From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=53516 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PfX8j-0000I1-0W for qemu-devel@nongnu.org; Wed, 19 Jan 2011 07:27:54 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PfX8e-0007Uj-B1 for qemu-devel@nongnu.org; Wed, 19 Jan 2011 07:27:49 -0500 Received: from mx1.redhat.com ([209.132.183.28]:34183) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PfX8e-0007UU-3H for qemu-devel@nongnu.org; Wed, 19 Jan 2011 07:27:48 -0500 From: Amit Shah Date: Wed, 19 Jan 2011 17:57:18 +0530 Message-Id: <475cfc6880f2f35f29358160dfa5d08be33d0c6a.1295439749.git.amit.shah@redhat.com> In-Reply-To: References: In-Reply-To: References: Subject: [Qemu-devel] [PATCH 6/7] virtio-serial: Add support for flow control List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu list Cc: Amit Shah , Juan Quintela , Gerd Hoffmann , Paul Brook 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 --- 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