Re: [PATCH v4 2/8] media: virtio: Add virtio-media driver structs and function declarations

[Brian Daniels <briandaniels@google.com>]

> > +extern char *virtio_media_driver_name;
> > +extern bool virtio_media_allow_userptr;
> 
> This looks a bit funny to me - why do you have externs in your header ?
> 
> ➜   grep -r virtio * | grep extern
> arch/mips/include/asm/mach-loongson64/builtin_dtbs.h:extern u32 
> __dtb_loongson64v_4core_virtio_begin[];
> Documentation/virt/kvm/api.rst:    - virtio external interrupt; external 
> interrupt
> drivers/gpu/drm/virtio/virtgpu_drv.h:extern struct drm_ioctl_desc 
> virtio_gpu_ioctls[DRM_VIRTIO_NUM_IOCTLS];
> drivers/net/wireless/virtual/mac80211_hwsim.c:extern int 
> hwsim_tx_virtio(struct mac80211_hwsim_data *data,
> include/linux/virtio_anchor.h:extern bool 
> (*virtio_check_mem_acc_cb)(struct virtio_device *dev);

You're command will only return lines that contain both `virtio` and `extern`.
If you instead wanted to find all header files that contain externs, I believe
you would want something like:

  find -type f -name '*.h' | xargs grep extern

When I run this I find many examples of `extern` in header files.

That all being said, the reason the `extern`s are in the header file is so
files that include said header file can access those variables. In this case,
these variables are used for different module parameters. We may be
removing them though, check the other discussion thread.