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Date:	Thu, 19 Mar 2015 13:27:40 +0100
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Gerd Hoffmann <kraxel@...hat.com>
Cc:	virtio-dev@...ts.oasis-open.org,
	virtualization@...ts.linux-foundation.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	open list <linux-kernel@...r.kernel.org>,
	"open list:ABI/API" <linux-api@...r.kernel.org>
Subject: Re: [PATCH 1/1] Add virtio-input driver.

On Thu, Mar 19, 2015 at 10:13:11AM +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@...hat.com>

What worries me is how well are these events specified.
Will we be able to write drivers for non-linux guests?
Not sure where to discuss this - this seems like an inappropriate
thread.

Comments on linux driver below.

> ---
>  drivers/virtio/Kconfig            |  10 ++
>  drivers/virtio/Makefile           |   1 +
>  drivers/virtio/virtio_input.c     | 313 ++++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/virtio_ids.h   |   1 +
>  include/uapi/linux/virtio_input.h |  65 ++++++++
>  5 files changed, 390 insertions(+)
>  create mode 100644 drivers/virtio/virtio_input.c
>  create mode 100644 include/uapi/linux/virtio_input.h
> 
> 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..2d425cf
> --- /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];
> +};
> +
> +static ssize_t serial_show(struct device *dev,
> +			   struct device_attribute *attr, char *buf)
> +{
> +	struct input_dev *idev = to_input_dev(dev);
> +	struct virtio_input *vi = input_get_drvdata(idev);
> +	return sprintf(buf, "%s\n", vi->serial);
> +}
> +static DEVICE_ATTR_RO(serial);
> +
> +static struct attribute *dev_attrs[] = {
> +	&dev_attr_serial.attr,
> +	NULL
> +};
> +
> +static umode_t dev_attrs_are_visible(struct kobject *kobj,
> +				     struct attribute *a, int n)
> +{
> +	struct device *dev = container_of(kobj, struct device, kobj);
> +	struct input_dev *idev = to_input_dev(dev);
> +	struct virtio_input *vi = input_get_drvdata(idev);
> +
> +	if (a == &dev_attr_serial.attr && !strlen(vi->serial))
> +		return 0;
> +
> +	return a->mode;
> +}
> +
> +static struct attribute_group dev_attr_grp = {
> +	.attrs =	dev_attrs,
> +	.is_visible =	dev_attrs_are_visible,
> +};
> +
> +static const struct attribute_group *dev_attr_groups[] = {
> +	&dev_attr_grp,
> +	NULL
> +};
> +
> +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 int len;
> +
> +	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));
> +		virtinput_queue_evtbuf(vi, event);
> +	}
> +	virtqueue_kick(vq);
> +}
> +
> +static int virtinput_send_status(struct virtio_input *vi,
> +				 u16 type, u16 code, s32 value)
> +{
> +	struct virtio_input_event *stsbuf;
> +	struct scatterlist sg[1];
> +
> +	stsbuf = kzalloc(sizeof(*stsbuf), GFP_ATOMIC);
> +	if (!stsbuf)
> +		return -ENOMEM;

Does this return an error to userspace?
If so it's not a good idea I think, GFP_ATOMIC failures are
transient conditions and should not be reported
to userspace.
Can use GFP_KERNEL here?

> +
> +	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));
> +	virtqueue_add_outbuf(vi->sts, sg, 1, stsbuf, GFP_ATOMIC);

This can fail if queue is full. What prevents this from happening?

> +	virtqueue_kick(vi->sts);

Also what prevents multiple virtinput_send_status calls
from racing with each other? Is there locking at a higher level?

> +	return 0;
> +}
> +
> +static void virtinput_recv_status(struct virtqueue *vq)
> +{
> +	struct virtio_input *vi = vq->vdev->priv;
> +	struct virtio_input_event *stsbuf;
> +	unsigned int len;
> +
> +	while ((stsbuf = virtqueue_get_buf(vi->sts, &len)) != NULL)

looks like this get_buf can race with add above.
Need some locking.

Also pls avoid != NULL, removing it makes code less verbose.

> +		kfree(stsbuf);
> +	virtqueue_kick(vq);

Why are you kicking here?

> +}
> +
> +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 cfg = 0;
> +
> +	bytes = virtinput_cfg_select(vi, select, subsel);
> +	if (!bytes)
> +		return;
> +	if (bitcount > bytes*8)
> +		bitcount = bytes*8;
> +	if (select == VIRTIO_INPUT_CFG_EV_BITS)
> +		set_bit(subsel, vi->idev->evbit);
> +	for (bit = 0; bit < bitcount; bit++) {
> +		if ((bit % 8) == 0)
> +			virtio_cread(vi->vdev, struct virtio_input_config,
> +				     u.bitmap[bit/8], &cfg);

coding style violations above. you need spaces around ops like / and *.
Please run checkpatch.pl

> +		if (cfg & (1 << (bit % 8)))
> +			set_bit(bit, bits);

what if not set? does something clear the mask?


