*** empty log message ***

[coreutils.git] / src / shred.c

/* TODO:
   - use consistent non-capitalization in error messages
   - add standard GNU copyleft comment

  - Add -r/-R/--recursive
  - Add -i/--interactive
  - Reserve -d
  - Add -L
  - Deal with the amazing variety of gettimeofday() implementation bugs.
    (Some systems use a one-arg form; still others insist that the timezone
    either be NULL or be non-NULL.  Whee.)
  - Add an unlink-all option to emulate rm.
 */

/*
 * shred.c - by Colin Plumb.
 *
 * Do a securer overwrite of given files or devices, to make it harder
 * for even very expensive hardware probing to recover the data.
 *
 * Although this process is also known as "wiping", I prefer the longer
 * name both because I think it is more evocative of what is happening and
 * because a longer name conveys a more appropriate sense of deliberateness.
 *
 * For the theory behind this, see "Secure Deletion of Data from Magnetic
 * and Solid-State Memory", on line at
 * http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html
 *
 * Just for the record, reversing one or two passes of disk overwrite
 * is not terribly difficult with hardware help.  Hook up a good-quality
 * digitizing oscilloscope to the output of the head preamplifier and copy
 * the high-res digitized data to a computer for some off-line analysis.
 * Read the "current" data and average all the pulses together to get an
 * "average" pulse on the disk.  Subtract this average pulse from all of
 * the actual pulses and you can clearly see the "echo" of the previous
 * data on the disk.
 *
 * Real hard drives have to balance the cost of the media, the head,
 * and the read circuitry.  They use better-quality media than absolutely
 * necessary to limit the cost of the read circuitry.  By throwing that
 * assumption out, and the assumption that you want the data processed
 * as fast as the hard drive can spin, you can do better.
 *
 * If asked to wipe a file, this also unlinks it, renaming it to in a
 * clever way to try to leave no trace of the original filename.
 *
 * Copyright 1997, 1998, 1999 Colin Plumb <colin@nyx.net>.  This program
 * may be freely distributed under the terms of the GNU GPL, the BSD license,
 * or Larry Wall's "Artistic License"   Even if you use the BSD license,
 * which does not require it, I'd really like to get improvements back.
 *
 * The ISAAC code still bears some resemblance to the code written
 * by Bob Jenkins, but he permits pretty unlimited use.
 *
 * This was inspired by a desire to improve on some code titled:
 * Wipe V1.0-- Overwrite and delete files.  S. 2/3/96
 * but I've rewritten everything here so completely that no trace of
 * the original remains.
 *
 * Thanks to:
 * Bob Jenkins, for his good RNG work and patience with the FSF copyright
 * paperwork.
 * Jim Meyering, for his work merging this into the GNU fileutils while
 * still letting me feel a sense of ownership and pride.  Getting me to
 * tolerate the GNU brace style was quite a feat of diplomacy.
 * Paul Eggert, for lots of useful discussion and code.  I disagree with
 * an awful lot of his suggestions, but they're disagreements worth having.
 *
 * Things to think about:
 * - Security: Is there any risk to the race
 *   between overwriting and unlinking a file?  Will it do anything
 *   drastically bad if told to attack a named pipe or socket?
 */

/* The official name of this program (e.g., no `g' prefix).  */
#define PROGRAM_NAME "shred"

#define AUTHORS "Colin Plumb"

#if HAVE_CONFIG_H
# include <config.h>
#endif

#include <getopt.h>
#include <stdio.h>
#include <assert.h>
#include <setjmp.h>
#include <signal.h>
#include <sys/types.h>

#if HAVE_CONFIG_H
/* Default fileutils build */
# include "system.h"
# include "xstrtol.h"
# include "closeout.h"
# include "error.h"
# include "human.h"
# include "quotearg.h"          /* For quotearg_colon */
# include "quote.h"             /* For quotearg_colon */
# include "xalloc.h"
char *xstrdup PARAMS ((char const *));

#else /* !HAVE_CONFIG_H */
/*
 * Standalone build - this file compiles by itself without autoconf and
 * the like.  No i18n, and I still have to write a stub for getopt_long,
 * but it's a lot less intertwingled than the usual GNU utilities.
 */

# include <ctype.h>     /* For isprint */
# include <string.h>    /* For memcpy, strerror */
# include <limits.h>    /* For ULONG_MAX etc. */
# include <stdlib.h>    /* For strtoul, EXIT_FAILURE */
# include <errno.h>
# include <fcntl.h>     /* For O_RDONLY etc. */
# include <unistd.h>    /* For getpid, etc. */
# include <sys/time.h>  /* For struct timeval */
# include <sys/stat.h>  /* For struct stat */

# define PACKAGE "standalone"
# define VERSION "2.0" /* Kind of arbitrary... */

# if __GNUC__ < 2 || __GNUC__ == 2 && __GNUC_MINOR__ < 5 || __STRICT_ANSI__
#  define attribute(x)
# else
#  define attribute __attribute__
#  if __GNUC__ == 2 && __GNUC_MINOR__ < 7
   /* The __-protected forms were introduced in GCC 2.6.4 */
#   define __format__ format
#   define __printf__ printf
#  endif
# endif

/* Reasonable default assumptions for time-getting */
# ifndef HAVE_GETTIMEOFDAY
#  define HAVE_GETTIMEOFDAY 1 /* Most systems have it these days */
# endif

# ifdef CLOCK_REALTIME
#  ifndef HAVE_CLOCK_GETTIME
#   define HAVE_CLOCK_GETTIME 1
#  endif
# endif

# ifndef STDOUT_FILENO
#  define STDOUT_FILENO 1
# endif

# define RETSIGTYPE int

# ifndef S_IWUSR
#  ifdef S_IWRITE
#   define S_IWUSR S_IWRITE
#  else
#   define S_IWUSR 0200
#  endif
# endif

/* POSIX doesn't require st_blksize, and 65536 is a reasonable
   upper bound for existing filesystem practice.  */
# define ST_BLKSIZE(Stat) 65536

# define uintmax_t unsigned long

/* Variant human-readable function that ignores last two args */
# define human_readable(v, b, f, t) (sprintf (b, "%lu", (unsigned long) v), b)
# define LONGEST_HUMAN_READABLE (sizeof (uintmax_t) * CHAR_BIT / 3)

