Re: [PATCH v3] Add virtio-input driver.

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Tue, Mar 24, 2015 at 11:36:31AM +0100, Michael S. Tsirkin wrote:
> On Tue, Mar 24, 2015 at 08:32:01AM +0100, Gerd Hoffmann wrote:
> > virtio-input is basically evdev-events-over-virtio, so this driver isn't
> > much more than reading configuration from config space and forwarding
> > incoming events to the linux input layer.
> > 
> > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> 
> Looks pretty neat overall. I think I still see some
> small issues, but it's getting there.
> 
> > ---
> >  MAINTAINERS                       |   6 +
> >  drivers/virtio/Kconfig            |  10 ++
> >  drivers/virtio/Makefile           |   1 +
> >  drivers/virtio/virtio_input.c     | 313 ++++++++++++++++++++++++++++++++++++++
> >  include/uapi/linux/Kbuild         |   1 +
> >  include/uapi/linux/virtio_ids.h   |   1 +
> >  include/uapi/linux/virtio_input.h |  76 +++++++++
> >  7 files changed, 408 insertions(+)
> >  create mode 100644 drivers/virtio/virtio_input.c
> >  create mode 100644 include/uapi/linux/virtio_input.h
> > 
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 358eb01..6f233dd 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -10442,6 +10442,12 @@ S:	Maintained
> >  F:	drivers/vhost/
> >  F:	include/uapi/linux/vhost.h
> >  
> > +VIRTIO INPUT DRIVER
> > +M:	Gerd Hoffmann <kraxel@redhat.com>
> > +S:	Maintained
> > +F:	drivers/virtio/virtio_input.c
> > +F:	include/uapi/linux/virtio_input.h
> > +
> >  VIA RHINE NETWORK DRIVER
> >  M:	Roger Luethi <rl@hellgate.ch>
> >  S:	Maintained
> > diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> > index b546da5..cab9f3f 100644
> > --- a/drivers/virtio/Kconfig
> > +++ b/drivers/virtio/Kconfig
> > @@ -48,6 +48,16 @@ config VIRTIO_BALLOON
> >  
> >  	 If unsure, say M.
> >  
> > +config VIRTIO_INPUT
> > +	tristate "Virtio input driver"
> > +	depends on VIRTIO
> > +	depends on INPUT
> > +	---help---
> > +	 This driver supports virtio input devices such as
> > +	 keyboards, mice and tablets.
> > +
> > +	 If unsure, say M.
> > +
> >   config VIRTIO_MMIO
> >  	tristate "Platform bus driver for memory mapped virtio devices"
> >  	depends on HAS_IOMEM
> > diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
> > index d85565b..41e30e3 100644
> > --- a/drivers/virtio/Makefile
> > +++ b/drivers/virtio/Makefile
> > @@ -4,3 +4,4 @@ obj-$(CONFIG_VIRTIO_PCI) += virtio_pci.o
> >  virtio_pci-y := virtio_pci_modern.o virtio_pci_common.o
> >  virtio_pci-$(CONFIG_VIRTIO_PCI_LEGACY) += virtio_pci_legacy.o
> >  obj-$(CONFIG_VIRTIO_BALLOON) += virtio_balloon.o
> > +obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
> > diff --git a/drivers/virtio/virtio_input.c b/drivers/virtio/virtio_input.c
> > new file mode 100644
> > index 0000000..cf112b2
> > --- /dev/null
> > +++ b/drivers/virtio/virtio_input.c
> > @@ -0,0 +1,313 @@
> > +#include <linux/module.h>
> > +#include <linux/virtio.h>
> > +#include <linux/input.h>
> > +
> > +#include <uapi/linux/virtio_ids.h>
> > +#include <uapi/linux/virtio_input.h>
> > +
> > +struct virtio_input {
> > +	struct virtio_device       *vdev;
> > +	struct input_dev           *idev;
> > +	char                       name[64];
> > +	char                       serial[64];
> > +	char                       phys[64];
> > +	struct virtqueue           *evt, *sts;
> > +	struct virtio_input_event  evts[64];
> > +	spinlock_t                 lock;
> > +};
> > +
> > +static void virtinput_queue_evtbuf(struct virtio_input *vi,
> > +				   struct virtio_input_event *evtbuf)
> > +{
> > +	struct scatterlist sg[1];
> > +
> > +	sg_init_one(sg, evtbuf, sizeof(*evtbuf));
> > +	virtqueue_add_inbuf(vi->evt, sg, 1, evtbuf, GFP_ATOMIC);
> > +}
> > +
> > +static void virtinput_recv_events(struct virtqueue *vq)
> > +{
> > +	struct virtio_input *vi = vq->vdev->priv;
> > +	struct virtio_input_event *event;
> > +	unsigned long flags;
> > +	unsigned int len;
> > +
> > +	spin_lock_irqsave(&vi->lock, flags);
> > +	while ((event = virtqueue_get_buf(vi->evt, &len)) != NULL) {
> > +		input_event(vi->idev,
> > +			    le16_to_cpu(event->type),
> > +			    le16_to_cpu(event->code),
> > +			    le32_to_cpu(event->value));
> 
> What happens if input layer gets an
> unexpected event code or value?
> Or does something prevent it?
> 
> 
> 
> > +		virtinput_queue_evtbuf(vi, event);
> > +	}
> > +	virtqueue_kick(vq);
> > +	spin_unlock_irqrestore(&vi->lock, flags);
> > +}
> > +
> > +static int virtinput_send_status(struct virtio_input *vi,
> > +				 u16 type, u16 code, s32 value)
> > +{
> > +	struct virtio_input_event *stsbuf;
> > +	struct scatterlist sg[1];
> > +	unsigned long flags;
> > +	int rc;
> > +
> > +	stsbuf = kzalloc(sizeof(*stsbuf), GFP_ATOMIC);
> > +	if (!stsbuf)
> > +		return -ENOMEM;
> > +
> > +	stsbuf->type  = cpu_to_le16(type);
> > +	stsbuf->code  = cpu_to_le16(code);
> > +	stsbuf->value = cpu_to_le32(value);
> > +	sg_init_one(sg, stsbuf, sizeof(*stsbuf));
> > +
> > +	spin_lock_irqsave(&vi->lock, flags);
> > +	rc = virtqueue_add_outbuf(vi->sts, sg, 1, stsbuf, GFP_ATOMIC);
> > +	virtqueue_kick(vi->sts);
> > +	spin_unlock_irqrestore(&vi->lock, flags);

