src/misc.c - master - niceSOFT/tar

src/misc.c
1 719 строк43 KB
Darren Carreras
tar: invalidate directory cache after failed open
06 авг 2026, 08:35
06 авг 2026, 08:35d1df7f4
/* Miscellaneous functions, not really specific to GNU tar.

   Copyright 1988-2026 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, see <http://www.gnu.org/licenses/>.  */

#define COMMON_INLINE _GL_EXTERN_INLINE
#include <system.h>
#include <rmt.h>
#include "common.h"
#include <c-ctype.h>
#include <quotearg.h>
#include <xgetcwd.h>
#include <unlinkdir.h>
#include <utimens.h>

#ifndef DOUBLE_SLASH_IS_DISTINCT_ROOT
# define DOUBLE_SLASH_IS_DISTINCT_ROOT 0
#endif

static void namebuf_add_dir (namebuf_t, char const *);
static char *namebuf_finish (namebuf_t);
static const char *tar_getcdpath (idx_t);
static struct fdbase fdbase_opendir (char const *, bool, int);

char const *
quote_n_colon (int n, char const *arg)
{
  return quotearg_n_style_colon (n, get_quoting_style (NULL), arg);
}

/* Handling strings.  */

/* Assign STRING to a copy of VALUE if not zero, or to zero.  If
   STRING was nonzero, it is freed first.  */
void
assign_string_or_null (char **string, const char *value)
{
  if (value)
    assign_string (string, value);
  else
    assign_null (string);
}

void
assign_string (char **string, const char *value)
{
  free (*string);
  *string = xstrdup (value);
}

void
assign_null (char **string)
{
  char *old = *string;
  *string = NULL;
  free (old);
}

void
assign_string_n (char **string, const char *value, idx_t n)
{
  free (*string);
  if (value)
    {
      idx_t l = strnlen (value, n);
      char *p = xmalloc (l + 1);
      memcpy (p, value, l);
      p[l] = 0;
      *string = p;
    }
  else
    *string = NULL;
}

#if 0
/* This function is currently unused; perhaps it should be removed?  */

/* Allocate a copy of the string quoted as in C, and returns that.  If
   the string does not have to be quoted, it returns a null pointer.
   The allocated copy should normally be freed with free() after the
   caller is done with it.

   This is used in one context only: generating the directory file in
   incremental dumps.  The quoted string is not intended for human
   consumption; it is intended only for unquote_string.  The quoting
   is locale-independent, so that users needn't worry about locale
   when reading directory files.  This means that we can't use
   quotearg, as quotearg is locale-dependent and is meant for human
   consumption.  */
static char *
quote_copy_string (const char *string)
{
  const char *source = string;
  char *destination = 0;
  char *buffer = 0;
  bool copying = false;

  while (*source)
    {
      char character = *source++;

      switch (character)
	{
	case '\n': case '\\':
	  if (!copying)
	    {
	      idx_t length = (source - string) - 1;

	      copying = true;
	      buffer = xmalloc (length + 2 + 2 * strlen (source) + 1);
	      memcpy (buffer, string, length);
	      destination = buffer + length;
	    }
	  *destination++ = '\\';
	  *destination++ = character == '\\' ? '\\' : 'n';
	  break;

	default:
	  if (copying)
	    *destination++ = character;
	  break;
	}
    }
  if (copying)
    {
      *destination = '\0';
      return buffer;
    }
  return 0;
}
#endif

/* Take a quoted C string (like those produced by quote_copy_string)
   and turn it back into the un-quoted original, in place.
   Complete the unquoting even if the string was not properly quoted.

   This is used for reading the saved directory file in incremental
   dumps.  It is used for decoding old 'N' records (demangling names).
   But also, it is used for decoding file arguments, would they come
   from the shell or a -T file, and for decoding the --exclude
   argument.  */
void
unquote_string (char *string)
{
  char *source = string;
  char *destination = string;

  /* Escape sequences other than \\ and \n are no longer generated by
     quote_copy_string, but accept them for backwards compatibility,
     and also because unquote_string is used for purposes other than
     parsing the output of quote_copy_string.  */

  while (*source)
    if (*source == '\\')
      switch (*++source)
	{
	case '\\':
	  *destination++ = '\\';
	  source++;
	  break;

	case 'a':
	  *destination++ = '\a';
	  source++;
	  break;

	case 'b':
	  *destination++ = '\b';
	  source++;
	  break;

	case 'f':
	  *destination++ = '\f';
	  source++;
	  break;

	case 'n':
	  *destination++ = '\n';
	  source++;
	  break;

	case 'r':
	  *destination++ = '\r';
	  source++;
	  break;

	case 't':
	  *destination++ = '\t';
	  source++;
	  break;

	case 'v':
	  *destination++ = '\v';
	  source++;
	  break;

	case '?':
	  *destination++ = 0177;
	  source++;
	  break;

	case '0':
	case '1':
	case '2':
	case '3':
	case '4':
	case '5':
	case '6':
	case '7':
	  {
	    unsigned char value = *source++ - '0';

	    if (*source < '0' || *source > '7')
	      {
		*destination++ = value;
		break;
	      }
	    unsigned char val1 = value * 8 + (*source++ - '0'), val2;
	    if (*source < '0' || *source > '7' || ckd_mul (&val2, val1, 8))
	      {
		*destination++ = value;
		break;
	      }
	    *destination++ = val2 + (*source++ - '0');
	    break;
	  }

	default:
	  *destination++ = '\\';
	  if (*source)
	    *destination++ = *source++;
	  break;
	}
    else if (source != destination)
      *destination++ = *source++;
    else
      source++, destination++;

  if (source != destination)
    *destination = '\0';
}

/* Zap trailing slashes.  */
char *
zap_slashes (char *name)
{
  char *q;

  if (!name || *name == 0)
    return name;
  q = name + strlen (name) - 1;
  while (q > name && ISSLASH (*q))
    *q-- = '\0';
  return name;
}

/* The number of file name slashes at the start of the string F.  */
static idx_t
slashlen (char const *f)
{
  idx_t i = 0;
  while (ISSLASH (f[i]))
    i++;
  return i;
}

/* The length of the longest initial prefix of F that consists
   entirely of a sequence of '.'s each followed by one or more slashes.
   This prefix acts like the working directory, i.e., the file name F
   acts like "." if 0 < dotslashlen (F) == strlen (F), and acts like
   &F[dotslashlen (F)] otherwise.  */
idx_t
dotslashlen (char const *f)
{
  idx_t i = 0;
  while (f[i] == '.' && ISSLASH (f[i + 1]))
    i += 2 + slashlen (&f[i + 2]);
  return i;
}

/* Normalize FILE_NAME by removing redundant slashes and "."
   components, including redundant trailing slashes.
   Leave ".." alone, as it may be significant in the presence
   of symlinks and on platforms where "/.." != "/".