/* Variant convert-to-uintmax_t function that accepts metric suffixes */
enum strtol_error
  {
    LONGINT_OK, LONGINT_INVALID, LONGINT_INVALID_SUFFIX_CHAR, LONGINT_OVERFLOW
  };
static uintmax_t
xstrtoumax (char const *ptr, char const **end, int base, uintmax_t *res,
            char const *valid_suffixes)
{
  char *end_ptr;
  char const *p;
  static char const metric_suffixes[] = "kMGTPEZY";
  int decimal_flag;
  uintmax_t n;
  char c;

  errno = 0;
  *res = n = strtoul (ptr, &end_ptr, base);
  if (end)
    *end = end_ptr;
  if (errno)
    return LONGINT_OVERFLOW;
  if (ptr == end_ptr)
    return LONGINT_INVALID;
  c = *end_ptr;
  if (!c)
    return LONGINT_OK;
  /* Now deal with metric-style suffixes */
  if (valid_suffixes && !strchr (valid_suffixes, c))
    return LONGINT_INVALID_SUFFIX_CHAR;

  decimal_flag = 0;
  switch (c)
    {
    case 'b':
      if (n > ULONG_MAX/512)
        return LONGINT_OVERFLOW;
      n *= 512;
      break;

    case 'B':
      if (n > ULONG_MAX/102412)
        return LONGINT_OVERFLOW;
      n *= 1024;
      break;

    case 'c':
      break;

    case 'K':
      c = 'k';
      goto def;

    case 'm':
      c = 'M';
      /*FALLTHROUGH*/
def:default:
      p = strchr (metric_suffixes, c);
      if (!p)
        return LONGINT_INVALID_SUFFIX_CHAR;
      /*
       * If valid_suffixes contains '0', then xD (decimal) and xB (binary)
       * are allowed as "supersuffixes".  Binary is the default.
       */
      if (strchr (valid_suffixes, '0'))
        {
          if (end_ptr[1] == 'B')
            end_ptr++;
          else if (end_ptr[1] == 'D')
            {
              decimal_flag = 1;
              end_ptr++;
            }
        }
      /* Now do the scaling */
      p++;
      if (decimal_flag)
        do {
          if (n > ULONG_MAX/1000)
            return LONGINT_OVERFLOW;
          n *= 1000;
        } while (--p > metric_suffixes);
      else
        do {
          if (n > ULONG_MAX/1024)
            return LONGINT_OVERFLOW;
          n *= 1024;
        } while (--p > metric_suffixes);
    }

  /* Final wrapup */
  if (end)
    *end = end_ptr+1;   /* Extra suffix is allowed if it's expected */
  else if (end_ptr[1])
    return LONGINT_INVALID_SUFFIX_CHAR;
  *res = n;
  return LONGINT_OK;
}

/* Dummy i18n stubs */
# define _(x) x
# define N_(x) x
# define setlocale(x,y) (void) 0
# define bindtextdomain(x,y) (void) 0
# define textdomain(x) (void) 0

/*
 * Print a message with `fprintf (stderr, FORMAT, ...)';
 *    if ERRNUM is nonzero, follow it with ": " and strerror (ERRNUM).
 *       If STATUS is nonzero, terminate the program with `exit (STATUS)'.
 */
static void error (int status, int errnum, const char *format, ...)
        attribute ((__format__ (__printf__, 3, 4)));

extern char const *program_name;
static void
error (int status, int errnum, const char *format, ...)
{
  va_list ap;

  if (program_name)
    {
      fputs (program_name, stderr);
      fputs (": ", stderr);
    }
  va_start (ap, format);
  vfprintf (stderr, format, ap);
  va_end (ap);
  if (errnum)
    {
      fputs (": ", stderr);
      fputs (strerror (errnum), stderr);
    }
  putc ('\n', stderr);

  if (status)
    exit (status);
}

/*
 * GNU programs actually check for failure closing standard output.
 * This seems unnecessary, until your shell script starts hitting
 * ENOSPC and doing bizarre things with zero-length files.
 */
static void
close_stdout (void)
{
  if (ferror (stdout))
    error (EXIT_FAILURE, 0, _("write error"));
  if (fclose (stdout) != 0)
    error (EXIT_FAILURE, errno, _("write error"));
}

/*
 * Quote the argument (including colon characters) into the buffer.
 * Return the buffer size used (including trailing null byte.)
 * If this is larger than the bufsize, it is an estimate of the space
 * needed.
 */
static size_t
quotearg_colon_buf (char const *arg, char *buf, size_t bufsize)
{
  /* Some systems don't have \a or \e, so this is ASCII-dependent */
  static char const escaped[] = "\7\b\33\f\n\r\t\v";
  static char const escapes[] = "abefnrtv";
  int c;
  size_t pos = 0;
  char const *p;

  while ((c = (unsigned char) *arg++) != 0)
    {
      if (isprint (c))
        {
          if (strchr ("\\:", c))        /* Anything else we should quote? */
            if (pos++ < bufsize) *buf++ = '\\';
        }
      else
        {
          if (pos++ < bufsize) *buf++ = '\\';
          p = strchr (escaped, c); /* c is never 0, so this is okay */
          if (p)
            {
              c = escapes[p-escaped];
            }
          else
            {
              if ('0' <= *arg && *arg <= '9')
                c += 256; /* Force 3-digit form if followed by a digit */
              if (c > 077)
                if (pos++ < bufsize) *buf++ = "0123"[c>>6 & 3];
              if (c > 07)
                if (pos++ < bufsize) *buf++ = "01234567"[c>>3 & 7];
              c = "01234567"[c & 7];
            }
        }
        if (pos++ < bufsize) *buf++ = c;
    }
    if (pos++ < bufsize) *buf++ = 0;
    return pos;
}

/* Quote metacharacters in a filename */
char const *
quotearg_colon (char const *arg)
{
  static char *buf = 0;
  size_t bufsize = 0;
  size_t newsize;

  while ((newsize = quotearg_colon_buf (arg, buf, bufsize)) > bufsize)
    {
      buf = realloc (buf, newsize);
      if (!buf)
        error (EXIT_FAILURE, 0, _("memory exhausted"));
      bufsize = newsize;
    }
  return buf;
}

void *
xmalloc (size_t n)
{
  void *p = malloc (n);
  if (!p)
    error (EXIT_FAILURE, 0, _("memory exhausted"));
  return p;
}

char *
xstrdup (char const *string)
{
  return strcpy (xmalloc (strlen (string) + 1), string);
}

#endif /* ! HAVE_CONFIG_H */

#ifndef O_NOCTTY
# define O_NOCTTY 0  /* This is a very optional frill */
#endif

/* Some systems don't support some file types.  */
#ifndef S_ISFIFO
# define S_ISFIFO(mode) 0
#endif
#ifndef S_ISLNK
# define S_ISLNK(mode) 0
#endif
#ifndef S_ISSOCK
# define S_ISSOCK(mode) 0
#endif

#define DEFAULT_PASSES 25       /* Default */

/* How often to update wiping display */
#define VERBOSE_UPDATE  150*1024

/* If positive, the units to use when printing sizes;
   if negative, the human-readable base.  */
#define OUTPUT_BLOCK_SIZE (-1024)

struct Options
{
  int force;            /* -f flag: chmod files if necessary */
  size_t n_iterations;  /* -n flag: Number of iterations */
  off_t size;           /* -s flag: size of file */
  int remove_file;      /* -u flag: remove file after shredding */
  int verbose;          /* -v flag: Print progress */
  int exact;            /* -x flag: Do not round up file size */
  int zero_fill;        /* -z flag: Add a final zero pass */
};

static struct option const long_opts[] =
{
  {"exact", no_argument, NULL, 'x'},
  {"force", no_argument, NULL, 'f'},
  {"iterations", required_argument, NULL, 'n'},
  {"size", required_argument, NULL, 's'},
  {"remove", no_argument, NULL, 'u'},
  {"verbose", no_argument, NULL, 'v'},
  {"zero", required_argument, NULL, 'z'},
  {GETOPT_HELP_OPTION_DECL},
  {GETOPT_VERSION_OPTION_DECL},
  {NULL, 0, NULL, 0}
};

