page % bytes_per_cluster)
			  >> store->log2_block_size),
			vm_page_size, (void **) buf, &read);

      if (read != vm_page_size)
	err = EIO;
    }

  if (lock)
    pthread_rwlock_unlock (lock);

  return err;
}

/* Read one page for the pager backing NODE at offset PAGE, into BUF.  This
   may need to read several filesystem blocks to satisfy one page, and tries
   to consolidate the i/o if possible.
   Assumes that vm_page_size is a power of two multiple of bytes_per_cluster.
*/
static error_t
file_pager_read_huge_page (struct node *node, vm_offset_t page,
			   void **buf, int *writelock)
{
  error_t err;
  int offs = 0;
  pthread_rwlock_t *lock = NULL;
  int left = vm_page_size;
  cluster_t pending_clusters = 0;
  int num_pending_clusters = 0;

  /* Read the NUM_PENDING_CLUSTERS cluster in PENDING_CLUSTERS, into the buffer
     pointed to by BUF (allocating it if necessary) at offset OFFS.  OFFS in
     adjusted by the amount read, and NUM_PENDING_CLUSTERS is zeroed.  Any read
     error is returned.  */
  error_t do_pending_reads ()
    {
      if (num_pending_clusters > 0)
        {
          size_t dev_block = FAT_FIRST_CLUSTER_BLOCK(pending_clusters);
          size_t amount = num_pending_clusters << log2_bytes_per_cluster;
	  /* The buffer we try to read into; on the first read, we pass in a
	     size of zero, so that the read is guaranteed to allocate a new
	     buffer, otherwise, we try to read directly into the tail of the
	     buffer we've already got.  */
	  void *new_buf = *buf + offs;
	  size_t new_len = offs == 0 ? 0 : vm_page_size - offs;

          STAT_INC (file_pagein_reads);
	  
	  err = store_read (store, dev_block, amount, &new_buf, &new_len);
	  if (err)
	    return err;
	  else if (amount != new_len)
	    return EIO;

	  if (new_buf != *buf + offs)
	    {
	      /* The read went into a different buffer than the one we
		 passed. */
	      if (offs == 0)
		/* First read, make the returned page be our buffer.  */
		*buf = new_buf;
	      else
		/* We've already got some buffer, so copy into it.  */
		{
		  memcpy (*buf + offs, new_buf, new_len);
                  free_page_buf (new_buf); /* Return NEW_BUF to our pool.  */
                  STAT_INC (file_pagein_freed_bufs);
		}
	    }
	  
	  offs += new_len;
	  num_pending_clusters = 0;
	}

      return 0;
    }

  STAT_INC (file_pageins);
 
  *writelock = 0;

  if (page >= node->allocsize)
    {
      err = EIO;
      left = 0;
    }
  else if (page + left > node->allocsize)
      left = node->allocsize - page;

  while (left > 0)
    {
      cluster_t cluster;

      err = find_cluster (node, page, &cluster, &lock);
      if (err)
        break;

      if (cluster != pending_clusters + num_pending_clusters)
        {
          err = do_pending_reads ();
          if (err)
            break;
          pending_clusters = cluster;
        }

      num_pending_clusters++;
      
      page += bytes_per_cluster;
      left -= bytes_per_cluster;
    }

  if (!err && num_pending_clusters > 0)
    err = do_pending_reads();

  if (lock)
    pthread_rwlock_unlock (lock);

  return err;
}

struct pending_clusters
  {
    /* The cluster number of the first of the clusters.  */
    cluster_t cluster;
    /* How many clusters we have.  */
    loff_t num;
    /* A (page-aligned) buffer pointing to the data we're dealing with.  */
    void *buf;
    /* And an offset into BUF.  */
    int offs;
};

