On 7/25/2013 5:24 PM, Vladimir 'φ-coder/phcoder' Serbinenko wrote:
On 15.07.2013 20:00, Konrad Rzeszutek Wilk wrote:
Hey,
There is a discussion on the linux-kernel mailing list in which the
Linus states that "if you depend on any config file, you're broken
by definition" (https://lkml.org/lkml/2013/7/15/368).
The world is broken by definition sometimes you just can't avoid being
broken unless a good facility for your needs is supplied. In this case
it would be a documentation on how to detect dom0 pv_ops. We could
ship a detector as a GRUB tool if appropriate documentation is provided.
One suggestion was to use readelf to see if the binary has an .Xen ELF
note in it. But then
that creates a dependency of grub tools on 'libelf' and that is probably
unwise for just one
case. I guess one could write a grub-detection code without depending on
libelf to do this too?
The .Xen ELF header is documented
here:http://wiki.xenproject.org/wiki/X86_Paravirtualised_Memory_Management#Start_Of_Day
The 20_linux_xen does that however it should not do it. In all fairness
this check is a bit of old as pretty much any upstream kernel
is being built by default from distros to boot with Xen. If it does
not, Xen will print a message telling the user that Linux does not
have the required components.
It depends on kernel config. Not everybody uses one-size-fits-all
major distro kernels (no offense for distros but sometimes you need or
prefer customized kernels).
What happens if one tries to load a kernel without pv_ops on top of
xen? Does he at least get a decent error message or just black screen?
Yes, there is an decent error message on the VGA console.
Some distros increase xen_linux priority above those of standard linux
and it may happen that xen is inadvertently installed but no pv_ops
kernel is available. With proposed change such setup becomes
needlessly unbootable.
Correct. That is the unfortunate part. But I am not sure how different
that is from somebody configuring the kernel and forgetting to compile
in a SATA controller.