/* Global variable for error printing purposes */
char const *program_name; /* Initialized before any possible use */

void
usage (int status)
{
  if (status != 0)
    fprintf (stderr, _("Try `%s --help' for more information.\n"),
             program_name);
  else
    {
      printf (_("Usage: %s [OPTIONS] FILE [...]\n"), program_name);
      printf (_("\
Overwrite the specified FILE(s) repeatedly, in order to make it harder\n\
for even very expensive hardware probing to recover the data.\n\
\n\
  -f, --force    change permissions to allow writing if necessary\n\
  -n, --iterations=N  Overwrite N times instead of the default (%d)\n\
  -s, --size=N   shred this many bytes (suffixes like k, M, G accepted)\n\
  -u, --remove   truncate and remove file after overwriting\n\
  -v, --verbose  show progress\n\
  -x, --exact    do not round file sizes up to the next full block\n\
  -z, --zero     add a final overwrite with zeros to hide shredding\n\
  -              shred standard output\n\
      --help     display this help and exit\n\
      --version  print version information and exit\n\
\n\
Delete FILE(s) if --remove (-u) is specified.  The default is not to remove\n\
the files because it is common to operate on device files like /dev/hda,\n\
and those files usually should not be removed.  When operating on regular\n\
files, most people use the --remove option.\n\
"), DEFAULT_PASSES);
      puts (_("\nReport bugs to <bug-fileutils@gnu.org>."));
    }
  exit (status);
}

#if ! HAVE_FDATASYNC
# define fdatasync(fd) -1
#endif

/*
 * --------------------------------------------------------------------
 *     Bob Jenkins' cryptographic random number generator, ISAAC.
 *     Hacked by Colin Plumb.
 *
 * We need a source of random numbers for some of the overwrite data.
 * Cryptographically secure is desirable, but it's not life-or-death
 * so I can be a little bit experimental in the choice of RNGs here.
 *
 * This generator is based somewhat on RC4, but has analysis
 * (http://ourworld.compuserve.com/homepages/bob_jenkins/randomnu.htm)
 * pointing to it actually being better.  I like it because it's nice
 * and fast, and because the author did good work analyzing it.
 * --------------------------------------------------------------------
 */

#if defined __STDC__ && __STDC__
# define UINT_MAX_32_BITS 4294967295U
#else
# define UINT_MAX_32_BITS 0xFFFFFFFF
#endif

#if ULONG_MAX == UINT_MAX_32_BITS
typedef unsigned long word32;
#else
# if UINT_MAX == UINT_MAX_32_BITS
typedef unsigned word32;
# else
#  if USHRT_MAX == UINT_MAX_32_BITS
typedef unsigned short word32;
#  else
#   if UCHAR_MAX == UINT_MAX_32_BITS
typedef unsigned char word32;
#   else
     "No 32-bit type available!"
#   endif
#  endif
# endif
#endif

/* Size of the state tables to use.  (You may change ISAAC_LOG) */
#define ISAAC_LOG 8
#define ISAAC_WORDS (1 << ISAAC_LOG)
#define ISAAC_BYTES (ISAAC_WORDS * sizeof (word32))

/* RNG state variables */
struct isaac_state
  {
    word32 mm[ISAAC_WORDS];     /* Main state array */
    word32 iv[8];               /* Seeding initial vector */
    word32 a, b, c;             /* Extra index variables */
  };

/* This index operation is more efficient on many processors */
#define ind(mm, x) \
  (* (word32 *) ((char *) (mm) + ((x) & (ISAAC_WORDS - 1) * sizeof (word32))))

/*
 * The central step.  This uses two temporaries, x and y.  mm is the
 * whole state array, while m is a pointer to the current word.  off is
 * the offset from m to the word ISAAC_WORDS/2 words away in the mm array,
 * i.e. +/- ISAAC_WORDS/2.
 */
#define isaac_step(mix, a, b, mm, m, off, r) \
( \
  a = ((a) ^ (mix)) + (m)[off], \
  x = *(m), \
  *(m) = y = ind (mm, x) + (a) + (b), \
  *(r) = b = ind (mm, (y) >> ISAAC_LOG) + x \
)

/*
 * Refill the entire R array, and update S.
 */
static void
isaac_refill (struct isaac_state *s, word32 r[/* ISAAC_WORDS */])
{
  register word32 a, b;         /* Caches of a and b */
  register word32 x, y;         /* Temps needed by isaac_step macro */
  register word32 *m = s->mm;   /* Pointer into state array */

  a = s->a;
  b = s->b + (++s->c);

  do
    {
      isaac_step (a << 13, a, b, s->mm, m, ISAAC_WORDS / 2, r);
      isaac_step (a >> 6, a, b, s->mm, m + 1, ISAAC_WORDS / 2, r + 1);
      isaac_step (a << 2, a, b, s->mm, m + 2, ISAAC_WORDS / 2, r + 2);
      isaac_step (a >> 16, a, b, s->mm, m + 3, ISAAC_WORDS / 2, r + 3);
      r += 4;
    }
  while ((m += 4) < s->mm + ISAAC_WORDS / 2);
  do
    {
      isaac_step (a << 13, a, b, s->mm, m, -ISAAC_WORDS / 2, r);
      isaac_step (a >> 6, a, b, s->mm, m + 1, -ISAAC_WORDS / 2, r + 1);
      isaac_step (a << 2, a, b, s->mm, m + 2, -ISAAC_WORDS / 2, r + 2);
      isaac_step (a >> 16, a, b, s->mm, m + 3, -ISAAC_WORDS / 2, r + 3);
      r += 4;
    }
  while ((m += 4) < s->mm + ISAAC_WORDS);
  s->a = a;
  s->b = b;
}

/*
 * The basic seed-scrambling step for initialization, based on Bob
 * Jenkins' 256-bit hash.
 */
#define mix(a,b,c,d,e,f,g,h) \
   (       a ^= b << 11, d += a, \
   b += c, b ^= c >>  2, e += b, \
   c += d, c ^= d <<  8, f += c, \
   d += e, d ^= e >> 16, g += d, \
   e += f, e ^= f << 10, h += e, \
   f += g, f ^= g >>  4, a += f, \
   g += h, g ^= h <<  8, b += g, \
   h += a, h ^= a >>  9, c += h, \
   a += b                        )

/* The basic ISAAC initialization pass.  */
static void
isaac_mix (struct isaac_state *s, word32 const seed[/* ISAAC_WORDS */])
{
  int i;
  word32 a = s->iv[0];
  word32 b = s->iv[1];
  word32 c = s->iv[2];
  word32 d = s->iv[3];
  word32 e = s->iv[4];
  word32 f = s->iv[5];
  word32 g = s->iv[6];
  word32 h = s->iv[7];

  for (i = 0; i < ISAAC_WORDS; i += 8)
    {
      a += seed[i];
      b += seed[i + 1];
      c += seed[i + 2];
      d += seed[i + 3];
      e += seed[i + 4];
      f += seed[i + 5];
      g += seed[i + 6];
      h += seed[i + 7];

      mix (a, b, c, d, e, f, g, h);

      s->mm[i] = a;
      s->mm[i + 1] = b;
      s->mm[i + 2] = c;
      s->mm[i + 3] = d;
      s->mm[i + 4] = e;
      s->mm[i + 5] = f;
      s->mm[i + 6] = g;
      s->mm[i + 7] = h;
    }

  s->iv[0] = a;
  s->iv[1] = b;
  s->iv[2] = c;
  s->iv[3] = d;
  s->iv[4] = e;
  s->iv[5] = f;
  s->iv[6] = g;
  s->iv[7] = h;
}

