Hi Laurent,
On Sat, Apr 20, 2024 at 01:45:19AM +0300, Laurent Pinchart wrote:
> Hi Sakari,
>
> Thank you for the patch.
>
> On Tue, Apr 16, 2024 at 10:32:48PM +0300, Sakari Ailus wrote:
> > The len_routes field is used to tell the size of the routes array in
> > struct v4l2_subdev_routing. This way the number of routes returned from
> > S_ROUTING IOCTL may be larger than the number of routes provided, in case
> > there are more routes returned by the driver.
> >
> > Note that this uAPI is still disabled in the code, so this change can
> > safely be done. Anyone who manually patched the code to enable this uAPI
> > must update their code.
> >
> > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> > ---
> > .../media/v4l/vidioc-subdev-g-routing.rst | 50 +++++++++++++------
> > drivers/media/v4l2-core/v4l2-ioctl.c | 4 +-
> > drivers/media/v4l2-core/v4l2-subdev.c | 12 ++---
> > include/media/v4l2-subdev.h | 2 +
> > include/uapi/linux/v4l2-subdev.h | 9 ++--
> > 5 files changed, 52 insertions(+), 25 deletions(-)
> >
> > diff --git a/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst b/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst
> > index 26b5004bfe6d..27eb4c82a0e1 100644
> > --- a/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst
> > +++ b/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst
> > @@ -43,23 +43,42 @@ The routing configuration determines the flows of data inside an entity.
> > Drivers report their current routing tables using the
> > ``VIDIOC_SUBDEV_G_ROUTING`` ioctl and application may enable or disable routes
> > with the ``VIDIOC_SUBDEV_S_ROUTING`` ioctl, by adding or removing routes and
> > -setting or clearing flags of the ``flags`` field of a
> > -struct :c:type:`v4l2_subdev_route`.
> > +setting or clearing flags of the ``flags`` field of a struct
> > +:c:type:`v4l2_subdev_route`.
> >
> > -All stream configurations are reset when ``VIDIOC_SUBDEV_S_ROUTING`` is called. This
> > -means that the userspace must reconfigure all streams after calling the ioctl
> > -with e.g. ``VIDIOC_SUBDEV_S_FMT``.
> > +All stream configurations are reset when ``VIDIOC_SUBDEV_S_ROUTING`` is called.
> > +This means that the userspace must reconfigure all stream formats and selections
> > +after calling the ioctl with e.g. ``VIDIOC_SUBDEV_S_FMT``.
> >
> > Only subdevices which have both sink and source pads can support routing.
> >
> > -When inspecting routes through ``VIDIOC_SUBDEV_G_ROUTING`` and the application
> > -provided ``num_routes`` is not big enough to contain all the available routes
> > -the subdevice exposes, drivers return the ENOSPC error code and adjust the
> > -value of the ``num_routes`` field. Application should then reserve enough memory
> > -for all the route entries and call ``VIDIOC_SUBDEV_G_ROUTING`` again.
> > -
> > -On a successful ``VIDIOC_SUBDEV_G_ROUTING`` call the driver updates the
> > -``num_routes`` field to reflect the actual number of routes returned.
> > +The ``len_routes`` field indicates the number of routes that can fit in the
> > +``routes`` array allocated by userspace. It is set by applications for both
> > +ioctls to indicate how many routes the kernel can return, and is never modified
> > +by the kernel.
> > +
> > +The ``num_routes`` field, when returned from the kernel on both IOCTLs,
> > +indicates the number of routes in the subdevice routing table and when calling
> > +``VIDIOC_SUBDEV_S_ROUTING``, it is set by userspace to the number of routes that
> > +the application stored in the ``routes`` array. The value returned by the kernel
> > +may be smaller or larger than the value of ``num_routes`` set by the application
> > +for ``VIDIOC_SUBDEV_S_ROUTING``, as drivers may adjust the requested routing
> > +table.
>
> I still think the proposal I made when reviewing the previous version is
> clearer :-)
>
> ----
> The ``num_routes`` field indicates the number of routes in the subdevice routing
> table. For ``VIDIOC_SUBDEV_S_ROUTING``, it is set by userspace to the number of
> routes that the application stored in the ``routes`` array. For both ioctls, it
> is returned by the kernel and indicates how many routes are stored in the
> subdevice routing table. This may be smaller or larger than the value of
> ``num_routes`` set by the application for ``VIDIOC_SUBDEV_S_ROUTING``, as
> drivers may adjust the requested routing table.
> ----
>
> You replied that
>
> > For S_ROUTING this is the number of routes in the IOCTL argument. The
> > routing table may contain more (static routes).
>
> and that's right, but, even when set by userspace for S_ROUTING, the
> num_routes fields is the number of routes that userspace tries to set in
> the routing table. I think starting with a first sentence that describes
> what the field contains, and then explaining how it's used for the
> different ioctls by userspace and kernel space, is clearer.
The problem with your suggestion is that it's not entirely correct:
num_routes is indeed used for two different purposes. Removing " in the
subdevice routing table" in the first sentence would be a simple fix.
>
> > +
> > +The kernel can return a ``num_routes`` value larger than ``len_routes`` from
> > +both ioctls. This indicates thare are more routes in the routing table than fits
> > +the ``routes`` array. In this case, the ``routes`` array is filled by the kernel
> > +with the first ``len_routes`` entries of the subdevice routing table. This is
> > +not considered to be an error, and the ioctl call succeeds. If the applications
> > +wants to retrieve the missing routes, it can issue a new
> > +``VIDIOC_SUBDEV_G_ROUTING`` call with a large enough ``routes`` array.