I think locking is wrong here. This is basically input_dev->event()
which is called with input_dev->event_lock spinlock held, and it is
taking vi->lock. OTOH virtinput_recv_events() takes vi->lock and then
calls input_event(), which will try taking input_dev->event_lock. It is
bound to deadlock at some point.

I guess the easiest way would be to drop vi->lock() after fetching
virtio event and before calling input_event().

> > +
> > +	if (rc != 0)
> > +		kfree(stsbuf);
> > +	return rc;
> 
> This means that caller will get errors if it happens to call
> send_status at a rate that's faster than host's consumption of them.
> To me this looks wrong.
> Poking at input layer, it seems to simply discard errors.
> Is it always safe to discard status updates?
> If yes, some kind of comment to clarify the logic would
> make sense IMHO.
> 
> 
> 
> > +}
> > +
> > +static void virtinput_recv_status(struct virtqueue *vq)
> > +{
> > +	struct virtio_input *vi = vq->vdev->priv;
> > +	struct virtio_input_event *stsbuf;
> > +	unsigned long flags;
> > +	unsigned int len;
> > +
> > +	spin_lock_irqsave(&vi->lock, flags);
> > +	while ((stsbuf = virtqueue_get_buf(vi->sts, &len)) != NULL)
> > +		kfree(stsbuf);
> > +	spin_unlock_irqrestore(&vi->lock, flags);
> > +}
> > +
> > +static int virtinput_status(struct input_dev *idev, unsigned int type,
> > +			    unsigned int code, int value)
> > +{
> > +	struct virtio_input *vi = input_get_drvdata(idev);
> > +
> > +	return virtinput_send_status(vi, type, code, value);
> > +}
> > +
> > +static size_t virtinput_cfg_select(struct virtio_input *vi,
> > +				   u8 select, u8 subsel)
> > +{
> > +	u8 size;
> > +
> > +	virtio_cwrite(vi->vdev, struct virtio_input_config, select, &select);
> > +	virtio_cwrite(vi->vdev, struct virtio_input_config, subsel, &subsel);
> > +	virtio_cread(vi->vdev, struct virtio_input_config, size, &size);
> > +	return size;
> > +}
> > +
> > +static void virtinput_cfg_bits(struct virtio_input *vi, int select, int subsel,
> > +			       unsigned long *bits, unsigned int bitcount)
> > +{
> > +	unsigned int bit;
> > +	size_t bytes;
> > +	u8 *virtio_bits;
> > +
> > +	bytes = virtinput_cfg_select(vi, select, subsel);
> > +	if (!bytes)
> > +		return;
> 
> How about limiting bytes to sizeof struct virtio_input_config->u?
> 
> > +	if (bitcount > bytes*8)
> > +		bitcount = bytes*8;
> 
> Space around * pls.
> 
> > +
> > +	/*
> > +	 * Bitmap in virtio config space is a simple stream of bytes,
> > +	 * with the first byte carrying bits 0-7, second bits 8-15 and
> > +	 * so on.
> > +	 */
> > +	virtio_bits = kzalloc(bytes, GFP_KERNEL);
> > +	if (!virtio_bits)
> > +		return;