   Destructive version: modifies its argument. */
void
normalize_filename_x (char *file_name)
{
  char *name = file_name + FILE_SYSTEM_PREFIX_LEN (file_name);
  char c;

  /* Don't squeeze leading "//" to "/", on hosts where they're distinct.  */
  name += (DOUBLE_SLASH_IS_DISTINCT_ROOT
	   && ISSLASH (*name) && ISSLASH (name[1]) && ! ISSLASH (name[2]));

  /* Omit redundant leading "." components.  */
  char *p = name;
  char const *q = name + dotslashlen (name);

  if (p < q && !*q)
    q = ".";  /* NAME is nonempty and equivalent to ".".  */

  /* Copy components from Q to P, omitting redundant slashes and
     internal "."  components.  */
  while ((*p++ = c = *q++) != '\0')
    if (ISSLASH (c))
      {
	q += slashlen (q);
	q += dotslashlen (q);
      }

  /* Omit redundant trailing "." component and slash.  */
  if (2 < p - name)
    {
      p -= p[-2] == '.' && ISSLASH (p[-3]);
      p -= 2 < p - name && ISSLASH (p[-2]);
      p[-1] = '\0';
    }
}

/* Normalize NAME by removing redundant slashes and "." components,
   including redundant trailing slashes.

   Return a normalized newly-allocated copy.  */

char *
normalize_filename (idx_t cdidx, const char *name)
{
  char *copy = NULL;

  if (IS_RELATIVE_FILE_NAME (name))
    {
      /* Set COPY to the absolute path for this name.

         FIXME: There should be no need to get the absolute file name.
         tar_getcdpath does not return a true "canonical" path, so
         this following approach may lead to situations where the same
         file or directory is processed twice under different absolute
         paths without that duplication being detected.  Perhaps we
         should use dev+ino pairs instead of names?  (See listed03.at for
         a related test case.) */
      const char *cdpath = tar_getcdpath (cdidx);
      idx_t copylen;
      bool need_separator;

      copylen = strlen (cdpath);
      need_separator = ! (DOUBLE_SLASH_IS_DISTINCT_ROOT
			  && copylen == 2 && ISSLASH (cdpath[1]));
      copy = xmalloc (copylen + need_separator + strlen (name) + 1);
      strcpy (copy, cdpath);
      copy[copylen] = DIRECTORY_SEPARATOR;
      strcpy (copy + copylen + need_separator, name);
    }

  if (!copy)
    copy = xstrdup (name);
  normalize_filename_x (copy);
  return copy;
}


void
replace_prefix (char **pname, const char *samp, idx_t slen,
		const char *repl, idx_t rlen)
{
  char *name = *pname;
  idx_t nlen = strlen (name);
  if (slen < nlen && memeq (name, samp, slen) && ISSLASH (name[slen]))
    {
      if (rlen > slen)
	{
	  name = xrealloc (name, nlen - slen + rlen + 1);
	  *pname = name;
	}
      memmove (name + rlen, name + slen, nlen - slen + 1);
      memcpy (name, repl, rlen);
    }
}


/* Handling numbers.  */

/* Convert VALUE, which is converted from a system integer type whose
   minimum value is MINVAL and maximum MINVAL, to a decimal
   integer string.  Use the storage in BUF and return a pointer to the
   converted string.  If VALUE is converted from a negative integer in
   the range MINVAL .. -1, represent it with a string representation
   of the negative integer, using leading '-'.  */
char *
sysinttostr (uintmax_t value, intmax_t minval, uintmax_t maxval,
	     char buf[SYSINT_BUFSIZE])
{
  static_assert (INTMAX_MAX <= UINTMAX_MAX / 2);

  if (value <= maxval)
    return umaxtostr (value, buf);
  else
    {
      intmax_t i = value - minval;
      return imaxtostr (i + minval, buf);
    }
}

/* Convert T to a decimal integer string.  Use the storage in BUF and
   return a pointer to the converted string.  */
char *
timetostr (time_t t, char buf[SYSINT_BUFSIZE])
{
  return sysinttostr (t, TYPE_MINIMUM (time_t), TYPE_MAXIMUM (time_t), buf);
}

/* Convert a prefix of the string ARG to a system integer type.
   If ARGLIM, set *ARGLIM to point to just after the prefix.
   If OVERFLOW, set *OVERFLOW to true or false
   depending on whether the input is out of MINVAL..MAXVAL range.
   If the input is out of that range, return an extreme value.
   MINVAL must not be positive.

   If MINVAL is negative, MAXVAL can be at most INTMAX_MAX, and
   negative integers MINVAL .. -1 are assumed to be represented using
   leading '-' in the usual way.  If the represented value exceeds
   INTMAX_MAX, return a negative integer V such that (uintmax_t) V
   yields the represented value.

   On conversion error: if ARGLIM set *ARGLIM = ARG; if OVERFLOW set
   *OVERFLOW = false; then return 0.

   This is the inverse of sysinttostr.

   Sample call to this function:

      char *s_end;
      bool overflow;
      idx_t i = stoint (s, &s_end, &overflow, 0, IDX_MAX);
      if ((s_end == s) | *s_end | overflow)
        diagnose_invalid (s);

   This example uses "|" instead of "||" for fewer branches at runtime,
   which tends to be more efficient on modern processors.

