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virtio-serial: Add support for flow control

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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.shah@redhat.com>
This commit is contained in:
Amit Shah 2010-12-10 16:51:14 +05:30
parent e300ac275b
commit f1925dff7e
2 changed files with 56 additions and 12 deletions
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51
hw/virtio-serial-bus.c
View File

@ -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;
port->info->have_data(port,
elem.out_sg[i].iov_base,
buf_size);
/* 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;
}
virtqueue_push(vq, &elem, 0);
port->iov_idx = 0;
port->iov_offset = 0;
}
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;
}
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];

17
hw/virtio-serial.h
View File

@ -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;