On Sat, Jul 18, 2026 at 10:29 AM Michael S. Tsirkin <[email protected]> wrote: > > On Sun, Jul 12, 2026 at 08:57:26AM +0200, Mauro Carvalho Chehab wrote: > > On Thu, 25 Jun 2026 16:18:48 -0400 > > Brian Daniels <[email protected]> wrote: > > > > > > > From: Alexandre Courbot <[email protected]> > > > > > > > > > > virtio_media_driver.c provides the expected driver hooks, and support > > > > > for mmapping and polling. > > > > > > > > > > Signed-off-by: Alexandre Courbot <[email protected]> > > > > > Co-developed-by: Brian Daniels <[email protected]> > > > > > Signed-off-by: Brian Daniels <[email protected]> > > > > > --- > > > > > drivers/media/virtio/virtio_media_driver.c | 959 > > > > > +++++++++++++++++++++ > > > > > 1 file changed, 959 insertions(+) > > > > > create mode 100644 drivers/media/virtio/virtio_media_driver.c > > > > > > > > > > diff --git a/drivers/media/virtio/virtio_media_driver.c > > > > > b/drivers/media/virtio/virtio_media_driver.c > > > > > new file mode 100644 > > > > > index 000000000..d6363c673 > > > > > --- /dev/null > > > > > +++ b/drivers/media/virtio/virtio_media_driver.c > > > > > @@ -0,0 +1,959 @@ > > > > > +// SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0+ > > > > > + > > > > > +/* > > > > > + * Virtio-media driver. > > > > > + * > > > > > + * Copyright (c) 2024-2025 Google LLC. > > > > > + */ > > > > > + > > > > > +#include <linux/delay.h> > > > > > +#include <linux/device.h> > > > > > +#include <linux/dev_printk.h> > > > > > +#include <linux/mm.h> > > > > > +#include <linux/mutex.h> > > > > > +#include <linux/scatterlist.h> > > > > > +#include <linux/types.h> > > > > > +#include <linux/videodev2.h> > > > > > +#include <linux/vmalloc.h> > > > > > +#include <linux/wait.h> > > > > > +#include <linux/workqueue.h> > > > > > +#include <linux/module.h> > > > > > +#include <linux/moduleparam.h> > > > > > +#include <linux/virtio.h> > > > > > +#include <linux/virtio_config.h> > > > > > +#include <linux/virtio_ids.h> > > > > > + > > > > > +#include <media/frame_vector.h> > > > > > +#include <media/v4l2-dev.h> > > > > > +#include <media/v4l2-event.h> > > > > > +#include <media/videobuf2-memops.h> > > > > > +#include <media/v4l2-device.h> > > > > > +#include <media/v4l2-ioctl.h> > > > > > + > > > > > +#include "protocol.h" > > > > > +#include "session.h" > > > > > +#include "virtio_media.h" > > > > > + > > > > > +#define VIRTIO_MEDIA_NUM_EVENT_BUFS 16 > > > > > + > > > > > +/* ID of the SHM region into which MMAP buffer will be mapped. */ > > > > > +#define VIRTIO_MEDIA_SHM_MMAP 0 > > > > > + > > > > > +/* > > > > > + * Name of the driver to expose to user-space. > > > > > + * > > > > > + * This is configurable because v4l2-compliance has workarounds > > > > > specific to > > > > > + * some drivers. When proxying these directly from the host, this > > > > > allows it to > > > > > + * apply them as needed. > > > > > + */ > > > > > +char *virtio_media_driver_name; > > > > > +module_param_named(driver_name, virtio_media_driver_name, charp, > > > > > 0660); > > > > > > > > > > > > Um. What? Not how it should be handled. > > > > > > I can remove this module param. I didn't end up using this when > > > compliance testing. > > > Instead, I patched v4l-utils: > > > https://lore.kernel.org/all/[email protected]/ > > > > > > Let me know if you think the v4l-utils patch is a good approach, > > > otherwise let > > > me know how you'd prefer to address the v4l2-compliance driver-specific > > > workounds > > > when they're being proxied with virtio-media. > > > > This kind of discussion should happen on a separate PR for v4l2-compliance, > > c/c to the proper developers and maintainers of it. > > > I wonder how migration can work when guest is tied to host driver model like > this.
