Implement VFS syscalls

libmsl/m/system.c

@@ -40,3 +40,15 @@ int device_do (int device_id, int cmd, void* a1, void* a2, void* a3, void* a4) {
 }
 
 int exec (const char* path) { return (int)do_syscall (SYS_EXEC, path); }
+
+int open (const char* path) { return (int)do_syscall (SYS_OPEN, path); }
+
+int close (const char* path) { return (int)do_syscall (SYS_CLOSE, path); }
+
+int read (const char* path, size_t off, uint8_t* buffer, size_t size) {
+  return (int)do_syscall (SYS_READ, path, off, buffer, size);
+}
+
+int describe (const char* path, struct fs_desc_buffer* desc) {
+  return (int)do_syscall (SYS_DESCRIBE, path, desc);
+}