/* Write the any pending clusters in PC.  */
static error_t
pending_clusters_write (struct pending_clusters *pc)
{
  if (pc->num > 0)
    {
      error_t err;
      size_t dev_block = FAT_FIRST_CLUSTER_BLOCK(pc->cluster);

      size_t length = pc->num << log2_bytes_per_cluster, amount;

      if (pc->offs > 0)
        /* Put what we're going to write into a page-aligned buffer.  */
        {
          void *page_buf = get_page_buf ();
          memcpy ((void *) page_buf, pc->buf + pc->offs, length);
          err = store_write (store, dev_block, page_buf, length, &amount);
          free_page_buf (page_buf);
        }
      else
        err = store_write (store, dev_block, pc->buf, length, &amount);
      if (err)
        return err;
      else if (amount != length)
        return EIO;

      pc->offs += length;
      pc->num = 0;
    }

  return 0;
}

static void
pending_clusters_init (struct pending_clusters *pc, void *buf)
{
  pc->buf = buf;
  pc->cluster = 0;
  pc->num = 0;
  pc->offs = 0;
}

/* Add the disk cluster CLUSTER to the list of destination disk clusters pending in
   PC.  */
static error_t
pending_clusters_add (struct pending_clusters *pc, cluster_t cluster)
{
  if (cluster != pc->cluster + pc->num)
    {
      error_t err = pending_clusters_write (pc);
      if (err)
        return err;
      pc->cluster = cluster;
    }
  pc->num++;
  return 0;
}

/* Write one page for the pager backing NODE, at offset PAGE, into BUF.  This
   may need to write several filesystem blocks to satisfy one page, and tries
   to consolidate the i/o if possible.
   Assumes that vm_page_size is a power of two multiple of bytes_per_cluster. 
*/
static error_t
file_pager_write_huge_page (struct node *node, vm_offset_t offset, void *buf)
{
  error_t err = 0;
  struct pending_clusters pc;
  pthread_rwlock_t *lock = &node->dn->alloc_lock;
  cluster_t cluster;
  int left = vm_page_size;

  pending_clusters_init (&pc, buf);

  /* Holding NODE->dn->alloc_lock effectively locks NODE->allocsize,
     at least for the cases we care about: pager_unlock_page,
     diskfs_grow and diskfs_truncate.  */
  pthread_rwlock_rdlock (&node->dn->alloc_lock);

  if (offset >= node->allocsize)
    left = 0;
  else if (offset + left > node->allocsize)
    left = node->allocsize - offset;

  STAT_INC (file_pageouts);

  while (left > 0)
    {
      err = find_cluster (node, offset, &cluster, &lock);
      if (err)
        break;
      pending_clusters_add (&pc, cluster);
      offset += bytes_per_cluster;
      left -= bytes_per_cluster;
    }

  if (!err)
    pending_clusters_write (&pc);

  pthread_rwlock_unlock (&node->dn->alloc_lock);

  return err;
}

/* Write one page for the root dir pager, at offset OFFSET, into BUF.  This
   may need to write several filesystem blocks to satisfy one page, and tries
   to consolidate the i/o if possible.
   Assumes that fat_type is FAT12 or FAT16 and that vm_page_size is a
   power of two multiple of bytes_per_sector.
*/
static error_t
root_dir_pager_write_page (vm_offset_t offset, void *buf)
{
  error_t err;
  daddr_t addr;
  size_t length;
  size_t write = 0;

  if (offset >= diskfs_root_node->allocsize)
    return 0;

  /* Holding NODE->dn->alloc_lock effectively locks NODE->allocsize,
     at least for the cases we care about: pager_unlock_page,
     diskfs_grow and diskfs_truncate.  */
  pthread_rwlock_rdlock (&diskfs_root_node->dn->alloc_lock);

  addr = first_root_dir_byte + offset;

  if (offset + vm_page_size > diskfs_root_node->allocsize)
    length = diskfs_root_node->allocsize - offset;
  else
    length = vm_page_size;

  err = store_write (store, addr >> store->log2_block_size, (void **) buf,
		     length, &write);
  if (!err && write != length)
    err = EIO;

  pthread_rwlock_unlock (&diskfs_root_node->dn->alloc_lock);

  return err;
}

/* Write one page for the pager backing NODE, at offset OFFSET, into BUF.  This
   may need to write several filesystem blocks to satisfy one page, and tries
   to consolidate the i/o if possible.
   Assumes that bytes_per_cluster is a power of two multiple of vm_page_size.
*/
static error_t
file_pager_write_small_page (struct node *node, vm_offset_t offset, void *buf)
{
  error_t err;
  pthread_rwlock_t *lock = NULL;
  cluster_t cluster;
  size_t write = 0;

  if (offset >= node->allocsize)
    return 0;