   This function is named "stoint" instead of "strtoint" because
   <string.h> reserves names beginning with "str".  */

intmax_t
stoint (char const *arg, char **arglim, bool *overflow,
	intmax_t minval, uintmax_t maxval)
{
  static_assert (INTMAX_MAX <= UINTMAX_MAX);
  char const *p = arg;
  intmax_t i;
  bool v = false;

  if (c_isdigit (*p))
    {
      if (minval < 0)
	{
	  i = *p - '0';

	  while (c_isdigit (*++p))
	    {
	      v |= ckd_mul (&i, i, 10);
	      v |= ckd_add (&i, i, *p - '0');
	    }

	  v |= maxval < i;
	  if (v)
	    i = maxval;
	}
      else
	{
	  uintmax_t u = *p - '0';

	  while (c_isdigit (*++p))
	    {
	      v |= ckd_mul (&u, u, 10);
	      v |= ckd_add (&u, u, *p - '0');
	    }

	  v |= maxval < u;
	  if (v)
	    u = maxval;
	  i = represent_uintmax (u);
	}
    }
  else if (minval < 0 && *p == '-' && c_isdigit (p[1]))
    {
      p++;
      i = - (*p - '0');

      while (c_isdigit (*++p))
	{
	  v |= ckd_mul (&i, i, 10);
	  v |= ckd_sub (&i, i, *p - '0');
	}

      v |= i < minval;
      if (v)
	i = minval;
    }
  else
    i = 0;

  if (arglim)
    *arglim = (char *) p;
  if (overflow)
    *overflow = v;
  return i;
}

/* Output fraction and trailing digits appropriate for a nanoseconds
   count equal to NS, but don't output unnecessary '.' or trailing
   zeros.  */

void
code_ns_fraction (int ns, char *p)
{
  if (ns == 0)
    *p = '\0';
  else
    {
      int i = 9;
      *p++ = '.';

      while (ns % 10 == 0)
	{
	  ns /= 10;
	  i--;
	}

      p[i] = '\0';

      for (;;)
	{
	  p[--i] = '0' + ns % 10;
	  if (i == 0)
	    break;
	  ns /= 10;
	}
    }
}

char const *
code_timespec (struct timespec t, char tsbuf[TIMESPEC_STRSIZE_BOUND])
{
  time_t s = t.tv_sec;
  int ns = t.tv_nsec;
  bool negative = s < 0;

  /* ignore invalid values of ns */
  if (BILLION <= ns || ns < 0)
    ns = 0;

  if (negative && ns != 0)
    {
      s++;
      ns = BILLION - ns;
    }

  bool minus_zero = negative & !s;
  char *sstr = timetostr (s, tsbuf + 1);
  sstr[-1] = '-';
  sstr -= minus_zero;
  code_ns_fraction (ns, sstr + strlen (sstr));
  return sstr;
}

struct timespec
decode_timespec (char const *arg, char **arg_lim, bool parse_fraction)
{
  int ns = -1;
  bool overflow;
  time_t s = stoint (arg, arg_lim, &overflow,
		     TYPE_MINIMUM (time_t), TYPE_MAXIMUM (time_t));
  char const *p = *arg_lim;
  if (p != arg)
    {
      ns = 0;

      if (parse_fraction && *p == '.')
	{
	  int digits = 0;
	  bool trailing_nonzero = false;

	  while (c_isdigit (*++p))
	    if (digits < LOG10_BILLION)
	      digits++, ns = 10 * ns + (*p - '0');
	    else
	      trailing_nonzero |= *p != '0';

	  *arg_lim = (char *) p;

	  while (digits < LOG10_BILLION)
	    digits++, ns *= 10;

	  if (*arg == '-')
	    {
	      /* Convert "-1.10000000000001" to s == -2, ns == 89999999.
		 I.e., truncate time stamps towards minus infinity while
		 converting them to internal form.  */
	      ns += trailing_nonzero;
	      if (ns != 0)
		ns = ckd_sub (&s, s, 1) ? -1 : BILLION - ns;
	    }
	}

      if (overflow)
	ns = -1;
    }

  return (struct timespec) { .tv_sec = s, .tv_nsec = ns };
}

/* File handling.  */

/* Saved names in case backup needs to be undone.  */
static char *before_backup_name;
static char *after_backup_name;

/* Return 1 if FILE_NAME must identify a working or root directory.
   FILE_NAME should not be empty.  */
bool
must_be_dot_or_slash (char const *file_name)
{
  file_name += FILE_SYSTEM_PREFIX_LEN (file_name);

  if (ISSLASH (file_name[0]))
    {
      /* It must be a root directory if all components are "." or "..".  */
      for (;;)
	if (ISSLASH (file_name[1]))
	  file_name++;
	else if (file_name[1] == '.'
                 && ISSLASH (file_name[2 + (file_name[2] == '.')]))
	  file_name += 2 + (file_name[2] == '.');
	else
	  return ! file_name[1];
    }
  else
    {
      /* It must be a working directory if it is "." or "",
	 after skipping ^(\./+)* ERE.  */
      file_name += dotslashlen (file_name);
      return ! file_name[file_name[0] == '.'];
    }
}

/* Act like rmdir (FILENAME) relative to chdir_fd, i.e., like rmdir (F).
   However, reject attempts to remove a root directory
   even on systems that allow such a thing.
   Also, do not try to change the removed directory's status later.  */
static int
safer_rmdir (const char *file_name, struct fdbase f)
{
  if (f.fd == BADFD)
    return -1; /* Preserve errno.  */

  if (IS_ABSOLUTE_FILE_NAME (f.base))
    {
      errno = EBUSY;
      return -1;
    }

  if (f.fd != BADFD && unlinkat (f.fd, f.base, AT_REMOVEDIR) == 0)
    {
      fdbase_clear ();
      remove_delayed_set_stat (file_name);
      return 0;
    }
  return -1;
}

/* Remove FILE_NAME, returning 1 on success.  If FILE_NAME is a directory,
   then if OPTION is RECURSIVE_REMOVE_OPTION is set remove FILE_NAME
   recursively; otherwise, remove it only if it is empty.  If FILE_NAME is
   a directory that cannot be removed (e.g., because it is nonempty)
   and if OPTION is WANT_DIRECTORY_REMOVE_OPTION, then return -1.
   Return 0 on error, with errno set; if FILE_NAME is obviously the working
   directory return zero with errno set to zero.  */
int
remove_any_file (const char *file_name, enum remove_option option)
{
  /* Try unlink first if we cannot unlink directories, as this saves
     us a system call in the common case where we're removing a
     non-directory.  */
  bool try_unlink_first = cannot_unlink_dir ();

  struct fdbase f = fdbase (file_name);

  if (try_unlink_first)
    {
      if (f.fd != BADFD && unlinkat (f.fd, f.base, 0) == 0)
	{
	  fdbase_clear ();
	  return 1;
	}

