/* `ln' program to create links between files.
Copyright (C) 1986, 1989-1991, 1995-2009 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 . */
/* Written by Mike Parker and David MacKenzie. */
#include
#include
#include
#include
#include "system.h"
#include "backupfile.h"
#include "error.h"
#include "filenamecat.h"
#include "file-set.h"
#include "hash.h"
#include "hash-triple.h"
#include "quote.h"
#include "same.h"
#include "yesno.h"
/* The official name of this program (e.g., no `g' prefix). */
#define PROGRAM_NAME "ln"
#define AUTHORS \
proper_name ("Mike Parker"), \
proper_name ("David MacKenzie")
/* In being careful not even to try to make hard links to directories,
we have to know whether link(2) follows symlinks. If it does, then
we have to *stat* the `source' to see if the resulting link would be
to a directory. Otherwise, we have to use *lstat* so that we allow
users to make hard links to symlinks-that-point-to-directories. */
#if LINK_FOLLOWS_SYMLINKS
# define STAT_LIKE_LINK(File, Stat_buf) \
stat (File, Stat_buf)
#else
# define STAT_LIKE_LINK(File, Stat_buf) \
lstat (File, Stat_buf)
#endif
/* FIXME: document */
static enum backup_type backup_type;
/* If true, make symbolic links; otherwise, make hard links. */
static bool symbolic_link;
/* If true, ask the user before removing existing files. */
static bool interactive;
/* If true, remove existing files unconditionally. */
static bool remove_existing_files;
/* If true, list each file as it is moved. */
static bool verbose;
/* If true, allow the superuser to *attempt* to make hard links
to directories. However, it appears that this option is not useful
in practice, since even the superuser is prohibited from hard-linking
directories on most (all?) existing systems. */
static bool hard_dir_link;
/* If nonzero, and the specified destination is a symbolic link to a
directory, treat it just as if it were a directory. Otherwise, the
command `ln --force --no-dereference file symlink-to-dir' deletes
symlink-to-dir before creating the new link. */
static bool dereference_dest_dir_symlinks = true;
/* This is a set of destination name/inode/dev triples for hard links
created by ln. Use this data structure to avoid data loss via a
sequence of commands like this:
rm -rf a b c; mkdir a b c; touch a/f b/f; ln -f a/f b/f c && rm -r a b */
static Hash_table *dest_set;
/* Initial size of the dest_set hash table. */
enum { DEST_INFO_INITIAL_CAPACITY = 61 };
static struct option const long_options[] =
{
{"backup", optional_argument, NULL, 'b'},
{"directory", no_argument, NULL, 'F'},
{"no-dereference", no_argument, NULL, 'n'},
{"no-target-directory", no_argument, NULL, 'T'},
{"force", no_argument, NULL, 'f'},
{"interactive", no_argument, NULL, 'i'},
{"suffix", required_argument, NULL, 'S'},
{"target-directory", required_argument, NULL, 't'},
{"symbolic", no_argument, NULL, 's'},
{"verbose", no_argument, NULL, 'v'},
{GETOPT_HELP_OPTION_DECL},
{GETOPT_VERSION_OPTION_DECL},
{NULL, 0, NULL, 0}
};
/* FILE is the last operand of this command. Return true if FILE is a
directory. But report an error there is a problem accessing FILE,
or if FILE does not exist but would have to refer to an existing
directory if it referred to anything at all. */
static bool
target_directory_operand (char const *file)
{
char const *b = last_component (file);
size_t blen = strlen (b);
bool looks_like_a_dir = (blen == 0 || ISSLASH (b[blen - 1]));
struct stat st;
int stat_result =
(dereference_dest_dir_symlinks ? stat (file, &st) : lstat (file, &st));
int err = (stat_result == 0 ? 0 : errno);
bool is_a_dir = !err && S_ISDIR (st.st_mode);
if (err && err != ENOENT)
error (EXIT_FAILURE, err, _("accessing %s"), quote (file));
if (is_a_dir < looks_like_a_dir)
error (EXIT_FAILURE, err, _("target %s is not a directory"), quote (file));
return is_a_dir;
}
/* Make a link DEST to the (usually) existing file SOURCE.
Symbolic links to nonexistent files are allowed.