#if 0 /* Provided for reference only; not used in this code */
/*
 * Initialize the ISAAC RNG with the given seed material.
 * Its size MUST be a multiple of ISAAC_BYTES, and may be
 * stored in the s->mm array.
 *
 * This is a generalization of the original ISAAC initialization code
 * to support larger seed sizes.  For seed sizes of 0 and ISAAC_BYTES,
 * it is identical.
 */
static void
isaac_init (struct isaac_state *s, word32 const *seed, size_t seedsize)
{
  static word32 const iv[8] =
  {
    0x1367df5a, 0x95d90059, 0xc3163e4b, 0x0f421ad8,
    0xd92a4a78, 0xa51a3c49, 0xc4efea1b, 0x30609119};
  int i;

# if 0
  /* The initialization of iv is a precomputed form of: */
  for (i = 0; i < 7; i++)
    iv[i] = 0x9e3779b9;         /* the golden ratio */
  for (i = 0; i < 4; ++i)       /* scramble it */
    mix (iv[0], iv[1], iv[2], iv[3], iv[4], iv[5], iv[6], iv[7]);
# endif
  s->a = s->b = s->c = 0;

  for (i = 0; i < 8; i++)
    s->iv[i] = iv[i];

  if (seedsize)
    {
      /* First pass (as in reference ISAAC code) */
      isaac_mix (s, seed);
      /* Second and subsequent passes (extension to ISAAC) */
      while (seedsize -= ISAAC_BYTES)
        {
          seed += ISAAC_WORDS;
          for (i = 0; i < ISAAC_WORDS; i++)
            s->mm[i] += seed[i];
          isaac_mix (s, s->mm);
        }
    }
  else
    {
      /* The no seed case (as in reference ISAAC code) */
      for (i = 0; i < ISAAC_WORDS; i++)
        s->mm[i] = 0;
    }

  /* Final pass */
  isaac_mix (s, s->mm);
}
#endif

/* Start seeding an ISAAC structire */
static void
isaac_seed_start (struct isaac_state *s)
{
  static word32 const iv[8] =
    {
      0x1367df5a, 0x95d90059, 0xc3163e4b, 0x0f421ad8,
      0xd92a4a78, 0xa51a3c49, 0xc4efea1b, 0x30609119
    };
  int i;

#if 0
  /* The initialization of iv is a precomputed form of: */
  for (i = 0; i < 7; i++)
    iv[i] = 0x9e3779b9;         /* the golden ratio */
  for (i = 0; i < 4; ++i)       /* scramble it */
    mix (iv[0], iv[1], iv[2], iv[3], iv[4], iv[5], iv[6], iv[7]);
#endif
  for (i = 0; i < 8; i++)
    s->iv[i] = iv[i];
  /* We could initialize s->mm to zero, but why bother? */

  /* s->c gets used for a data pointer during the seeding phase */
  s->a = s->b = s->c = 0;
}

/* Add a buffer of seed material */
static void
isaac_seed_data (struct isaac_state *s, void const *buf, size_t size)
{
  unsigned char *p;
  size_t avail;
  size_t i;

  avail = sizeof s->mm - (size_t) s->c; /* s->c is used as a write pointer */

  /* Do any full buffers that are necessary */
  while (size > avail)
    {
      p = (unsigned char *) s->mm + s->c;
      for (i = 0; i < avail; i++)
        p[i] ^= ((unsigned char const *) buf)[i];
      buf = (char const *) buf + avail;
      size -= avail;
      isaac_mix (s, s->mm);
      s->c = 0;
      avail = sizeof s->mm;
    }

  /* And the final partial block */
  p = (unsigned char *) s->mm + s->c;
  for (i = 0; i < size; i++)
    p[i] ^= ((unsigned char const *) buf)[i];
  s->c = (word32) size;
}


/* End of seeding phase; get everything ready to produce output. */
static void
isaac_seed_finish (struct isaac_state *s)
{
  isaac_mix (s, s->mm);
  isaac_mix (s, s->mm);
  /* Now reinitialize c to start things off right */
  s->c = 0;
}
#define ISAAC_SEED(s,x) isaac_seed_data (s, &(x), sizeof (x))


#if __GNUC__ >= 2 && (__i386__ || __alpha__)
/*
 * Many processors have very-high-resolution timer registers,
 * The timer registers can be made inaccessible, so we have to deal with the
 * possibility of SIGILL while we're working.
 */
static jmp_buf env;
static RETSIGTYPE
sigill_handler (int signum)
{
  (void) signum;
  longjmp (env, 1);  /* Trivial, just return an indication that it happened */
}

static void
isaac_seed_machdep (struct isaac_state *s)
{
  RETSIGTYPE (*oldhandler) (int);

  /* This is how one does try/except in C */
  oldhandler = signal (SIGILL, sigill_handler);
  if (setjmp (env))  /* ANSI: Must be entire controlling expression */
    {
      (void) signal (SIGILL, oldhandler);
    }
  else
    {
# if __i386__
      word32 t[2];
      __asm__ __volatile__ ("rdtsc" : "=a" (t[0]), "=d" (t[1]));
# endif
# if __alpha__
      unsigned long t;
      __asm__ __volatile__ ("rpcc %0" : "=r" (t));
# endif
# if _ARCH_PPC
      /* Code not used because this instruction is available only on first-
         generation PPCs and evokes a SIGBUS on some Linux 2.4 kernels.  */
      word32 t;
      __asm__ __volatile__ ("mfspr %0,22" : "=r" (t));
# endif
# if __mips
      /* Code not used because this is not accessible from userland */
      word32 t;
      __asm__ __volatile__ ("mfc0\t%0,$9" : "=r" (t));
# endif
# if __sparc__
      /* This doesn't compile on all platforms yet.  How to fix? */
      unsigned long t;
      __asm__ __volatile__ ("rd %%tick, %0" : "=r" (t));
# endif
     (void) signal (SIGILL, oldhandler);
     isaac_seed_data (s, &t, sizeof t);
  }
}

#else /* !(__i386__ || __alpha__) */

/* Do-nothing stub */
# define isaac_seed_machdep(s) (void) 0

#endif /* !(__i386__ || __alpha__) */


/*
 * Get seed material.  16 bytes (128 bits) is plenty, but if we have
 * /dev/urandom, we get 32 bytes = 256 bits for complete overkill.
 */
static void
isaac_seed (struct isaac_state *s)
{
  isaac_seed_start (s);

  { pid_t t = getpid ();   ISAAC_SEED (s, t); }
  { pid_t t = getppid ();  ISAAC_SEED (s, t); }
  { uid_t t = getuid ();   ISAAC_SEED (s, t); }
  { gid_t t = getgid ();   ISAAC_SEED (s, t); }