      /* POSIX 1003.1-2001 requires EPERM when attempting to unlink a
	 directory without appropriate privileges, but many Linux
	 kernels return the more-sensible EISDIR.  */
      if (errno != EPERM && errno != EISDIR)
	return 0;
    }

  if (safer_rmdir (file_name, f) == 0)
    return 1;

  switch (errno)
    {
    case ENOTDIR:
      if (try_unlink_first || f.fd == BADFD || unlinkat (f.fd, f.base, 0) < 0)
	return 0;
      fdbase_clear ();
      return 1;

    case 0:
    case EEXIST:
#if defined ENOTEMPTY && ENOTEMPTY != EEXIST
    case ENOTEMPTY:
#endif
      switch (option)
	{
	case ORDINARY_REMOVE_OPTION:
	  break;

	case WANT_DIRECTORY_REMOVE_OPTION:
	  return -1;

	case RECURSIVE_REMOVE_OPTION:
	  {
	    char *directory = tar_savedir (file_name, false);
	    char const *entry;
	    idx_t entrylen;

	    if (! directory)
	      return 0;

	    for (entry = directory;
		 (entrylen = strlen (entry)) != 0;
		 entry += entrylen + 1)
	      {
		char *file_name_buffer = make_file_name (file_name, entry);
		int r = remove_any_file (file_name_buffer,
                                         RECURSIVE_REMOVE_OPTION);
		free (file_name_buffer);

		if (! r)
		  {
		    free (directory);
		    return 0;
		  }
	      }

	    free (directory);
	    return safer_rmdir (file_name, fdbase (file_name)) == 0;
	  }
	}
      break;
    }

  return 0;
}

/* Check if FILE_NAME already exists and make a backup of it right now.
   Return success (nonzero) only if the backup is either unneeded, or
   successful.  For now, directories are considered to never need
   backup.  If THIS_IS_THE_ARCHIVE is nonzero, this is the archive and
   so, we do not have to backup block or character devices, nor remote
   entities.  */
bool
maybe_backup_file (const char *file_name, bool this_is_the_archive)
{
  struct stat file_stat;

  assign_string (&before_backup_name, file_name);

  /* A run situation may exist between Emacs or other GNU programs trying to
     make a backup for the same file simultaneously.  If theoretically
     possible, real problems are unlikely.  Doing any better would require a
     convention, GNU-wide, for all programs doing backups.  */

  assign_null (&after_backup_name);

  /* Check if we really need to backup the file.  */

  if (this_is_the_archive && _remdev (file_name))
    return true;

  if (deref_stat (file_name, &file_stat) < 0)
    {
      if (errno == ENOENT)
	return true;

      stat_error (file_name);
      return false;
    }

  if (S_ISDIR (file_stat.st_mode))
    return true;

  if (this_is_the_archive
      && (S_ISBLK (file_stat.st_mode) || S_ISCHR (file_stat.st_mode)))
    return true;

  struct fdbase f = fdbase (file_name);
  if (f.fd == BADFD)
    {
      open_error (file_name);
      return false;
    }
  idx_t subdirlen = f.base - file_name;
  after_backup_name = find_backup_file_name (f.fd, f.base, backup_type);
  if (! after_backup_name)
    xalloc_die ();
  idx_t after_backup_namelen = strlen (after_backup_name);
  after_backup_name = xrealloc (after_backup_name,
				subdirlen + after_backup_namelen + 1);
  memmove (after_backup_name + subdirlen, after_backup_name,
	   after_backup_namelen + 1);
  memcpy (after_backup_name, file_name, subdirlen);

  if (renameat (f.fd, f.base, f.fd, &after_backup_name[subdirlen]) == 0)
    {
      if (S_ISLNK (file_stat.st_mode))
	fdbase_clear ();
      if (verbose_option)
	fprintf (stdlis, _("Renaming %s to %s\n"),
		 quote_n (0, before_backup_name),
		 quote_n (1, after_backup_name));
      return true;
    }
  else
    {
      /* The backup operation failed.  */
      int e = errno;
      paxerror (e, _("%s: Cannot rename to %s"),
		quotearg_colon (before_backup_name),
		quote_n (1, after_backup_name));
      assign_null (&after_backup_name);
      return false;
    }
}

/* Try to restore the recently backed up file to its original name.
   This is usually only needed after a failed extraction.  */
void
undo_last_backup (void)
{
  if (after_backup_name)
    {
      struct fdbase f = fdbase (before_backup_name);
      if (f.fd == BADFD
	  || (renameat (f.fd, &after_backup_name[f.base - before_backup_name],
			f.fd, f.base)
	      < 0))
	{
	  int e = errno;
	  paxerror (e, _("%s: Cannot rename to %s"),
		    quotearg_colon (after_backup_name),
		    quote_n (1, before_backup_name));
	}
      if (verbose_option)
	fprintf (stdlis, _("Renaming %s back to %s\n"),
		 quote_n (0, after_backup_name),
		 quote_n (1, before_backup_name));
      assign_null (&after_backup_name);
    }
}

/* Apply either stat or lstat to (NAME, BUF), depending on the
   presence of the --dereference option.  NAME is relative to the
   most-recent argument to chdir_do.  */
int
deref_stat (char const *name, struct stat *buf)
{
  struct fdbase f = fdbase (name);
  return f.fd == BADFD ? -1 : fstatat (f.fd, f.base, buf, fstatat_flags);
}

/* Read from FD into the buffer BUF with COUNT bytes.  Attempt to fill
   BUF.  Wait until input is available; this matters because files are
   opened O_NONBLOCK for security reasons, and on some file systems
   this can cause read to fail with errno == EAGAIN.
   If returning less than COUNT, set errno to indicate the error
   except set errno = 0 to indicate EOF.  */
idx_t
blocking_read (int fd, void *buf, idx_t count)
{
  idx_t bytes = full_read (fd, buf, count);

