[Pkg-xen-devel] build-depend on libzstd-dev

[Andy Smith]

On Thu, Sep 01, 2022 at 01:56:41PM +0200, Hans van Kranenburg wrote:
> .oO(What we recommend is using grub for Xen PV and PVH domU, and in that
> case I think (like, "99% sure, this is probably how it works") Xen just
> kicks off the domU with the grub code, and then grub can handle the zstd
> kernel image that it loads. So, even if we already have Debian users now
> who might run an Ubuntu dom0, this might have masked the issue)

That is correct for the PVH case. The PVH code in grub just calls
grub's own image loading stuff so it works for any kernel that grub
can read.

Sadly the PV code in grub doesn't work like that; it has to
understand how to decompress kernels itself and it hasn't seen any
updates in quite a while so it's not just ZSTD but also LZ4 and
maybe other compression schemes that it is missing.

So, for PVH guests pvhgrub is a good way forward, but for PV guests
pvgrub can still be problematic. Though Debian still uses
conservative kernel compressions by default so not as bad a problem
if you only run Debian guests.

Cheers,
Andy