> > +	virtio_cread_bytes(vi->vdev, offsetof(struct virtio_input_config, u),
> > +			   virtio_bits, bytes);
> > +	for (bit = 0; bit < bitcount; bit++) {
> > +		if (virtio_bits[bit / 8] & (1 << (bit % 8)))
> > +			__set_bit(bit, bits);
> > +	}
> > +	kfree(virtio_bits);
> > +
> > +	if (select == VIRTIO_INPUT_CFG_EV_BITS)
> > +		__set_bit(subsel, vi->idev->evbit);
> > +}
> > +
> > +static void virtinput_cfg_abs(struct virtio_input *vi, int abs)
> > +{
> > +	u32 mi, ma, re, fu, fl;
> > +
> > +	virtinput_cfg_select(vi, VIRTIO_INPUT_CFG_ABS_INFO, abs);
> > +	virtio_cread(vi->vdev, struct virtio_input_config, u.abs.min, &mi);
> > +	virtio_cread(vi->vdev, struct virtio_input_config, u.abs.max, &ma);
> > +	virtio_cread(vi->vdev, struct virtio_input_config, u.abs.res, &re);
> > +	virtio_cread(vi->vdev, struct virtio_input_config, u.abs.fuzz, &fu);
> > +	virtio_cread(vi->vdev, struct virtio_input_config, u.abs.flat, &fl);
> > +	input_set_abs_params(vi->idev, abs, mi, ma, fu, fl);
> > +	input_abs_set_res(vi->idev, abs, re);
> > +}
> > +
> > +static int virtinput_init_vqs(struct virtio_input *vi)
> > +{
> > +	struct virtqueue *vqs[2];
> > +	vq_callback_t *cbs[] = { virtinput_recv_events,
> > +				 virtinput_recv_status };
> > +	static const char * names[] = { "events", "status" };
> 
> No space between * and names expected
> 
> > +	int i, err, size;
> > +
> > +	err = vi->vdev->config->find_vqs(vi->vdev, 2, vqs, cbs, names);
> > +	if (err)
> > +		return err;
> > +	vi->evt = vqs[0];
> > +	vi->sts = vqs[1];
> > +
> > +	size = virtqueue_get_vring_size(vi->evt);
> > +	if (size > ARRAY_SIZE(vi->evts))
> > +		size = ARRAY_SIZE(vi->evts);
> > +	for (i = 0; i < size; i++)
> > +		virtinput_queue_evtbuf(vi, &vi->evts[i]);
> > +	virtqueue_kick(vi->evt);
> > +
> > +	return 0;
> > +}
> > +
> > +static int virtinput_probe(struct virtio_device *vdev)
> > +{
> > +	struct virtio_input *vi;
> > +	size_t size;
> > +	int abs, err;
> > +
> > +	if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1))
> > +		return -ENODEV;
> > +
> > +	vi = kzalloc(sizeof(*vi), GFP_KERNEL);
> > +	if (!vi)
> > +		return -ENOMEM;
> > +
> > +	vdev->priv = vi;
> > +	vi->vdev = vdev;
> > +	spin_lock_init(&vi->lock);
> > +
> > +	err = virtinput_init_vqs(vi);
> > +	if (err)
> > +		goto err_init_vq;
> > +
> > +	vi->idev = input_allocate_device();
> > +	if (!vi->idev) {
> > +		err = -ENOMEM;
> > +		goto err_input_alloc;
> > +	}
> > +	input_set_drvdata(vi->idev, vi);
> > +
> > +	size = virtinput_cfg_select(vi, VIRTIO_INPUT_CFG_ID_NAME, 0);
> > +	virtio_cread_bytes(vi->vdev, offsetof(struct virtio_input_config, u),
> > +			   vi->name, min(size, sizeof(vi->name)));