#if defined F_SETFL && O_NONBLOCK
  if (bytes < count && errno == EAGAIN)
    {
      int flags = fcntl (fd, F_GETFL);
      if (0 <= flags && flags & O_NONBLOCK
	  && fcntl (fd, F_SETFL, flags & ~O_NONBLOCK) != -1)
	{
	  char *cbuf = buf;
	  count -= bytes;
	  bytes += full_read (fd, cbuf + bytes, count);
	}
    }
#endif

  return bytes;
}

/* Write to FD from the buffer BUF with COUNT bytes.  Do a full write.
   Wait until an output buffer is available; this matters because
   files are opened O_NONBLOCK for security reasons, and on some file
   systems this can cause write to fail with errno == EAGAIN.  Return
   the actual number of bytes written, setting errno if that is less
   than COUNT.  Return -1 on write error.  */
idx_t
blocking_write (int fd, void const *buf, idx_t count)
{
  idx_t bytes = full_write (fd, buf, count);

#if defined F_SETFL && O_NONBLOCK
  if (bytes < count && errno == EAGAIN)
    {
      int flags = fcntl (fd, F_GETFL);
      if (0 <= flags && flags & O_NONBLOCK
	  && fcntl (fd, F_SETFL, flags & ~O_NONBLOCK) != -1)
	{
	  char const *buffer = buf;
	  bytes += full_write (fd, buffer + bytes, count - bytes);
	}
    }
#endif

  return bytes;
}

/* Set FD's (i.e., assuming the working directory is PARENTFD, FILE's)
   access time to ATIME.  */
int
set_file_atime (int fd, int parentfd, char const *file, struct timespec atime)
{
  struct timespec ts[2];
  ts[0] = atime;
  ts[1].tv_nsec = UTIME_OMIT;
  return fdutimensat (fd, parentfd, file, ts, fstatat_flags);
}

/* A description of a working directory.  */
struct wd
{
  /* The directory's name.  */
  char *name;
  /* "Absolute" path representing this directory; in the contrast to
     the real absolute pathname, it can contain /../ components (see
     normalize_filename_x for the reason of it).  It is NULL if the
     absolute path could not be determined.  */
  char *abspath;
  /* If nonzero, the file descriptor of the directory, or AT_FDCWD if
     the working directory.  If zero, the directory needs to be opened
     to be used.  */
  int fd;
  /* If ID.err is zero, the directory's identity;
     if positive, a failure indication with errno = ID.err;
     if negative, no attempt has been made yet to get the identity.  */
  struct chdir_id id;
};

/* A vector of chdir targets.  wd[0] is the initial working
   directory.  Ordinarily the remaining entries are for -C options.
   But if --one-top-level, each entry is followed by another entry for
   its --one-top-level counterpart, so that ordinary entries are
   even-numbered and --one-top-level entries are odd-numbered.  */
static struct wd *wd;

/* The number of working directories in the vector.  */
static idx_t wd_count;

/* The allocated size of the vector.  */
static idx_t wd_alloc;

/* The maximum number of chdir targets with open directories.
   Don't make it too large, as many operating systems have a small
   limit on the number of open file descriptors.  Also, the current
   implementation does not scale well.  */
enum { CHDIR_CACHE_SIZE = 16 };

/* Indexes into WD of chdir targets with open file descriptors, sorted
   most-recently used first.  Zero indexes are unused.  */
static idx_t wdcache[CHDIR_CACHE_SIZE];

/* Number of nonzero entries in WDCACHE.  */
static idx_t wdcache_count;

idx_t
chdir_count (void)
{
  return (wd_count - !!wd_count) >> !!one_top_level_dir;
}

/* Add DIR to the WD table.  If one_top_level_dir, add that too.
   There must already be room.
   DFD is either AT_FDWD for the initial "." entry,
   or 0 meaning the file descriptor is not open yet.  */
static void
add_wd (char *dir, int dfd)
{
  wd[wd_count].name = dir;
  wd[wd_count].abspath = NULL;
  wd[wd_count].fd = dfd;
  wd[wd_count].id.err = -1;
  wd_count++;

  if (one_top_level_dir)
    {
      wd[wd_count].name = one_top_level_dir;
      wd[wd_count].abspath = NULL;
      wd[wd_count].fd = 0;
      wd[wd_count].id.err = -1;
      wd_count++;
    }
}

/* Ensure that WD exists, with an initial "." entry.  */
static void
ensure_wd (void)
{
  if (!wd)
    {
      /* This must be at least 1 + !!top_level_dir.  Make it 4, to lessen
	 reallocation effort when -C and --one-top-level are both used.  */
      int n_incr_min = 4;

      wd = xpalloc (NULL, &wd_alloc, n_incr_min, -1, sizeof *wd);
      add_wd ((char *) ".", AT_FDCWD);
    }
}

/* DIR is the operand of a -C option; add it to vector of chdir targets,
   and return the index of its location.  If --one-top-level-dir, add
   two targets to the vector.  However, if DIR is "." or an equivalent,
   or if --one-top-level-dir is an absolute file name,
   just reuse the last item in the vector.  */
idx_t
chdir_arg (char *dir)
{
  ensure_wd ();

  /* Optimize the common special case of the working directory,
     or the working directory as a prefix.  */
  if (dir[0])
    {
      dir += dotslashlen (dir);
      if (!dir[dir[0] == '.'])
	return wd_count - 1;
    }

  /* Optimize --one-top-level=X where X is an absolute file name.  */
  if (one_top_level_dir && IS_ABSOLUTE_FILE_NAME (one_top_level_dir))
    return wd_count - 1;

  ptrdiff_t shortage = 1 + !!one_top_level_dir - (wd_alloc - wd_count);
  if (0 < shortage)
    wd = xpalloc (wd, &wd_alloc, shortage, -1, sizeof *wd);
  add_wd (dir, 0);
  return wd_count - 1;
}

/* Index of current directory.  */
idx_t chdir_current;

/* Value suitable for use as the first argument to openat, and in
   similar locations for fstatat, etc.  This is an open file
   descriptor, or AT_FDCWD if the working directory is current,
   or BADFD if the directory has not been opened yet.  It is
   valid until the next invocation of chdir_do.  */
static int chdir_fd = AT_FDCWD;

