Add writing to existing files and overwriting cp

src/user/app/cp/cp.c

@@ -0,0 +1,55 @@
+#include "src/lib/util.h"
+#include "src/user/syscall.h"
+
+#define BLOCK_SIZE 65536
+
+#define PRINT_S(s) write(1, s, sizeof(s) - 1);
+#define PRINT_D(s) write(1, s, string_length(s));
+
+exit_code_t main(uint64_t argc, const char **argv) {
+  if (argc != 3) {
+    PRINT_S("cp: requires source and target");
+    return EXIT_CODE_GENERAL_FAILURE;
+  }
+
+  uint64_t source = open(argv[1]);
+  if (source == (uint64_t)-1) {
+    PRINT_S("cp: source does not exist\n");
+    return EXIT_CODE_GENERAL_FAILURE;
+  }
+
+  uint64_t target = open(argv[2]);
+  if (target == (uint64_t)-1) {
+    PRINT_S("cp: target does not exist\n");
+    close(source);
+    return EXIT_CODE_GENERAL_FAILURE;
+  }
+
+  if (truncate(target, 0) == (uint64_t)-1) {
+    close(source);
+    close(target);
+    return EXIT_CODE_GENERAL_FAILURE;
+  }
+
+  static char buffer[BLOCK_SIZE];
+  uint64_t bytes;
+  while ((bytes = read(source, BLOCK_SIZE, buffer))) {
+    if (bytes == (uint64_t)-1) {
+      PRINT_S("cp: could not read file\n");
+      close(source);
+      close(target);
+      return EXIT_CODE_GENERAL_FAILURE;
+    }
+    if (write(target, buffer, bytes) == (uint64_t)-1) {
+      PRINT_S("cp: could not write file\n");
+      close(source);
+      close(target);
+      return EXIT_CODE_GENERAL_FAILURE;
+    }
+  }
+
+  close(source);
+  close(target);
+
+  return EXIT_CODE_OK;
+}