path: root/ext2fs/truncate.c

/* File truncation

   Copyright (C) 1995, 1996, 1997, 1999 Free Software Foundation, Inc.

   Written by Miles Bader <miles@gnu.ai.mit.edu>

   This program 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.

   This program 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., 675 Mass Ave, Cambridge, MA 02139, USA. */

#include "ext2fs.h"

#ifdef DONT_CACHE_MEMORY_OBJECTS
#define MAY_CACHE 0
#else
#define MAY_CACHE 1
#endif

/* ---------------------------------------------------------------- */

/* A sequence of blocks to be freed in NODE.  */
struct free_block_run
{
  block_t first_block;
  unsigned long num_blocks;
  struct node *node;
};

/* Initialize FBR, pointing to NODE.  */
static inline void
free_block_run_init (struct free_block_run *fbr, struct node *node)
{
  fbr->num_blocks = 0;
  fbr->node = node;
}

static inline void
_free_block_run_flush (struct free_block_run *fbr, unsigned long count)
{
  fbr->node->dn_stat.st_blocks -= count << log2_stat_blocks_per_fs_block;
  fbr->node->dn_stat_dirty = 1;
  ext2_free_blocks (fbr->first_block, count);
}

/* Add BLOCK to the list of blocks to be freed in FBR.  */
static inline void
free_block_run_add (struct free_block_run *fbr, block_t block)
{
  unsigned long count = fbr->num_blocks;
  if (count == 0)
    {
      fbr->first_block = block;
      fbr->num_blocks++;
    }
  else if (count > 0 && fbr->first_block == block - count)
    fbr->num_blocks++;
  else
    {
      _free_block_run_flush (fbr, count);
      fbr->first_block = block;
      fbr->num_blocks = 1;
    }
}

/* If *P is non-zero, set it to zero, and add the block it pointed to the
   list of blocks to be freed in FBR.  */
static inline void
free_block_run_free_ptr (struct free_block_run *fbr, block_t *p)
{
  block_t block = *p;
  if (block)
    {
      *p = 0;
      free_block_run_add (fbr, block);
    }
}

/* Free any blocks left in FBR, and cleanup any resources it's using.  */
static inline void
free_block_run_finish (struct free_block_run *fbr)
{
  unsigned long count = fbr->num_blocks;
  if (count > 0)
    _free_block_run_flush (fbr, count);
}

/* ---------------------------------------------------------------- */

/* Free any direct blocks starting with block END.  */
static void
trunc_direct (struct node *node, block_t end, struct free_block_run *fbr)
{
  block_t *blocks = node->dn->info.i_data;

  ext2_debug ("truncating direct blocks from %ld", end);

  while (end < EXT2_NDIR_BLOCKS)
    free_block_run_free_ptr (fbr, blocks + end++);
}

/* Free any blocks in NODE greater than or equal to END that are rooted in
   the indirect block *P; OFFSET should be the block position that *P
   corresponds to.  For each block pointer in *P that should be freed,
   FREE_BLOCK is called with a pointer to the entry for that block, and the
   index of the entry within *P.  If every block in *P is freed, then *P is
   set to 0, otherwise it is left alone.  */
static void
trunc_indirect (struct node *node, block_t end,
		block_t *p, block_t offset,
		void (*free_block)(block_t *p, unsigned index),
		struct free_block_run *fbr)
{
  if (*p)
    {
      unsigned index;
      int modified = 0, all_freed = 1;
      block_t *ind_bh = (block_t *)bptr (*p);
      unsigned first = end < offset ? 0 : end - offset;

      for (index = first; index < addr_per_block; index++)
	if (ind_bh[index])
	  {
	    (*free_block)(ind_bh + index, index);
	    if (ind_bh[index])
	      all_freed = 0;	/* Some descendent hasn't been freed.  */
	    else
	      modified = 1;
	  }

      if (first == 0 && all_freed)
	free_block_run_free_ptr (fbr, p);
      else if (modified)
	record_indir_poke (node, ind_bh);
    }
}

static void
trunc_single_indirect (struct node *node, block_t end,
		       block_t *p, block_t offset,
		       struct free_block_run *fbr)
{
  void free_block (block_t *p, unsigned index)
    {
      free_block_run_free_ptr (fbr, p);
    }
  trunc_indirect (node, end, p, offset, free_block, fbr);
}

static void
trunc_double_indirect (struct node *node, block_t end,
		       block_t *p, block_t offset,
		       struct free_block_run *fbr)
{
  void free_block (block_t *p, unsigned index)
    {
      block_t entry_offs = offset + (index * addr_per_block);
      trunc_single_indirect (node, end, p, entry_offs, fbr);
    }
  trunc_indirect (node, end, p, offset, free_block, fbr);
}

static void
trunc_triple_indirect (struct node *node, block_t end,
		       block_t *p, block_t offset,
		       struct free_block_run *fbr)
{
  void free_block (block_t *p, unsigned index)
    {
      block_t entry_offs = offset + (index * addr_per_block * addr_per_block);
      trunc_double_indirect (node, end, p, entry_offs, fbr);
    }
  trunc_indirect (node, end, p, offset, free_block, fbr);
}

