userspace: Implement `ln` utility

userspace/programs/CMakeLists.txt

@@ -14,6 +14,7 @@ set(USERSPACE_PROGRAMS
 	id
 	image
 	init
+	ln
 	loadfont
 	loadkeys
 	ls

userspace/programs/ln/CMakeLists.txt

@@ -0,0 +1,8 @@
+set(SOURCES
+	main.cpp
+)
+
+add_executable(ln ${SOURCES})
+banan_link_library(ln libc)
+
+install(TARGETS ln OPTIONAL)

userspace/programs/ln/main.cpp

@@ -0,0 +1,65 @@
+#include <libgen.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+int usage(const char* argv0, int ret)
+{
+	FILE* fout = ret ? stderr : stdout;
+	fprintf(fout, "usage: %s [OPTION]... TARGET [LINK_NAME]\n", argv0);
+	fprintf(fout, "  -s, --symbolic   create symbolic link instead of hard link\n");
+	fprintf(fout, "  -h, --help       show this message and exit\n");
+	return ret;
+}
+
+int main(int argc, const char* argv[])
+{
+	bool do_symlink = false;
+
+	int i = 1;
+	for (; i < argc; i++)
+	{
+		if (argv[i][0] != '-')
+			break;
+
+		if (strcmp(argv[i], "-s") == 0 || strcmp(argv[i], "--symbolic") == 0)
+			do_symlink = true;
+		else if (strcmp(argv[i], "-h") == 0 || strcmp(argv[i], "--help") == 0)
+			return usage(argv[0], 0);
+		else
+		{
+			fprintf(stderr, "unrecognized option '%s'\n", argv[i]);
+			return usage(argv[0], 1);
+		}
+	}
+
+	if (i == argc)
+	{
+		fprintf(stderr, "missing target\n");
+		return usage(argv[0], 1);
+	}
+
+	const char* target = argv[i++];
+
+	struct stat st;
+	if (stat(target, &st) == -1)
+	{
+		perror("stat");
+		return 1;
+	}
+
+	const char* link_name = (i == argc)
+		? basename(const_cast<char*>(target))
+		: argv[i];
+
+	int (*link_func)(const char*, const char*) = do_symlink ? &symlink : &link;
+
+	if (link_func(target, link_name) == -1)
+	{
+		perror(do_symlink ? "symlink" : "link");
+		return 1;
+	}
+
+	return 0;
+}