/* Change to directory I, in a virtual way.  This does not actually
   invoke chdir; it merely sets chdir_fd to an int suitable as the
   first argument for openat, etc.  If I is 0, change to the initial
   working directory; otherwise, I must be a value returned by
   chdir_arg.  */
void
chdir_do (idx_t i, bool create)
{
  struct wd *curr = &wd[i];
  int fd = curr->fd;
  bool one_top_level = !!one_top_level_dir;

  /* Nothing to create unless we are at a one_top_level dir that has
     not been created yet.  */
  create &= i & one_top_level & (fd == BADFD || fd == 0);

  if (chdir_current != i || create)
    {
      if (! fd || create)
	{
	  if (! IS_ABSOLUTE_FILE_NAME (curr->name))
	    chdir_do ((i - 1) & ~+one_top_level, false);

	  int oflags = open_searchdir_how.flags & ~O_NOFOLLOW;
	  fd = fdbase_opendir (curr->name, false, oflags).fd;
	  if (fd < 0)
	    {
	      if (errno == ENOENT)
		{
		  if (create)
		    {
		      if (!create_dir (curr->name))
			fatal_exit ();
		      /* Directory likely exists now; retry.  */
		      fd = fdbase_opendir (curr->name, false, oflags).fd;
		    }
		  else if (i & one_top_level)
		    {
		      /* Mark it to be created later if called with CREATE.  */
		      chdir_fd = curr->fd = BADFD;
		      chdir_current = i;
		      /* Do not add it to the cache.  */
		      return;
		    }
		}

	      if (fd < 0)
		open_fatal (curr->name);
	    }

	  curr->fd = fd;

	  /* Add I to the cache, tossing out the lowest-ranking entry if the
	     cache is full.  */
	  if (wdcache_count < CHDIR_CACHE_SIZE)
	    wdcache[wdcache_count++] = i;
	  else
	    {
	      struct wd *stale = &wd[wdcache[CHDIR_CACHE_SIZE - 1]];
	      if (fdbase_close (stale->fd) < 0)
		close_diag (stale->name);
	      stale->fd = 0;
	      wdcache[CHDIR_CACHE_SIZE - 1] = i;
	    }
	}

      if (0 < fd && /* no assumption about sign of BADFD */ fd != BADFD)
	{
	  /* Move the i value to the front of the cache.  This is
	     O(CHDIR_CACHE_SIZE), but the cache is small.  */
	  idx_t ci;
	  idx_t prev = wdcache[0];
	  for (ci = 1; prev != i; ci++)
	    {
	      idx_t cur = wdcache[ci];
	      wdcache[ci] = prev;
	      if (cur == i)
		break;
	      prev = cur;
	    }
	  wdcache[0] = i;
	}

      chdir_current = i;
      chdir_fd = fd;
    }
}

/* Return the identity of the current directory.  */
struct chdir_id
chdir_id (void)
{
  ensure_wd ();

  struct wd *curr = &wd[chdir_current];
  if (curr->id.err < 0)
    {
      struct stat st;
      curr->id = ((chdir_fd < 0 ? stat (".", &st) : fstat (chdir_fd, &st)) < 0
		  ? (struct chdir_id) { .err = errno }
		  : (struct chdir_id) { .st_dev = st.st_dev,
		                        .st_ino = st.st_ino });
    }
  return curr->id;
}

/* Caches of recent calls to fdbase and fdbase1.  */
static struct fdbase_cache
{
  /* Length of subdirectory name, which need not be null-terminated.
     If the length is zero, no subdir is cached here:
     SUBDIR (if nonnull) is merely a buffer available for use later,
     and CHDIR_CURRENT and FD are irrelevant.  */
  idx_t subdirlen;

  /* Index of ancestor of this subdirectory.  */
  idx_t chdir_current;

  /* Buffer containing name of subdirectory relative to the ancestor.  */
  char *subdir;

  /* Number of bytes allocated for SUBDIR.  */
  idx_t subdiralloc;

  /* FD of subdirectory.  */
  int fd;
} fdbase_cache[2];


/* Return true if positive FD is for a directory searched because of a
   -C or a --one-top-dir option.  */
static bool
chdirable (int fd)
{
  /* Optimize for most common case.  */
  if (fd == chdir_fd)
    return true;

  for (idx_t i = 0; i < wdcache_count; i++)
    if (fd == wd[wdcache[i]].fd)
      return true;
  return false;
}

/* Clear the fdbase cache.  Call this after any action that might
   invalidate the cache.  Such actions include removing or renaming
   directories or symlinks to directories.  Call this if in doubt,
   e.g., if it is not known whether a removed directory entry is a
   symlink to a directory.  */
void
fdbase_clear (void)
{
  for (int i = 0; i < 2; i++)
    {
      struct fdbase_cache *c = &fdbase_cache[i];
      if (c->subdirlen)
	{
	  if (0 <= c->fd && !chdirable (c->fd))
	    close (c->fd);
	  c->subdirlen = 0;
	}
    }
}

/* Close the file descriptor FD,
   and remove from the fdbase cache any entry corresponding to FD.  */
int
fdbase_close (int fd)
{
  for (int i = 0; i < 2; i++)
    {
      struct fdbase_cache *c = &fdbase_cache[i];
      if (c->subdirlen && c->fd == fd)
	c->subdirlen = 0;
    }
  return close (fd);
}

/* Starting from the directory FD, open a subdirectory SUBDIR for search.
   If OFLAGS, open with OFLAGS.  Otherwise, open_searchdir_how
   determines whether SUBDIR can escape FD, i.e., whether it must
   be at or under FD in the directory hierarchy.  */
static int
open_subdir (int fd, char const *subdir, int oflags)
{
  return
    (oflags
     ? openat (fd, subdir, oflags)
     : openat2 (fd, subdir, &open_searchdir_how, sizeof open_searchdir_how));
}