> > +	size = virtinput_cfg_select(vi, VIRTIO_INPUT_CFG_ID_SERIAL, 0);
> > +	virtio_cread_bytes(vi->vdev, offsetof(struct virtio_input_config, u),
> > +			   vi->serial, min(size, sizeof(vi->serial)));
> > +	snprintf(vi->phys, sizeof(vi->phys),
> > +		 "virtio%d/input0", vdev->index);
> > +	vi->idev->name = vi->name;
> > +	vi->idev->phys = vi->phys;
> > +	vi->idev->uniq = vi->serial;
> > +
> > +	size = virtinput_cfg_select(vi, VIRTIO_INPUT_CFG_ID_DEVIDS, 0);
> > +	if (size >= 8) {
> 
> What does 8 mean here? Should be sizeof virtio_input_devids?
> 
> > +		virtio_cread(vi->vdev, struct virtio_input_config,
> > +			     u.ids.bustype, &vi->idev->id.bustype);
> > +		virtio_cread(vi->vdev, struct virtio_input_config,
> > +			     u.ids.vendor, &vi->idev->id.vendor);
> > +		virtio_cread(vi->vdev, struct virtio_input_config,
> > +			     u.ids.product, &vi->idev->id.product);
> > +		virtio_cread(vi->vdev, struct virtio_input_config,
> > +			     u.ids.version, &vi->idev->id.version);
> > +	} else {
> > +		vi->idev->id.bustype = BUS_VIRTUAL;
> > +	}
> > +
> > +	virtinput_cfg_bits(vi, VIRTIO_INPUT_CFG_PROP_BITS, 0,
> > +			   vi->idev->propbit, INPUT_PROP_CNT);
> > +	size = virtinput_cfg_select(vi, VIRTIO_INPUT_CFG_EV_BITS, EV_REP);
> > +	if (size)
> > +		__set_bit(EV_REP, vi->idev->evbit);
> > +
> > +	vi->idev->dev.parent = &vdev->dev;
> > +	vi->idev->event = virtinput_status;
> > +
> > +	/* device -> kernel */
> > +	virtinput_cfg_bits(vi, VIRTIO_INPUT_CFG_EV_BITS, EV_KEY,
> > +			   vi->idev->keybit, KEY_CNT);
> > +	virtinput_cfg_bits(vi, VIRTIO_INPUT_CFG_EV_BITS, EV_REL,
> > +			   vi->idev->relbit, REL_CNT);
> > +	virtinput_cfg_bits(vi, VIRTIO_INPUT_CFG_EV_BITS, EV_ABS,
> > +			   vi->idev->absbit, ABS_CNT);
> > +	virtinput_cfg_bits(vi, VIRTIO_INPUT_CFG_EV_BITS, EV_MSC,
> > +			   vi->idev->mscbit, MSC_CNT);
> > +	virtinput_cfg_bits(vi, VIRTIO_INPUT_CFG_EV_BITS, EV_SW,
> > +			   vi->idev->swbit,  SW_CNT);
> > +
> > +	/* kernel -> device */
> > +	virtinput_cfg_bits(vi, VIRTIO_INPUT_CFG_EV_BITS, EV_LED,
> > +			   vi->idev->ledbit, LED_CNT);
> > +	virtinput_cfg_bits(vi, VIRTIO_INPUT_CFG_EV_BITS, EV_SND,
> > +			   vi->idev->sndbit, SND_CNT);
> > +
> > +	if (test_bit(EV_ABS, vi->idev->evbit)) {
> > +		for (abs = 0; abs < ABS_CNT; abs++) {
> > +			if (!test_bit(abs, vi->idev->absbit))
> > +				continue;
> > +			virtinput_cfg_abs(vi, abs);
> > +		}
> > +	}
> > +	virtio_device_ready(vdev);
> > +
> At this point you can already get interrupts.
> This will cause events to be forwarded.
> I'm guessing this is ok since you called
> input_allocate_device, but worth checking,
> and maybe adding a comment.

