On Wed, Jul 22, 2020 at 05:09:27PM +0200, Guennadi Liakhovetski wrote:

Linux supports running the RPMsg protocol over the VirtIO transport protocol, but currently there is only support for VirtIO clients and no support for a VirtIO server. This patch adds a vhost-based RPMsg server implementation.

Signed-off-by: Guennadi Liakhovetski guennadi.liakhovetski@linux.intel.com

drivers/vhost/Kconfig | 7 + drivers/vhost/Makefile | 3 + drivers/vhost/rpmsg.c | 375 ++++++++++++++++++++++++++++++++++++ drivers/vhost/vhost_rpmsg.h | 74 +++++++ 4 files changed, 459 insertions(+) create mode 100644 drivers/vhost/rpmsg.c create mode 100644 drivers/vhost/vhost_rpmsg.h

diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig index d3688c6afb87..602421bf1d03 100644 --- a/drivers/vhost/Kconfig +++ b/drivers/vhost/Kconfig @@ -38,6 +38,13 @@ config VHOST_NET To compile this driver as a module, choose M here: the module will be called vhost_net.

+config VHOST_RPMSG

• tristate

So this lacks a description line so it does not appear in menuconfig. How is user supposed to set it? I added a one-line description.

• depends on VHOST

Other drivers select VHOST instead. Any reason not to do it like this here?

• help

•  Vhost RPMsg API allows vhost drivers to communicate with VirtIO
  

•  drivers, using the RPMsg over VirtIO protocol.
  

config VHOST_SCSI tristate "VHOST_SCSI TCM fabric driver" depends on TARGET_CORE && EVENTFD diff --git a/drivers/vhost/Makefile b/drivers/vhost/Makefile index f3e1897cce85..9cf459d59f97 100644 --- a/drivers/vhost/Makefile +++ b/drivers/vhost/Makefile @@ -2,6 +2,9 @@ obj-$(CONFIG_VHOST_NET) += vhost_net.o vhost_net-y := net.o

+obj-$(CONFIG_VHOST_RPMSG) += vhost_rpmsg.o +vhost_rpmsg-y := rpmsg.o

obj-$(CONFIG_VHOST_SCSI) += vhost_scsi.o vhost_scsi-y := scsi.o

diff --git a/drivers/vhost/rpmsg.c b/drivers/vhost/rpmsg.c new file mode 100644 index 000000000000..d7ab48414224 --- /dev/null +++ b/drivers/vhost/rpmsg.c @@ -0,0 +1,375 @@ +// SPDX-License-Identifier: GPL-2.0-only +/*

• • Copyright(c) 2020 Intel Corporation. All rights reserved.
• • Author: Guennadi Liakhovetski guennadi.liakhovetski@linux.intel.com
• • Vhost RPMsg VirtIO interface. It provides a set of functions to match the
• • guest side RPMsg VirtIO API, provided by drivers/rpmsg/virtio_rpmsg_bus.c
• • These functions handle creation of 2 virtual queues, handling of endpoint
• • addresses, sending a name-space announcement to the guest as well as any
• • user messages. This API can be used by any vhost driver to handle RPMsg
• • specific processing.
• • Specific vhost drivers, using this API will use their own VirtIO device
• • IDs, that should then also be added to the ID table in virtio_rpmsg_bus.c
• */

+#include <linux/compat.h> +#include <linux/file.h> +#include <linux/miscdevice.h> +#include <linux/module.h> +#include <linux/mutex.h> +#include <linux/vhost.h> +#include <linux/virtio_rpmsg.h> +#include <uapi/linux/rpmsg.h>

+#include "vhost.h" +#include "vhost_rpmsg.h"

+/*

• • All virtio-rpmsg virtual queue kicks always come with just one buffer -
• • either input or output
• */

+static int vhost_rpmsg_get_single(struct vhost_virtqueue *vq) +{

• struct vhost_rpmsg *vr = container_of(vq->dev, struct vhost_rpmsg, dev);
• unsigned int out, in;
• int head = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov), &out, &in,

• 		     NULL, NULL);
  

• if (head < 0) {

• vq_err(vq, "%s(): error %d getting buffer\n",
  

•        __func__, head);
  

• return head;
  

• }
• /* Nothing new? */
• if (head == vq->num)

• return head;
  

• if (vq == &vr->vq[VIRTIO_RPMSG_RESPONSE] && (out || in != 1)) {

This in != 1 looks like a dependency on a specific message layout. virtio spec says to avoid these. Using iov iters it's not too hard to do ...

