Re: [Xen-devel] [GSoc] GSoc Introduction : Xen on ARM: create multiple guests from device tree

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

Thank you! I am looking forward to your contribution on the list! If you
encounter any issues, please let us know.

The code contribution is more important, but if you find the time in the
next few days, it would be nice to add more details to the
implementation plan, such as where the memory gets allocated, whether it
is taken from a VM, and if so, which one. Also what kind of "token"
could be used in the config option and how the toolstack could keep
track of the token - memory page references.

Thanks,

Stefano

On Mon, 3 Apr 2017, Methuku Karthik wrote:
> Hi Stefano,
> 
> Thanks for Input. I was not able to spend enough time last couple of weeks 
> due to
> projects. I have received mail from Lars Kurt explaining submission of draft
> proposal and possibility to work on micro tasks.
> 
> I have created a draft proposal from with your inputs and what i learnt about
> sharing pages and memory management in Xen, please access it from here
> 
> https://docs.google.com/document/d/1xLmR7x4yfCbRgpuefZQNhZ4lAu-6slW0oXPmjnxcnz0/edi
> t#heading=h.1yvc35w6t3fu
> 
> I haven't written anything about maintenance. I have included some links i 
> thought
> will be helpful under references and referenced wherever applicable.
> 
> Please suggest comments and inputs.
> 
> On Tue, Mar 28, 2017 at 8:12 PM, Stefano Stabellini <sstabellini@xxxxxxxxxx> 
> wrote:
> > CC'ing a couple of maintainers that might have more insights on this
> > project.
> >
> > On Tue, 28 Mar 2017, Stefano Stabellini wrote:
> >> On Tue, 28 Mar 2017, Methuku Karthik wrote:
> >> > Hi Stefano,
> >> >
> >> > Kindly suggest me reading material that could help me understand and
> >> > come up with the proposal.
> >>
> >> Sure! For the "Xen on ARM: create multiple guests from device tree"
> >> project, the idea is that on many embedded systems the user knows how
> >> many guests to create beforehand, and usually it is a small number, like
> >> 2 or 3. Often these guests don't even have any PV frontends, but just a
> >> set of devices assigned to them. An example could be an extremely simple
> >> guest that only accesses one physical device (which is assigned to it at
> >> boot) and prints messages using the debug hypercalls (see
> >> xen/arch/arm/traps.c:do_debug_trap).
> >>
> >> In this scenario, there is no need to wait for Dom0 to boot to create
> >> this second guest (I'll call it Dom1, to distinguish it from Dom0). Xen
> >> could actually create it directly by itself, the same way it starts Dom0
> >> (see xen/arch/arm/domain_build.c:construct_dom0 and
> >> docs/misc/arm/device-tree/booting.txt).
> >>
> >> The project is about extending the existing device interface to pass an
> >> additional kernel, initrd, command line arguments for the second virtual
> >> machine. It would also need to include which devices should be assigned
> >> to it. In response, Xen should build the second VM the same way it would
> >> do normally when done via the toolstack (xl/libxl), but it would happen
> >> at boot time, before Dom0 is fully up and running.
> >>
> >>
> >>
> >> For the "Share a page in memory from the VM config file" project,
> >
> > Ops, I forgot to add this description :-)
> >
> > I was saying, for the "Share a page in memory from the VM config file"
> > project, the idea is that we want to share a page in memory between two
> > VMs just by adding one line to their VM config files. They should be
> > able to communicate with each others straight away by writing at the
> > right address in memory. That way, even small embedded systems with no
> > xenstore support can still setup a communication channel with each
> > others.
> >
> > Fundamentally, it just requires the xl/libxl toolstack (see tools/xl and
> > tools/libxl) to parse a new VM config file option, and in response share
> > a page at the specified address, or map a page at a specified address.
> > If the memory address is wrong, the toolstack needs to be able to handle
> > the failure. Sharing pages and mapping pages in xl/libxl is easy; the
> > difficulty of the project is coming up with the right parameter in the
> > VM config file so that multiple VMs can share different pages with each
> > others. It probably requires the introduction of a "token" to identify
> > the page you want to share across multiple VM config files.
> >
> > For example, Dom1 should be able to share a page with Dom2 and a
> > different page with Dom3. It needs to be clear which page is shared with
> > which VM from the VM config files.
> >
> when we create vms using xl create , for example if i am planning create 
> three VMs,
> 
> Dom1, Dom2 and Dom3, because of the page sharing are we imposing any order of
> creating VMs.
> 
> I am asking this question to clarify this point, while creation of Dom1 if its
> sharing pages with Dom 2 and Dom 3 , should Xen already be aware of Dom2 and 
> Dom3?
> 
> I am referring to following links to understand about mem sharing.
> 
> http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=tools/tests/mem-sharing/memshrtoo
> l.c;h=8e5e22b9e95d91f1441d8eb226b64852eca075d5;hb=HEAD
> http://xenbits.xen.org/docs/unstable/misc/grant-tables.txt
> 
> I also want to figure out how domains are created and how xl tool parses the 
> file
> and passes on the information to domain creation . Let me know if i am 
> thinking in
> right direction.
> 
> suggest any resource or work which would help with designing config file 
> options.
> 
> >
> >
> >> > On Tue, Mar 28, 2017 at 1:38 PM, Stefano Stabellini
> >> > <sstabellini@xxxxxxxxxx> wrote:
> >> > > I would also like to take the opportunity to remind you of the upcoming
