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/* Create a hard link relative to open directories.
Copyright (C) 2009 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 Eric Blake */
#include <config.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <sys/stat.h>
#include "areadlink.h"
#include "dirname.h"
#include "filenamecat.h"
#include "openat-priv.h"
#if HAVE_SYS_PARAM_H
# include <sys/param.h>
#endif
#ifndef MAXSYMLINKS
# ifdef SYMLOOP_MAX
# define MAXSYMLINKS SYMLOOP_MAX
# else
# define MAXSYMLINKS 20
# endif
#endif
/* Create a link. If FILE1 is a symlink, either create a hardlink to
that symlink, or fake it by creating an identical symlink. */
#if LINK_FOLLOWS_SYMLINKS == 0
# define link_immediate link
#else
static int
link_immediate (char const *file1, char const *file2)
{
char *target = areadlink (file1);
if (target)
{
/* A symlink cannot be modified in-place. Therefore, creating
an identical symlink behaves like a hard link to a symlink,
except for incorrect st_ino and st_nlink. However, we must
be careful of EXDEV. */
struct stat st1;
struct stat st2;
char *dir = mdir_name (file2);
if (!dir)
{
free (target);
errno = ENOMEM;
return -1;
}
if (lstat (file1, &st1) == 0 && stat (dir, &st2) == 0)
{
if (st1.st_dev == st2.st_dev)
{
int result = symlink (target, file2);
int saved_errno = errno;
free (target);
free (dir);
errno = saved_errno;
return result;
}
free (target);
free (dir);
errno = EXDEV;
return -1;
}
free (target);
free (dir);
}
if (errno == ENOMEM)
return -1;
return link (file1, file2);
}
#endif
/* Create a link. If FILE1 is a symlink, create a hardlink to the
canonicalized file. */
#if 0 < LINK_FOLLOWS_SYMLINKS
# define link_follow link
#else
static int
link_follow (char const *file1, char const *file2)
{
char *name = (char *) file1;
char *target;
int result;
int i = MAXSYMLINKS;
/* Using realpath or canonicalize_file_name is too heavy-handed: we
don't need an absolute name, and we don't need to resolve
intermediate symlinks, just the basename of each iteration. */
while (i-- && (target = areadlink (name)))
{
if (IS_ABSOLUTE_FILE_NAME (target))
{
if (name != file1)
free (name);
name = target;
}
else
{
char *dir = mdir_name (name);
if (name != file1)
free (name);
if (!dir)
{
free (target);
errno = ENOMEM;
return -1;
}
name = mfile_name_concat (dir, target, NULL);
free (dir);
free (target);
if (!name)
{
errno = ENOMEM;
return -1;
}
}
}
if (i < 0)
{
target = NULL;
errno = ELOOP;
}
if (!target && errno != EINVAL)
{
if (name != file1)
{
int saved_errno = errno;
free (name);
errno = saved_errno;
}
return -1;
}
result = link (name, file2);
if (name != file1)
{
int saved_errno = errno;
free (name);
errno = saved_errno;
}
return result;
}
#endif
/* Create a link to FILE1, in the directory open on descriptor FD1, to FILE2,
in the directory open on descriptor FD2. If FILE1 is a symlink, FLAG
controls whether to dereference FILE1 first. If possible, do it without
changing the working directory. Otherwise, resort to using
save_cwd/fchdir, then rename/restore_cwd. If either the save_cwd or
the restore_cwd fails, then give a diagnostic and exit nonzero. */
int
linkat (int fd1, char const *file1, int fd2, char const *file2, int flag)
{
if (flag & ~AT_SYMLINK_FOLLOW)
{
errno = EINVAL;
return -1;
}
return at_func2 (fd1, file1, fd2, file2,
flag ? link_follow : link_immediate);
}
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