• vq_err(vq,
  

•        "%s(): invalid %d input and %d output in response queue\n",
  

•        __func__, in, out);
  

• goto return_buf;
  

• }
• if (vq == &vr->vq[VIRTIO_RPMSG_REQUEST] && (in || out != 1)) {

• vq_err(vq,
  

•        "%s(): invalid %d input and %d output in request queue\n",
  

•        __func__, in, out);
  

• goto return_buf;
  

• }
• return head;

+return_buf:

• /*

• * FIXME: might need to return the buffer using vhost_add_used()
  

• * or vhost_discard_vq_desc(). vhost_discard_vq_desc() is
  

• * described as "being useful for error handling," but it makes
  

• * the thus discarded buffers "unseen," so next time we look we
  

• * retrieve them again?
  

Yes. It's your decision what to do on error. if you also signal an eventfd using vq_err, then discarding will make it so userspace can poke at ring and hopefully fix it ...

• */
  

• return -EINVAL;

+}

+static const struct vhost_rpmsg_ept *vhost_rpmsg_ept_find(struct vhost_rpmsg *vr, int addr) +{

• unsigned int i;
• for (i = 0; i < vr->n_epts; i++)

• if (vr->ept[i].addr == addr)
  

• 	return vr->ept + i;
  

• return NULL;

+}

+/*

• • if len < 0, then for reading a request, the complete virtual queue buffer
• • size is prepared, for sending a response, the length in the iterator is used
• */

+int vhost_rpmsg_start_lock(struct vhost_rpmsg *vr, struct vhost_rpmsg_iter *iter,

• 	   unsigned int qid, ssize_t len)
  

• __acquires(vq->mutex)

+{

• struct vhost_virtqueue *vq = vr->vq + qid;
• size_t tmp;
• if (qid >= VIRTIO_RPMSG_NUM_OF_VQS)

• return -EINVAL;
  

• iter->vq = vq;
• mutex_lock(&vq->mutex);
• vhost_disable_notify(&vr->dev, vq);
• iter->head = vhost_rpmsg_get_single(vq);
• if (iter->head == vq->num)

• iter->head = -EAGAIN;
  

• if (iter->head < 0)

• goto unlock;
  

• tmp = vq->iov[0].iov_len;
• if (tmp < sizeof(iter->rhdr)) {

• vq_err(vq, "%s(): size %zu too small\n", __func__, tmp);
  

• iter->head = -ENOBUFS;
  

• goto return_buf;
  

• }
• switch (qid) {
• case VIRTIO_RPMSG_REQUEST:

• if (len < 0) {
  

• 	len = tmp - sizeof(iter->rhdr);
  

• } else if (tmp < sizeof(iter->rhdr) + len) {
  

• 	iter->head = -ENOBUFS;
  

• 	goto return_buf;
  

• }
  

• /* len is now the size of the payload */
  

• iov_iter_init(&iter->iov_iter, WRITE,
  

• 	      vq->iov, 1, sizeof(iter->rhdr) + len);
  

• /* Read the RPMSG header with endpoint addresses */
  

• tmp = copy_from_iter(&iter->rhdr, sizeof(iter->rhdr), &iter->iov_iter);
  

• if (tmp != sizeof(iter->rhdr)) {
  

• 	vq_err(vq, "%s(): got %zu instead of %zu\n", __func__,
  

• 	       tmp, sizeof(iter->rhdr));
  

• 	iter->head = -EIO;
  

