coreutils/lib/openat.c

/* provide a replacement openat function
   Copyright (C) 2004, 2005 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 2, or (at your option)
   any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */

/* written by Jim Meyering */

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

#include "openat.h"

#include <stdlib.h>
#include <stdarg.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>

#include "alloca.h"
#include "dirname.h" /* solely for definition of IS_ABSOLUTE_FILE_NAME */
#include "intprops.h"
#include "save-cwd.h"

#include "gettext.h"
#define _(msgid) gettext (msgid)

/* Set PROC_FD_FILENAME to the expansion of "/proc/self/fd/%d/%s" in
   alloca'd memory, using FD and FILE, respectively for %d and %s. */
#define BUILD_PROC_NAME(Proc_fd_filename, Fd, File)			\
  do									\
    {									\
      size_t filelen = strlen (File);					\
      static const char procfd[] = "/proc/self/fd/%d/%s";		\
      /* Buffer for the file name we are going to use.  It consists of	\
	 - the string /proc/self/fd/					\
	 - the file descriptor number					\
	 - the file name provided.					\
	 The final NUL is included in the sizeof.			\
	 Subtract 4 to account for %d and %s.  */			\
      size_t buflen = sizeof (procfd) - 4 + INT_STRLEN_BOUND (Fd) + filelen; \
      (Proc_fd_filename) = alloca (buflen);				\
      snprintf ((Proc_fd_filename), buflen, procfd, (Fd), (File));	\
    }									\
  while (0)

/* Trying to access a BUILD_PROC_NAME file will fail on systems without
   /proc support, and even on systems *with* ProcFS support.  Return
   nonzero if the failure may be legitimate, e.g., because /proc is not
   readable, or the particular .../fd/N directory is not present.  */
#define EXPECTED_ERRNO(Errno) \
  ((Errno) == ENOTDIR || (Errno) == ENOENT \
   || (Errno) == EPERM || (Errno) == EACCES \
   || (Errno) == EOPNOTSUPP /* FreeBSD */)

/* Replacement for Solaris' openat function.
   <http://www.google.com/search?q=openat+site:docs.sun.com>
   Simulate it by doing save_cwd/fchdir/open/restore_cwd.
   If either the save_cwd or the restore_cwd fails (relatively unlikely,
   and usually indicative of a problem that deserves close attention),
   then give a diagnostic and exit nonzero.
   Otherwise, upon failure, set errno and return -1, as openat does.
   Upon successful completion, return a file descriptor.  */
int
rpl_openat (int fd, char const *file, int flags, ...)
{
  struct saved_cwd saved_cwd;
  int saved_errno;
  int err;
  mode_t mode = 0;

  if (flags & O_CREAT)
    {
      va_list arg;
      va_start (arg, flags);
      /* Use the promoted type (int), not mode_t, as second argument.  */
      mode = (mode_t) va_arg (arg, int);
      va_end (arg);
    }

  if (fd == AT_FDCWD || IS_ABSOLUTE_FILE_NAME (file))
    return open (file, flags, mode);

  {
    char *proc_file;
    BUILD_PROC_NAME (proc_file, fd, file);
    err = open (proc_file, flags, mode);
    /* If the syscall succeeds, or if it fails with an unexpected
       errno value, then return right away.  Otherwise, fall through
       and resort to using save_cwd/restore_cwd.  */
    if (0 <= err || ! EXPECTED_ERRNO (errno))
      return err;
  }

  if (save_cwd (&saved_cwd) != 0)
    openat_save_fail (errno);

  if (fchdir (fd) != 0)
    {
      saved_errno = errno;
      free_cwd (&saved_cwd);
      errno = saved_errno;
      return -1;
    }

  err = open (file, flags, mode);
  saved_errno = (err < 0 ? errno : 0);

  if (restore_cwd (&saved_cwd) != 0)
    openat_restore_fail (errno);

  free_cwd (&saved_cwd);

  if (saved_errno)
    errno = saved_errno;
  return err;
}

/* Like openat above, but set *RESTORE_FAILED if unable to save
   or restore the initial working directory.  This is needed only
   the first time remove.c's remove_dir opens a command-line
   directory argument.

