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+/* 'ln' program to create links between files.
+ Copyright (C) 1986-2022 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 <https://www.gnu.org/licenses/>. */
+
+/* Written by Mike Parker and David MacKenzie. */
+
+#include <config.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <getopt.h>
+
+#include "system.h"
+#include "backupfile.h"
+#include "die.h"
+#include "error.h"
+#include "fcntl-safer.h"
+#include "filenamecat.h"
+#include "file-set.h"
+#include "force-link.h"
+#include "hash.h"
+#include "hash-triple.h"
+#include "priv-set.h"
+#include "relpath.h"
+#include "same.h"
+#include "unlinkdir.h"
+#include "yesno.h"
+#include "canonicalize.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")
+
+/* FIXME: document */
+static enum backup_type backup_type;
+
+/* If true, make symbolic links; otherwise, make hard links. */
+static bool symbolic_link;
+
+/* If true, make symbolic links relative */
+static bool relative;
+
+/* If true, hard links are logical rather than physical. */
+static bool logical = !!LINK_FOLLOWS_SYMLINKS;
+
+/* 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 existing systems (Solaris being an exception). */
+static bool hard_dir_link;
+
+/* If true, watch out for creating or removing hard links to directories. */
+static bool beware_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'},
+ {"logical", no_argument, NULL, 'L'},
+ {"physical", no_argument, NULL, 'P'},
+ {"relative", no_argument, NULL, 'r'},
+ {"symbolic", no_argument, NULL, 's'},
+ {"verbose", no_argument, NULL, 'v'},
+ {GETOPT_HELP_OPTION_DECL},
+ {GETOPT_VERSION_OPTION_DECL},
+ {NULL, 0, NULL, 0}
+};
+
+/* Return an errno value for a system call that returned STATUS.
+ This is zero if STATUS is zero, and is errno otherwise. */
+
+static int
+errnoize (int status)
+{
+ return status < 0 ? errno : 0;
+}
+
+/* Return FROM represented as relative to the dir of TARGET.
+ The result is malloced. */
+
+static char *
+convert_abs_rel (char const *from, char const *target)
+{
+ /* Get dirname to generate paths relative to. We don't resolve
+ the full TARGET as the last component could be an existing symlink. */
+ char *targetdir = dir_name (target);
+
+ char *realdest = canonicalize_filename_mode (targetdir, CAN_MISSING);
+ char *realfrom = canonicalize_filename_mode (from, CAN_MISSING);
+
+ char *relative_from = NULL;
+ if (realdest && realfrom)
+ {
+ /* Write to a PATH_MAX buffer. */
+ relative_from = xmalloc (PATH_MAX);
+
+ if (!relpath (realfrom, realdest, relative_from, PATH_MAX))
+ {
+ free (relative_from);
+ relative_from = NULL;
+ }
+ }
+
+ free (targetdir);
+ free (realdest);
+ free (realfrom);
+
+ return relative_from ? relative_from : xstrdup (from);
+}
+
+/* Link SOURCE to DESTDIR_FD + DEST_BASE atomically. DESTDIR_FD is
+ the directory containing DEST_BASE. Return 0 if successful, a
+ positive errno value on failure, and -1 if an atomic link cannot be
+ done. This handles the common case where the destination does not
+ already exist and -r is not specified. */
+
+static int
+atomic_link (char const *source, int destdir_fd, char const *dest_base)
+{
+ return (symbolic_link
+ ? (relative ? -1
+ : errnoize (symlinkat (source, destdir_fd, dest_base)))
+ : beware_hard_dir_link ? -1
+ : errnoize (linkat (AT_FDCWD, source, destdir_fd, dest_base,
+ logical ? AT_SYMLINK_FOLLOW : 0)));
+}
+
+/* Link SOURCE to a directory entry under DESTDIR_FD named DEST_BASE.
+ DEST is the full name of the destination, useful for diagnostics.
+ LINK_ERRNO is zero if the link has already been made,
+ positive if attempting the link failed with errno == LINK_ERRNO,
+ -1 if no attempt has been made to create the link.