• 	goto return_buf;
  

• }
  

• iter->ept = vhost_rpmsg_ept_find(vr, vhost32_to_cpu(vq, iter->rhdr.dst));
  

• if (!iter->ept) {
  

• 	vq_err(vq, "%s(): no endpoint with address %d\n",
  

• 	       __func__, vhost32_to_cpu(vq, iter->rhdr.dst));
  

• 	iter->head = -ENOENT;
  

• 	goto return_buf;
  

• }
  

• /* Let the endpoint read the payload */
  

• if (iter->ept->read) {
  

• 	ssize_t ret = iter->ept->read(vr, iter);
  

• 	if (ret < 0) {
  

• 		iter->head = ret;
  

• 		goto return_buf;
  

• 	}
  

• 	iter->rhdr.len = cpu_to_vhost16(vq, ret);
  

• } else {
  

• 	iter->rhdr.len = 0;
  

• }
  

• /* Prepare for the response phase */
  

• iter->rhdr.dst = iter->rhdr.src;
  

• iter->rhdr.src = cpu_to_vhost32(vq, iter->ept->addr);
  

• break;
  

• case VIRTIO_RPMSG_RESPONSE:

• if (!iter->ept && iter->rhdr.dst != cpu_to_vhost32(vq, RPMSG_NS_ADDR)) {
  

• 	/*
  

• 	 * Usually the iterator is configured when processing a
  

• 	 * message on the request queue, but it's also possible
  

• 	 * to send a message on the response queue without a
  

• 	 * preceding request, in that case the iterator must
  

• 	 * contain source and destination addresses.
  

• 	 */
  

• 	iter->ept = vhost_rpmsg_ept_find(vr, vhost32_to_cpu(vq, iter->rhdr.src));
  

• 	if (!iter->ept) {
  

• 		iter->head = -ENOENT;
  

• 		goto return_buf;
  

• 	}
  

• }
  

• if (len < 0) {
  

• 	len = tmp - sizeof(iter->rhdr);
  

• } else if (tmp < sizeof(iter->rhdr) + len) {
  

• 	iter->head = -ENOBUFS;
  

• 	goto return_buf;
  

• } else {
  

• 	iter->rhdr.len = cpu_to_vhost16(vq, len);
  

• }
  

• /* len is now the size of the payload */
  

• iov_iter_init(&iter->iov_iter, READ, vq->iov, 1, sizeof(iter->rhdr) + len);
  

• /* Write the RPMSG header with endpoint addresses */
  

• tmp = copy_to_iter(&iter->rhdr, sizeof(iter->rhdr), &iter->iov_iter);
  

• if (tmp != sizeof(iter->rhdr)) {
  

• 	iter->head = -EIO;
  

• 	goto return_buf;
  

• }
  

• /* Let the endpoint write the payload */
  

• if (iter->ept && iter->ept->write) {
  

• 	ssize_t ret = iter->ept->write(vr, iter);
  

• 	if (ret < 0) {
  

• 		iter->head = ret;
  

• 		goto return_buf;
  

• 	}
  

• }
  

• break;
  

• }
• return 0;

+return_buf:

• /*

• * FIXME: vhost_discard_vq_desc() or vhost_add_used(), see comment in
  

• * vhost_rpmsg_get_single()
  

• */
  

What's to be done with this FIXME?

+unlock:

• vhost_enable_notify(&vr->dev, vq);
• mutex_unlock(&vq->mutex);
• return iter->head;

+} +EXPORT_SYMBOL_GPL(vhost_rpmsg_start_lock);

+size_t vhost_rpmsg_copy(struct vhost_rpmsg *vr, struct vhost_rpmsg_iter *iter,

• 	void *data, size_t size)
  

+{

• /*

• * We could check for excess data, but copy_{to,from}_iter() don't do
  

• * that either
  

• */
  

• if (iter->vq == vr->vq + VIRTIO_RPMSG_RESPONSE)

• return copy_to_iter(data, size, &iter->iov_iter);
  

