int hv_ringbuffer_write()

in ring_buffer.c [284:387]

• 67 lines of code
• 13 McCabe index (conditional complexity)

int hv_ringbuffer_write(struct vmbus_channel *channel,
			const struct kvec *kv_list, u32 kv_count,
			u64 requestid)
{
	int i;
	u32 bytes_avail_towrite;
	u32 totalbytes_towrite = sizeof(u64);
	u32 next_write_location;
	u32 old_write;
	u64 prev_indices;
	unsigned long flags;
	struct hv_ring_buffer_info *outring_info = &channel->outbound;
	struct vmpacket_descriptor *desc = kv_list[0].iov_base;
	u64 rqst_id = VMBUS_NO_RQSTOR;

	if (channel->rescind)
		return -ENODEV;

	for (i = 0; i < kv_count; i++)
		totalbytes_towrite += kv_list[i].iov_len;

	spin_lock_irqsave(&outring_info->ring_lock, flags);

	bytes_avail_towrite = hv_get_bytes_to_write(outring_info);

	/*
	 * If there is only room for the packet, assume it is full.
	 * Otherwise, the next time around, we think the ring buffer
	 * is empty since the read index == write index.
	 */
	if (bytes_avail_towrite <= totalbytes_towrite) {
		++channel->out_full_total;

		if (!channel->out_full_flag) {
			++channel->out_full_first;
			channel->out_full_flag = true;
		}

		spin_unlock_irqrestore(&outring_info->ring_lock, flags);
		return -EAGAIN;
	}

	channel->out_full_flag = false;

	/* Write to the ring buffer */
	next_write_location = hv_get_next_write_location(outring_info);

	old_write = next_write_location;

	for (i = 0; i < kv_count; i++) {
		next_write_location = hv_copyto_ringbuffer(outring_info,
						     next_write_location,
						     kv_list[i].iov_base,
						     kv_list[i].iov_len);
	}

	/*
	 * Allocate the request ID after the data has been copied into the
	 * ring buffer.  Once this request ID is allocated, the completion
	 * path could find the data and free it.
	 */

	if (desc->flags == VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED) {
		if (channel->next_request_id_callback != NULL) {
			rqst_id = channel->next_request_id_callback(channel, requestid);
			if (rqst_id == VMBUS_RQST_ERROR) {
				spin_unlock_irqrestore(&outring_info->ring_lock, flags);
				return -EAGAIN;
			}
		}
	}
	desc = hv_get_ring_buffer(outring_info) + old_write;
	desc->trans_id = (rqst_id == VMBUS_NO_RQSTOR) ? requestid : rqst_id;

	/* Set previous packet start */
	prev_indices = hv_get_ring_bufferindices(outring_info);

	next_write_location = hv_copyto_ringbuffer(outring_info,
					     next_write_location,
					     &prev_indices,
					     sizeof(u64));

	/* Issue a full memory barrier before updating the write index */
	virt_mb();

	/* Now, update the write location */
	hv_set_next_write_location(outring_info, next_write_location);


	spin_unlock_irqrestore(&outring_info->ring_lock, flags);

	hv_signal_on_write(old_write, channel);

	if (channel->rescind) {
		if (rqst_id != VMBUS_NO_RQSTOR) {
			/* Reclaim request ID to avoid leak of IDs */
			if (channel->request_addr_callback != NULL)
				channel->request_addr_callback(channel, rqst_id);
		}
		return -ENODEV;
	}

	return 0;
}