+ Return true if successful. */
+
+static bool
+do_link (char const *source, int destdir_fd, char const *dest_base,
+ char const *dest, int link_errno)
+{
+ struct stat source_stats;
+ int source_status = 1;
+ char *backup_base = NULL;
+ char *rel_source = NULL;
+ int nofollow_flag = logical ? 0 : AT_SYMLINK_NOFOLLOW;
+ if (link_errno < 0)
+ link_errno = atomic_link (source, destdir_fd, dest_base);
+
+ /* Get SOURCE_STATS if later code will need it, if only for sharper
+ diagnostics. */
+ if ((link_errno || dest_set) && !symbolic_link)
+ {
+ source_status = fstatat (AT_FDCWD, source, &source_stats, nofollow_flag);
+ if (source_status != 0)
+ {
+ error (0, errno, _("failed to access %s"), quoteaf (source));
+ return false;
+ }
+ }
+
+ if (link_errno)
+ {
+ if (!symbolic_link && !hard_dir_link && S_ISDIR (source_stats.st_mode))
+ {
+ error (0, 0, _("%s: hard link not allowed for directory"),
+ quotef (source));
+ return false;
+ }
+
+ if (relative)
+ source = rel_source = convert_abs_rel (source, dest);
+
+ bool force = (remove_existing_files || interactive
+ || backup_type != no_backups);
+ if (force)
+ {
+ struct stat dest_stats;
+ if (fstatat (destdir_fd, dest_base, &dest_stats, AT_SYMLINK_NOFOLLOW)
+ != 0)
+ {
+ if (errno != ENOENT)
+ {
+ error (0, errno, _("failed to access %s"), quoteaf (dest));
+ goto fail;
+ }
+ force = false;
+ }
+ else if (S_ISDIR (dest_stats.st_mode))
+ {
+ error (0, 0, _("%s: cannot overwrite directory"), quotef (dest));
+ goto fail;
+ }
+ else if (seen_file (dest_set, dest, &dest_stats))
+ {
+ /* The current target was created as a hard link to another
+ source file. */
+ error (0, 0,
+ _("will not overwrite just-created %s with %s"),
+ quoteaf_n (0, dest), quoteaf_n (1, source));
+ goto fail;
+ }
+ else
+ {
+ /* Beware removing DEST if it is the same directory entry as
+ SOURCE, because in that case removing DEST can cause the
+ subsequent link creation either to fail (for hard links), or
+ to replace a non-symlink DEST with a self-loop (for symbolic
+ links) which loses the contents of DEST. So, when backing
+ up, worry about creating hard links (since the backups cover
+ the symlink case); otherwise, worry about about -f. */
+ if (backup_type != no_backups
+ ? !symbolic_link
+ : remove_existing_files)
+ {
+ /* Detect whether removing DEST would also remove SOURCE.
+ If the file has only one link then both are surely the
+ same directory entry. Otherwise check whether they point
+ to the same name in the same directory. */
+ if (source_status != 0)
+ source_status = stat (source, &source_stats);
+ if (source_status == 0
+ && SAME_INODE (source_stats, dest_stats)
+ && (source_stats.st_nlink == 1
+ || same_nameat (AT_FDCWD, source,
+ destdir_fd, dest_base)))
+ {
+ error (0, 0, _("%s and %s are the same file"),
+ quoteaf_n (0, source), quoteaf_n (1, dest));
+ goto fail;
+ }
+ }
+
+ if (link_errno < 0 || link_errno == EEXIST)
+ {
+ if (interactive)
+ {
+ fprintf (stderr, _("%s: replace %s? "),
+ program_name, quoteaf (dest));
+ if (!yesno ())
+ {
+ free (rel_source);
+ return true;
+ }
+ }
+
+ if (backup_type != no_backups)
+ {
+ backup_base = find_backup_file_name (destdir_fd,
+ dest_base,
+ backup_type);
+ if (renameat (destdir_fd, dest_base,
+ destdir_fd, backup_base)
+ != 0)
+ {
+ int rename_errno = errno;
+ free (backup_base);
+ backup_base = NULL;
+ if (rename_errno != ENOENT)
+ {
+ error (0, rename_errno, _("cannot backup %s"),
+ quoteaf (dest));
+ goto fail;
+ }
+ force = false;
+ }
+ }
+ }
+ }
+ }
+
+ /* If the attempt to create a link fails and we are removing or
+ backing up destinations, unlink the destination and try again.