• return copy_from_iter(data, size, &iter->iov_iter);

+} +EXPORT_SYMBOL_GPL(vhost_rpmsg_copy);

+int vhost_rpmsg_finish_unlock(struct vhost_rpmsg *vr,

• 	      struct vhost_rpmsg_iter *iter)
  

• __releases(vq->mutex)

+{

• if (iter->head >= 0)

• vhost_add_used_and_signal(iter->vq->dev, iter->vq, iter->head,
  

• 			  vhost16_to_cpu(iter->vq, iter->rhdr.len) +
  

• 			  sizeof(iter->rhdr));
  

• vhost_enable_notify(&vr->dev, iter->vq);
• mutex_unlock(&iter->vq->mutex);
• return iter->head;

+} +EXPORT_SYMBOL_GPL(vhost_rpmsg_finish_unlock);

+/*

• • Return false to terminate the external loop only if we fail to obtain either
• • a request or a response buffer
• */

+static bool handle_rpmsg_req_single(struct vhost_rpmsg *vr,

• 		    struct vhost_virtqueue *vq)
  

+{

• struct vhost_rpmsg_iter iter;
• int ret = vhost_rpmsg_start_lock(vr, &iter, VIRTIO_RPMSG_REQUEST, -EINVAL);
• if (!ret)

• ret = vhost_rpmsg_finish_unlock(vr, &iter);
  

• if (ret < 0) {

• if (ret != -EAGAIN)
  

• 	vq_err(vq, "%s(): RPMSG processing failed %d\n",
  

• 	       __func__, ret);
  

• return false;
  

• }
• if (!iter.ept->write)

• return true;
  

• ret = vhost_rpmsg_start_lock(vr, &iter, VIRTIO_RPMSG_RESPONSE, -EINVAL);
• if (!ret)

• ret = vhost_rpmsg_finish_unlock(vr, &iter);
  

• if (ret < 0) {

• vq_err(vq, "%s(): RPMSG finalising failed %d\n", __func__, ret);
  

• return false;
  

• }
• return true;

+}

+static void handle_rpmsg_req_kick(struct vhost_work *work) +{

• struct vhost_virtqueue *vq = container_of(work, struct vhost_virtqueue,

• 				  poll.work);
  

• struct vhost_rpmsg *vr = container_of(vq->dev, struct vhost_rpmsg, dev);
• while (handle_rpmsg_req_single(vr, vq))

• ;
  

+}

+/*

• • initialise two virtqueues with an array of endpoints,
• • request and response callbacks
• */

+void vhost_rpmsg_init(struct vhost_rpmsg *vr, const struct vhost_rpmsg_ept *ept,

•       unsigned int n_epts)
  

+{

• unsigned int i;
• for (i = 0; i < ARRAY_SIZE(vr->vq); i++)

• vr->vq_p[i] = &vr->vq[i];
  

• /* vq[0]: host -> guest, vq[1]: host <- guest */
• vr->vq[VIRTIO_RPMSG_REQUEST].handle_kick = handle_rpmsg_req_kick;
• vr->vq[VIRTIO_RPMSG_RESPONSE].handle_kick = NULL;
• vr->ept = ept;
• vr->n_epts = n_epts;
• vhost_dev_init(&vr->dev, vr->vq_p, VIRTIO_RPMSG_NUM_OF_VQS,

•        UIO_MAXIOV, 0, 0, true, NULL);
  

+} +EXPORT_SYMBOL_GPL(vhost_rpmsg_init);

+void vhost_rpmsg_destroy(struct vhost_rpmsg *vr) +{

• if (vhost_dev_has_owner(&vr->dev))

• vhost_poll_flush(&vr->vq[VIRTIO_RPMSG_REQUEST].poll);
  

• vhost_dev_cleanup(&vr->dev);

+} +EXPORT_SYMBOL_GPL(vhost_rpmsg_destroy);

+/* send namespace */ +int vhost_rpmsg_ns_announce(struct vhost_rpmsg *vr, const char *name, unsigned int src) +{