  {
#if HAVE_GETHRTIME
    hrtime_t t = gethrtime ();
    ISAAC_SEED (s, t);
#else
# if HAVE_CLOCK_GETTIME         /* POSIX ns-resolution */
    struct timespec t;
    clock_gettime (CLOCK_REALTIME, &t);
# else
#  if HAVE_GETTIMEOFDAY
    struct timeval t;
    gettimeofday (&t, (struct timezone *) 0);
#  else
    time_t t;
    t = time ((time_t *) 0);
#  endif
# endif
#endif
    ISAAC_SEED (s, t);
  }

  isaac_seed_machdep (s);

  {
    char buf[32];
    int fd = open ("/dev/urandom", O_RDONLY | O_NOCTTY);
    if (fd >= 0)
      {
        read (fd, buf, 32);
        close (fd);
        isaac_seed_data (s, buf, 32);
      }
    else
      {
        fd = open ("/dev/random", O_RDONLY | O_NONBLOCK | O_NOCTTY);
        if (fd >= 0)
          {
            /* /dev/random is more precious, so use less */
            read (fd, buf, 16);
            close (fd);
            isaac_seed_data (s, buf, 16);
          }
      }
  }

  isaac_seed_finish (s);
}

/* Single-word RNG built on top of ISAAC */
struct irand_state
{
  word32 r[ISAAC_WORDS];
  unsigned numleft;
  struct isaac_state *s;
};

static void
irand_init (struct irand_state *r, struct isaac_state *s)
{
  r->numleft = 0;
  r->s = s;
}

/*
 * We take from the end of the block deliberately, so if we need
 * only a small number of values, we choose the final ones which are
 * marginally better mixed than the initial ones.
 */
static word32
irand32 (struct irand_state *r)
{
  if (!r->numleft)
    {
      isaac_refill (r->s, r->r);
      r->numleft = ISAAC_WORDS;
    }
  return r->r[--r->numleft];
}

/*
 * Return a uniformly distributed random number between 0 and n,
 * inclusive.  Thus, the result is modulo n+1.
 *
 * Theory of operation: as x steps through every possible 32-bit number,
 * x % n takes each value at least 2^32 / n times (rounded down), but
 * the values less than 2^32 % n are taken one additional time.  Thus,
 * x % n is not perfectly uniform.  To fix this, the values of x less
 * than 2^32 % n are disallowed, and if the RNG produces one, we ask
 * for a new value.
 */
static word32
irand_mod (struct irand_state *r, word32 n)
{
  word32 x;
  word32 lim;

  if (!++n)
    return irand32 (r);

  lim = -n % n;                 /* == (2**32-n) % n == 2**32 % n */
  do
    {
      x = irand32 (r);
    }
  while (x < lim);
  return x % n;
}

/*
 * Fill a buffer with a fixed pattern.
 *
 * The buffer must be at least 3 bytes long, even if
 * size is less.  Larger sizes are filled exactly.
 */
static void
fillpattern (int type, unsigned char *r, size_t size)
{
  size_t i;
  unsigned bits = type & 0xfff;

  bits |= bits << 12;
  ((unsigned char *) r)[0] = (bits >> 4) & 255;
  ((unsigned char *) r)[1] = (bits >> 8) & 255;
  ((unsigned char *) r)[2] = bits & 255;
  for (i = 3; i < size / 2; i *= 2)
    memcpy ((char *) r + i, (char *) r, i);
  if (i < size)
    memcpy ((char *) r + i, (char *) r, size - i);

  /* Invert the first bit of every 512-byte sector. */
  if (type & 0x1000)
    for (i = 0; i < size; i += 512)
      r[i] ^= 0x80;
}

/*
 * Fill a buffer, R (of size SIZE_MAX), with random data.
 * SIZE is rounded UP to a multiple of ISAAC_BYTES.
 */
static void
fillrand (struct isaac_state *s, word32 *r, size_t size_max, size_t size)
{
  size = (size + ISAAC_BYTES - 1) / ISAAC_BYTES;
  assert (size <= size_max);

  while (size--)
    {
      isaac_refill (s, r);
      r += ISAAC_WORDS;
    }
}

/*
 * Generate a 6-character (+ nul) pass name string
 * FIXME: allow translation of "random".
 */
#define PASS_NAME_SIZE 7
static void
passname (unsigned char const *data, char name[PASS_NAME_SIZE])
{
  if (data)
    sprintf (name, "%02x%02x%02x", data[0], data[1], data[2]);
  else
    memcpy (name, "random", PASS_NAME_SIZE);
}

/*
 * Do pass number k of n, writing "size" bytes of the given pattern "type"
 * to the file descriptor fd.   Qname, k and n are passed in only for verbose
 * progress message purposes.  If n == 0, no progress messages are printed.
 *
 * If *sizep == -1, the size is unknown, and it will be filled in as soon
 * as writing fails.
 */
static int
dopass (int fd, char const *qname, off_t *sizep, int type,
        struct isaac_state *s, unsigned long k, unsigned long n)
{
  off_t size = *sizep;
  off_t offset;                 /* Current file posiiton */
  off_t thresh;                 /* Offset to print next status update */
  size_t lim;                   /* Amount of data to try writing */
  size_t soff;                  /* Offset into buffer for next write */
  ssize_t ssize;                /* Return value from write */
#if ISAAC_WORDS > 1024
  word32 r[ISAAC_WORDS * 3];    /* Multiple of 4K and of pattern size */
#else
  word32 r[1024 * 3];           /* Multiple of 4K and of pattern size */
#endif
  char pass_string[PASS_NAME_SIZE];     /* Name of current pass */

  if (lseek (fd, (off_t) 0, SEEK_SET) == -1)
    {
      error (0, errno, _("%s: cannot rewind"), qname);
      return -1;
    }

  /* Constant fill patterns need only be set up once. */
  if (type >= 0)
    {
      lim = sizeof r;
      if ((off_t) lim > size && size != -1)
        {
          lim = (size_t) size;
        }
      fillpattern (type, (unsigned char *) r, lim);
      passname ((unsigned char *) r, pass_string);
    }
  else
    {
      passname (0, pass_string);
    }

  /* Set position if first status update */
  thresh = 0;
  if (n)
    {
      error (0, 0, _("%s: pass %lu/%lu (%s)..."), qname, k, n, pass_string);
      thresh = VERBOSE_UPDATE;
      if (thresh > size && size != -1)
        thresh = size;
    }

  offset = 0;
  for (;;)
    {
      /* How much to write this time? */
      lim = sizeof r;
      if ((off_t) lim > size - offset && size != -1)
        {
          if (size < offset)
            break;
          lim = (size_t) (size - offset);
          if (!lim)
            break;
        }
      if (type < 0)
        fillrand (s, r, sizeof r, lim);
      /* Loop to retry partial writes. */
      for (soff = 0; soff < lim; soff += ssize)
        {
          ssize = write (fd, (char *) r + soff, lim - soff);
          if (ssize <= 0)
            {
              if ((ssize == 0 || errno == ENOSPC)
                  && size == -1)
                {
                  /* Ah, we have found the end of the file */
                  *sizep = thresh = size = offset + soff;
                  break;
                }
              else
                {
                  int errnum = errno;
                  char buf[LONGEST_HUMAN_READABLE + 1];
                  error (0, errnum, _("%s: error writing at offset %s"),
                         qname,
                         human_readable ((uintmax_t) (offset + soff),
                                         buf, 1, 1));
                  /*
                   * I sometimes use shred on bad media, before throwing it
                   * out.  Thus, I don't want it to give up on bad blocks.
                   * This code assumes 512-byte blocks and tries to skip
                   * over them.  It works because lim is always a multiple
                   * of 512, except at the end.
                   */
                  if (errnum == EIO && soff % 512 == 0 && lim >= soff + 512
                      && size != -1)
                    {
                      if (lseek (fd, (off_t) (offset + soff + 512), SEEK_SET)
                          != -1)
                        {
                          soff += 512;
                          continue;
                        }
                      error (0, errno, "%s: lseek", qname);
                    }
                  return -1;
                }
            }
        }

