Re: [Xen-devel] [PATCH] add privileged/unprivileged kernel feature indication

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Tue, 2011-07-05 at 15:15 +0100, Jan Beulich wrote:
> >>> On 05.07.11 at 15:55, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> > On Tue, 2011-07-05 at 13:48 +0100, Jan Beulich wrote:
> >> With our switching away from supporting 32-bit Dom0 operation, users
> >> complained that attempts (perhaps due to lack of knowledge of that
> >> change) to boot the no longer privileged kernel in Dom0 resulted in
> >> apparently silent failure. To make the mismatch explicit and visible,
> >> add feature flags that the kernel can set to indicate operation in
> >> what modes it supports. For backward compatibility, absence of both
> >> feature flags is taken to indicate a kernel that may be capable of
> >> operating in both modes.
> > 
> > While I agree that this is a useful change I think you should also try
> > and ensure that your bootloader configuration tool tries not to add
> > invalid combinations to the configuration. For example grub2's
> > "update-grub" command checks for CONFIG_XEN_PRIVILEGED_GUEST=y before
> > creating a dom0 style entry. IIRC grub1 did the same (although that may
> > have been Debian specific).
> 
> That I would consider completely bogus - the boot loader should not
> have a need to know *anything* about the kind of kernel it boots.

I said bootloader configuration tool (i.e. the thing which helps users
generate /boot/grub/grub.cfg), not the bootloader itself. i.e. the tool
should not be adding xen+domU-only-kernel as an option in grub.cfg.

If this tool doesn't understand these things you end up presenting users
with booloader options which cannot ever work and then they get
confused.

Ian.



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