+
−/* Define 2-FD at-style functions like linkat or renameat.
+
−   Copyright (C) 2006, 2009-2013 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 and Eric Blake */
+
−
+
−#include <config.h>
+
−
+
−#include "openat-priv.h"
+
−
+
−#include <errno.h>
+
−#include <stdlib.h>
+
−#include <string.h>
+
−#include <unistd.h>
+
−
+
−#include "dosname.h" /* solely for definition of IS_ABSOLUTE_FILE_NAME */
+
−#include "filenamecat.h"
+
−#include "openat.h"
+
−#include "same-inode.h"
+
−#include "save-cwd.h"
+
−
+
−/* Call FUNC to operate on a pair of files, where FILE1 is relative to FD1,
+
−   and FILE2 is relative to FD2.  If possible, do it without changing the
+
−   working directory.  Otherwise, resort to using save_cwd/fchdir,
+
−   FUNC, restore_cwd (up to two times).  If either the save_cwd or the
+
−   restore_cwd fails, then give a diagnostic and exit nonzero.  */
+
−int
+
−at_func2 (int fd1, char const *file1,
+
−          int fd2, char const *file2,
+
−          int (*func) (char const *file1, char const *file2))
+
−{
+
−  struct saved_cwd saved_cwd;
+
−  int saved_errno;
+
−  int err;
+
−  char *file1_alt;
+
−  char *file2_alt;
+
−  struct stat st1;
+
−  struct stat st2;
+
−
+
−  /* There are 16 possible scenarios, based on whether an fd is
+
−     AT_FDCWD or real, and whether a file is absolute or relative:
+
−
+
−         fd1  file1 fd2  file2  action
+
−     0   cwd  abs   cwd  abs    direct call
+
−     1   cwd  abs   cwd  rel    direct call
+
−     2   cwd  abs   fd   abs    direct call
+
−     3   cwd  abs   fd   rel    chdir to fd2
+
−     4   cwd  rel   cwd  abs    direct call
+
−     5   cwd  rel   cwd  rel    direct call
+
−     6   cwd  rel   fd   abs    direct call
+
−     7   cwd  rel   fd   rel    convert file1 to abs, then case 3
+
−     8   fd   abs   cwd  abs    direct call
+
−     9   fd   abs   cwd  rel    direct call
+
−     10  fd   abs   fd   abs    direct call
+
−     11  fd   abs   fd   rel    chdir to fd2
+
−     12  fd   rel   cwd  abs    chdir to fd1
+
−     13  fd   rel   cwd  rel    convert file2 to abs, then case 12
+
−     14  fd   rel   fd   abs    chdir to fd1
+
−     15a fd1  rel   fd1  rel    chdir to fd1
+
−     15b fd1  rel   fd2  rel    chdir to fd1, then case 7
+
−
+
−     Try some optimizations to reduce fd to AT_FDCWD, or to at least
+
−     avoid converting an absolute name or doing a double chdir.  */
+
−
+
−  if ((fd1 == AT_FDCWD || IS_ABSOLUTE_FILE_NAME (file1))
+
−      && (fd2 == AT_FDCWD || IS_ABSOLUTE_FILE_NAME (file2)))
+
−    return func (file1, file2); /* Case 0-2, 4-6, 8-10.  */
+
−
+
−  /* If /proc/self/fd works, we don't need any stat or chdir.  */
+
−  {
+
−    char proc_buf1[OPENAT_BUFFER_SIZE];
+
−    char *proc_file1 = ((fd1 == AT_FDCWD || IS_ABSOLUTE_FILE_NAME (file1))
+
−                        ? (char *) file1
+
−                        : openat_proc_name (proc_buf1, fd1, file1));
+
−    if (proc_file1)
+
−      {
+
−        char proc_buf2[OPENAT_BUFFER_SIZE];
+
−        char *proc_file2 = ((fd2 == AT_FDCWD || IS_ABSOLUTE_FILE_NAME (file2))
+
−                            ? (char *) file2
+
−                            : openat_proc_name (proc_buf2, fd2, file2));
+
−        if (proc_file2)
+
−          {
+
−            int proc_result = func (proc_file1, proc_file2);
+
−            int proc_errno = errno;
+
−            if (proc_file1 != proc_buf1 && proc_file1 != file1)
+
−              free (proc_file1);
+
−            if (proc_file2 != proc_buf2 && proc_file2 != file2)
+
−              free (proc_file2);
+
−            /* 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 <= proc_result)
+
−              return proc_result;
+
−            if (! EXPECTED_ERRNO (proc_errno))
+
−              {
+
−                errno = proc_errno;
+
−                return proc_result;
+
−              }
+
−          }
+
−        else if (proc_file1 != proc_buf1 && proc_file1 != file1)
+
−          free (proc_file1);
+
−      }
+
−  }
+
−
+
−  /* Cases 3, 7, 11-15 remain.  Time to normalize directory fds, if
+
−     possible.  */
+
−  if (IS_ABSOLUTE_FILE_NAME (file1))
+
−    fd1 = AT_FDCWD; /* Case 11 reduced to 3.  */
+
−  else if (IS_ABSOLUTE_FILE_NAME (file2))
+
−    fd2 = AT_FDCWD; /* Case 14 reduced to 12.  */
+
−
+
−  /* Cases 3, 7, 12, 13, 15 remain.  */
+
−
+
−  if (fd1 == AT_FDCWD) /* Cases 3, 7.  */
+
−    {
+
−      if (stat (".", &st1) == -1 || fstat (fd2, &st2) == -1)