  /* Holding NODE->dn->alloc_lock effectively locks NODE->allocsize,
     at least for the cases we care about: pager_unlock_page,
     diskfs_grow and diskfs_truncate.  */
  pthread_rwlock_rdlock (&node->dn->alloc_lock);

  err = find_cluster (node, offset, &cluster, &lock);

  if (!err)
    {
      err = store_write (store, FAT_FIRST_CLUSTER_BLOCK(cluster)
			+ ((offset % bytes_per_cluster)
			   >> store->log2_block_size),
			(void **) buf, vm_page_size, &write);
      if (write != vm_page_size)
	err = EIO;
    }

  if (lock)
    pthread_rwlock_unlock (lock);

  return err;
}

static error_t
fat_pager_read_page (vm_offset_t page, void **buf, int *writelock)
{
  error_t err;
  size_t length = vm_page_size, read = 0;
  vm_size_t fat_end = bytes_per_sector * sectors_per_fat;

  if (page + vm_page_size > fat_end)
    length = fat_end - page;

  page += first_fat_sector * bytes_per_sector;
  err = store_read (store, page >> store->log2_block_size, length, buf, &read);
  if (read != length)
    return EIO;
  if (!err && length != vm_page_size)
    memset ((void *)(*buf + length), 0, vm_page_size - length);

  *writelock = 0;

  return err;
}

static error_t
fat_pager_write_page (vm_offset_t page, void *buf)
{
  error_t err = 0;
  size_t length = vm_page_size, amount;
  vm_size_t fat_end = bytes_per_sector * sectors_per_fat;

  if (page + vm_page_size > fat_end)
    length = fat_end - page;

  page += first_fat_sector * bytes_per_sector;
  err = store_write (store, page >> store->log2_block_size,
		     buf, length, &amount);
  if (!err && length != amount)
    err = EIO;

  return err;
}

/* Satisfy a pager read request for either the disk pager or file pager
   PAGER, to the page at offset PAGE into BUF.  WRITELOCK should be set if
   the pager should make the page writeable.  */
error_t
pager_read_page (struct user_pager_info *pager, vm_offset_t page,
                 vm_address_t *buf, int *writelock)
{
  if (pager->type == FAT)
    return fat_pager_read_page (page, (void **)buf, writelock);
  else
    {
      if (pager->node == diskfs_root_node
	  && (fat_type == FAT12 || fat_type == FAT16))
	return root_dir_pager_read_page (page, (void **)buf, writelock);
      else
	{
	  if (bytes_per_cluster < vm_page_size)
	    return file_pager_read_huge_page (pager->node, page,
					      (void **)buf, writelock);
	  else
	    return file_pager_read_small_page (pager->node, page,
					       (void **)buf, writelock);
	}
    }
}

/* Satisfy a pager write request for either the disk pager or file pager
   PAGER, from the page at offset PAGE from BUF.  */
error_t
pager_write_page (struct user_pager_info *pager, vm_offset_t page,
                  vm_address_t buf)
{
  if (pager->type == FAT)
    return fat_pager_write_page (page, (void *)buf);
  else
    {
      if (pager->node == diskfs_root_node
	  && (fat_type == FAT12 || fat_type == FAT16))
	return root_dir_pager_write_page (page, (void *)buf);
      else
	{
	  if (bytes_per_cluster < vm_page_size)
	    return file_pager_write_huge_page (pager->node, page,
					       (void *)buf);
	  else
	    return file_pager_write_small_page (pager->node, page,
						(void *)buf);
	}
    }
}

/* Make page PAGE writable, at least up to ALLOCSIZE.  */
error_t
pager_unlock_page (struct user_pager_info *pager,
		   vm_offset_t page)
{
  /* All pages are writeable. The disk pages anyway, and the file
     pages because blocks are directly allocated in diskfs_grow.  */
  return 0;
}