      /* Okay, we have written "lim" bytes. */

      if (offset + lim < offset)
        {
          error (0, 0, _("%s: file too large"), qname);
          return -1;
        }

      offset += lim;

      /* Time to print progress? */
      if (offset >= thresh && n)
        {
          char offset_buf[LONGEST_HUMAN_READABLE + 1];
          char size_buf[LONGEST_HUMAN_READABLE + 1];
          char const *human_offset
            = human_readable ((uintmax_t) offset, offset_buf, 1,
                              OUTPUT_BLOCK_SIZE);
          if (size != -1)
            error (0, 0, _("%s: pass %lu/%lu (%s)...%s/%s"), qname, k, n,
                   pass_string, human_offset,
                   human_readable ((uintmax_t) size, size_buf, 1,
                                   OUTPUT_BLOCK_SIZE));
          else
            error (0, 0, _("%s: pass %lu/%lu (%s)...%s"), qname, k, n,
                   pass_string, human_offset);

          thresh += VERBOSE_UPDATE;
          if (thresh > size && size != -1)
            thresh = size;
          /*
           * Force periodic syncs to keep displayed progress accurate
           * FIXME: Should these be present even if -v is not enabled,
           * to keep the buffer cache from filling with dirty pages?
           * It's a common problem with programs that do lots of writes,
           * like mkfs.
           */
          if (fdatasync (fd) < 0 && fsync (fd) < 0)
            {
              error (0, errno, "%s: fsync", qname);
              return -1;
            }
        }
    }

  /* Force what we just wrote to hit the media. */
  if (fdatasync (fd) < 0 && fsync (fd) < 0)
    {
      error (0, errno, "%s: fsync", qname);
      return -1;
    }
  return 0;
}

/*
 * The passes start and end with a random pass, and the passes in between
 * are done in random order.  The idea is to deprive someone trying to
 * reverse the process of knowledge of the overwrite patterns, so they
 * have the additional step of figuring out what was done to the disk
 * before they can try to reverse or cancel it.
 *
 * First, all possible 1-bit patterns.  There are two of them.
 * Then, all possible 2-bit patterns.  There are four, but the two
 * which are also 1-bit patterns can be omitted.
 * Then, all possible 3-bit patterns.  Likewise, 8-2 = 6.
 * Then, all possible 4-bit patterns.  16-4 = 12.
 *
 * The basic passes are:
 * 1-bit: 0x000, 0xFFF
 * 2-bit: 0x555, 0xAAA
 * 3-bit: 0x249, 0x492, 0x924, 0x6DB, 0xB6D, 0xDB6 (+ 1-bit)
 *        100100100100         110110110110
 *           9   2   4            D   B   6
 * 4-bit: 0x111, 0x222, 0x333, 0x444, 0x666, 0x777,
 *        0x888, 0x999, 0xBBB, 0xCCC, 0xDDD, 0xEEE (+ 1-bit, 2-bit)
 * Adding three random passes at the beginning, middle and end
 * produces the default 25-pass structure.
 *
 * The next extension would be to 5-bit and 6-bit patterns.
 * There are 30 uncovered 5-bit patterns and 64-8-2 = 46 uncovered
 * 6-bit patterns, so they would increase the time required
 * significantly.  4-bit patterns are enough for most purposes.
 *
 * The main gotcha is that this would require a trickier encoding,
 * since lcm(2,3,4) = 12 bits is easy to fit into an int, but
 * lcm(2,3,4,5) = 60 bits is not.
 *
 * One extension that is included is to complement the first bit in each
 * 512-byte block, to alter the phase of the encoded data in the more
 * complex encodings.  This doesn't apply to MFM, so the 1-bit patterns
 * are considered part of the 3-bit ones and the 2-bit patterns are
 * considered part of the 4-bit patterns.
 *
 *
 * How does the generalization to variable numbers of passes work?
 *
 * Here's how...
 * Have an ordered list of groups of passes.  Each group is a set.
 * Take as many groups as will fit, plus a random subset of the
 * last partial group, and place them into the passes list.
 * Then shuffle the passes list into random order and use that.
 *
 * One extra detail: if we can't include a large enough fraction of the
 * last group to be interesting, then just substitute random passes.
 *
 * If you want more passes than the entire list of groups can
 * provide, just start repeating from the beginning of the list.
 */
static int const
  patterns[] =
{
  -2,                           /* 2 random passes */
  2, 0x000, 0xFFF,              /* 1-bit */
  2, 0x555, 0xAAA,              /* 2-bit */
  -1,                           /* 1 random pass */
  6, 0x249, 0x492, 0x6DB, 0x924, 0xB6D, 0xDB6,  /* 3-bit */
  12, 0x111, 0x222, 0x333, 0x444, 0x666, 0x777,
  0x888, 0x999, 0xBBB, 0xCCC, 0xDDD, 0xEEE,     /* 4-bit */
  -1,                           /* 1 random pass */
        /* The following patterns have the frst bit per block flipped */
  8, 0x1000, 0x1249, 0x1492, 0x16DB, 0x1924, 0x1B6D, 0x1DB6, 0x1FFF,
  14, 0x1111, 0x1222, 0x1333, 0x1444, 0x1555, 0x1666, 0x1777,
  0x1888, 0x1999, 0x1AAA, 0x1BBB, 0x1CCC, 0x1DDD, 0x1EEE,
  -1,                           /* 1 random pass */
  0                             /* End */
};

/*
 * Generate a random wiping pass pattern with num passes.
 * This is a two-stage process.  First, the passes to include
 * are chosen, and then they are shuffled into the desired
 * order.
 */
static void
genpattern (int *dest, size_t num, struct isaac_state *s)
{
  struct irand_state r;
  size_t randpasses;
  int const *p;
  int *d;
  size_t n;
  size_t accum, top, swap;
  int k;

  if (!num)
    return;

  irand_init (&r, s);

  /* Stage 1: choose the passes to use */
  p = patterns;
  randpasses = 0;
  d = dest;                     /* Destination for generated pass list */
  n = num;                      /* Passes remaining to fill */

  for (;;)
    {
      k = *p++;                 /* Block descriptor word */
      if (!k)
        {                       /* Loop back to the beginning */
          p = patterns;
        }
      else if (k < 0)
        {                       /* -k random passes */
          k = -k;
          if ((size_t) k >= n)
            {
              randpasses += n;
              n = 0;
              break;
            }
          randpasses += k;
          n -= k;
        }
      else if ((size_t) k <= n)
        {                       /* Full block of patterns */
          memcpy (d, p, k * sizeof (int));
          p += k;
          d += k;
          n -= k;
        }
      else if (n < 2 || 3 * n < (size_t) k)
        {                       /* Finish with random */
          randpasses += n;
          break;
        }
      else
        {                       /* Pad out with k of the n available */
          do
            {
              if (n == (size_t) k-- || irand_mod (&r, k) < n)
                {
                  *d++ = *p;
                  n--;
                }
              p++;
            }
          while (n);
          break;
        }
    }
  top = num - randpasses;       /* Top of initialized data */
  /* assert (d == dest+top); */