• struct vhost_virtqueue *vq = &vr->vq[VIRTIO_RPMSG_RESPONSE];
• struct vhost_rpmsg_iter iter = {

• .rhdr = {
  

• 	.src = 0,
  

• 	.dst = cpu_to_vhost32(vq, RPMSG_NS_ADDR),
  

• 	.flags = cpu_to_vhost16(vq, RPMSG_NS_CREATE), /* rpmsg_recv_single() */
  

• },
  

• };
• struct rpmsg_ns_msg ns = {

• .addr = cpu_to_vhost32(vq, src),
  

• .flags = cpu_to_vhost32(vq, RPMSG_NS_CREATE), /* for rpmsg_ns_cb() */
  

• };
• int ret = vhost_rpmsg_start_lock(vr, &iter, VIRTIO_RPMSG_RESPONSE, sizeof(ns));
• if (ret < 0)

• return ret;
  

• strlcpy(ns.name, name, sizeof(ns.name));
• ret = vhost_rpmsg_copy(vr, &iter, &ns, sizeof(ns));
• if (ret != sizeof(ns))

• vq_err(iter.vq, "%s(): added %d instead of %zu bytes\n",
  

•        __func__, ret, sizeof(ns));
  

• ret = vhost_rpmsg_finish_unlock(vr, &iter);
• if (ret < 0)

• vq_err(iter.vq, "%s(): namespace announcement failed: %d\n",
  

•        __func__, ret);
  

• return ret;

+} +EXPORT_SYMBOL_GPL(vhost_rpmsg_ns_announce);

+MODULE_LICENSE("GPL v2"); +MODULE_AUTHOR("Intel, Inc."); +MODULE_DESCRIPTION("Vhost RPMsg API"); diff --git a/drivers/vhost/vhost_rpmsg.h b/drivers/vhost/vhost_rpmsg.h new file mode 100644 index 000000000000..30072cecb8a0 --- /dev/null +++ b/drivers/vhost/vhost_rpmsg.h @@ -0,0 +1,74 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/*

• • Copyright(c) 2020 Intel Corporation. All rights reserved.
• • Author: Guennadi Liakhovetski guennadi.liakhovetski@linux.intel.com
• */

+#ifndef VHOST_RPMSG_H +#define VHOST_RPMSG_H

+#include <linux/uio.h> +#include <linux/virtio_rpmsg.h>

+#include "vhost.h"

+/* RPMsg uses two VirtQueues: one for each direction */ +enum {

• VIRTIO_RPMSG_RESPONSE, /* RPMsg response (host->guest) buffers */
• VIRTIO_RPMSG_REQUEST, /* RPMsg request (guest->host) buffers */
• /* Keep last */
• VIRTIO_RPMSG_NUM_OF_VQS,

+};

+struct vhost_rpmsg_ept;

+struct vhost_rpmsg_iter {

• struct iov_iter iov_iter;
• struct rpmsg_hdr rhdr;
• struct vhost_virtqueue *vq;
• const struct vhost_rpmsg_ept *ept;
• int head;
• void *priv;

+};

+struct vhost_rpmsg {

• struct vhost_dev dev;
• struct vhost_virtqueue vq[VIRTIO_RPMSG_NUM_OF_VQS];
• struct vhost_virtqueue *vq_p[VIRTIO_RPMSG_NUM_OF_VQS];
• const struct vhost_rpmsg_ept *ept;
• unsigned int n_epts;

+};

+struct vhost_rpmsg_ept {

• ssize_t (*read)(struct vhost_rpmsg *, struct vhost_rpmsg_iter *);
• ssize_t (*write)(struct vhost_rpmsg *, struct vhost_rpmsg_iter *);
• int addr;

+};

+static inline size_t vhost_rpmsg_iter_len(const struct vhost_rpmsg_iter *iter) +{

• return iter->rhdr.len;

