sparse.c

gnu tar 源码包。 tar 软件是 Unix 系统下的一个打包软件

/* Functions for dealing with sparse files

   Copyright (C) 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.

   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 3, 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.,
   51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */

#include <system.h>
#include <inttostr.h>
#include <quotearg.h>
#include "common.h"

struct tar_sparse_file;
static bool sparse_select_optab (struct tar_sparse_file *file);

enum sparse_scan_state
  {
    scan_begin,
    scan_block,
    scan_end
  };

struct tar_sparse_optab
{
  bool (*init) (struct tar_sparse_file *);
  bool (*done) (struct tar_sparse_file *);
  bool (*sparse_member_p) (struct tar_sparse_file *);
  bool (*dump_header) (struct tar_sparse_file *);
  bool (*fixup_header) (struct tar_sparse_file *);
  bool (*decode_header) (struct tar_sparse_file *);
  bool (*scan_block) (struct tar_sparse_file *, enum sparse_scan_state,
		      void *);
  bool (*dump_region) (struct tar_sparse_file *, size_t);
  bool (*extract_region) (struct tar_sparse_file *, size_t);
};

struct tar_sparse_file
{
  int fd;                           /* File descriptor */
  bool seekable;                    /* Is fd seekable? */
  off_t offset;                     /* Current offset in fd if seekable==false.
				       Otherwise unused */
  off_t dumped_size;                /* Number of bytes actually written
				       to the archive */
  struct tar_stat_info *stat_info;  /* Information about the file */
  struct tar_sparse_optab const *optab; /* Operation table */
  void *closure;                    /* Any additional data optab calls might
				       require */
};

/* Dump zeros to file->fd until offset is reached. It is used instead of
   lseek if the output file is not seekable */
static bool
dump_zeros (struct tar_sparse_file *file, off_t offset)
{
  static char const zero_buf[BLOCKSIZE];

  if (offset < file->offset)
    {
      errno = EINVAL;
      return false;
    }

  while (file->offset < offset)
    {
      size_t size = (BLOCKSIZE < offset - file->offset
		     ? BLOCKSIZE
		     : offset - file->offset);
      ssize_t wrbytes;

      wrbytes = write (file->fd, zero_buf, size);
      if (wrbytes <= 0)
	{
	  if (wrbytes == 0)
	    errno = EINVAL;
	  return false;
	}
      file->offset += wrbytes;
    }

  return true;
}

static bool
tar_sparse_member_p (struct tar_sparse_file *file)
{
  if (file->optab->sparse_member_p)
    return file->optab->sparse_member_p (file);
  return false;
}

static bool
tar_sparse_init (struct tar_sparse_file *file)
{
  memset (file, 0, sizeof *file);

  if (!sparse_select_optab (file))
    return false;

  if (file->optab->init)
    return file->optab->init (file);

  return true;
}

static bool
tar_sparse_done (struct tar_sparse_file *file)
{
  if (file->optab->done)
    return file->optab->done (file);
  return true;
}

static bool
tar_sparse_scan (struct tar_sparse_file *file, enum sparse_scan_state state,
		 void *block)
{
  if (file->optab->scan_block)
    return file->optab->scan_block (file, state, block);
  return true;
}

static bool
tar_sparse_dump_region (struct tar_sparse_file *file, size_t i)
{
  if (file->optab->dump_region)
    return file->optab->dump_region (file, i);
  return false;
}

static bool
tar_sparse_extract_region (struct tar_sparse_file *file, size_t i)
{
  if (file->optab->extract_region)
    return file->optab->extract_region (file, i);
  return false;
}

static bool
tar_sparse_dump_header (struct tar_sparse_file *file)
{
  if (file->optab->dump_header)
    return file->optab->dump_header (file);
  return false;
}

static bool
tar_sparse_decode_header (struct tar_sparse_file *file)
{
  if (file->optab->decode_header)
    return file->optab->decode_header (file);
  return true;
}

static bool
tar_sparse_fixup_header (struct tar_sparse_file *file)
{
  if (file->optab->fixup_header)
    return file->optab->fixup_header (file);
  return true;
}


static bool
lseek_or_error (struct tar_sparse_file *file, off_t offset)
{
  if (file->seekable
      ? lseek (file->fd, offset, SEEK_SET) < 0
      : ! dump_zeros (file, offset))
    {
      seek_diag_details (file->stat_info->orig_file_name, offset);
      return false;
    }
  return true;
}

/* Takes a blockful of data and basically cruises through it to see if
   it's made *entirely* of zeros, returning a 0 the instant it finds
   something that is a nonzero, i.e., useful data.  */
static bool
zero_block_p (char const *buffer, size_t size)
{
  while (size--)
    if (*buffer++)
      return false;
  return true;
}

static void
sparse_add_map (struct tar_stat_info *st, struct sp_array const *sp)
{
  struct sp_array *sparse_map = st->sparse_map;
  size_t avail = st->sparse_map_avail;
  if (avail == st->sparse_map_size)
    st->sparse_map = sparse_map =
      x2nrealloc (sparse_map, &st->sparse_map_size, sizeof *sparse_map);
  sparse_map[avail] = *sp;
  st->sparse_map_avail = avail + 1;
}