Return true if successful. */
static bool
do_link (const char *source, const char *dest)
{
struct stat source_stats;
struct stat dest_stats;
char *dest_backup = NULL;
bool dest_lstat_ok = false;
bool source_is_dir = false;
bool ok;
/* Use stat here instead of lstat.
On SVR4, link does not follow symlinks, so this check disallows
making hard links to symlinks that point to directories. Big deal.
On other systems, link follows symlinks, so this check is right.
FIXME - POSIX 2008 added the AT_SYMLINK_FOLLOW flag to linkat so
that we can specify either behavior, via the new options -L
(hard-link to symlinks) and -P (hard-link to the referent). Once
gnulib has a decent implementation, we should use it here. */
if (!symbolic_link)
{
if (STAT_LIKE_LINK (source, &source_stats) != 0)
{
error (0, errno, _("accessing %s"), quote (source));
return false;
}
if (S_ISDIR (source_stats.st_mode))
{
source_is_dir = true;
if (! hard_dir_link)
{
error (0, 0, _("%s: hard link not allowed for directory"),
quote (source));
return false;
}
}
}
if (remove_existing_files || interactive || backup_type != no_backups)
{
dest_lstat_ok = (lstat (dest, &dest_stats) == 0);
if (!dest_lstat_ok && errno != ENOENT)
{
error (0, errno, _("accessing %s"), quote (dest));
return false;
}
}
/* If the current target was created as a hard link to another
source file, then refuse to unlink it. */
if (dest_lstat_ok
&& dest_set != NULL
&& seen_file (dest_set, dest, &dest_stats))
{
error (0, 0,
_("will not overwrite just-created %s with %s"),
quote_n (0, dest), quote_n (1, source));
return false;
}
/* If --force (-f) has been specified without --backup, then before
making a link ln must remove the destination file if it exists.
(with --backup, it just renames any existing destination file)
But if the source and destination are the same, don't remove
anything and fail right here. */
if ((remove_existing_files
/* Ensure that "ln --backup f f" fails here, with the
"... same file" diagnostic, below. Otherwise, subsequent
code would give a misleading "file not found" diagnostic.
This case is different than the others handled here, since
the command in question doesn't use --force. */
|| (!symbolic_link && backup_type != no_backups))
&& dest_lstat_ok
/* Allow `ln -sf --backup k k' to succeed in creating the
self-referential symlink, but don't allow the hard-linking
equivalent: `ln -f k k' (with or without --backup) to get
beyond this point, because the error message you'd get is
misleading. */
&& (backup_type == no_backups || !symbolic_link)
&& (!symbolic_link || stat (source, &source_stats) == 0)
&& SAME_INODE (source_stats, dest_stats)
/* The following detects whether removing DEST will also remove
SOURCE. If the file has only one link then both are surely
the same link. Otherwise check whether they point to the same
name in the same directory. */
&& (source_stats.st_nlink == 1 || same_name (source, dest)))
{
error (0, 0, _("%s and %s are the same file"),
quote_n (0, source), quote_n (1, dest));
return false;
}
if (dest_lstat_ok)
{
if (S_ISDIR (dest_stats.st_mode))
{
error (0, 0, _("%s: cannot overwrite directory"), quote (dest));
return false;
}
if (interactive)
{
fprintf (stderr, _("%s: replace %s? "), program_name, quote (dest));
if (!yesno ())
return true;
remove_existing_files = true;
}
if (backup_type != no_backups)
{
dest_backup = find_backup_file_name (dest, backup_type);
if (rename (dest, dest_backup) != 0)
{
int rename_errno = errno;
free (dest_backup);
dest_backup = NULL;
if (rename_errno != ENOENT)
{
error (0, rename_errno, _("cannot backup %s"), quote (dest));
return false;
}
}
}
}
ok = ((symbolic_link ? symlink (source, dest) : link (source, dest))
== 0);
/* If the attempt to create a link failed and we are removing or
backing up destinations, unlink the destination and try again.
On the surface, POSIX describes an algorithm that states that
'ln -f A B' will call unlink() on B before ever attempting
link() on A. But strictly following this has the counterintuitive
effect of losing the contents of B, if A does not exist.
Fortunately, POSIX 2008 clarified that an application is free
to fail early if it can prove that continuing onwards cannot
succeed, so we are justified in trying link() before blindly
removing B, thus sometimes calling link() a second time during
a successful 'ln -f A B'.
Try to unlink DEST even if we may have backed it up successfully.
