Userspace: Add basic chmod command

userspace/CMakeLists.txt

@@ -5,6 +5,7 @@ project(userspace CXX)
 set(USERSPACE_PROJECTS
 	cat
 	cat-mmap
+	chmod
 	cp
 	dd
 	echo

userspace/chmod/CMakeLists.txt

@@ -0,0 +1,17 @@
+cmake_minimum_required(VERSION 3.26)
+
+project(chmod CXX)
+
+set(SOURCES
+	main.cpp
+)
+
+add_executable(chmod ${SOURCES})
+target_compile_options(chmod PUBLIC -O2 -g)
+target_link_libraries(chmod PUBLIC libc)
+
+add_custom_target(chmod-install
+	COMMAND sudo cp ${CMAKE_CURRENT_BINARY_DIR}/chmod ${BANAN_BIN}/
+	DEPENDS chmod
+	USES_TERMINAL
+)

userspace/chmod/main.cpp

@@ -0,0 +1,43 @@
+#include <ctype.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+
+void usage(const char* argv0, int ret)
+{
+	FILE* out = (ret == 0) ? stdout : stderr;
+	fprintf(out, "usage: %s MODE FILE...\n", argv0);
+	fprintf(out, "  Change the mode of each FILE to MODE.\n");
+	exit(ret);
+}
+
+int main(int argc, char** argv)
+{
+	if (argc <= 2)
+		usage(argv[0], 1);
+
+	int base = (argv[1][0] == '0') ? 8 : 10;
+
+	mode_t mode = 0;
+	for (const char* ptr = argv[1]; *ptr; ptr++)
+	{
+		if (!isdigit(*ptr))
+		{
+			fprintf(stderr, "Invalid MODE %s\n", argv[1]);
+			usage(argv[0], 1);
+		}
+		mode = (mode * base) + (*ptr - '0');
+	}
+
+	int ret = 0;
+	for (int i = 2; i < argc; i++)
+	{
+		if (chmod(argv[i], mode) == -1)
+		{
+			perror("chmod");
+			ret = 1;
+		}
+	}
+
+	return ret;
+}