Yes, it is OK to send events though yet unregistered input device, as
long as it was allocated with input_allocate_device().

> 
> > +	err = input_register_device(vi->idev);
> > +	if (err)
> > +		goto err_input_register;
> > +
> > +	return 0;
> > +
> > +err_input_register:
> 
> > +	input_free_device(vi->idev);
> 
> At this point you can already get interrupts
> since you called virtio_device_ready, and
> getting events from a freed device likely won't
> DTRT.

Right. I guess you want to mark the virtio device ready only after
registering input device.

> 
> > +err_input_alloc:
> > +	vdev->config->del_vqs(vdev);
> > +err_init_vq:
> > +	kfree(vi);
> > +	return err;
> > +}
> > +
> > +static void virtinput_remove(struct virtio_device *vdev)
> > +{
> > +	struct virtio_input *vi = vdev->priv;
> > +
> > +	input_unregister_device(vi->idev);
> 
> same thing here, you might get an event at this point.
> You need to somehow block new events
> being sent to device while keeping
> device around.
> 
> Since you already do everything under a spinlock,
> it's probably easiest to add a flag discarding
> recv events. You can then check it in virtinput_recv_events
> before calling input_event.

Instead of checking the flag is it possible to pause virio device? Maybe
virtio_break_device()?

> 
> 
> 
> > +	vdev->config->del_vqs(vdev);
> > +	kfree(vi);
> > +}
> > +
> > +static unsigned int features[] = {
> > +};
> > +static struct virtio_device_id id_table[] = {
> > +	{ VIRTIO_ID_INPUT, VIRTIO_DEV_ANY_ID },
> > +	{ 0 },
> > +};
> > +
> > +static struct virtio_driver virtio_input_driver = {
> > +	.driver.name         = KBUILD_MODNAME,
> > +	.driver.owner        = THIS_MODULE,
> > +	.feature_table       = features,
> > +	.feature_table_size  = ARRAY_SIZE(features),
> > +	.id_table            = id_table,
> > +	.probe               = virtinput_probe,
> > +	.remove              = virtinput_remove,
> 
> I note this driver doesn't seem to handle hybernation,
> that's probably a bug?
> 
> 
> > +};
> > +
> > +module_virtio_driver(virtio_input_driver);
> > +MODULE_DEVICE_TABLE(virtio, id_table);
> > +
> > +MODULE_LICENSE("GPL");
> > +MODULE_DESCRIPTION("Virtio input device driver");
> > +MODULE_AUTHOR("Gerd Hoffmann <kraxel@redhat.com>");
> > diff --git a/include/uapi/linux/Kbuild b/include/uapi/linux/Kbuild
> > index 68ceb97..04b829e 100644
> > --- a/include/uapi/linux/Kbuild
> > +++ b/include/uapi/linux/Kbuild
> > @@ -430,6 +430,7 @@ header-y += virtio_blk.h
> >  header-y += virtio_config.h
> >  header-y += virtio_console.h
> >  header-y += virtio_ids.h
> > +header-y += virtio_input.h
> >  header-y += virtio_net.h
> >  header-y += virtio_pci.h
> >  header-y += virtio_ring.h
> > diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
> > index 284fc3a..5f60aa4 100644
> > --- a/include/uapi/linux/virtio_ids.h
> > +++ b/include/uapi/linux/virtio_ids.h
> > @@ -39,5 +39,6 @@
> >  #define VIRTIO_ID_9P		9 /* 9p virtio console */
> >  #define VIRTIO_ID_RPROC_SERIAL 11 /* virtio remoteproc serial link */
> >  #define VIRTIO_ID_CAIF	       12 /* Virtio caif */
> > +#define VIRTIO_ID_INPUT        18 /* virtio input */
> >  
> >  #endif /* _LINUX_VIRTIO_IDS_H */
> > diff --git a/include/uapi/linux/virtio_input.h b/include/uapi/linux/virtio_input.h