+}

+#define VHOST_RPMSG_ITER(_vq, _src, _dst) { \

• .rhdr = { \

• 	.src = cpu_to_vhost32(_vq, _src),	\
  

• 	.dst = cpu_to_vhost32(_vq, _dst),	\
  

• },						\
  

• }

+void vhost_rpmsg_init(struct vhost_rpmsg *vr, const struct vhost_rpmsg_ept *ept,

•       unsigned int n_epts);
  

+void vhost_rpmsg_destroy(struct vhost_rpmsg *vr); +int vhost_rpmsg_ns_announce(struct vhost_rpmsg *vr, const char *name,

• 	    unsigned int src);
  

+int vhost_rpmsg_start_lock(struct vhost_rpmsg *vr,

• 	   struct vhost_rpmsg_iter *iter,
  

• 	   unsigned int qid, ssize_t len);
  

+size_t vhost_rpmsg_copy(struct vhost_rpmsg *vr, struct vhost_rpmsg_iter *iter,

• 	void *data, size_t size);
  

+int vhost_rpmsg_finish_unlock(struct vhost_rpmsg *vr,

• 	      struct vhost_rpmsg_iter *iter);
  

+#endif

2.27.0

On Tue, Aug 04, 2020 at 05:19:17PM +0200, Guennadi Liakhovetski wrote:

On Tue, Aug 04, 2020 at 10:27:08AM -0400, Michael S. Tsirkin wrote:

...

On Wed, Jul 22, 2020 at 05:09:27PM +0200, Guennadi Liakhovetski wrote:

...

Linux supports running the RPMsg protocol over the VirtIO transport protocol, but currently there is only support for VirtIO clients and no support for a VirtIO server. This patch adds a vhost-based RPMsg server implementation.

Signed-off-by: Guennadi Liakhovetski guennadi.liakhovetski@linux.intel.com

drivers/vhost/Kconfig | 7 + drivers/vhost/Makefile | 3 + drivers/vhost/rpmsg.c | 375 ++++++++++++++++++++++++++++++++++++ drivers/vhost/vhost_rpmsg.h | 74 +++++++ 4 files changed, 459 insertions(+) create mode 100644 drivers/vhost/rpmsg.c create mode 100644 drivers/vhost/vhost_rpmsg.h

diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig index d3688c6afb87..602421bf1d03 100644 --- a/drivers/vhost/Kconfig +++ b/drivers/vhost/Kconfig @@ -38,6 +38,13 @@ config VHOST_NET To compile this driver as a module, choose M here: the module will be called vhost_net.

+config VHOST_RPMSG

• tristate

So this lacks a description line so it does not appear in menuconfig. How is user supposed to set it? I added a one-line description.

That was on purpose. I don't think there's any value in this API stand-alone, so I let users select it as needed. But we can change that too, id desired.

I guess the patches actually selecting this are separate then?

...

...

• depends on VHOST

Other drivers select VHOST instead. Any reason not to do it like this here?

I have

• select VHOST
• select VHOST_RPMSG

in my client driver patch.

Any issues selecting from here so others get it for free? If this is selected then dependencies are ignored ...

...

...

• help

•  Vhost RPMsg API allows vhost drivers to communicate with VirtIO
  

•  drivers, using the RPMsg over VirtIO protocol.
  

...

config VHOST_SCSI tristate "VHOST_SCSI TCM fabric driver" depends on TARGET_CORE && EVENTFD diff --git a/drivers/vhost/Makefile b/drivers/vhost/Makefile index f3e1897cce85..9cf459d59f97 100644 --- a/drivers/vhost/Makefile +++ b/drivers/vhost/Makefile @@ -2,6 +2,9 @@ obj-$(CONFIG_VHOST_NET) += vhost_net.o vhost_net-y := net.o

+obj-$(CONFIG_VHOST_RPMSG) += vhost_rpmsg.o +vhost_rpmsg-y := rpmsg.o

obj-$(CONFIG_VHOST_SCSI) += vhost_scsi.o vhost_scsi-y := scsi.o

diff --git a/drivers/vhost/rpmsg.c b/drivers/vhost/rpmsg.c new file mode 100644 index 000000000000..d7ab48414224 --- /dev/null +++ b/drivers/vhost/rpmsg.c @@ -0,0 +1,375 @@ +// SPDX-License-Identifier: GPL-2.0-only +/*