+
−        return -1;
+
−      if (!S_ISDIR (st2.st_mode))
+
−        {
+
−          errno = ENOTDIR;
+
−          return -1;
+
−        }
+
−      if (SAME_INODE (st1, st2)) /* Reduced to cases 1, 5.  */
+
−        return func (file1, file2);
+
−    }
+
−  else if (fd2 == AT_FDCWD) /* Cases 12, 13.  */
+
−    {
+
−      if (stat (".", &st2) == -1 || fstat (fd1, &st1) == -1)
+
−        return -1;
+
−      if (!S_ISDIR (st1.st_mode))
+
−        {
+
−          errno = ENOTDIR;
+
−          return -1;
+
−        }
+
−      if (SAME_INODE (st1, st2)) /* Reduced to cases 4, 5.  */
+
−        return func (file1, file2);
+
−    }
+
−  else if (fd1 != fd2) /* Case 15b.  */
+
−    {
+
−      if (fstat (fd1, &st1) == -1 || fstat (fd2, &st2) == -1)
+
−        return -1;
+
−      if (!S_ISDIR (st1.st_mode) || !S_ISDIR (st2.st_mode))
+
−        {
+
−          errno = ENOTDIR;
+
−          return -1;
+
−        }
+
−      if (SAME_INODE (st1, st2)) /* Reduced to case 15a.  */
+
−        {
+
−          fd2 = fd1;
+
−          if (stat (".", &st1) == 0 && SAME_INODE (st1, st2))
+
−            return func (file1, file2); /* Further reduced to case 5.  */
+
−        }
+
−    }
+
−  else /* Case 15a.  */
+
−    {
+
−      if (fstat (fd1, &st1) == -1)
+
−        return -1;
+
−      if (!S_ISDIR (st1.st_mode))
+
−        {
+
−          errno = ENOTDIR;
+
−          return -1;
+
−        }
+
−      if (stat (".", &st2) == 0 && SAME_INODE (st1, st2))
+
−        return func (file1, file2); /* Reduced to case 5.  */
+
−    }
+
−
+
−  /* Cases 3, 7, 12, 13, 15a, 15b remain.  With all reductions in
+
−     place, it is time to start changing directories.  */
+
−
+
−  if (save_cwd (&saved_cwd) != 0)
+
−    openat_save_fail (errno);
+
−
+
−  if (fd1 != AT_FDCWD && fd2 != AT_FDCWD && fd1 != fd2) /* Case 15b.  */
+
−    {
+
−      if (fchdir (fd1) != 0)
+
−        {
+
−          saved_errno = errno;
+
−          free_cwd (&saved_cwd);
+
−          errno = saved_errno;
+
−          return -1;
+
−        }
+
−      fd1 = AT_FDCWD; /* Reduced to case 7.  */
+
−    }
+
−
+
−  /* Cases 3, 7, 12, 13, 15a remain.  Convert one relative name to
+
−     absolute, if necessary.  */
+
−
+
−  file1_alt = (char *) file1;
+
−  file2_alt = (char *) file2;
+
−
+
−  if (fd1 == AT_FDCWD && !IS_ABSOLUTE_FILE_NAME (file1)) /* Case 7.  */
+
−    {
+
−      /* It would be nicer to use:
+
−         file1_alt = file_name_concat (xgetcwd (), file1, NULL);
+
−         but libraries should not call xalloc_die.  */
+
−      char *cwd = getcwd (NULL, 0);
+
−      if (!cwd)
+
−        {
+
−          saved_errno = errno;
+
−          free_cwd (&saved_cwd);
+
−          errno = saved_errno;
+
−          return -1;
+
−        }
+
−      file1_alt = mfile_name_concat (cwd, file1, NULL);
+
−      if (!file1_alt)
+
−        {
+
−          saved_errno = errno;
+
−          free (cwd);
+
−          free_cwd (&saved_cwd);
+
−          errno = saved_errno;
+
−          return -1;
+
−        }
+
−      free (cwd); /* Reduced to case 3.  */
+
−    }
+
−  else if (fd2 == AT_FDCWD && !IS_ABSOLUTE_FILE_NAME (file2)) /* Case 13.  */
+
−    {
+
−      char *cwd = getcwd (NULL, 0);
+
−      if (!cwd)
+
−        {
+
−          saved_errno = errno;
+
−          free_cwd (&saved_cwd);
+
−          errno = saved_errno;
+
−          return -1;
+
−        }
+
−      file2_alt = mfile_name_concat (cwd, file2, NULL);
+
−      if (!file2_alt)
+
−        {
+
−          saved_errno = errno;
+
−          free (cwd);
+
−          free_cwd (&saved_cwd);
+
−          errno = saved_errno;
+
−          return -1;
+
−        }
+
−      free (cwd); /* Reduced to case 12.  */
+
−    }
+
−
+
−  /* Cases 3, 12, 15a remain.  Change to the correct directory.  */
+
−  if (fchdir (fd1 == AT_FDCWD ? fd2 : fd1) != 0)
+
−    {
+
−      saved_errno = errno;
+
−      free_cwd (&saved_cwd);
+
−      if (file1 != file1_alt)
+
−        free (file1_alt);
+
−      else if (file2 != file2_alt)
+
−        free (file2_alt);
+
−      errno = saved_errno;
+
−      return -1;
+
−    }
+
−
+
−  /* Finally safe to perform the user's function, then clean up.  */
+
−
+
−  err = func (file1_alt, file2_alt);
+
−  saved_errno = (err < 0 ? errno : 0);
+
−
+
−  if (file1 != file1_alt)
+
−    free (file1_alt);
+
−  else if (file2 != file2_alt)
+
−    free (file2_alt);
+
−
+
−  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