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virtio-serial: Add support for flow control 

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;
}
port->iov_idx = 0;
port->iov_offset = 0;
}
virtqueue_push(vq, &elem, 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;