• • Copyright(c) 2020 Intel Corporation. All rights reserved.
• • Author: Guennadi Liakhovetski guennadi.liakhovetski@linux.intel.com
• • Vhost RPMsg VirtIO interface. It provides a set of functions to match the
• • guest side RPMsg VirtIO API, provided by drivers/rpmsg/virtio_rpmsg_bus.c
• • These functions handle creation of 2 virtual queues, handling of endpoint
• • addresses, sending a name-space announcement to the guest as well as any
• • user messages. This API can be used by any vhost driver to handle RPMsg
• • specific processing.
• • Specific vhost drivers, using this API will use their own VirtIO device
• • IDs, that should then also be added to the ID table in virtio_rpmsg_bus.c
• */

+#include <linux/compat.h> +#include <linux/file.h> +#include <linux/miscdevice.h> +#include <linux/module.h> +#include <linux/mutex.h> +#include <linux/vhost.h> +#include <linux/virtio_rpmsg.h> +#include <uapi/linux/rpmsg.h>

+#include "vhost.h" +#include "vhost_rpmsg.h"

+/*

• • All virtio-rpmsg virtual queue kicks always come with just one buffer -
• • either input or output
• */

+static int vhost_rpmsg_get_single(struct vhost_virtqueue *vq) +{

• struct vhost_rpmsg *vr = container_of(vq->dev, struct vhost_rpmsg, dev);
• unsigned int out, in;
• int head = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov), &out, &in,

• 		     NULL, NULL);
  

• if (head < 0) {

• vq_err(vq, "%s(): error %d getting buffer\n",
  

•        __func__, head);
  

• return head;
  

• }
• /* Nothing new? */
• if (head == vq->num)

• return head;
  

• if (vq == &vr->vq[VIRTIO_RPMSG_RESPONSE] && (out || in != 1)) {

This in != 1 looks like a dependency on a specific message layout. virtio spec says to avoid these. Using iov iters it's not too hard to do ...

This is an RPMsg VirtIO implementation, and it has to match the virtio_rpmsg_bus.c driver, and that one has specific VirtIO queue and message usage patterns.

That could be fine for legacy virtio, but now you are claiming support for virtio 1, so need to fix these assumptions in the device.

...

...

• vq_err(vq,
  

•        "%s(): invalid %d input and %d output in response queue\n",
  

•        __func__, in, out);
  

• goto return_buf;
  

• }
• if (vq == &vr->vq[VIRTIO_RPMSG_REQUEST] && (in || out != 1)) {

• vq_err(vq,
  

•        "%s(): invalid %d input and %d output in request queue\n",
  

•        __func__, in, out);
  

• goto return_buf;
  

• }
• return head;

+return_buf:

• /*

• * FIXME: might need to return the buffer using vhost_add_used()
  

• * or vhost_discard_vq_desc(). vhost_discard_vq_desc() is
  

• * described as "being useful for error handling," but it makes
  

• * the thus discarded buffers "unseen," so next time we look we
  

• * retrieve them again?
  

Yes. It's your decision what to do on error. if you also signal an eventfd using vq_err, then discarding will make it so userspace can poke at ring and hopefully fix it ...

I assume the user-space in this case is QEMU. Would it be the safest to use vhost_add_used() then?

Your call.

...

...

• */
  

• return -EINVAL;

+}

[snip]

...

...

• return 0;

+return_buf:

• /*

• * FIXME: vhost_discard_vq_desc() or vhost_add_used(), see comment in
  

• * vhost_rpmsg_get_single()
  

• */
  

What's to be done with this FIXME?

This is the same question as above - I just wasn't sure which error handling was appropriate here, don't think many vhost drivers do any od this...

Thanks Guennadi