  /*
   * We now have fixed patterns in the dest buffer up to
   * "top", and we need to scramble them, with "randpasses"
   * random passes evenly spaced among them.
   *
   * We want one at the beginning, one at the end, and
   * evenly spaced in between.  To do this, we basically
   * use Bresenham's line draw (a.k.a DDA) algorithm
   * to draw a line with slope (randpasses-1)/(num-1).
   * (We use a positive accumulator and count down to
   * do this.)
   *
   * So for each desired output value, we do the following:
   * - If it should be a random pass, copy the pass type
   *   to top++, out of the way of the other passes, and
   *   set the current pass to -1 (random).
   * - If it should be a normal pattern pass, choose an
   *   entry at random between here and top-1 (inclusive)
   *   and swap the current entry with that one.
   */
  randpasses--;                 /* To speed up later math */
  accum = randpasses;           /* Bresenham DDA accumulator */
  for (n = 0; n < num; n++)
    {
      if (accum <= randpasses)
        {
          accum += num - 1;
          dest[top++] = dest[n];
          dest[n] = -1;
        }
      else
        {
          swap = n + irand_mod (&r, top - n - 1);
          k = dest[n];
          dest[n] = dest[swap];
          dest[swap] = k;
        }
      accum -= randpasses;
    }
  /* assert (top == num); */

  memset (&r, 0, sizeof r);     /* Wipe this on general principles */
}

/*
 * The core routine to actually do the work.  This overwrites the first
 * size bytes of the given fd.  Returns -1 on error, 0 on success.
 */
static int
do_wipefd (int fd, char const *qname, struct isaac_state *s,
           struct Options const *flags)
{
  size_t i;
  struct stat st;
  off_t size;                   /* Size to write, size to read */
  unsigned long n;              /* Number of passes for printing purposes */
  int *passarray;

  n = 0;                /* dopass takes n -- 0 to mean "don't print progress" */
  if (flags->verbose)
    n = flags->n_iterations + ((flags->zero_fill) != 0);

  if (fstat (fd, &st))
    {
      error (0, errno, "%s: fstat", qname);
      return -1;
    }

  /* If we know that we can't possibly shred the file, give up now.
     Otherwise, we may go into a infinite loop writing data before we
     find that we can't rewind the device.  */
  if ((S_ISCHR (st.st_mode) && isatty (fd))
      || S_ISFIFO (st.st_mode)
      || S_ISSOCK (st.st_mode))
    {
      error (0, 0, _("%s: invalid file type"), qname);
      return -1;
    }

  /* Allocate pass array */
  passarray = xmalloc (flags->n_iterations * sizeof (int));

  size = flags->size;
  if (size == -1)
    {
      /* Accept a length of zero only if it's a regular file.
         For any other type of file, try to get the size another way.  */
      if (S_ISREG (st.st_mode))
        {
          size = st.st_size;
          if (size < 0)
            {
              error (0, 0, _("%s: file has negative size"), qname);
              return -1;
            }
        }
      else
        {
          size = lseek (fd, (off_t) 0, SEEK_END);
          if (size <= 0)
            {
              /* We are unable to determine the length, up front.
                 Let dopass do that as part of its first iteration.  */
              size = -1;
            }
        }

      if (0 <= size && !(flags->exact))
        {
          size += ST_BLKSIZE (st) - 1 - (size - 1) % ST_BLKSIZE (st);

          /* If in rounding up, we've just overflowed, use the maximum.  */
          if (size < 0)
            size = TYPE_MAXIMUM (off_t);
        }
    }

  /* Schedule the passes in random order. */
  genpattern (passarray, flags->n_iterations, s);

  /* Do the work */
  for (i = 0; i < flags->n_iterations; i++)
    {
      if (dopass (fd, qname, &size, passarray[i], s, i + 1, n) < 0)
        {
          memset (passarray, 0, flags->n_iterations * sizeof (int));
          free (passarray);
          return -1;
        }
    }

  memset (passarray, 0, flags->n_iterations * sizeof (int));
  free (passarray);

  if (flags->zero_fill)
    if (dopass (fd, qname, &size, 0, s, flags->n_iterations + 1, n) < 0)
      return -1;

  /* Okay, now deallocate the data.  The effect of ftruncate on
     non-regular files is unspecified, so don't worry about any
     errors reported for them.  */
  if (flags->remove_file && ftruncate (fd, (off_t) 0) != 0
      && S_ISREG (st.st_mode))
    {
      error (0, errno, _("%s: error truncating"), qname);
      return -1;
    }

  return 0;
}

/* A wrapper with a little more checking for fds on the command line */
static int
wipefd (int fd, char const *qname, struct isaac_state *s,
        struct Options const *flags)
{
  int fd_flags = fcntl (fd, F_GETFL);

  if (fd_flags < 0)
    {
      error (0, errno, "%s: fcntl", qname);
      return -1;
    }
  if (fd_flags & O_APPEND)
    {
      error (0, 0, _("%s: cannot shred append-only file descriptor"), qname);
      return -1;
    }
  return do_wipefd (fd, qname, s, flags);
}

/* --- Name-wiping code --- */

/* Characters allowed in a file name - a safe universal set. */
static char const nameset[] =
"0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_+=%@#.";

/*
 * This increments the name, considering it as a big-endian base-N number
 * with the digits taken from nameset.  Characters not in the nameset
 * are considered to come before nameset[0].
 *
 * It's not obvious, but this will explode if name[0..len-1] contains
 * any 0 bytes.
 *
 * This returns the carry (1 on overflow).
 */
static int
incname (char *name, unsigned len)
{
  char const *p;

  if (!len)
    return 1;

  p = strchr (nameset, name[--len]);
  /* If the character is not found, replace it with a 0 digit */
  if (!p)
    {
      name[len] = nameset[0];
      return 0;
    }
  /* If this character has a successor, use it */
  if (p[1])
    {
      name[len] = p[1];
      return 0;
    }
  /* Otherwise, set this digit to 0 and increment the prefix */
  name[len] = nameset[0];
  return incname (name, len);
}

