Userland: Make a simple /bin/cp for copying files.

Userland/cp.cpp

@@ -0,0 +1,42 @@
+#include <unistd.h>
+#include <fcntl.h>
+#include <assert.h>
+#include <stdio.h>
+
+int main(int argc, char** argv)
+{
+    if (argc != 3) {
+        printf("usage: cp <source> <destination>\n");
+        return 0;
+    }
+    int src_fd = open(argv[1], O_RDONLY);
+    if (src_fd < 0) {
+        perror("open src");
+        return 1;
+    }
+    int dst_fd = open(argv[2], O_WRONLY | O_CREAT);
+    if (dst_fd < 0) {
+        perror("open dst");
+        return 1;
+    }
+
+    for (;;) {
+        char buffer[BUFSIZ];
+        ssize_t nread = read(src_fd, buffer, sizeof(buffer));
+        if (nread < 0) {
+            perror("read src");
+            return 1;
+        }
+        if (nread == 0)
+            break;
+        ssize_t nwritten = write(dst_fd, buffer, nread);
+        if (nwritten < 0) {
+            perror("write dst");
+            return 1;
+        }
+        assert(nwritten != 0);
+    }
+    close(src_fd);
+    close(dst_fd);
+    return 0;
+}