   If a previous attempt to restore the current working directory
   failed, then we must not even try to access a `.'-relative name.
   It is the caller's responsibility to not to call this function
   in that case.  */

int
openat_permissive (int fd, char const *file, int flags,
		   bool *cwd_restore_failed, ...)
{
  struct saved_cwd saved_cwd;
  int saved_errno;
  int save_restore_errno = 0;
  int err;
  mode_t mode = 0;

  if (flags & O_CREAT)
    {
      va_list arg;
      va_start (arg, cwd_restore_failed);
      /* Use the promoted type (int), not mode_t, as second argument.  */
      mode = (mode_t) va_arg (arg, int);
      va_end (arg);
    }

  if (fd == AT_FDCWD || IS_ABSOLUTE_FILE_NAME (file))
    return open (file, flags, mode);

  {
    char *proc_file;
    BUILD_PROC_NAME (proc_file, fd, file);
    err = open (proc_file, flags, mode);
    /* If the syscall succeeds, or if it fails with an unexpected
       errno value, then return right away.  Otherwise, fall through
       and resort to using save_cwd/restore_cwd.  */
    if (0 <= err || ! EXPECTED_ERRNO (errno))
      return err;
  }

  if (save_cwd (&saved_cwd) != 0)
    {
      *cwd_restore_failed = true;
      save_restore_errno = errno;
    }

  if (fchdir (fd) != 0)
    {
      saved_errno = errno;
      free_cwd (&saved_cwd);
      errno = saved_errno;
      return -1;
    }

  err = open (file, flags, mode);
  saved_errno = (err < 0 ? errno : 0);

  if ( ! *cwd_restore_failed && restore_cwd (&saved_cwd) != 0)
    {
      *cwd_restore_failed = true;
      save_restore_errno = errno;
    }

  if ( ! *cwd_restore_failed)
    free_cwd (&saved_cwd);

  if (saved_errno)
    errno = saved_errno;
  else if (save_restore_errno)
    errno = save_restore_errno;

  return err;
}

#if !HAVE_FDOPENDIR

/* Replacement for Solaris' function by the same name.
   <http://www.google.com/search?q=fdopendir+site:docs.sun.com>
   Simulate it by doing save_cwd/fchdir/opendir(".")/restore_cwd.
   If either the save_cwd or the restore_cwd fails (relatively unlikely,
   and usually indicative of a problem that deserves close attention),
   then give a diagnostic and exit nonzero.
   Otherwise, this function works just like Solaris' fdopendir.

   W A R N I N G:
   Unlike the other fd-related functions here, this one
   effectively consumes its FD parameter.  The caller should not
   close or otherwise manipulate FD if this function returns successfully.  */
DIR *
fdopendir (int fd)
{
  struct saved_cwd saved_cwd;
  int saved_errno;
  DIR *dir;

  {
    char *proc_file;
    BUILD_PROC_NAME (proc_file, fd, ".");
    dir = opendir (proc_file);
    saved_errno = (dir == NULL ? errno : 0);
    /* If the syscall succeeds, or if it fails with an unexpected
       errno value, then return right away.  Otherwise, fall through
       and resort to using save_cwd/restore_cwd.  */
    if (dir != NULL || ! EXPECTED_ERRNO (errno))
      goto close_and_return;
  }

  if (save_cwd (&saved_cwd) != 0)
    openat_save_fail (errno);

  if (fchdir (fd) != 0)
    {
      saved_errno = errno;
      free_cwd (&saved_cwd);
      errno = saved_errno;
      return NULL;
    }

  dir = opendir (".");
  saved_errno = (dir == NULL ? errno : 0);

  if (restore_cwd (&saved_cwd) != 0)
    openat_restore_fail (errno);

  free_cwd (&saved_cwd);

