Re: Kexec and libxenctlr.so

[Jürgen Groß <jgross@xxxxxxxx>]

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).

> > 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