> > +
> > +indicate there are more routes than fits to the ``routes`` array. In this
> > +case first ``len_routes`` were returned back to the userspace in the
> > +``routes`` array. This is not considered as an error.
>
> I think these 3 lines are a leftover.
Yes, I'll remove them.
>
> > +
> > +Also ``VIDIOC_SUBDEV_S_ROUTING`` may return more route than the user provided in
>
> s/Also //
> s/route/routes/
Yes.
>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Thanks!
>
> > +``num_routes`` field due to e.g. hardware properties.
> >
> > .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
> >
> > @@ -74,6 +93,9 @@ On a successful ``VIDIOC_SUBDEV_G_ROUTING`` call the driver updates the
> > - ``which``
> > - Routing table to be accessed, from enum
> > :ref:`v4l2_subdev_format_whence <v4l2-subdev-format-whence>`.
> > + * - __u32
> > + - ``len_routes``
> > + - The length of the array (as in memory reserved for the array)
> > * - struct :c:type:`v4l2_subdev_route`
> > - ``routes[]``
> > - Array of struct :c:type:`v4l2_subdev_route` entries
> > @@ -81,7 +103,7 @@ On a successful ``VIDIOC_SUBDEV_G_ROUTING`` call the driver updates the
> > - ``num_routes``
> > - Number of entries of the routes array
> > * - __u32
> > - - ``reserved``\ [5]
> > + - ``reserved``\ [11]
> > - Reserved for future extensions. Applications and drivers must set
> > the array to zero.
> >
> > diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> > index 1863ecae9ec9..f30f61c008c7 100644
> > --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> > +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> > @@ -3185,13 +3185,13 @@ static int check_array_args(unsigned int cmd, void *parg, size_t *array_size,
> > case VIDIOC_SUBDEV_S_ROUTING: {
> > struct v4l2_subdev_routing *routing = parg;
> >
> > - if (routing->num_routes > 256)
> > + if (routing->len_routes > 256)
> > return -E2BIG;
> >
> > *user_ptr = u64_to_user_ptr(routing->routes);
> > *kernel_ptr = (void **)&routing->routes;
> > *array_size = sizeof(struct v4l2_subdev_route)
> > - * routing->num_routes;
> > + * routing->len_routes;
> > ret = 1;
> > break;
> > }
> > diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> > index 2ba11e5343f0..904378007a79 100644
> > --- a/drivers/media/v4l2-core/v4l2-subdev.c
> > +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> > @@ -927,6 +927,9 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
> > if (routing->which != V4L2_SUBDEV_FORMAT_TRY && ro_subdev)
> > return -EPERM;
> >
> > + if (routing->num_routes > routing->len_routes)
> > + return -EINVAL;
> > +
> > memset(routing->reserved, 0, sizeof(routing->reserved));
> >
> > for (i = 0; i < routing->num_routes; ++i) {
> > @@ -953,6 +956,7 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
> > }
> >
> > krouting.num_routes = routing->num_routes;
> > + krouting.len_routes = routing->len_routes;
> > krouting.routes = routes;
> >
> > return v4l2_subdev_call(sd, pad, set_routing, state,
> > @@ -973,14 +977,10 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
> >
> > krouting = &state->routing;
> >
> > - if (routing->num_routes < krouting->num_routes) {
> > - routing->num_routes = krouting->num_routes;
> > - return -ENOSPC;
> > - }
> > -
> > memcpy((struct v4l2_subdev_route *)(uintptr_t)routing->routes,
> > krouting->routes,
> > - krouting->num_routes * sizeof(*krouting->routes));
> > + min(krouting->num_routes, routing->len_routes) *
> > + sizeof(*krouting->routes));
> > routing->num_routes = krouting->num_routes;
> >
> > return 0;
> > diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
> > index 9cce48365975..1df6b963a1c9 100644
> > --- a/include/media/v4l2-subdev.h
> > +++ b/include/media/v4l2-subdev.h
> > @@ -728,12 +728,14 @@ struct v4l2_subdev_stream_configs {
> > /**
> > * struct v4l2_subdev_krouting - subdev routing table
> > *
> > + * @len_routes: length of routes array, in routes
> > * @num_routes: number of routes
> > * @routes: &struct v4l2_subdev_route
> > *
> > * This structure contains the routing table for a subdev.
> > */
> > struct v4l2_subdev_krouting {
> > + unsigned int len_routes;
> > unsigned int num_routes;
> > struct v4l2_subdev_route *routes;
> > };
> > diff --git a/include/uapi/linux/v4l2-subdev.h b/include/uapi/linux/v4l2-subdev.h
> > index 81a24bd38003..6a39128d0606 100644
> > --- a/include/uapi/linux/v4l2-subdev.h
> > +++ b/include/uapi/linux/v4l2-subdev.h
> > @@ -228,15 +228,18 @@ struct v4l2_subdev_route {
> > * struct v4l2_subdev_routing - Subdev routing information
> > *
> > * @which: configuration type (from enum v4l2_subdev_format_whence)
> > - * @num_routes: the total number of routes in the routes array
> > + * @len_routes: the length of the routes array, in routes
> > * @routes: pointer to the routes array
> > + * @num_routes: the total number of routes, possibly more than fits in the
> > + * routes array
> > * @reserved: drivers and applications must zero this array
> > */
> > struct v4l2_subdev_routing {
> > __u32 which;
> > - __u32 num_routes;
> > + __u32 len_routes;
> > __u64 routes;
> > - __u32 reserved[6];
> > + __u32 num_routes;
> > + __u32 reserved[11];
> > };
> >
> > /*
>
--
Regards,
Sakari Ailus