> > new file mode 100644
> > index 0000000..7fceabd
> > --- /dev/null
> > +++ b/include/uapi/linux/virtio_input.h
> > @@ -0,0 +1,76 @@
> > +#ifndef _LINUX_VIRTIO_INPUT_H
> > +#define _LINUX_VIRTIO_INPUT_H
> > +/* This header is BSD licensed so anyone can use the definitions to implement
> > + * compatible drivers/servers.
> > + *
> > + * Redistribution and use in source and binary forms, with or without
> > + * modification, are permitted provided that the following conditions
> > + * are met:
> > + * 1. Redistributions of source code must retain the above copyright
> > + *    notice, this list of conditions and the following disclaimer.
> > + * 2. Redistributions in binary form must reproduce the above copyright
> > + *    notice, this list of conditions and the following disclaimer in the
> > + *    documentation and/or other materials provided with the distribution.
> > + * 3. Neither the name of IBM nor the names of its contributors
> > + *    may be used to endorse or promote products derived from this software
> > + *    without specific prior written permission.
> > + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
> > + * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
> > + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
> > + * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR
> > + * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
> > + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
> > + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
> > + * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
> > + * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
> > + * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
> > + * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
> > + * SUCH DAMAGE. */
> > +#include <linux/virtio_ids.h>
> > +#include <linux/virtio_config.h>
> > +
> > +enum virtio_input_config_select {
> > +	VIRTIO_INPUT_CFG_UNSET      = 0x00,
> > +	VIRTIO_INPUT_CFG_ID_NAME    = 0x01,
> > +	VIRTIO_INPUT_CFG_ID_SERIAL  = 0x02,
> > +	VIRTIO_INPUT_CFG_ID_DEVIDS  = 0x03,
> > +	VIRTIO_INPUT_CFG_PROP_BITS  = 0x10,
> > +	VIRTIO_INPUT_CFG_EV_BITS    = 0x11,
> > +	VIRTIO_INPUT_CFG_ABS_INFO   = 0x12,
> > +};
> > +
> > +struct virtio_input_absinfo {
> > +	__virtio32  min;
> > +	__virtio32  max;
> > +	__virtio32  fuzz;
> > +	__virtio32  flat;
> > +	__virtio32  res;
> > +};
> > +
> > +struct virtio_input_devids {
> > +	__virtio16  bustype;
> > +	__virtio16  vendor;
> > +	__virtio16  product;
> > +	__virtio16  version;
> > +};
> > +
> 
> this padding bt two spaces looks weird.
> 
> > +struct virtio_input_config {
> > +	__u8    select;
> > +	__u8    subsel;
> > +	__u8    size;
> > +	__u8    reserved;
> > +	union {
> > +		char string[128];
> > +		__u8 bitmap[128];
> 
> I note that neither string nor bitmap are used by
> driver. What are they in aid of?

Also, what happens if we need more than 1024 bits to pass bitmap data?
We might get there with keyboards.

> 
> > +		struct virtio_input_absinfo abs;
> > +		struct virtio_input_devids ids;
> > +	} u;
> > +};
> > +
> > +struct virtio_input_event {
> > +	__le16 type;
> > +	__le16 code;
> > +	__le32 value;
> > +};
> > +
> > +#endif /* _LINUX_VIRTIO_INPUT_H */
> > -- 
> > 1.8.3.1

Thanks.

-- 
Dmitry