In some unusual cases (when DEST and DEST_BACKUP are hard-links
that refer to the same file), rename succeeds and DEST remains.
If we didn't remove DEST in that case, the subsequent symlink or link
call would fail. */
if (!ok && errno == EEXIST && (remove_existing_files || dest_backup))
{
if (unlink (dest) != 0)
{
error (0, errno, _("cannot remove %s"), quote (dest));
free (dest_backup);
return false;
}
ok = ((symbolic_link ? symlink (source, dest) : link (source, dest))
== 0);
}
if (ok)
{
/* Right after creating a hard link, do this: (note dest name and
source_stats, which are also the just-linked-destinations stats) */
record_file (dest_set, dest, &source_stats);
if (verbose)
{
if (dest_backup)
printf ("%s ~ ", quote (dest_backup));
printf ("%s %c> %s\n", quote_n (0, dest), (symbolic_link ? '-' : '='),
quote_n (1, source));
}
}
else
{
error (0, errno,
(symbolic_link
? (errno != ENAMETOOLONG && *source
? _("creating symbolic link %s")
: _("creating symbolic link %s -> %s"))
: (errno == EMLINK && !source_is_dir
? _("creating hard link to %.0s%s")
: (errno == EDQUOT || errno == EEXIST || errno == ENOSPC
|| errno == EROFS)
? _("creating hard link %s")
: _("creating hard link %s => %s"))),
quote_n (0, dest), quote_n (1, source));
if (dest_backup)
{
if (rename (dest_backup, dest) != 0)
error (0, errno, _("cannot un-backup %s"), quote (dest));
}
}
free (dest_backup);
return ok;
}
void
usage (int status)
{
if (status != EXIT_SUCCESS)
fprintf (stderr, _("Try `%s --help' for more information.\n"),
program_name);
else
{
printf (_("\
Usage: %s [OPTION]... [-T] TARGET LINK_NAME (1st form)\n\
or: %s [OPTION]... TARGET (2nd form)\n\
or: %s [OPTION]... TARGET... DIRECTORY (3rd form)\n\
or: %s [OPTION]... -t DIRECTORY TARGET... (4th form)\n\
"),
program_name, program_name, program_name, program_name);
fputs (_("\
In the 1st form, create a link to TARGET with the name LINK_NAME.\n\
In the 2nd form, create a link to TARGET in the current directory.\n\
In the 3rd and 4th forms, create links to each TARGET in DIRECTORY.\n\
Create hard links by default, symbolic links with --symbolic.\n\
When creating hard links, each TARGET must exist. Symbolic links\n\
can hold arbitrary text; if later resolved, a relative link is\n\
interpreted in relation to its parent directory.\n\
\n\
"), stdout);
fputs (_("\
Mandatory arguments to long options are mandatory for short options too.\n\
"), stdout);
fputs (_("\
--backup[=CONTROL] make a backup of each existing destination file\n\
-b like --backup but does not accept an argument\n\
-d, -F, --directory allow the superuser to attempt to hard link\n\
directories (note: will probably fail due to\n\
system restrictions, even for the superuser)\n\
-f, --force remove existing destination files\n\
"), stdout);
fputs (_("\
-n, --no-dereference treat destination that is a symlink to a\n\
directory as if it were a normal file\n\
-i, --interactive prompt whether to remove destinations\n\
-s, --symbolic make symbolic links instead of hard links\n\
"), stdout);
fputs (_("\
-S, --suffix=SUFFIX override the usual backup suffix\n\
-t, --target-directory=DIRECTORY specify the DIRECTORY in which to create\n\
the links\n\
-T, --no-target-directory treat LINK_NAME as a normal file\n\
-v, --verbose print name of each linked file\n\
"), stdout);
fputs (HELP_OPTION_DESCRIPTION, stdout);
fputs (VERSION_OPTION_DESCRIPTION, stdout);
fputs (_("\
\n\
The backup suffix is `~', unless set with --suffix or SIMPLE_BACKUP_SUFFIX.\n\
The version control method may be selected via the --backup option or through\n\
the VERSION_CONTROL environment variable. Here are the values:\n\
\n\
"), stdout);
fputs (_("\
none, off never make backups (even if --backup is given)\n\
numbered, t make numbered backups\n\
existing, nil numbered if numbered backups exist, simple otherwise\n\
