Re: [PATCH] selftests: Open /dev/udmabuf O_RDONLY

[T.J. Mercier]

On Fri, Jun 26, 2026 at 6:09 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
>
> On Thu, 25 Jun 2026 11:15:55 -0700 T.J. Mercier wrote:
> > Write permissions on the /dev/udmabuf device file are not required to
> > issue ioctls and allocate udmabufs. Applications should be opening this
> > file as O_RDONLY. The BPF dmabuf_iter selftest already does this. [1]
> >
> > Remove the write access mode from the drivers/dma-buf/udmabuf.c and
> > drivers/net/hw/ncdevmem.c selftests.
>
> You need to explain "why", too. Why change it if it clearly
> worked for everyone running this test until now.
> --
> pw-bot: cr

Principle of least privilege. Folks use or point to these selftests as
examples, and then wonder why O_RDWR doesn't work on systems where
write permissions are not available on /dev/udmabuf.