From 7ec5f1490c84fce3c63cedfd0c9da45cb1297db8 Mon Sep 17 00:00:00 2001
From: Amit Shah <amit.shah@redhat.com>
Date: Fri, 4 Feb 2011 08:20:41 -0200
Subject: [RHEL6 qemu-kvm PATCH 10/27] virtio-serial: Add support for flow control
RH-Author: Amit Shah <amit.shah@redhat.com>
Message-id: <181eb3013a7bde8c711023a8b6c489d893c56bf9.1296806194.git.amit.shah@redhat.com>
Patchwork-id: 17711
O-Subject: [RHEL6.1 qemu PATCH v5 10/19] virtio-serial: Add support for flow
control
Bugzilla: 588916
RH-Acked-by: Alon Levy <alevy@redhat.com>
RH-Acked-by: Juan Quintela <quintela@redhat.com>
RH-Acked-by: Jes Sorensen <Jes.Sorensen@redhat.com>
RH-Acked-by: Michael S. Tsirkin <mst@redhat.com>
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>
(cherry picked from commit f1925dff7e6c4799f5951cf167a437c0737a266c)
Signed-off-by: Amit Shah <amit.shah@redhat.com>
---
hw/virtio-serial-bus.c | 49 +++++++++++++++++++++++++++++++++++++----------
hw/virtio-serial.h | 17 ++++++++++++++++
2 files changed, 55 insertions(+), 11 deletions(-)
Signed-off-by: Eduardo Habkost <ehabkost@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 e23b4eb..554bb99 100644
--- a/hw/virtio-serial-bus.c
+++ b/hw/virtio-serial-bus.c
@@ -129,24 +129,49 @@ 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);
}
@@ -719,6 +744,8 @@ 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 89078d9..de624c3 100644
--- a/hw/virtio-serial.h
+++ b/hw/virtio-serial.h
@@ -107,6 +107,23 @@ 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;
--
1.7.3.2