utils-std

ln.c (4333B)

// utils-std: Collection of commonly available Unix tools
// SPDX-FileCopyrightText: 2017 Haelwenn (lanodan) Monnier <contact+utils@hacktivis.me>
// SPDX-License-Identifier: MPL-2.0
#define _POSIX_C_SOURCE 200809L
#include "../lib/bitmasks.h"
// NetBSD (9.3 and 10) hides symlink behind _XOPEN_SOURCE / _NETBSD_SOURCE
#ifdef __NetBSD__
#define _XOPEN_SOURCE 700
#endif
#include <assert.h>
#include <errno.h>
#include <fcntl.h>  // linkat, AT_SYMLINK_FOLLOW
#include <limits.h> // PATH_MAX
#include <stdbool.h>
#include <stdio.h>  // fprintf
#include <string.h> // strerror
#include <sys/stat.h>
#include <unistd.h> // getopt, symlink, link
static bool opt_s = false, force = false;
static int link_flags = 0;
static int open_dir_flags = O_RDONLY | O_DIRECTORY;
static int
do_link(char *src, char *dest)
{
	assert(errno == 0);
	if(opt_s)
	{
		if(symlinkat(src, AT_FDCWD, dest) == 0) return 0;
		if(errno != EEXIST)
		{
			fprintf(stderr, "ln: Failed creating symlink '%s': %s\n", dest, strerror(errno));
			return -1;
		}
	}
	else
	{
		if(linkat(AT_FDCWD, src, AT_FDCWD, dest, link_flags) == 0) return 0;
		if(errno != EEXIST)
		{
			fprintf(stderr,
			        "ln: Failed creating hard link from '%s' to '%s': %s\n",
			        src,
			        dest,
			        strerror(errno));
			return -1;
		}
	}
	// Fallback
	assert(errno == EEXIST);
	errno = 0;
	int dirfd = open(dest, open_dir_flags);
	if(dirfd < 0)
	{
		assert(errno != 0);
		// ENOTDIR: Found but not a directory
		// ELOOP: POSIX return code when O_NOFOLLOW encounters a symbolic link
		// EMLINK: Same as ELOOP but FreeBSD *sigh*
		if(errno == ENOTDIR || errno == ELOOP || errno == EMLINK)
		{
			if(!force)
			{
				fprintf(stderr, "ln: Error: Destination '%s' already exists\n", dest);
				return -1;
			}
			errno = 0;
			dirfd = AT_FDCWD;
			if(unlink(dest) < 0)
			{
				fprintf(stderr,
				        "ln: Failed removing already existing destination '%s': %s\n",
				        dest,
				        strerror(errno));
				return -1;
			}
		}
	}
	if(errno != 0)
	{
		fprintf(
		    stderr, "ln: Failed opening destination as directory '%s': %s\n", dest, strerror(errno));
		return -1;
	}
	if(opt_s)
	{
		if(symlinkat(src, dirfd, dest) == 0) goto cleanup;
		fprintf(stderr, "ln: Failed creating symlink '%s': %s\n", dest, strerror(errno));
		return -1;
	}
	else
	{
		if(linkat(AT_FDCWD, src, dirfd, dest, link_flags) == 0) goto cleanup;
		fprintf(stderr,
		        "ln: Failed creating hard link from '%s' to '%s': %s\n",
		        src,
		        dest,
		        strerror(errno));
		return -1;
	}
cleanup:
	if(dirfd == AT_FDCWD) return 0;
	if(close(dirfd) != 0)
	{
		fprintf(stderr, "ln: Failed closing directory '%s': %s\n", dest, strerror(errno));
		return -1;
	}
	return 0;
}
static void
usage(void)
{
	fprintf(stderr, "\
Usage: ln [-f] [-L|-P] source... target\n\
       ln -s [-f] reference... target\n\
");
}
int
main(int argc, char *argv[])
{
	int c = -1;
	while((c = getopt(argc, argv, ":fnsLP")) != -1)
	{
		switch(c)
		{
		case 'f':
			force = true;
			break;
		case 'n':
			FIELD_SET(open_dir_flags, O_NOFOLLOW);
			break;
		case 's':
			opt_s = true;
			break;
		case 'L':
			FIELD_SET(link_flags, AT_SYMLINK_FOLLOW);
			break;
		case 'P':
			FIELD_CLR(link_flags, AT_SYMLINK_FOLLOW);
			break;
		case '?':
			fprintf(stderr, "ln: Unknown option '-%c'\n", optopt);
			usage();
			break;
		}
	}
	assert(errno == 0);
	argc -= optind;
	argv += optind;
	if(argc <= 1)
	{
		fprintf(stderr, "ln: Not enough operands, %d given, expect >= 2\n", argc);
		return 1;
	}
	else if(argc == 2)
	{
		struct stat dest_status;
		int ret_stat = fstatat(AT_FDCWD, argv[1], &dest_status, AT_SYMLINK_NOFOLLOW);
		if(argc == 2 && (errno == ENOENT || (ret_stat == 0 && !S_ISDIR(dest_status.st_mode))))
		{
			errno = 0;
			int ret = do_link(argv[0], argv[1]);
			return ret < 0 ? 1 : 0;
		}
		errno = 0;
	}
	char *dest = argv[argc - 1];
	char target[PATH_MAX] = "";
	for(int i = 0; i < argc - 1; i++)
	{
		char *src = argv[i];
		char *src_sep = strrchr(src, '/');
		char *src_basename = src_sep != NULL ? src_sep + 1 : src;
		if(snprintf(target, PATH_MAX, "%s/%s", dest, src_basename) < 0)
		{
			fprintf(stderr, "ln: Failed joining destination '%s' and target '%s'\n", dest, src);
			return 1;
		}
		if(do_link(src, target) < 0) return 1;
	}
	return 0;
}