 close_and_return:;
  if (dir)
    close (fd);

  if (saved_errno)
    errno = saved_errno;
  return dir;
}

#endif

/* Replacement for Solaris' function by the same name.
   <http://www.google.com/search?q=fstatat+site:docs.sun.com>
   Simulate it by doing save_cwd/fchdir/(stat|lstat)/restore_cwd.
   If either the save_cwd or the restore_cwd fails (relatively unlikely,
   and usually indicative of a problem that deserves close attention),
   then give a diagnostic and exit nonzero.
   Otherwise, this function works just like Solaris' fstatat.  */
int
fstatat (int fd, char const *file, struct stat *st, int flag)
{
  struct saved_cwd saved_cwd;
  int saved_errno;
  int err;

  if (fd == AT_FDCWD || IS_ABSOLUTE_FILE_NAME (file))
    return (flag == AT_SYMLINK_NOFOLLOW
	    ? lstat (file, st)
	    : stat (file, st));

  {
    char *proc_file;
    BUILD_PROC_NAME (proc_file, fd, file);
    err = (flag == AT_SYMLINK_NOFOLLOW
	   ? lstat (proc_file, st)
	   : stat (proc_file, st));
    /* If the syscall succeeds, or if it fails with an unexpected
       errno value, then return right away.  Otherwise, fall through
       and resort to using save_cwd/restore_cwd.  */
    if (0 <= err || ! EXPECTED_ERRNO (errno))
      return err;
  }

  if (save_cwd (&saved_cwd) != 0)
    openat_save_fail (errno);

  if (fchdir (fd) != 0)
    {
      saved_errno = errno;
      free_cwd (&saved_cwd);
      errno = saved_errno;
      return -1;
    }

  err = (flag == AT_SYMLINK_NOFOLLOW
	 ? lstat (file, st)
	 : stat (file, st));
  saved_errno = (err < 0 ? errno : 0);

  if (restore_cwd (&saved_cwd) != 0)
    openat_restore_fail (errno);

  free_cwd (&saved_cwd);

  if (saved_errno)
    errno = saved_errno;
  return err;
}

/* Replacement for Solaris' function by the same name.
   <http://www.google.com/search?q=unlinkat+site:docs.sun.com>
   Simulate it by doing save_cwd/fchdir/(unlink|rmdir)/restore_cwd.
   If either the save_cwd or the restore_cwd fails (relatively unlikely,
   and usually indicative of a problem that deserves close attention),
   then give a diagnostic and exit nonzero.
   Otherwise, this function works just like Solaris' unlinkat.  */
int
unlinkat (int fd, char const *file, int flag)
{
  struct saved_cwd saved_cwd;
  int saved_errno;
  int err;

  if (fd == AT_FDCWD || IS_ABSOLUTE_FILE_NAME (file))
    return (flag == AT_REMOVEDIR ? rmdir (file) : unlink (file));

  {
    char *proc_file;
    BUILD_PROC_NAME (proc_file, fd, file);
    err = (flag == AT_REMOVEDIR ? rmdir (proc_file) : unlink (proc_file));
    /* If the syscall succeeds, or if it fails with an unexpected
       errno value, then return right away.  Otherwise, fall through
       and resort to using save_cwd/restore_cwd.  */
    if (0 <= err || ! EXPECTED_ERRNO (errno))
      return err;
  }

  if (save_cwd (&saved_cwd) != 0)
    openat_save_fail (errno);

  if (fchdir (fd) != 0)
    {
      saved_errno = errno;
      free_cwd (&saved_cwd);
      errno = saved_errno;
      return -1;
    }

  err = (flag == AT_REMOVEDIR ? rmdir (file) : unlink (file));
  saved_errno = (err < 0 ? errno : 0);

  if (restore_cwd (&saved_cwd) != 0)
    openat_restore_fail (errno);

  free_cwd (&saved_cwd);

  if (saved_errno)
    errno = saved_errno;
  return err;
}