libguestfs/daemon/zero.c

/* libguestfs - the guestfsd daemon
 * Copyright (C) 2009-2011 Red Hat 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 2 of the License, 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 <config.h>

#include <stdio.h>
#include <stdlib.h>
#include <inttypes.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>

#include "daemon.h"
#include "actions.h"

/* Return true iff the buffer is all zero bytes.
 *
 * Note that gcc is smart enough to optimize this properly:
 * http://stackoverflow.com/questions/1493936/faster-means-of-checking-for-an-empty-buffer-in-c/1493989#1493989
 */
static int
is_zero (const char *buffer, size_t size)
{
  size_t i;

  for (i = 0; i < size; ++i) {
    if (buffer[i] != 0)
      return 0;
  }

  return 1;
}

static const char zero_buf[4096];

int
do_zero (const char *device)
{
  char buf[sizeof zero_buf];
  int fd;
  size_t i, offset;

  fd = open (device, O_RDWR);
  if (fd == -1) {
    reply_with_perror ("%s", device);
    return -1;
  }

  for (i = 0; i < 32; ++i) {
    offset = i * sizeof zero_buf;

    /* Check if the block is already zero before overwriting it. */
    if (pread (fd, buf, sizeof buf, offset) != sizeof buf) {
      reply_with_perror ("pread: %s", device);
      close (fd);
      return -1;
    }

    if (!is_zero (buf, sizeof buf)) {
      if (pwrite (fd, zero_buf, sizeof zero_buf, offset) != sizeof zero_buf) {
        reply_with_perror ("pwrite: %s", device);
        close (fd);
        return -1;
      }
    }

    notify_progress ((uint64_t) i, 32);
  }

  if (close (fd) == -1) {
    reply_with_perror ("close: %s", device);
    return -1;
  }

  return 0;
}

int
do_zero_device (const char *device)
{
  int64_t ssize = do_blockdev_getsize64 (device);
  if (ssize == -1)
    return -1;
  uint64_t size = (uint64_t) ssize;

  int fd = open (device, O_RDWR);
  if (fd == -1) {
    reply_with_perror ("%s", device);
    return -1;
  }

  char buf[sizeof zero_buf];

  uint64_t pos = 0;

  while (pos < size) {
    uint64_t n64 = size - pos;
    size_t n;
    if (n64 > sizeof buf)
      n = sizeof buf;
    else
      n = (size_t) n64; /* safe because of if condition */

    /* Check if the block is already zero before overwriting it. */
    ssize_t r;
    r = pread (fd, buf, n, pos);
    if (r == -1) {
      reply_with_perror ("pread: %s at offset %" PRIu64, device, pos);
      close (fd);
      return -1;
    }

    if (!is_zero (buf, sizeof buf)) {
      r = pwrite (fd, zero_buf, n, pos);
      if (r == -1) {
        reply_with_perror ("pwrite: %s (with %" PRId64 " bytes left to write)",
                           device, size);
        close (fd);
        return -1;
      }
      pos += r;
    }
    else
      pos += n;

    notify_progress (pos, size);
  }

  if (close (fd) == -1) {
    reply_with_perror ("close: %s", device);
    return -1;
  }

  return 0;
}

int
do_is_zero (const char *path)
{
  int fd;
  char buf[1024*1024];
  ssize_t r;

  CHROOT_IN;
  fd = open (path, O_RDONLY);
  CHROOT_OUT;

  if (fd == -1) {
    reply_with_perror ("open: %s", path);
    return -1;
  }

  while ((r = read (fd, buf, sizeof buf)) > 0) {
    if (!is_zero (buf, r)) {
      close (fd);
      return 0;
    }
  }

  if (r == -1) {
    reply_with_perror ("read: %s", path);
    close (fd);
    return -1;
  }

  if (close (fd) == -1) {
    reply_with_perror ("close: %s", path);
    return -1;
  }

  return 1;
}

int
do_is_zero_device (const char *device)
{
  int fd;
  char buf[1024*1024];
  ssize_t r;

  fd = open (device, O_RDONLY);
  if (fd == -1) {
    reply_with_perror ("open: %s", device);
    return -1;
  }

  while ((r = read (fd, buf, sizeof buf)) > 0) {
    if (!is_zero (buf, r)) {
      close (fd);
      return 0;
    }
  }

  if (r == -1) {
    reply_with_perror ("read: %s", device);
    close (fd);
    return -1;
  }

  if (close (fd) == -1) {
    reply_with_perror ("close: %s", device);
    return -1;
  }

  return 1;
}