We haven't given migration much thought yet, but I think it wouldn't be so different to GPU, where to do snapshot/migration we have to record all initialization / context setup state and replay it against the GPU driver on restore (see https://github.com/google/gfxstream). Some migrations will be possible, some will not, and the host should be able to decide. Also, Brian mentioned the host device pass-through use case, but we also have device implementations on the host that work with camera emulators or some other data source like video/webrtc, which will support snapshot/migration more easily. This use case will probably will see more real-world use and migration will be more relevant. > > > > > > > > + > > > > > +/* > > > > > + * Whether USERPTR buffers are allowed. > > > > > + * > > > > > + * This is disabled by default as USERPTR buffers are dangerous, but > > > > > the option > > > > > + * is left to enable them if desired. > > > > > + */ > > > > > +bool virtio_media_allow_userptr; > > > > > +module_param_named(allow_userptr, virtio_media_allow_userptr, bool, > > > > > 0660); > > > > > > > > > > > > is this kind of thing common? > > > > There is one old media device that has it (saa7134). > > > > > > > > To be honest, I don't really know. I'm also not that familiar with the > > > USERPTR > > > issues. I see a few references online about their use being discouraged > > > due to > > > possible race conditions, perhaps that was the original motivation for > > > this > > > parameter (I'm not the original author of this driver). > > > > > > I'm open to alternatives, feel free to let me know if you have a > > > preference. > > > > We tend to not implement USERPTR on newer drivers. I suggest you > > to place the logic with regards to V4L2_MEMORY_USERPTR on a separate > > patch for further discussions. > > > > > > > > > > + > > > > > +/** > > > > > + * virtio_media_session_alloc - Allocate a new session. > > > > > + * @vv: virtio-media device the session belongs to. > > > > > + * @id: ID of the session. > > > > > + * @nonblocking_dequeue: whether dequeuing of buffers should be > > > > > blocking or > > > > > + * not. > > > > > + * > > > > > + * The ``id`` and ``list`` fields must still be set by the caller. > > > > > > > > still in what sense? > > > > > > Based on the code below, I'm not so sure that the caller is responsible > > > for > > > setting these values. They seem to be initialized in the function. > > > > > > Perhaps Alexandre Courbot (the original author) would know more. Unless he > > > says otherwise though I'm inclined to remove this comment. > > > > > > > > + */ > > > > > +static struct virtio_media_session * > > > > > +virtio_media_session_alloc(struct virtio_media *vv, u32 id, > > > > > + struct file *file) > > > > > +{ > > > > > + struct virtio_media_session *session; > > > > > + int i; > > > > > + int ret; > > > > > + > > > > > + session = kzalloc_obj(*session, GFP_KERNEL); > > > > > + if (!session) > > > > > + goto err_session; > > > > > + > > > > > + session->shadow_buf = kzalloc(VIRTIO_SHADOW_BUF_SIZE, > > > > > GFP_KERNEL); > > > > > + if (!session->shadow_buf) > > > > > + goto err_shadow_buf; > > > > > + > > > > > + ret = sg_alloc_table(&session->command_sgs, > > > > > DESC_CHAIN_MAX_LEN, > > > > > + GFP_KERNEL); > > > > > + if (ret) > > > > > + goto err_payload_sgs; > > > > > + > > > > > + session->id = id; > > > > > + session->nonblocking_dequeue = file->f_flags & O_NONBLOCK; > > > > > + > > > > > + INIT_LIST_HEAD(&session->list); > > > > > + v4l2_fh_init(&session->fh, &vv->video_dev); > > > > > + virtio_media_session_fh_add(session, file); > > > > > + > > > > > + for (i = 0; i <= VIRTIO_MEDIA_LAST_QUEUE; i++) > > > > > + INIT_LIST_HEAD(&session->queues[i].pending_dqbufs); > > > > > + mutex_init(&session->queues_lock); > > > > > + > > > > > + init_waitqueue_head(&session->dqbuf_wait); > > > > > + > > > > > + mutex_lock(&vv->sessions_lock); > > > > > + list_add_tail(&session->list, &vv->sessions); > > > > > + mutex_unlock(&vv->sessions_lock); > > > > > + > > > > > + return session; > > > > > + > > > > > +err_payload_sgs: > > > > > + kfree(session->shadow_buf); > > > > > +err_shadow_buf: > > > > > + kfree(session); > > > > > +err_session: > > > > > + return ERR_PTR(-ENOMEM); > > > > > +} > > > > > + > > > > > +/** > > > > > + * virtio_media_session_free - Free all resources of a session. > > > > > + * @vv: virtio-media device the session belongs to. > > > > > + * @session: session to destroy. > > > > > + * > > > > > + * All the resources of @sesssion, as well as the backing memory of > > > > > @session > > > > > + * itself, are freed. > > > > > > > > why @ here and `` above? And typo in the name. > > > > > > The `@` here was an attempt to follow the guide here for referencing > > > function > > > parameters: > > > https://docs.kernel.org/doc-guide/kernel-doc.html#highlights-and-cross-references > > > > Yes. This is part of Linux Kernel kernel-doc markup: when referring to > > struct fields, you should use @field (or ``field`` if one wants to place an > > asterisk on it, like ``*field``). > > > > > > > > That being said, I don't believe this file is 100% consistent with that. > > > I will > > > spend some time cleaning up the comments throughout this patch set to get > > > them > > > consistent for v5. Thanks! > > > > Please use it on a consistent way along the driver. > > > > > > Thanks, > > Mauro >
