george_read.c

struct retval myread(int fd_id, void *buf, size_t nbytes) {
	struct retval retval;
	retval.errno = NO_ERROR;
	retval.val_h = (int*) FAILED;
	retval.val_l = (int*) FAILED;

	if (fd_id <= FREE_FD || fd_id >= OPEN_MAX) {
		retval.errno = EBADF;
		return retval;
	}

	lock_acquire(curthread->fd_table_lock);
	struct file_descriptor* fd = curthread->file_descriptors[fd_id];
	if (fd == NULL) {
		lock_release(curthread->fd_table_lock);
		retval.errno = EBADF;
		return retval;
	}
	lock_release(curthread->fd_table_lock);

	if ((fd->flags & O_WRONLY) == O_WRONLY) {
		retval.errno = EACCES;
		return retval;
	}

	lock_acquire(fd->lock);

	struct iovec iov;
	struct uio uio_reader;
	uio_kinit(&iov, &uio_reader, (void*) buf, nbytes, fd->offset, UIO_READ);
	uio_reader.uio_segflg = UIO_USERSPACE;
	uio_reader.uio_space = curthread->t_proc->p_addrspace;	
	
	int err = VOP_READ(fd->vnode, &uio_reader);
	if (err) {
		lock_release(fd->lock);
		retval.errno = err;
		return retval;
	}

	fd->offset += nbytes - uio_reader.uio_resid;
	retval.val_h = (void*)(nbytes - uio_reader.uio_resid);

	lock_release(fd->lock);

	return retval;