/* ---------------------------------------------------------------- */

/* Write something to each page from START to END inclusive of memory
   object OBJ, but make sure the data doesns't actually change. */
static void
poke_pages (memory_object_t obj, vm_offset_t start, vm_offset_t end)
{
  while (start < end)
    {
      error_t err;
      vm_size_t len = 8 * vm_page_size;
      vm_address_t addr = 0;

      if (len > end - start)
	len = end - start;

      err = vm_map (mach_task_self (), &addr, len, 0, 1, obj, start, 0,
		    VM_PROT_WRITE|VM_PROT_READ, VM_PROT_READ|VM_PROT_WRITE, 0);
      if (!err)
	{
	  vm_address_t poke;
	  for (poke = addr; poke < addr + len; poke += vm_page_size)
	    *(volatile int *)poke = *(volatile int *)poke;
	  munmap ((caddr_t) addr, len);
	}

      start += len;
    }
}

/* Flush all the data past the new size from the kernel.  Also force any
   delayed copies of this data to take place immediately.  (We are implicitly
   changing the data to zeros and doing it without the kernel's immediate
   knowledge; accordingl we must help out the kernel thusly.) */
static void
force_delayed_copies (struct node *node, off_t length)
{
  struct pager *pager;

  spin_lock (&node_to_page_lock);
  pager = node->dn->pager;
  if (pager)
    ports_port_ref (pager);
  spin_unlock (&node_to_page_lock);
 
  if (pager)
    {
      mach_port_t obj;
      
      pager_change_attributes (pager, MAY_CACHE, MEMORY_OBJECT_COPY_NONE, 1);
      obj = diskfs_get_filemap (node, VM_PROT_READ);
      if (obj != MACH_PORT_NULL)
	{
	  /* XXX should cope with errors from diskfs_get_filemap */
	  poke_pages (obj, round_page (length), round_page (node->allocsize));
	  mach_port_deallocate (mach_task_self (), obj);
	  pager_flush_some (pager, round_page(length), 
			    node->allocsize - length, 1);
	}
      
      ports_port_deref (pager);
    }
}

static void
enable_delayed_copies (struct node *node)
{
  struct pager *pager;

  spin_lock (&node_to_page_lock);
  pager = node->dn->pager;
  if (pager)
    ports_port_ref (pager);
  spin_unlock (&node_to_page_lock);

  if (pager)
    {
      pager_change_attributes (pager, MAY_CACHE, MEMORY_OBJECT_COPY_DELAY, 0);
      ports_port_deref (pager);
    }
}

/* ---------------------------------------------------------------- */

/* The user must define this function.  Truncate locked node NODE to be SIZE
   bytes long.  (If NODE is already less than or equal to SIZE bytes
   long, do nothing.)  If this is a symlink (and diskfs_shortcut_symlink
   is set) then this should clear the symlink, even if 
   diskfs_create_symlink_hook stores the link target elsewhere.  */
error_t
diskfs_truncate (struct node *node, off_t length)
{
  error_t err;
  off_t offset;

  diskfs_check_readonly ();
  assert (!diskfs_readonly);

  if (length >= node->dn_stat.st_size)
    return 0;

  if (! node->dn_stat.st_blocks)
    /* There aren't really any blocks allocated, so just frob the size.  This
       is true for fast symlinks, and also apparently for some device nodes
       in linux.  */
    {
      node->dn_stat.st_size = length;
      node->dn_set_mtime = 1;
      node->dn_set_ctime = 1;
      diskfs_node_update (node, 1);
      return 0;
    }

  /*
   * If the file is not being truncated to a block boundary, the
   * contents of the partial block following the end of the file must be
   * zeroed in case it ever becomes accessible again because of
   * subsequent file growth.
   */
  offset = length % block_size;
  if (offset > 0)
    {
      diskfs_node_rdwr (node, (void *)zeroblock, length, block_size - offset,
			1, 0, 0);
      diskfs_file_update (node, 1);
    }

  ext2_discard_prealloc(node);

  force_delayed_copies (node, length);

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

  /* Update the size on disk; fsck will finish freeing blocks if necessary
     should we crash. */
  node->dn_stat.st_size = length;
  node->dn_set_mtime = 1;
  node->dn_set_ctime = 1;
  diskfs_node_update (node, 1);

  err = diskfs_catch_exception();
  if (!err)
    {
      block_t end = boffs_block (round_block (length)), offs;
      block_t *bptrs = node->dn->info.i_data;
      struct free_block_run fbr;

      free_block_run_init (&fbr, node);

      trunc_direct (node, end, &fbr);

      offs = EXT2_NDIR_BLOCKS;
      trunc_single_indirect (node, end, bptrs + EXT2_IND_BLOCK, offs, &fbr);
      offs += addr_per_block;
      trunc_double_indirect (node, end, bptrs + EXT2_DIND_BLOCK, offs, &fbr);
      offs += addr_per_block * addr_per_block;
      trunc_triple_indirect (node, end, bptrs + EXT2_TIND_BLOCK, offs, &fbr);

      free_block_run_finish (&fbr);

      node->allocsize = round_block (length);

      /* Set our last_page_partially_writable to a pessimistic state -- it
	 won't hurt if is wrong.  */
      node->dn->last_page_partially_writable =
	trunc_page (node->allocsize) != node->allocsize;
    }

  node->dn_set_mtime = 1;
  node->dn_set_ctime = 1;
  node->dn_stat_dirty = 1;

  /* Now we can permit delayed copies again. */
  enable_delayed_copies (node);

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

  return err;
}