Re: [PATCH for-4.16] freebsd/privcmd: fix MMAP_RESOURCE ioctl definition

[Andrew Cooper <amc96@srcf.net>]

On 15/11/2021 11:08, Roger Pau Monne wrote:
> Current ioctl definition was wrong in both FreeBSD and Xen sources, as
> the MMAP_RESOURCE ioctl needs to copy back the size of the resource
> when passed a zero address and size. FreeBSD encodes in the definition
> of the ioctl number whether parameters should be copied in (W) and/or
> copied out (R). The current definition for MMAP_RESOURCE is lacking
> the copy out part (R), and thus the call to query the size of a
> resource would always return 0.
>
> This change will break the current ioctl interface, the tools can
> however fall back to using the foreign memory interface in order to
> map resources from guests.
>
> This was a shortcoming from when the hypercall and ioctl gained the
> ability to query the size of the resources, as originally the
> MMAP_RESOURCE ioctl didn't need to copy out any data.
>
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> ---
> Cc: Ian Jackson <iwj@xenproject.org>
>
> The change only affects FreeBSD, and it's only a change in a
> definition of an ioctl, so it's unlikely to break existing code logic.
> Without this change Xen tools won't be able to use the MMAP_RESOURCE
> ioctl.

I guess you found this while trying to fix test-resource, in which case
a further argument for the change is "the unit tests now pass on FreeBSD" ?

~Andrew