utils-std

ln.c (5727B)

// 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 _GNU_SOURCE     // O_PATH with glibc
#define _DEFAULT_SOURCE // due to O_PATH
// Don't define _POSIX_C_SOURCE otherwise FreeBSD hides O_PATH
#include "../lib/bitmasks.h"
#include "../libutils/getopt_nolong.h"
#include <errno.h>
#include <fcntl.h>  // linkat, AT_SYMLINK_FOLLOW
#include <libgen.h> // basename
#include <limits.h> // PATH_MAX
#include <stdbool.h>
#include <stdio.h>    // fprintf
#include <string.h>   // strerror
#include <sys/stat.h> // fstat
#include <unistd.h>   // getopt, symlink, link
const char *argv0 = "ln";
static bool opt_s = false, force = false;
static int link_flags = 0;
static int open_target_flags = O_RDONLY | O_PATH;
static int open_dest_flags = O_RDONLY | O_PATH | O_NOFOLLOW;
static struct stat dest_stat;
static int
do_link(char *src, char *dest, int destfd)
{
	if(opt_s)
	{
		if(symlinkat(src, AT_FDCWD, dest) == 0) return 0;
		if(errno != EEXIST)
		{
			fprintf(stderr, "ln: error: 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: error: Failed creating hard link from '%s' to '%s': %s\n",
			        src,
			        dest,
			        strerror(errno));
			return -1;
		}
	}
	if(strcmp(src, dest) == 0)
	{
		fprintf(stderr, "ln: error: Path '%s' passed to both source and destination\n", src);
		return 1;
	}
	errno = 0;
	if(!force)
	{
		fprintf(stderr, "ln: error: Destination '%s' already exists\n", dest);
		return -1;
	}
	if(destfd < 0)
	{
		destfd = open(dest, open_dest_flags);
		if(destfd < 0)
		{
			if(errno != ENOENT)
			{
				fprintf(stderr,
				        "ln: error: Failed opening destination as path '%s': %s\n",
				        dest,
				        strerror(errno));
				return -1;
			}
		}
		else if(fstat(destfd, &dest_stat) < 0)
		{
			fprintf(stderr,
			        "ln: error: Failed getting status for destination '%s': %s\n",
			        dest,
			        strerror(errno));
			return -1;
		}
	}
	int dirfd = AT_FDCWD;
	if(S_ISDIR(dest_stat.st_mode))
	{
		dirfd = destfd;
	}
	else
	{
		/* check if symbolic/hard link refers to same file */
		struct stat src_stat;
		if(stat(src, &src_stat) < 0)
		{
			if(errno != ENOENT)
			{
				fprintf(
				    stderr, "ln: error: Failed getting status for source '%s': %s\n", src, strerror(errno));
				return -1;
			}
		}
		else if(src_stat.st_dev == dest_stat.st_dev && src_stat.st_ino == dest_stat.st_ino)
		{
			fprintf(stderr,
			        "ln: error: Source '%s' and destination '%s' refer to the same file\n",
			        src,
			        dest);
			return -1;
		}
		if(unlink(dest) < 0)
		{
			fprintf(stderr, "ln: error: Failed unlinking destination '%s': %s\n", dest, strerror(errno));
			return -1;
		}
	}
	if(opt_s)
	{
		if(symlinkat(src, dirfd, dest) == 0) goto cleanup;
		fprintf(stderr, "ln: error: 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: error: Failed creating hard link from '%s' to '%s': %s\n",
		        src,
		        dest,
		        strerror(errno));
		return -1;
	}
cleanup:
	if(destfd < 0) return 0;
	if(close(destfd) != 0)
	{
		fprintf(stderr,
		        "ln: error: Failed closing destination directory '%s': %s\n",
		        dest,
		        strerror(errno));
		return -1;
	}
	return 0;
}
static void
usage(void)
{
	fprintf(stderr, "\
Usage: ln [-fnv] [-L|-P] source... target\n\
       ln -s [-fnv] reference... target\n\
");
}
int
main(int argc, char *argv[])
{
	bool verbose = false;
	for(int c = -1; (c = getopt_nolong(argc, argv, ":fnsLPv")) != -1;)
	{
		switch(c)
		{
		case 'f':
			force = true;
			break;
		case 'n':
			FIELD_SET(open_target_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 'v':
			verbose = true;
			break;
		case '?':
			GETOPT_UNKNOWN_OPT
			usage();
			return 1;
		}
	}
	argc -= optind;
	argv += optind;
	char *target = argv[argc - 1];
	char dest[PATH_MAX] = "";
	if(argc <= 0)
	{
		fprintf(stderr, "ln: error: Not enough operands, %d given, expect >= 1\n", argc);
		return 1;
	}
	else if(argc == 1)
	{
		target = (char *)".";
		argc++;
	}
	else if(argc == 2)
	{
		int targetfd = open(target, open_target_flags);
		if(targetfd >= 0)
		{
			if(fstat(targetfd, &dest_stat) < 0)
			{
				fprintf(stderr,
				        "ln: error: Failed getting status for target '%s': %s\n",
				        dest,
				        strerror(errno));
				return -1;
			}
			if(!S_ISDIR(dest_stat.st_mode))
			{
				int ret = do_link(argv[0], argv[1], targetfd);
				return ret < 0 ? 1 : 0;
			}
			if(close(targetfd) < 0)
			{
				fprintf(stderr,
				        "ln: error: Failed closing target directory '%s': %s\n",
				        target,
				        strerror(errno));
				return -1;
			}
		}
		else
		{
			int ret = do_link(argv[0], argv[1], -1);
			return ret < 0 ? 1 : 0;
		}
	}
	for(int i = 0; i < argc - 1; i++)
	{
		char *src = argv[i];
		char *src_basename = basename(src);
		if(snprintf(dest, PATH_MAX, "%s/%s", target, src_basename) < 0)
		{
			fprintf(stderr,
			        "ln: error: Failed joining target '%s' and source basename '%s'\n",
			        target,
			        src_basename);
			return 1;
		}
		if(do_link(src, dest, -1) < 0) return 1;
		if(verbose) printf("'%s' -> '%s'\n", src, dest);
	}
	return 0;
}