/* Grow the disk allocated to locked node NODE to be at least SIZE
   bytes, and set NODE->allocsize to the actual allocated size.  (If
   the allocated size is already SIZE bytes, do nothing.)  CRED
   identifies the user responsible for the call.  Note that this will
   only be called for real files, so there is no need to be careful
   about the root dir node on FAT12/16.  */
error_t
diskfs_grow (struct node *node, loff_t size, struct protid *cred)
{
  diskfs_check_readonly ();
  assert (!diskfs_readonly);
  
  if (size > node->allocsize)
    {
      error_t err = 0;
      loff_t old_size;
      volatile loff_t new_size;
      volatile cluster_t end_cluster;
      cluster_t new_end_cluster;
      struct disknode *dn = node->dn;

      pthread_rwlock_wrlock (&dn->alloc_lock);

      old_size = node->allocsize;
      new_size = ((size + bytes_per_cluster - 1) >> log2_bytes_per_cluster)
						 << log2_bytes_per_cluster;

      /* The first unallocated clusters after the old and new ends of
         the file, respectively.  */
      end_cluster = old_size >> log2_bytes_per_cluster;
      new_end_cluster = new_size >> log2_bytes_per_cluster;

      if (new_end_cluster > end_cluster)
        {
	  err = diskfs_catch_exception ();
	  while (!err && end_cluster < new_end_cluster)
	    {
	      cluster_t disk_cluster;
	      err = fat_getcluster (node, end_cluster++, 1, &disk_cluster);
	    }
	  diskfs_end_catch_exception ();

	  if (err)
	    /* Reflect how much we allocated successfully.  */
	    new_size = (end_cluster - 1) >> log2_bytes_per_cluster;
	}
      
      STAT_INC (file_grows);

      node->allocsize = new_size;

      pthread_rwlock_unlock (&dn->alloc_lock);

      return err;
    }
  else
    return 0;
}

/* This syncs a single file (NODE) to disk.  Wait for all I/O to
   complete if WAIT is set.  NODE->lock must be held.  */
void
diskfs_file_update (struct node *node, int wait)
{
  struct pager *pager;

  pthread_spin_lock (&node_to_page_lock);
  pager = node->dn->pager;
  if (pager)
    ports_port_ref (pager);
  pthread_spin_unlock (&node_to_page_lock);

  if (pager)
    {
      pager_sync (pager, wait);
      ports_port_deref (pager);
    }

  diskfs_node_update (node, wait);
}

/* Invalidate any pager data associated with NODE.  */
void
flush_node_pager (struct node *node)
{
  struct pager *pager;
  struct disknode *dn = node->dn;

  pthread_spin_lock (&node_to_page_lock);
  pager = dn->pager;
  if (pager)
    ports_port_ref (pager);
  pthread_spin_unlock (&node_to_page_lock);

  if (pager)
    {
      pager_flush (pager, 1);
      ports_port_deref (pager);
    }
}

/* Return in *OFFSET and *SIZE the minimum valid address the pager
   will accept and the size of the object.  */
inline error_t
pager_report_extent (struct user_pager_info *pager,
                     vm_address_t *offset, vm_size_t *size)
{
  assert (pager->type == FAT || pager->type == FILE_DATA);

  *offset = 0;

  if (pager->type == FAT)
    *size = bytes_per_sector * sectors_per_fat;
  else
    *size = pager->node->allocsize;

  return 0;
}

/* This is called when a pager is being deallocated after all extant
   send rights have been destroyed.  */
void
pager_clear_user_data (struct user_pager_info *upi)
{
  if (upi->type == FILE_DATA)
    {
      struct pager *pager;
      
      pthread_spin_lock (&node_to_page_lock);
      pager = upi->node->dn->pager;
      if (pager && pager_get_upi (pager) == upi)
	upi->node->dn->pager = 0;
      pthread_spin_unlock (&node_to_page_lock);
      
      diskfs_nrele_light (upi->node);
    }
  
  free (upi);
}

/* This will be called when the ports library wants to drop weak
   references.  The pager library creates no weak references itself.
   If the user doesn't either, then it's OK for this function to do
   nothing.  */
void
pager_dropweak (struct user_pager_info *p __attribute__ ((unused)))
{
}