+
+ On the surface, POSIX states that 'ln -f A B' unlinks B before trying
+ to link A to B. 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 can try to
+ link A to B before blindly unlinking B, thus sometimes attempting to
+ 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 the 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. */
+ link_errno
+ = (symbolic_link
+ ? force_symlinkat (source, destdir_fd, dest_base,
+ force, link_errno)
+ : force_linkat (AT_FDCWD, source, destdir_fd, dest_base,
+ logical ? AT_SYMLINK_FOLLOW : 0,
+ force, link_errno));
+ /* Until now, link_errno < 0 meant the link has not been tried.
+ From here on, link_errno < 0 means the link worked but
+ required removing the destination first. */
+ }
+
+ if (link_errno <= 0)
+ {
+ /* Right after creating a hard link, do this: (note dest name and
+ source_stats, which are also the just-linked-destinations stats) */
+ if (! symbolic_link)
+ record_file (dest_set, dest, &source_stats);
+
+ if (verbose)
+ {
+ char const *quoted_backup = "";
+ char const *backup_sep = "";
+ if (backup_base)
+ {
+ char *backup = backup_base;
+ void *alloc = NULL;
+ ptrdiff_t destdirlen = dest_base - dest;
+ if (0 < destdirlen)
+ {
+ alloc = xmalloc (destdirlen + strlen (backup_base) + 1);
+ backup = memcpy (alloc, dest, destdirlen);
+ strcpy (backup + destdirlen, backup_base);
+ }
+ quoted_backup = quoteaf_n (2, backup);
+ backup_sep = " ~ ";
+ free (alloc);
+ }
+ printf ("%s%s%s %c> %s\n", quoted_backup, backup_sep,
+ quoteaf_n (0, dest), symbolic_link ? '-' : '=',
+ quoteaf_n (1, source));
+ }
+ }
+ else
+ {
+ error (0, link_errno,
+ (symbolic_link
+ ? (link_errno != ENAMETOOLONG && *source
+ ? _("failed to create symbolic link %s")
+ : _("failed to create symbolic link %s -> %s"))
+ : (link_errno == EMLINK
+ ? _("failed to create hard link to %.0s%s")
+ : (link_errno == EDQUOT || link_errno == EEXIST
+ || link_errno == ENOSPC || link_errno == EROFS)
+ ? _("failed to create hard link %s")
+ : _("failed to create hard link %s => %s"))),
+ quoteaf_n (0, dest), quoteaf_n (1, source));
+
+ if (backup_base)
+ {
+ if (renameat (destdir_fd, backup_base, destdir_fd, dest_base) != 0)
+ error (0, errno, _("cannot un-backup %s"), quoteaf (dest));
+ }
+ }
+
+ free (backup_base);
+ free (rel_source);
+ return link_errno <= 0;
+
+fail:
+ free (rel_source);
+ return false;
+}
+
+void
+usage (int status)
+{
+ if (status != EXIT_SUCCESS)
+ emit_try_help ();
+ else
+ {
+ printf (_("\
+Usage: %s [OPTION]... [-T] TARGET LINK_NAME\n\
+ or: %s [OPTION]... TARGET\n\
+ or: %s [OPTION]... TARGET... DIRECTORY\n\
+ or: %s [OPTION]... -t DIRECTORY TARGET...\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\
+By default, each destination (name of new link) should not already exist.\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\
+"), stdout);
+
+ emit_mandatory_arg_note ();
+
+ 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 (_("\
+ -i, --interactive prompt whether to remove destinations\n\
+ -L, --logical dereference TARGETs that are symbolic links\n\
+ -n, --no-dereference treat LINK_NAME as a normal file if\n\
+ it is a symbolic link to a directory\n\
+ -P, --physical make hard links directly to symbolic links\n\
+ -r, --relative with -s, create links relative to link location\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 always\n\
+ -v, --verbose print name of each linked file\n\
+"), stdout);
+ fputs (HELP_OPTION_DESCRIPTION, stdout);
+ fputs (VERSION_OPTION_DESCRIPTION, stdout);
+ emit_backup_suffix_note ();
+ printf (_("\
+\n\
+Using -s ignores -L and -P. Otherwise, the last option specified controls\n\
