This commit lets apps signal an incomplete write. When that happens, stop sending out any more data to the app and wait for it to unthrottle the port.
Signed-off-by: Amit Shah <amit.s...@redhat.com> --- hw/virtio-serial-bus.c | 49 +++++++++++++++++++++++++++++++++++++---------- hw/virtio-serial.h | 17 ++++++++++++++++ 2 files changed, 55 insertions(+), 11 deletions(-) diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c index 6726f72..32938b5 100644 --- a/hw/virtio-serial-bus.c +++ b/hw/virtio-serial-bus.c @@ -126,24 +126,49 @@ static void discard_vq_data(VirtQueue *vq, VirtIODevice *vdev) static void do_flush_queued_data(VirtIOSerialPort *port, VirtQueue *vq, VirtIODevice *vdev) { - VirtQueueElement elem; - assert(port); assert(virtio_queue_ready(vq)); - while (!port->throttled && virtqueue_pop(vq, &elem)) { + while (!port->throttled) { unsigned int i; - for (i = 0; i < elem.out_num; i++) { - size_t buf_size; - - buf_size = elem.out_sg[i].iov_len; + /* Pop an elem only if we haven't left off a previous one mid-way */ + if (!port->elem.out_num) { + if (!virtqueue_pop(vq, &port->elem)) { + break; + } + port->iov_idx = 0; + port->iov_offset = 0; + } - port->info->have_data(port, - elem.out_sg[i].iov_base, - buf_size); + for (i = port->iov_idx; i < port->elem.out_num; i++) { + size_t buf_size; + ssize_t ret; + + buf_size = port->elem.out_sg[i].iov_len - port->iov_offset; + ret = port->info->have_data(port, + port->elem.out_sg[i].iov_base + + port->iov_offset, + buf_size); + if (ret < 0 && ret != -EAGAIN) { + /* We don't handle any other type of errors here */ + abort(); + } + if (ret == -EAGAIN || (ret >= 0 && ret < buf_size)) { + virtio_serial_throttle_port(port, true); + port->iov_idx = i; + if (ret > 0) { + port->iov_offset += ret; + } + break; + } + port->iov_offset = 0; } - virtqueue_push(vq, &elem, 0); + if (port->throttled) { + break; + } + virtqueue_push(vq, &port->elem, 0); + port->elem.out_num = 0; } virtio_notify(vdev, vq); } @@ -709,6 +734,8 @@ static int virtser_port_qdev_init(DeviceState *qdev, DeviceInfo *base) port->guest_connected = true; } + port->elem.out_num = 0; + QTAILQ_INSERT_TAIL(&port->vser->ports, port, next); port->ivq = port->vser->ivqs[port->id]; port->ovq = port->vser->ovqs[port->id]; diff --git a/hw/virtio-serial.h b/hw/virtio-serial.h index 9cc0fb3..a308196 100644 --- a/hw/virtio-serial.h +++ b/hw/virtio-serial.h @@ -102,6 +102,23 @@ struct VirtIOSerialPort { */ uint32_t id; + /* + * This is the elem that we pop from the virtqueue. A slow + * backend that consumes guest data (e.g. the file backend for + * qemu chardevs) can cause the guest to block till all the output + * is flushed. This isn't desired, so we keep a note of the last + * element popped and continue consuming it once the backend + * becomes writable again. + */ + VirtQueueElement elem; + + /* + * The index and the offset into the iov buffer that was popped in + * elem above. + */ + uint32_t iov_idx; + uint64_t iov_offset; + /* Identify if this is a port that binds with hvc in the guest */ uint8_t is_console; -- 1.7.3.4