minimal required kernel CONFIG options

[saloniamatteo]

Greetings.

After various debugging attemps, I've come up with what I think is a list of minimal required CONFIG options, in order to build v4l2loopback and run it successfully.

Here is the list:

CONFIG_V4L2_FWNODE=m
CONFIG_V4L_MEM2MEM_DRIVERS=y
CONFIG_V4L_PLATFORM_DRIVERS=y
CONFIG_V4L_TEST_DRIVERS=y
CONFIG_VIDEO=y
CONFIG_VIDEOBUF2_CORE=m
CONFIG_VIDEOBUF2_MEMOPS=m
CONFIG_VIDEOBUF2_V4L2=m
CONFIG_VIDEOBUF2_VMALLOC=m
CONFIG_VIDEO_DEV=m

I'll be doing some further testing to see if this list can be made smaller.

From issue #603: Please check if CONFIG_TRIM_UNUSED_KSYMS is enabled: if it is, it WILL NOT allow you to compile v4l2loopback, unless you manually set the whitelist.

Some (if not all) of the functions needed by v4l2loopback are:

__video_register_device()
ktime_get_ts64()
v4l2_ctrl_handler_free()
v4l2_ctrl_handler_init_class()
v4l2_ctrl_new_custom()
v4l2_ctrl_subscribe_event()
v4l2_device_register()
v4l2_event_queue()
v4l2_fill_pixfmt()
v4l2_fill_pixfmt_mp()
video_devdata()
video_device_alloc()
video_device_release()
video_ioctl2()
video_unregister_device()
vm_insert_page()

[saloniamatteo]

Update: after various tests, I can confirm the following CONFIG options are NOT needed:

CONFIG_V4L2_ASYNC
CONFIG_V4L2_FWNODE
CONFIG_V4L2_MEM2MEM_DEV
CONFIG_V4L_MEM2MEM_DRIVERS
CONFIG_V4L_TEST_DRIVERS
CONFIG_VIDEOBUF2_DMA_CONTIG
CONFIG_VIDEO_MEM2MEM_DEINTERLACE
CONFIG_VIDEO_MUX
CONFIG_VIDEO_V4L2_SUBDEV_API

[saloniamatteo]

Tested on Gentoo Linux, Kernel 6.11.7-gentoo (sys-kernel/gentoo-sources).

So far, the required options would be the following:

CONFIG_V4L_PLATFORM_DRIVERS=y
CONFIG_VIDEO=y
CONFIG_VIDEOBUF2_CORE=m
CONFIG_VIDEOBUF2_MEMOPS=m
CONFIG_VIDEOBUF2_V4L2=m
CONFIG_VIDEOBUF2_VMALLOC=m
CONFIG_VIDEO_DEV=m

Make sure CONFIG_TRIM_UNUSED_KSYMS is not enabled.