Re: Kexec and libxenctlr.so

[Julien Grall <julien@xxxxxxx>]

On 11/06/2020 16:35, Jürgen Groß wrote:
> On 11.06.20 17:27, Julien Grall wrote:
> > Hi,
> >
> > On 11/06/2020 16:21, Jürgen Groß wrote:
> > > On 11.06.20 16:57, Julien Grall wrote:
> > > > Hi all,
> > > >
> > > > kexec-tools has an option to load dynamically libxenctlr.so (not 
> > > > .so.4.x) (see [1]).
> > > > Given that the library has never been considered stable, it is 
> > > > probably a disaster that is waiting to happen.
> > > > Looking at the tree kexec is using the follow libxc functions:
> > > >     - xc_kexec_get_range()
> > > >     - xc_kexec_load()
> > > >     - xc_kexec_unload()
> > > >     - xc_kexec_status()
> > > >     - xc_kexec_exec()
> > > >     - xc_version()
> > > >     - xc_interface_open()
> > > >     - xc_interface_close()
> > > >     - xc_get_max_cpus()
> > > >     - xc_get_machine_memory_map()
> > > >
> > > > I think it is uncontroversial that we want a new stable library for 
> > > > all the xc_kexec_* functions (maybe libxenexec)?
> > > > However I am not entirely sure where to put the others.
> > > >
> > > > I am thinking to introduce libxensysctl for xc_get_max_cpus() as it 
> > > > is a XEN_SYSCTL. We could possibly include 
> > > > xc_get_machine_memory_map() (despite it is a XENMEM_).
> > > > For xc_version(), I am thinking to extend libxentoolcore to also 
> > > > include "stable xen API".
> > > > Any opinion on the approach?
> > > You could consider hypfs (at least for some of the functionality).
> > That would work!
> >
> > > xc_version() and xc_get_max_cpus() would be rather easy.
> > I am guessing we will need a fallback to the normal hypercalls if 
> > hypfs is not present.
> Or we don't support kexec-tools running on a system without hypfs
> (or the related functions would return an error on those systems).
AFAICT, hypfs allows you to modify runtime parameters which is not 
required for kexec.
Such feature could be undesirable in some setup and therefore I don't 
think this is acceptable to impose that for kexec.
> > > xc_get_machine_memory_map() is using a stable hypercall used by
> > > the kernel, too.
> > IIUC, you are suggesting to put this one in hypfs library as well. Is 
> > that correct?
> Not really. I wanted to point out that this call would be a good
> candidate for another stable library, maybe part of libxenexec?
>
> In theory the memory map could be dumped via a hypfs node, either
> as a string (not nice for working with it) or as binary blob, of
> course.
>
>
> Juergen
--
Julien Grall