Re: Should linuxkpi linux_file_ioctl support flexible array copy?

On Fri, Feb 13, 2026 at 09:42:58PM +0800, Zhenlei Huang wrote:
> Probably it does not matter. It is good to keep the ABI stable, well that
implies
> stable ABI cross different versions of OS, but not different OSes. Am I
right ?
>
> I think make it work first, make it better second !

Thanks for your kind reply!

You are absolutely right. I think the best way forward is to change the
ABI to use an explicit pointer rather than a flexible array, which
conforms better to the FreeBSD style.

However, I noticed that the Linux ioctl scheme is designed to pass the
raw user space pointer to the low level driver. Currently, the FreeBSD
linuxkpi only provides a "fake" user space pointer (backed by kernel
memory), which cannot be used for parameters involving flexible arrays.
This implementation does not seem to fully conform to the Linux ioctl
scheme.

Do you think improving linuxkpi to support this pattern (flexible arrays
in ioctl) is worth pursuing in the long run? It seems like a valuable
compatibility improvement for future driver ports.

But as you said, "make it work first, make it better second", I will use
the above method to get it working first.

Best Regards,
Zishun Yi