/* Scan the sparse file and create its map */
static bool
sparse_scan_file (struct tar_sparse_file *file)
{
  struct tar_stat_info *st = file->stat_info;
  int fd = file->fd;
  char buffer[BLOCKSIZE];
  size_t count;
  off_t offset = 0;
  struct sp_array sp = {0, 0};

  if (!lseek_or_error (file, 0))
    return false;

  st->archive_file_size = 0;
  
  if (!tar_sparse_scan (file, scan_begin, NULL))
    return false;

  while ((count = safe_read (fd, buffer, sizeof buffer)) != 0
	 && count != SAFE_READ_ERROR)
    {
      /* Analyze the block.  */
      if (zero_block_p (buffer, count))
	{
	  if (sp.numbytes)
	    {
	      sparse_add_map (st, &sp);
	      sp.numbytes = 0;
	      if (!tar_sparse_scan (file, scan_block, NULL))
		return false;
	    }
	}
      else
	{
	  if (sp.numbytes == 0)
	    sp.offset = offset;
	  sp.numbytes += count;
	  st->archive_file_size += count;
	  if (!tar_sparse_scan (file, scan_block, buffer))
	    return false;
	}

      offset += count;
    }

  if (sp.numbytes == 0)
    sp.offset = offset;

  sparse_add_map (st, &sp);
  st->archive_file_size += count;
  return tar_sparse_scan (file, scan_end, NULL);
}

static struct tar_sparse_optab const oldgnu_optab;
static struct tar_sparse_optab const star_optab;
static struct tar_sparse_optab const pax_optab;

static bool
sparse_select_optab (struct tar_sparse_file *file)
{
  switch (current_format == DEFAULT_FORMAT ? archive_format : current_format)
    {
    case V7_FORMAT:
    case USTAR_FORMAT:
      return false;

    case OLDGNU_FORMAT:
    case GNU_FORMAT: /*FIXME: This one should disappear? */
      file->optab = &oldgnu_optab;
      break;

    case POSIX_FORMAT:
      file->optab = &pax_optab;
      break;

    case STAR_FORMAT:
      file->optab = &star_optab;
      break;

    default:
      return false;
    }
  return true;
}

static bool
sparse_dump_region (struct tar_sparse_file *file, size_t i)
{
  union block *blk;
  off_t bytes_left = file->stat_info->sparse_map[i].numbytes;

  if (!lseek_or_error (file, file->stat_info->sparse_map[i].offset))
    return false;

  while (bytes_left > 0)
    {
      size_t bufsize = (bytes_left > BLOCKSIZE) ? BLOCKSIZE : bytes_left;
      size_t bytes_read;

      blk = find_next_block ();
      bytes_read = safe_read (file->fd, blk->buffer, bufsize);
      if (bytes_read == SAFE_READ_ERROR)
	{
          read_diag_details (file->stat_info->orig_file_name,
	                     (file->stat_info->sparse_map[i].offset
			      + file->stat_info->sparse_map[i].numbytes
			      - bytes_left),
			     bufsize);
	  return false;
	}

      memset (blk->buffer + bytes_read, 0, BLOCKSIZE - bytes_read);
      bytes_left -= bytes_read;
      file->dumped_size += bytes_read;
      mv_size_left (file->stat_info->archive_file_size - file->dumped_size);
      set_next_block_after (blk);
    }

  return true;
}

static bool
sparse_extract_region (struct tar_sparse_file *file, size_t i)
{
  size_t write_size;

  if (!lseek_or_error (file, file->stat_info->sparse_map[i].offset))
    return false;

  write_size = file->stat_info->sparse_map[i].numbytes;

  if (write_size == 0)
    {
      /* Last block of the file is a hole */
      if (file->seekable && sys_truncate (file->fd))
	truncate_warn (file->stat_info->orig_file_name);
    }
  else while (write_size > 0)
    {
      size_t count;
      size_t wrbytes = (write_size > BLOCKSIZE) ? BLOCKSIZE : write_size;
      union block *blk = find_next_block ();
      if (!blk)
	{
	  ERROR ((0, 0, _("Unexpected EOF in archive")));
	  return false;
	}
      set_next_block_after (blk);
      count = full_write (file->fd, blk->buffer, wrbytes);
      write_size -= count;
      file->dumped_size += count;
      mv_size_left (file->stat_info->archive_file_size - file->dumped_size);
      file->offset += count;
      if (count != wrbytes)
	{
	  write_error_details (file->stat_info->orig_file_name,
			       count, wrbytes);
	  return false;
	}
    }
  return true;
}



/* Interface functions */
enum dump_status
sparse_dump_file (int fd, struct tar_stat_info *st)
{
  bool rc;
  struct tar_sparse_file file;

  if (!tar_sparse_init (&file))
    return dump_status_not_implemented;

  file.stat_info = st;
  file.fd = fd;
  file.seekable = true; /* File *must* be seekable for dump to work */

  rc = sparse_scan_file (&file);