/* Create the disk pager.  */
void
create_fat_pager (void)
{
  struct user_pager_info *upi = malloc (sizeof (struct user_pager_info));
  upi->type = FAT;
  pager_bucket = ports_create_bucket ();
  diskfs_start_disk_pager (upi, pager_bucket, MAY_CACHE,
			   bytes_per_sector * sectors_per_fat,
			   &fat_image);
}

/* Call this to create a FILE_DATA pager and return a send right.
   NODE must be locked.  */
mach_port_t
diskfs_get_filemap (struct node *node, vm_prot_t prot)
{
  mach_port_t right;
  
  assert (S_ISDIR (node->dn_stat.st_mode)
	  || S_ISREG (node->dn_stat.st_mode)
	  || (S_ISLNK (node->dn_stat.st_mode)));
  
  pthread_spin_lock (&node_to_page_lock);
  do
    {
      struct pager *pager = node->dn->pager;
      if (pager)
	{
          /* Because PAGER is not a real reference, this might be
             nearly deallocated.  If that's so, then the port right
             will be null.  In that case, clear here and loop.  The
             deallocation will complete separately. */
          right = pager_get_port (pager);
          if (right == MACH_PORT_NULL)
            node->dn->pager = 0;
          else
            pager_get_upi (pager)->max_prot |= prot;
        }
      else
        {
          struct user_pager_info *upi =
            malloc (sizeof (struct user_pager_info));
          upi->type = FILE_DATA;
          upi->node = node;
          upi->max_prot = prot;
          diskfs_nref_light (node);
          node->dn->pager =
            pager_create (upi, pager_bucket, MAY_CACHE,
                          MEMORY_OBJECT_COPY_DELAY);
          if (node->dn->pager == 0)
            {
              diskfs_nrele_light (node);
              free (upi);
              pthread_spin_unlock (&node_to_page_lock);
              return MACH_PORT_NULL;
            }

          right = pager_get_port (node->dn->pager);
          ports_port_deref (node->dn->pager);
        }
    }
  while (right == MACH_PORT_NULL);
  pthread_spin_unlock (&node_to_page_lock);

  mach_port_insert_right (mach_task_self (), right, right,
                          MACH_MSG_TYPE_MAKE_SEND);

  return right;
}

/* Call this when we should turn off caching so that unused memory
   object ports get freed.  */
void
drop_pager_softrefs (struct node *node)
{
  struct pager *pager;

  pthread_spin_lock (&node_to_page_lock);
  pager = node->dn->pager;
  if (pager)
    ports_port_ref (pager);
  pthread_spin_unlock (&node_to_page_lock);

  if (MAY_CACHE && pager)
    pager_change_attributes (pager, 0, MEMORY_OBJECT_COPY_DELAY, 0);
  if (pager)
    ports_port_deref (pager);
}

/* Call this when we should turn on caching because it's no longer
   important for unused memory object ports to get freed.  */
void
allow_pager_softrefs (struct node *node)
{
  struct pager *pager;

  pthread_spin_lock (&node_to_page_lock);
  pager = node->dn->pager;
  if (pager)
    ports_port_ref (pager);
  pthread_spin_unlock (&node_to_page_lock);

  if (MAY_CACHE && pager)
    pager_change_attributes (pager, 1, MEMORY_OBJECT_COPY_DELAY, 0);
  if (pager)
    ports_port_deref (pager);
}

/* Call this to find out the struct pager * corresponding to the
   FILE_DATA pager of inode IP.  This should be used *only* as a
   subsequent argument to register_memory_fault_area, and will be
   deleted when the kernel interface is fixed.  NODE must be
   locked.  */
struct pager *
diskfs_get_filemap_pager_struct (struct node *node)
{
  /* This is safe because pager can't be cleared; there must be an
     active mapping for this to be called. */
  return node->dn->pager;
}