/* Return an fd open to a directory related to FILE_NAME
   along with the corresponding base name.
   If ALTERNATE, use either the main or the alternate cache but update
   only the alternate cache; otherwise, use and update only the main cache;
   this means a call with ALTERNATE cannot invalidate a call without.
   If FILE_NAME is relative, it is relative to chdir_fd.
   If CHILD_OFLAGS, open FILE_NAME itself, posssibly letting it escape from
   chdir_fd; otherwise, open FILE_NAME's parent but do not let it escape.
   Return AT_FDCWD if FILE_NAME is relative to the working directory.
   Return BADFD (setting errno) on failure.  */
static struct fdbase
fdbase_opendir (char const *file_name, bool alternate, int child_oflags)
{
  char const *name = file_name;
  int dfd = IS_ABSOLUTE_FILE_NAME (file_name) ? AT_FDCWD : chdir_fd;

  if (dfd == BADFD)
    {
      /* BADFD is a sentinel value meaning that the chdir directory
	 needs to be created lazily, therefore if we encounter it, the
	 directory does not exist yet. */
      errno = ENOENT;
      return (struct fdbase) { .fd = BADFD, .base = name };
    }
  /* Skip past leading "./"s,
     but not past the last "./" if that ends the name.  */
  idx_t dslen = dotslashlen (name);
  if (dslen)
    {
      name += dslen;
      if (!*name)
	for (name--; *--name != '.'; )
	  continue;
    }

  /* For files immediately under CHDIR_FD, and for root directories,
     just use CHDIR_FD and NAME.  Empty NAME is invalid, though.  */
  char const *base = last_component (name);
  idx_t subdirlen = base + (child_oflags ? strlen (base) : 0) - name;
  if (!subdirlen | !*base)
    {
      if (*name)
	return (struct fdbase) { .fd = dfd, .base = name };
      errno = EINVAL;
      return (struct fdbase) { .fd = BADFD, .base = name };
    }

  int fd;

  /* Try to reuse fdbase_cache[0] or (if ALTERNATE) fdbase_cache[1].  */
  for (struct fdbase_cache *c = fdbase_cache; ; c++)
    {
      fd = c->fd;
      bool submatch = (0 < c->subdirlen && c->subdirlen <= subdirlen
		       && c->chdir_current == chdir_current
		       && !ISSLASH (name[c->subdirlen])
		       && memeq (c->subdir, name, c->subdirlen));
      if (submatch && c->subdirlen == subdirlen)
	break;
      if (c == fdbase_cache + alternate)
	{
	  /* Cannot reuse, so evict and reget fdbase_cache[ALTERNATE].
	     Start by copying the new directory's name into the cache.  */
	  char *subdir = c->subdir;
	  if (c->subdiralloc <= subdirlen)
	    c->subdir = subdir = xpalloc (subdir, &c->subdiralloc,
					  subdirlen - c->subdiralloc + 1,
					  -1, 1);
	  char *p = mempcpy (subdir, name, subdirlen);
	  *p = '\0';

	  if (submatch && c->subdirlen < subdirlen
	      && !ISSLASH (subdir[c->subdirlen]))
	    {
	      /* The new directory is a subdirectory of the old,
		 so open relative to FD rather than to chdir_fd.  */
	      int subfd = open_subdir (fd, &subdir[c->subdirlen],
				       child_oflags);
	      if (subfd < 0)
		{
		  /* Keep the old directory cached and report open failure,
		     unless EMFILE/ENFILE means it's possible that falling
		     through to close the old directory would mean we
		     could successfully retry from the chdir_fd level.
		     When reporting failure, there is no need to
		     null-terminate the old directory, since the code does
		     not assume null termination.  */
		  if (errno != EMFILE && errno != ENFILE)
		    return (struct fdbase) { .fd = BADFD, .base = base };
		}
	      else
		{
		  /* Replace the old directory with the new one.  */
		  if (!chdirable (fd))
		    close (fd);
		  c->fd = subfd;
		  c->subdirlen = subdirlen;
		  return (struct fdbase) { .fd = subfd, .base = base };
		}
	    }

	  /* Remove any old directory info, and add new info if the new
	     directory can be opened.  */
	  if (0 < c->subdirlen && !chdirable (fd))
	    close (fd);

	  int newfd = open_subdir (chdir_fd, c->subdir, child_oflags);
	  if (newfd < 0)
	    {
	      c->subdirlen = 0;
	      fd = BADFD == -1 ? newfd : BADFD;
	    }
	  else
	    {
	      c->chdir_current = chdir_current;
	      c->fd = fd = newfd;
	      c->subdirlen = subdirlen;
	    }

	  break;
	}
    }

  return (struct fdbase) { .fd = fd, .base = base };
}

struct fdbase
fdbase (char const *name)
{
  return fdbase_opendir (name, false, 0);
}

struct fdbase
fdbase1 (char const *name)
{
  return fdbase_opendir (name, true, 0);
}

int
open_searchdir (char const *name)
{
  return fdbase_opendir (name, false, open_searchdir_how.flags).fd;
}


const char *
tar_dirname (void)
{
  return wd[chdir_current].name;
}

/* Return a newly allocated string that shows NAME from the user's
   viewpoint, given that --one-top-level may be in effect.  */
char *
transform_top_level (const char *name)
{
  if (chdir_current & !!one_top_level_dir)
    {
      if (streq (name, "."))
	{
	  /* nothing to append - .../. is the same as ... */
	  return xstrdup (wd[chdir_current].name);
	}
      else
	{
	  namebuf_t nbuf = namebuf_create (wd[chdir_current].name);
	  namebuf_add_dir (nbuf, name);
	  return namebuf_finish (nbuf);
	}
    }
  else
    return xstrdup (name);
}

/* Return the absolute path that represents the working
   directory referenced by IDX.

