Re: [PATCH kvmtool 0/2] Fixes for virtio_balloon stats printing

[Andre Przywara <andre.przywara@arm.com>]

On Fri, 20 May 2022 21:51:07 +0100
Will Deacon <will@kernel.org> wrote:

Hi,

> On Fri, 20 May 2022 14:37:04 +0000, Keir Fraser wrote:
> > While playing with kvmtool's virtio_balloon device I found a couple of
> > niggling issues with the printing of memory stats. Please consider
> > these fairly trivial fixes.

Unfortunately patch 2/2 breaks compilation on userland with older kernel
headers, like Ubuntu 18.04:
...
  CC       builtin-stat.o
builtin-stat.c: In function 'do_memstat':
builtin-stat.c:86:8: error: 'VIRTIO_BALLOON_S_HTLB_PGALLOC' undeclared (first use in this function); did you mean 'VIRTIO_BALLOON_S_AVAIL'?
   case VIRTIO_BALLOON_S_HTLB_PGALLOC:
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        VIRTIO_BALLOON_S_AVAIL
(repeated for VIRTIO_BALLOON_S_HTLB_PGFAIL and VIRTIO_BALLOON_S_CACHES).

I don't quite remember what we did here in the past in those cases,
conditionally redefine the symbols in a local header, or protect the
new code with an #ifdef?

I would lean towards the former (and hacking this in works), but then we
would need to redefine VIRTIO_BALLOON_S_NR, to encompass the new symbols,
which sounds fragile.

Happy to send a patch if we agree on an approach.

Cheers,
Andre

> > 
> > Keir Fraser (2):
> >   virtio/balloon: Fix a crash when collecting stats
> >   stat: Add descriptions for new virtio_balloon stat types
> > 
> > [...]  
> 
> Applied to kvmtool (master), thanks!
> 
> [1/2] virtio/balloon: Fix a crash when collecting stats
>       https://git.kernel.org/will/kvmtool/c/3a13530ae99a
> [2/2] stat: Add descriptions for new virtio_balloon stat types
>       https://git.kernel.org/will/kvmtool/c/bc77bf49df6e
> 
> Cheers,