Hi Wren, How about you submit the loopback driver for integration in mainline? We can review the driver, give feedback and help you get it merged. Ezequiel On Mon, 1 Mar 2021 at 17:32, Wren Turkal <wt@xxxxxxxxxxxxxxxx> wrote: > > Okay, so I have found how to enable the option to be manually selected. > Would a patch like the following be acceptable? Or is there a better > way to do this? > > diff --git a/drivers/media/v4l2-core/Kconfig > b/drivers/media/v4l2-core/Kconfig > index bf49f83cb86f..25004137a982 100644 > --- a/drivers/media/v4l2-core/Kconfig > +++ b/drivers/media/v4l2-core/Kconfig > @@ -54,7 +54,7 @@ config V4L2_H264 > > # Used by drivers that need v4l2-mem2mem.ko > config V4L2_MEM2MEM_DEV > - tristate > + tristate "V4L2 mem2mem framework support" > depends on VIDEOBUF2_CORE > > # Used by LED subsystem flash drivers > > > Thanks, > wt > > On 2/28/21 2:07 PM, Wren Turkal wrote: > > Hi there linux-media experts, > > > > I am working on the out-of-tree v4l2loopback module[1]. My > > current goal is to implement the videobuf2 api. However, > > it appears that I must use a different vbuf2_queue for the > > OUTPUT and CAPTURE types. It appears that the mem2mem > > framework has the ability to do just this. I came to this > > conclusion while looking at the vim2m test module's code. > > While trying to modify the loopback module, I have added > > some code to try to call v4l2_m2m_init. You can see my very > > WIP attempt at code here[2]. > > > > I have installed the kernel-devel package on Fedora, which. > > Unfortunately, I get he following error messages when trying > > to compile: > > > > <errors> > > ERROR: modpost: "v4l2_m2m_release" > > [/home/wt/projects/kernel/v4l2loopback/v4l2loopback.ko] undefined! > > ERROR: modpost: "v4l2_m2m_init" > > [/home/wt/projects/kernel/v4l2loopback/v4l2loopback.ko] undefined! > > </errors> > > > > So, I looked into it, and Module.symvers and /proc/kallsyms > > don't have those symbols listed, so I think the Fedora kernel > > was not compiled with those symbols exported. > > > > Okay, so next I tried to build a custom kernel that does > > export those symbols. I managed to get it done by enabling > > the vim2m (VIDEO_VIM2M config option) module. The new > > Module.symvers includes the symbols; and the compile succeeds, > > which brings me to my final act. > > > > I need to expose those symbols without enabling the vim2m > > module since it is a testing module. I do not see a way > > to do that explicitly. The config option in question > > appears to be V4L2_MEM2MEM_DEV. And I haven't found a > > way to enable it without enabling something that implicitly > > selects it (which vim2m does). Do y'all have any suggestions > > for how to get these symbols exported properly when vim2m is > > not enabled? > > > > > > Thanks, > > Wren Turkal (wt) > > > > [1] https://github.com/umlaeute/v4l2loopback > > [2] https://github.com/wt/v4l2loopback/tree/m2m_try >
