at-func.c

/* at-func.c: Define at-style functions like fstatat, unlinkat, fchownat, etc.
 * Copyright (C) 2006, 2009-2012 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 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/* written by Jim Meyering */

#if defined(__GNUC__) && defined(__GNUC_MINOR__)
# if (__GNUC__ > 4) || ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 1))
#   pragma GCC diagnostic ignored "-Wunused-macros"
# endif /* GCC 4.1+ */
#endif /* gcc */

#include "dosname.h" /* solely for definition of IS_ABSOLUTE_FILE_NAME */
#include "openat.h"
#include "openat-priv.h"
#include "save-cwd.h"

#ifdef AT_FUNC_USE_F1_COND
# define CALL_FUNC(F)                           \
  ((flag == AT_FUNC_USE_F1_COND)                \
    ? AT_FUNC_F1(F AT_FUNC_POST_FILE_ARGS)      \
    : AT_FUNC_F2(F AT_FUNC_POST_FILE_ARGS))
# define VALIDATE_FLAG(F)                       \
  if (flag & ~AT_FUNC_USE_F1_COND)              \
    {                                           \
      errno = EINVAL;                           \
      return FUNC_FAIL;                         \
    }
#else /* not AT_FUNC_USE_F1_COND: */
# ifndef CALL_FUNC
#  define CALL_FUNC(F) (AT_FUNC_F1(F AT_FUNC_POST_FILE_ARGS))
# endif /* !CALL_FUNC */
# ifndef VALIDATE_FLAG
#  define VALIDATE_FLAG(F) /* empty */
# endif /* !VALIDATE_FLAG */
#endif /* AT_FUNC_USE_F1_COND */

#ifdef AT_FUNC_RESULT
# define FUNC_RESULT AT_FUNC_RESULT
#else
# define FUNC_RESULT int
#endif /* AT_FUNC_RESULT */

#ifdef AT_FUNC_FAIL
# define FUNC_FAIL AT_FUNC_FAIL
#else
# ifndef FUNC_FAIL
#  define FUNC_FAIL -1
# endif /* !FUNC_FAIL */
#endif /* AT_FUNC_FAIL */

/* Call AT_FUNC_F1 to operate on FILE, which is in the directory
 * open on descriptor FD.  If AT_FUNC_USE_F1_COND is defined to a value,
 * AT_FUNC_POST_FILE_PARAM_DECLS must include a parameter named flag;
 * call AT_FUNC_F2 if FLAG is 0 or fail if FLAG contains more bits than
 * AT_FUNC_USE_F1_COND.  Return int and fail with -1 unless AT_FUNC_RESULT
 * or AT_FUNC_FAIL are defined.  If possible, do it without changing the
 * working directory.  Otherwise, resort to using save_cwd/fchdir,
 * then AT_FUNC_F?/restore_cwd.  If either the save_cwd or the restore_cwd
 * fails, then give a diagnostic and exit nonzero.  */
#if defined(FUNC_RESULT) && defined(AT_FUNC_NAME) && defined(CALL_FUNC) && defined(FUNC_FAIL)
FUNC_RESULT
AT_FUNC_NAME(int fd, char const *file AT_FUNC_POST_FILE_PARAM_DECLS)
{
  /* Be careful to choose names unlikely to conflict with
   * AT_FUNC_POST_FILE_PARAM_DECLS.  */
  struct saved_cwd saved_cwd;
  int saved_errno;
  FUNC_RESULT err;

  VALIDATE_FLAG(flag);

  if ((fd == AT_FDCWD) || IS_ABSOLUTE_FILE_NAME(file)) {
    return CALL_FUNC(file);
  }

  {
    char proc_buf[OPENAT_BUFFER_SIZE];
    char *proc_file = openat_proc_name (proc_buf, fd, file);
    if (proc_file) {
        FUNC_RESULT proc_result = CALL_FUNC(proc_file);
        int proc_errno = errno;
        if (proc_file != proc_buf)
          free (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 (FUNC_FAIL != proc_result)
          return proc_result;
        if (! EXPECTED_ERRNO(proc_errno)) {
            errno = proc_errno;
            return proc_result;
        }
    }
  }

  if (save_cwd(&saved_cwd) != 0)
    openat_save_fail(errno);
  if ((0 <= fd) && (fd == saved_cwd.desc)) {
      /* If saving the working directory collides with the user's
       * requested fd, then the user's fd must have been closed to
       * begin with.  */
      free_cwd (&saved_cwd);
      errno = EBADF;
      return FUNC_FAIL;
  }

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

  err = CALL_FUNC(file);
  saved_errno = ((err == FUNC_FAIL) ? errno : 0);

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

  free_cwd(&saved_cwd);

  if (saved_errno) {
    errno = saved_errno;
  }
  return err;
}
# undef CALL_FUNC
# undef FUNC_RESULT
# undef FUNC_FAIL
#else
# if defined(__GNUC__) && !defined(__STRICT_ANSI__) && !defined(__STDC__)
#  warning "Not all of the things that an at-func is required to define were defined; did you include at-func.c from the proper file?"
# endif /* __GNUC__ && !__STRICT_ANSI__ && !__STDC__ */
#endif /* FUNC_RESULT && AT_FUNC_NAME && CALL_FUNC && FUNC_FAIL */

/* EOF */