+behavior when a TARGET is a symbolic link, defaulting to %s.\n\
+"), LINK_FOLLOWS_SYMLINKS ? "-L" : "-P");
+ emit_ancillary_info (PROGRAM_NAME);
+ }
+ exit (status);
+}
+
+int
+main (int argc, char **argv)
+{
+ int c;
+ bool ok;
+ bool make_backups = false;
+ char const *backup_suffix = NULL;
+ char *version_control_string = NULL;
+ char const *target_directory = NULL;
+ int destdir_fd;
+ bool no_target_directory = false;
+ int n_files;
+ char **file;
+ int link_errno = -1;
+
+ initialize_main (&argc, &argv);
+ set_program_name (argv[0]);
+ setlocale (LC_ALL, "");
+ bindtextdomain (PACKAGE, LOCALEDIR);
+ textdomain (PACKAGE);
+
+ atexit (close_stdin);
+
+ symbolic_link = remove_existing_files = interactive = verbose
+ = hard_dir_link = false;
+
+ while ((c = getopt_long (argc, argv, "bdfinrst:vFLPS: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 'L':
+ logical = true;
+ break;
+ case 'n':
+ dereference_dest_dir_symlinks = false;
+ break;
+ case 'P':
+ logical = false;
+ break;
+ case 'r':
+ relative = true;
+ break;
+ case 's':
+ symbolic_link = true;
+ break;
+ case 't':
+ if (target_directory)
+ die (EXIT_FAILURE, 0, _("multiple target directories specified"));
+ else
+ {
+ struct stat st;
+ if (stat (optarg, &st) != 0)
+ die (EXIT_FAILURE, errno, _("failed to access %s"),
+ quoteaf (optarg));
+ if (! S_ISDIR (st.st_mode))
+ die (EXIT_FAILURE, 0, _("target %s is not a directory"),
+ quoteaf (optarg));
+ }
+ target_directory = optarg;
+ break;
+ case 'T':
+ no_target_directory = true;
+ break;
+ case 'v':
+ verbose = true;
+ break;
+ case 'S':
+ make_backups = true;
+ backup_suffix = 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 (relative && !symbolic_link)
+ die (EXIT_FAILURE, 0, _("cannot do --relative without --symbolic"));
+
+ if (!hard_dir_link)
+ {
+ priv_set_remove_linkdir ();
+ beware_hard_dir_link = !cannot_unlink_dir ();
+ }
+
+ if (no_target_directory)
+ {
+ if (target_directory)
+ die (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"),
+ quoteaf (file[0]));
+ else
+ error (0, 0, _("extra operand %s"), quoteaf (file[2]));
+ usage (EXIT_FAILURE);
+ }
+ }
+ else if (n_files < 2 && !target_directory)
+ {
+ target_directory = ".";
+ destdir_fd = AT_FDCWD;
+ }
+ else
+ {
+ if (n_files == 2 && !target_directory)
+ link_errno = atomic_link (file[0], AT_FDCWD, file[1]);
+ if (link_errno < 0 || link_errno == EEXIST || link_errno == ENOTDIR
+ || link_errno == EINVAL)
+ {
+ char const *d
+ = target_directory ? target_directory : file[n_files - 1];
+ int flags = (O_PATHSEARCH | O_DIRECTORY
+ | (dereference_dest_dir_symlinks ? 0 : O_NOFOLLOW));
+ destdir_fd = openat_safer (AT_FDCWD, d, flags);
+ int err = errno;
+ if (!O_DIRECTORY && 0 <= destdir_fd)
+ {
+ struct stat st;
+ err = (fstat (destdir_fd, &st) != 0 ? errno
+ : S_ISDIR (st.st_mode) ? 0 : ENOTDIR);
+ if (err != 0)
+ {
+ close (destdir_fd);
+ destdir_fd = -1;
+ }
+ }
+ if (0 <= destdir_fd)
+ {
+ n_files -= !target_directory;
+ target_directory = d;
+ }
+ else if (! (n_files == 2 && !target_directory))
+ die (EXIT_FAILURE, err, _("target %s"), quoteaf (d));
+ }
+ }
+
+ backup_type = (make_backups
+ ? xget_version (_("backup type"), version_control_string)
+ : no_backups);
+ set_simple_backup_suffix (backup_suffix);
+
+
+ if (target_directory)
+ {
+ /* 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 (int 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], destdir_fd, dest_base, dest, -1);
+ free (dest);
+ }
+ }
+ else
+ ok = do_link (file[0], AT_FDCWD, file[1], file[1], link_errno);
+
+ main_exit (ok ? EXIT_SUCCESS : EXIT_FAILURE);
+}