/*
 * Repeatedly rename a file with shorter and shorter names,
 * to obliterate all traces of the file name on any system that
 * adds a trailing delimiter to on-disk file names and reuses
 * the same directory slot.  Finally, unlink it.
 * The passed-in filename is modified in place to the new filename.
 * (Which is unlinked if this function succeeds, but is still present if
 * it fails for some reason.)
 *
 * The main loop is written carefully to not get stuck if all possible
 * names of a given length are occupied.  It counts down the length from
 * the original to 0.  While the length is non-zero, it tries to find an
 * unused file name of the given length.  It continues until either the
 * name is available and the rename succeeds, or it runs out of names
 * to try (incname wraps and returns 1).  Finally, it unlinks the file.
 *
 * The unlink is Unix-specific, as ANSI-standard remove has more
 * portability problems with C libraries making it "safe".  rename
 * is ANSI-standard.
 *
 * To force the directory data out, we try to open the directory and
 * invoke fdatasync on it.  This is rather non-standard, so we don't
 * insist that it works, just fall back to a global sync in that case.
 * This is fairly significantly Unix-specific.  Of course, on any
 * filesystem with synchronous metadata updates, this is unnecessary.
 */
static int
wipename (char *oldname, char const *qoldname, struct Options const *flags)
{
  char *newname, *base;   /* Base points to filename part of newname */
  unsigned len;
  int err;
  int dir_fd;                   /* Try to open directory to sync *it* */

  newname = xstrdup (oldname);
  if (flags->verbose)
    error (0, 0, _("%s: removing"), qoldname);

  /* Find the file name portion */
  base = strrchr (newname, '/');
  /* Temporary hackery to get a directory fd */
  if (base)
    {
      *base = '\0';
      dir_fd = open (newname, O_RDONLY | O_NOCTTY);
      *base = '/';
    }
  else
    {
      dir_fd = open (".", O_RDONLY | O_NOCTTY);
    }
  base = base ? base + 1 : newname;
  len = strlen (base);

  while (len)
    {
      memset (base, nameset[0], len);
      base[len] = 0;
      do
        {
          struct stat st;
          if (lstat (newname, &st) < 0)
            {
              if (rename (oldname, newname) == 0)
                {
                  if (dir_fd < 0
                      || (fdatasync (dir_fd) < 0 && fsync (dir_fd) < 0))
                    sync ();    /* Force directory out */
                  if (flags->verbose)
                    {
                      /*
                       * People seem to understand this better than talking
                       * about renaming oldname.  newname doesn't need
                       * quoting because we picked it.
                       */
                      error (0, 0, _("%s: renamed to %s"), qoldname,
                             quote (newname));
                    }
                  memcpy (oldname + (base - newname), base, len + 1);
                  break;
                }
              else
                {
                  /* The rename failed: give up on this length.  */
                  break;
                }
            }
          else
            {
              /* newname exists, so increment BASE so we use another */
            }
        }
      while (!incname (base, len));
      len--;
    }
  free (newname);
  err = unlink (oldname);
  if (dir_fd < 0 || (fdatasync (dir_fd) < 0 && fsync (dir_fd) < 0))
    sync ();
  close (dir_fd);
  if (!err && flags->verbose)
    error (0, 0, _("%s: removed"), qoldname);
  return err;
}

/*
 * Finally, the function that actually takes a filename and grinds
 * it into hamburger.
 *
 * FIXME
 * Detail to note: since we do not restore errno to EACCES after
 * a failed chmod, we end up printing the error code from the chmod.
 * This is actually the error that stopped us from proceeding, so
 * it's arguably the right one, and in practice it'll be either EACCES
 * again or EPERM, which both give similar error messages.
 * Does anyone disagree?
 */
static int
wipefile (char *name, char const *qname,
          struct isaac_state *s, struct Options const *flags)
{
  int err, fd;

  fd = open (name, O_WRONLY | O_NOCTTY);
  if (fd < 0)
    {
      if (errno == EACCES && flags->force)
        {
          if (chmod (name, S_IWUSR) >= 0) /* 0200, user-write-only */
            fd = open (name, O_WRONLY | O_NOCTTY);
        }
      else if ((errno == ENOENT || errno == ENOTDIR)
               && strncmp (name, "/dev/fd/", 8) == 0)
        {
          /* We accept /dev/fd/# even if the OS doesn't support it */
          int errnum = errno;
          unsigned long num;
          char *p;
          errno = 0;
          num = strtoul (name + 8, &p, 10);
          /* If it's completely decimal with no leading zeros... */
          if (errno == 0 && !*p && num <= INT_MAX &&
              (('1' <= name[8] && name[8] <= '9')
               || (name[8] == '0' && !name[9])))
            {
              return wipefd ((int) num, qname, s, flags);
            }
          errno = errnum;
        }
    }
  if (fd < 0)
    {
      error (0, errno, "%s", qname);
      return -1;
    }

  err = do_wipefd (fd, qname, s, flags);
  if (close (fd) != 0)
    {
      error (0, 0, "%s: close", qname);
      err = -1;
    }
  if (err == 0 && flags->remove_file)
    {
      err = wipename (name, qname, flags);
      if (err < 0)
        error (0, 0, _("%s: cannot remove"), qname);
    }
  return err;
}

int
main (int argc, char **argv)
{
  struct isaac_state s;
  int err = 0;
  struct Options flags;
  char **file;
  int n_files;
  int c;
  int i;

  program_name = argv[0];
  setlocale (LC_ALL, "");
  bindtextdomain (PACKAGE, LOCALEDIR);
  textdomain (PACKAGE);

  atexit (close_stdout);

  isaac_seed (&s);

  memset (&flags, 0, sizeof flags);

  flags.n_iterations = DEFAULT_PASSES;
  flags.size = -1;

  while ((c = getopt_long (argc, argv, "fn:s:uvxz", long_opts, NULL)) != -1)
    {
      switch (c)
        {
        case 0:
          break;

        case 'f':
          flags.force = 1;
          break;

        case 'n':
          {
            uintmax_t tmp;
            if (xstrtoumax (optarg, NULL, 10, &tmp, NULL) != LONGINT_OK
                || (word32) tmp != tmp
                || ((size_t) (tmp * sizeof (int)) / sizeof (int) != tmp))
              {
                error (1, 0, _("%s: invalid number of passes"),
                       quotearg_colon (optarg));
              }
            flags.n_iterations = (size_t) tmp;
          }
          break;

        case 'u':
          flags.remove_file = 1;
          break;

        case 's':
          {
            uintmax_t tmp;
            if (xstrtoumax (optarg, NULL, 0, &tmp, "cbBkMGTPEZY0")
                != LONGINT_OK)
              {
                error (1, 0, _("%s: invalid file size"),
                       quotearg_colon (optarg));
              }
            flags.size = tmp;
          }
          break;

        case 'v':
          flags.verbose = 1;
          break;

        case 'x':
          flags.exact = 1;
          break;

        case 'z':
          flags.zero_fill = 1;
          break;

        case_GETOPT_HELP_CHAR;

        case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);

        default:
          usage (1);
        }
    }

  file = argv + optind;
  n_files = argc - optind;

  if (n_files == 0)
    {
      error (0, 0, _("missing file argument"));
      usage (1);
    }

  for (i = 0; i < n_files; i++)
    {
      char const *qname = quotearg_colon (file[i]);
      if (strcmp (file[i], "-") == 0)
        {
          if (wipefd (STDOUT_FILENO, qname, &s, &flags) < 0)
            err = 1;
        }
      else
        {
          /* Plain filename - Note that this overwrites *argv! */
          if (wipefile (file[i], qname, &s, &flags) < 0)
            err = 1;
        }
    }

  /* Just on general principles, wipe s. */
  memset (&s, 0, sizeof s);

  exit (err);
}
/*
 * vim:sw=2:sts=2:
 */