/* Shutdown all the pagers (except the disk pager). */
void
diskfs_shutdown_pager ()
{
  error_t shutdown_one (void *v_p)
    {
      struct pager *p = v_p;
      if (p != diskfs_disk_pager)
        pager_shutdown (p);
      return 0;
    }

  write_all_disknodes ();

  ports_bucket_iterate (pager_bucket, shutdown_one);

  pager_sync (diskfs_disk_pager, 1);

  /* Despite the name of this function, we never actually shutdown the
     disk pager, just make sure it's synced. */
}

/* Sync all the pagers. */
void
diskfs_sync_everything (int wait)
{
  error_t sync_one (void *v_p)
    {
      struct pager *p = v_p;
      if (p != diskfs_disk_pager)
        pager_sync (p, wait);
      return 0;
    }

  write_all_disknodes ();
  ports_bucket_iterate (pager_bucket, sync_one);
  pager_sync (diskfs_disk_pager, wait);
}

static void
disable_caching ()
{
  error_t block_cache (void *arg)
    {
      struct pager *p = arg;

      pager_change_attributes (p, 0, MEMORY_OBJECT_COPY_DELAY, 1);
      return 0;
    }

  /* Loop through the pagers and turn off caching one by one,
     synchronously.  That should cause termination of each pager.  */
  ports_bucket_iterate (pager_bucket, block_cache);
}
	  
static void
enable_caching ()
{
  error_t enable_cache (void *arg)
    {
      struct pager *p = arg;
      struct user_pager_info *upi = pager_get_upi (p);

      pager_change_attributes (p, 1, MEMORY_OBJECT_COPY_DELAY, 0);

      /* It's possible that we didn't have caching on before, because
	 the user here is the only reference to the underlying node
	 (actually, that's quite likely inside this particular
	 routine), and if that node has no links.  So dinkle the node
	 ref counting scheme here, which will cause caching to be
	 turned off, if that's really necessary.  */
      if (upi->type == FILE_DATA)
	{
	  diskfs_nref (upi->node);
	  diskfs_nrele (upi->node);
	}

      return 0;
    }

  ports_bucket_iterate (pager_bucket, enable_cache);
}
	    
/* Tell diskfs if there are pagers exported, and if none, then
   prevent any new ones from showing up.  */
int
diskfs_pager_users ()
{
  int npagers = ports_count_bucket (pager_bucket);

  if (npagers <= 1)
    return 0;

  if (MAY_CACHE)
    {
      disable_caching ();
      
      /* Give it a second; the kernel doesn't actually shutdown
	 immediately.  XXX */
      sleep (1);
      
      npagers = ports_count_bucket (pager_bucket);
      if (npagers <= 1)
	return 0;

      /* Darn, there are actual honest users.  Turn caching back on,
	 and return failure.  */
      enable_caching ();
    }
  
  ports_enable_bucket (pager_bucket);

  return 1;
}

/* Return the bitwise or of the maximum prot parameter (the second arg
   to diskfs_get_filemap) for all active user pagers.  */
vm_prot_t
diskfs_max_user_pager_prot ()
{
  vm_prot_t max_prot = 0;
  int npagers = ports_count_bucket (pager_bucket);

  if (npagers > 1)
    /* More than just the disk pager.  */
    {
      error_t add_pager_max_prot (void *v_p)
        {
          struct pager *p = v_p;
          struct user_pager_info *upi = pager_get_upi (p);
          if (upi->type == FILE_DATA)
            max_prot |= upi->max_prot;
          /* Stop iterating if MAX_PROT is as filled as it is going to
	     get.  */
          return (max_prot
		  == (VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE)) ? 1 : 0;
        }

      disable_caching ();               /* Make any silly pagers go away.  */

      /* Give it a second; the kernel doesn't actually shutdown
         immediately.  XXX */
      sleep (1);

      ports_bucket_iterate (pager_bucket, add_pager_max_prot);

      enable_caching ();
    }

  ports_enable_bucket (pager_bucket);

  return max_prot;
}