   If wd is empty, then no -C options were given, and
   chdir_arg has never been called, so simply return the
   process's actual cwd.  (Note that in this case IDX is ignored,
   since it should always be 0.) */
static const char *
tar_getcdpath (idx_t idx)
{
  if (!wd)
    {
      static char *cwd;
      if (!cwd)
	{
	  cwd = xgetcwd ();
	  if (!cwd)
	    call_arg_fatal ("getcwd", ".");
	}
      return cwd;
    }

  if (!wd[idx].abspath)
    {
      bool one_top_level = !!one_top_level_dir;
      idx_t save_cwdi = chdir_current, i = idx;
      while (0 < i && (((i - 1) & one_top_level) || !wd[i - 1].abspath))
	i--;

      for (; i <= idx; i++)
	{
	  if (! (i & one_top_level))
	    chdir_do (i, false);
	  if (i == 0)
	    {
	      if ((wd[i].abspath = xgetcwd ()) == NULL)
		call_arg_fatal ("getcwd", ".");
	    }
	  else if (IS_ABSOLUTE_FILE_NAME (wd[i].name))
	    /* If the given name is absolute, use it to represent this
	       directory; otherwise, construct a name based on the
	       previous -C option.  */
	    wd[i].abspath = xstrdup (wd[i].name);
	  else
	    {
	      idx_t j = (i - 1) & ~+one_top_level;
	      namebuf_t nbuf = namebuf_create (wd[j].abspath);
	      namebuf_add_dir (nbuf, wd[i].name);
	      wd[i].abspath = namebuf_finish (nbuf);
	    }
	}
      chdir_do (save_cwdi, false);
    }

  return wd[idx].abspath;
}

void
close_diag (char const *name)
{
  if (ignore_failed_read_option)
    {
      if (warning_enabled (WARN_FAILED_READ))
	close_warn (name);
    }
  else
    close_error (name);
}

void
open_diag (char const *name)
{
  if (ignore_failed_read_option)
    {
      if (warning_enabled (WARN_FAILED_READ))
	open_warn (name);
    }
  else
    open_error (name);
}

void
read_diag_details (char const *name, off_t offset, idx_t size)
{
  if (ignore_failed_read_option)
    {
      if (warning_enabled (WARN_FAILED_READ))
	read_warn_details (name, offset, size);
    }
  else
    read_error_details (name, offset, size);
}

void
readlink_diag (char const *name)
{
  if (ignore_failed_read_option)
    {
      if (warning_enabled (WARN_FAILED_READ))
	readlink_warn (name);
    }
  else
    readlink_error (name);
}

void
savedir_diag (char const *name)
{
  if (ignore_failed_read_option)
    {
      if (warning_enabled (WARN_FAILED_READ))
	savedir_warn (name);
    }
  else
    savedir_error (name);
}

void
seek_diag_details (char const *name, off_t offset)
{
  if (ignore_failed_read_option)
    {
      if (warning_enabled (WARN_FAILED_READ))
	seek_warn_details (name, offset);
    }
  else
    seek_error_details (name, offset);
}

void
stat_diag (char const *name)
{
  if (ignore_failed_read_option)
    {
      if (warning_enabled (WARN_FAILED_READ))
	stat_warn (name);
    }
  else
    stat_error (name);
}

void
file_removed_diag (const char *name, bool top_level,
		   void (*diagfn) (char const *name))
{
  if (!top_level && errno == ENOENT)
    {
      warnopt (WARN_FILE_REMOVED, 0, _("%s: File removed before we read it"),
	       quotearg_colon (name));
      if (!ignore_failed_read_option)
	  set_exit_status (TAREXIT_DIFFERS);
    }
  else
    diagfn (name);
}

/* Fork, aborting if unsuccessful.  */
pid_t
xfork (void)
{
  pid_t p = fork ();
  if (p < 0)
    call_arg_fatal ("fork", _("child process"));
  return p;
}

/* Create a pipe, aborting if unsuccessful.  */
void
xpipe (int fd[2])
{
  if (pipe (fd) < 0)
    call_arg_fatal ("pipe", _("interprocess channel"));
}



struct namebuf
{
  char *buffer;		/* directory, '/', and directory member */
  idx_t buffer_size;	/* allocated size of name_buffer */
  idx_t dir_length;	/* length of directory part in buffer */
};

namebuf_t
namebuf_create (const char *dir)
{
  namebuf_t buf = xmalloc (sizeof (*buf));
  buf->buffer_size = strlen (dir) + 2;
  buf->buffer = xmalloc (buf->buffer_size);
  strcpy (buf->buffer, dir);
  buf->dir_length = strlen (buf->buffer);
  if (!ISSLASH (buf->buffer[buf->dir_length - 1]))
    buf->buffer[buf->dir_length++] = DIRECTORY_SEPARATOR;
  return buf;
}

void
namebuf_free (namebuf_t buf)
{
  free (buf->buffer);
  free (buf);
}

char *
namebuf_name (namebuf_t buf, const char *name)
{
  idx_t len = strlen (name);
  ptrdiff_t incr_min = buf->dir_length + len + 2 - buf->buffer_size;
  if (0 < incr_min)
    buf->buffer = xpalloc (buf->buffer, &buf->buffer_size, incr_min, -1, 1);
  strcpy (buf->buffer + buf->dir_length, name);
  return buf->buffer;
}

static void
namebuf_add_dir (namebuf_t buf, const char *name)
{
  static char dirsep[] = { DIRECTORY_SEPARATOR, 0 };
  if (!ISSLASH (buf->buffer[buf->dir_length - 1]))
    {
      namebuf_name (buf, dirsep);
      buf->dir_length++;
    }
  namebuf_name (buf, name);
  buf->dir_length += strlen (name);
}

static char *
namebuf_finish (namebuf_t buf)
{
  char *res = buf->buffer;

  if (ISSLASH (buf->buffer[buf->dir_length - 1]))
    buf->buffer[buf->dir_length] = 0;
  free (buf);
  return res;
}

/* Return the filenames in directory NAME, relative to the chdir_fd.
   If the directory does not exist, report error if MUST_EXIST is
   true.

   Return NULL on errors.
*/
char *
tar_savedir (const char *name, bool must_exist)
{
  char *ret = NULL;
  DIR *dir = NULL;
  struct fdbase f = fdbase (name);
  int fd = (f.fd == BADFD ? -1
	    : openat (f.fd, f.base, open_read_flags | O_DIRECTORY));
  if (fd < 0)
    {
      if (!must_exist && errno == ENOENT)
	return NULL;
      open_error (name);
    }
  else if (! ((dir = fdopendir (fd))
	      && (ret = streamsavedir (dir, savedir_sort_order))))
    savedir_error (name);

  if (dir ? closedir (dir) < 0 : 0 <= fd && close (fd) < 0)
    savedir_error (name);

  return ret;
}