> +	}

doesn't above just implement bitmap_copy or bitmap_or?  Will it hurt to
just do virtio_cread_bytes into a temporary buffer and then invoke
bitmap ops? Looks like the buffer is at most 256 bytes:
too large to be on stack, but you can allocate it at probe time.


> +}
> +
> +static void virtinput_cfg_abs(struct virtio_input *vi, int abs)
> +{
> +	u32 size, mi, ma, fu, fl;
> +
> +	size = 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.fuzz, &fu);
> +	virtio_cread(vi->vdev, struct virtio_input_config, u.abs.flat, &fl);

you read le field into u32 value.
Please run sparse on this code. you will get a ton
of warnings. Same error appears elsewhere.

> +	input_set_abs_params(vi->idev, abs,
> +			     le32_to_cpu(mi), le32_to_cpu(ma),
> +			     le32_to_cpu(fu), le32_to_cpu(fl));
> +}
> +
> +static int virtinput_init_vqs(struct virtio_input *vi)
> +{
> +	struct virtqueue *vqs[2];
> +	vq_callback_t *cbs[] = { virtinput_recv_events,
> +				 virtinput_recv_status };
> +	const char *names[] = { "events", "status" };
> +	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]);
> +

you add a bunch of bufs but never kick apparently.
you really must kick otherwise device might not
see the buffers.

> +	return 0;
> +}
> +
> +static int virtinput_probe(struct virtio_device *vdev)
> +{
> +	struct virtio_input *vi;
> +	size_t size;
> +	int abs, err;

How about checking VERSION_1 and bailing out of not there?

> +
> +	vi = kzalloc(sizeof(*vi), GFP_KERNEL);
> +	if (!vi) {
> +		err = -ENOMEM;
> +		goto out1;
> +	}
> +	vdev->priv = vi;
> +	vi->vdev = vdev;
> +
> +	err = virtinput_init_vqs(vi);
> +	if (err)
> +		goto out2;
> +
> +	vi->idev = input_allocate_device();
> +	if (!vi->idev) {
> +		err = -ENOMEM;
> +		goto out3;
> +	}
> +	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);
> +
> +	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->name = vi->name;
> +	vi->idev->phys = vi->phys;
> +	vi->idev->id.bustype = BUS_VIRTUAL;
> +	vi->idev->id.vendor  = 0x0001;
> +	vi->idev->id.product = 0x0001;
> +	vi->idev->id.version = 0x0100;

Add comments explaining why these #s make sense?


> +	vi->idev->dev.parent = &vdev->dev;
> +	vi->idev->dev.groups = dev_attr_groups;
> +	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);
> +		}
> +	}
> +
> +	err = input_register_device(vi->idev);

Once you do this, virtinput_status can get called,
and that will kick, correct?
If so, you must call device_ready before this.

> +	if (err)
> +		goto out4;
> +
> +	return 0;
> +
> +out4:
> +	input_free_device(vi->idev);
> +out3:
> +	vdev->config->del_vqs(vdev);
> +out2:
> +	kfree(vi);
> +out1:
> +	return err;

free on error is out of order with initialization.
Might lead to leaks or other bugs.
Also - can you name labels something sensible pls?
out is usually for exiting on success too...
E.g. out4 -> err_register etc.


> +}
> +
> +static void virtinput_remove(struct virtio_device *vdev)
> +{
> +	struct virtio_input *vi = vdev->priv;
> +
> +	input_unregister_device(vi->idev);
> +	vdev->config->reset(vdev);

You don't really need a reset if you just to del_vqs.
People do this if they want to prevent interrupts
without deleting vqs.

> +	vdev->config->del_vqs(vdev);
> +	kfree(vi);

free_device seems to be missing?

> +}
> +
> +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,
> +};
> +
> +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@...hat.com>");
> 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..190d04a
> --- /dev/null
> +++ b/include/uapi/linux/virtio_input.h
> @@ -0,0 +1,65 @@
> +#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_PROP_BITS  = 0x10,
> +	VIRTIO_INPUT_CFG_EV_BITS    = 0x11,
> +	VIRTIO_INPUT_CFG_ABS_INFO   = 0x12,
> +};
> +
> +struct virtio_input_absinfo {
> +	__le32  min;
> +	__le32  max;
> +	__le32  fuzz;
> +	__le32  flat;
> +};
> +
> +struct virtio_input_config {
> +	__u8    select;
> +	__u8    subsel;
> +	__u8    size;
> +	__u8    reserved;
> +	union {
> +		char string[128];
> +		__u8 bitmap[128];
> +		struct virtio_input_absinfo abs;
> +	} u;
> +};
> +
> +struct virtio_input_event {
> +	__le16 type;
> +	__le16 code;
> +	__le32 value;
> +};
> +
> +#endif /* _LINUX_VIRTIO_INPUT_H */
> -- 
> 1.8.3.1
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