simple, never always make simple backups\n\
"), stdout);
emit_ancillary_info ();
}
exit (status);
}
int
main (int argc, char **argv)
{
int c;
bool ok;
bool make_backups = false;
char *backup_suffix_string;
char *version_control_string = NULL;
char const *target_directory = NULL;
bool no_target_directory = false;
int n_files;
char **file;
initialize_main (&argc, &argv);
set_program_name (argv[0]);
setlocale (LC_ALL, "");
bindtextdomain (PACKAGE, LOCALEDIR);
textdomain (PACKAGE);
atexit (close_stdin);
/* FIXME: consider not calling getenv for SIMPLE_BACKUP_SUFFIX unless
we'll actually use backup_suffix_string. */
backup_suffix_string = getenv ("SIMPLE_BACKUP_SUFFIX");
symbolic_link = remove_existing_files = interactive = verbose
= hard_dir_link = false;
while ((c = getopt_long (argc, argv, "bdfinst:vFS:T", long_options, NULL))
!= -1)
{
switch (c)
{
case 'b':
make_backups = true;
if (optarg)
version_control_string = optarg;
break;
case 'd':
case 'F':
hard_dir_link = true;
break;
case 'f':
remove_existing_files = true;
interactive = false;
break;
case 'i':
remove_existing_files = false;
interactive = true;
break;
case 'n':
dereference_dest_dir_symlinks = false;
break;
case 's':
symbolic_link = true;
break;
case 't':
if (target_directory)
error (EXIT_FAILURE, 0, _("multiple target directories specified"));
else
{
struct stat st;
if (stat (optarg, &st) != 0)
error (EXIT_FAILURE, errno, _("accessing %s"), quote (optarg));
if (! S_ISDIR (st.st_mode))
error (EXIT_FAILURE, 0, _("target %s is not a directory"),
quote (optarg));
}
target_directory = optarg;
break;
case 'T':
no_target_directory = true;
break;
case 'v':
verbose = true;
break;
case 'S':
make_backups = true;
backup_suffix_string = optarg;
break;
case_GETOPT_HELP_CHAR;
case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
default:
usage (EXIT_FAILURE);
break;
}
}
n_files = argc - optind;
file = argv + optind;
if (n_files <= 0)
{
error (0, 0, _("missing file operand"));
usage (EXIT_FAILURE);
}
if (no_target_directory)
{
if (target_directory)
error (EXIT_FAILURE, 0,
_("cannot combine --target-directory "
"and --no-target-directory"));
if (n_files != 2)
{
if (n_files < 2)
error (0, 0,
_("missing destination file operand after %s"),
quote (file[0]));
else
error (0, 0, _("extra operand %s"), quote (file[2]));
usage (EXIT_FAILURE);
}
}
else if (!target_directory)
{
if (n_files < 2)
target_directory = ".";
else if (2 <= n_files && target_directory_operand (file[n_files - 1]))
target_directory = file[--n_files];
else if (2 < n_files)
error (EXIT_FAILURE, 0, _("target %s is not a directory"),
quote (file[n_files - 1]));
}
if (backup_suffix_string)
simple_backup_suffix = xstrdup (backup_suffix_string);
backup_type = (make_backups
? xget_version (_("backup type"), version_control_string)
: no_backups);
if (target_directory)
{
int i;
/* Create the data structure we'll use to record which hard links we
create. Used to ensure that ln detects an obscure corner case that
might result in user data loss. Create it only if needed. */
if (2 <= n_files
&& remove_existing_files
/* Don't bother trying to protect symlinks, since ln clobbering
a just-created symlink won't ever lead to real data loss. */
&& ! symbolic_link
/* No destination hard link can be clobbered when making
numbered backups. */
&& backup_type != numbered_backups)
{
dest_set = hash_initialize (DEST_INFO_INITIAL_CAPACITY,
NULL,
triple_hash,
triple_compare,
triple_free);
if (dest_set == NULL)
xalloc_die ();
}
ok = true;
for (i = 0; i < n_files; ++i)
{
char *dest_base;
char *dest = file_name_concat (target_directory,
last_component (file[i]),
&dest_base);
strip_trailing_slashes (dest_base);
ok &= do_link (file[i], dest);
free (dest);
}
}
else
ok = do_link (file[0], file[1]);
exit (ok ? EXIT_SUCCESS : EXIT_FAILURE);
}