> >> > > deadline for applications submissions, which is the 3rd of April for
> >> > > GSoC, see:
> >> > >
> >> > > http://marc.info/?l=xen-devel&m=149071502330534
> >> > >
> >> > > The GSoC application system is
> >> > > https://summerofcode.withgoogle.com/get-started/.
> >> > >
> >> > > Please give a look at the Xen Project application template here:
> >> > >
> >> > > https://wiki.xenproject.org/wiki/GSoC_Student_Application_Template
> >> > >
> >> > > It also includes an "Implementation Plan", where you have the chance to
> >> > > explain the implementation plan for the projects you would like to 
> >> > > apply
> >> > > for. You can apply for more than one project if you want to.
> >> >
> >> > Thanks for the reminder Stefano. I will post some questions about my
> >> > implementation plan.
> >> >
> >> > I would like to spend my time fixing the bug but as deadline is
> >> > approaching , I would like to know the bare essential expected in the
> >> > proposal?
> >>
> >> It needs to include the basic milestones and how long you estimate it is
> >> going to take to complete each of them. More details you add, more
> >> you'll show your understanding of the problem.
> >>
> >>
> >> > >
> >> > > Thanks,
> >> > >
> >> > > Stefano
> >> > >
> >> > >
> >> > > On Mon, 27 Mar 2017, Stefano Stabellini wrote:
> >> > >> Hello Methuku,
> >> > >>
> >> > >> It is great to hear that you are interested in working on Xen on ARM.
> >> > >> It's good that you already know how to build and install Xen on an ARM
> >> > >> board.
> >> > >>
> >> > >> Do you have serial access to your Nvidia Jetson TK1? If not, I would
> >> > >> suggest to setup another test environment based on a different board, 
> >> > >> or
> >> > >> simply use the ARM Foundation Platform which is a free (as in beer)
> >> > >> software emulator.
> >> > >>
> >> > >> In terms of bug fixes, you could give a look at
> >> > >>
> >> > >> https://xenproject.atlassian.net/projects/XEN/issues
> >> > >>
> >> > >> Most of the items listed are large projects, but some of them are 
> >> > >> pretty
> >> > >> small, small enough to be a starting point. For example XEN-29 (Add
> >> > >> -fstack-protector support to the hypervisor), XEN-30 (Make out-of-tree
> >> > >> builds work) or XEN-38 (Xen - Embed .config in Xen binary).
> >> >
> >> > I  started working on XEN-38 for now. But i am also interested to look
> >> > into XEN-30.
> >>
> >> Be careful that XEN-30 is longer than it looks because there are lots of
> >> Makefiles to fix. However, even if you don't convert all Makefiles to
> >> support out-of-tree builds but only some, it would still be OK.
> 
> I will start with Xen-38 that would help me in exploring init code. Correct 
> me if i
> am wrong.
> 
> I have a few questions and clarifications before proceeding further. I have 
> checked
> how config.gz file is generated in linux kernel source.
> In linux kernel sources, if CONFIG_IKCONFIG_PROC option is set, .conifg file 
> which
> is generated after choosing options with lets say from make menuconfig  is 
> read into
> a variable, this way its part of build.
> 
> during init time proc_create service is used to create this file config.gz.
> http://lxr.free-electrons.com/source/kernel/configs.c
> 
> 
> I guess i have to do something similar.
> 
> Questions :
> 
> 1. When Xen is build using the make command, we effectively set 
> XEN_COMPILE_ARCH,
> XEN_OS, XEN_TARGET which allow using corresponding .mk file from config 
> folder.
> These variable in turn decide what are the config options. I wasnt able to 
> find any
> .config. Please direct me to find the file or if i am missing something. 
> 
> 2. Where and how this config file should be accessible to  User once in Dom0. 
> Is the
> xen folder created to keep the information about guest domains like proc for 
> process
> in linux kernel ? Will that be suitable location to have config file.
> 
> 3. if i assume that i will approach similarly, i have to add services to be 
> called
> during init stage. As am not acquainted with code base, i could just grep with
> _start or _init or similar strings to find out initialization code. Any
> input(function name or filename) to look for will be of great help.
> 
> Best,
> Karthik.
> 
> >>
> >>
> >> > >> Cheers,
> >> > >>
> >> > >> Stefano
> >> > >>
> >> > >>
> >> > >> On Mon, 27 Mar 2017, Methuku Karthik wrote:
> >> > >> > Hi Everyone,
> >> > >> >
> >> > >> > My name is Karthik. I am a first year graduate student in Embedded 
> >> > >> > Systems
> at University of Pennsylvania. I am avid c, c++ and python programmer.I have 
> 4 years
> of
> >> > >> > work experience as Embedded Software developer at Airbus.
> >> > >> >
> >> > >> > For the last four months I have been working as a research 
> >> > >> > assistant in
> PRECISE lab at the University of Pennsylvania, helping Meng Xu (cc.ed) to 
> evaluate
> the
> >> > >> > performance of the Xen's RTDS scheduler.
> >> > >> >
> >> > >> > I'm interested in the following two projects. I'm happy to work on 
> >> > >> > one of
> them.
> >> > >> > (1) Share a page in memory from the VM config file.
> >> > >> > (2)  Xen on ARM: create multiple guests from device tree.
> >> > >> >
> >> > >> > I have experience in compiling Xen and installing it on ARM 
> >> > >> > board(Nvidia
> Jetson TK1). I'm also well equiped in using the xl tool to manage the VMs.
> >> > >> >
> >> > >> > I noticed that I should contribute some bug fixes to be able to get 
> >> > >> > the
> ticket to the Xen GSoC.
> >> > >> > Do you have some suggestions on how I should start?
> >> > >> > Do you have a list of simple bugs that I can fix?
> >> > >> >
> >> > >> > I'm very interested in the Xen Project. I want to become a Xen 
> >> > >> > contributor
> in the near future.
> >> > >> >
> >> > >> > Thank you very much for your help!
> >> > >> >
> >> > >> > Best,
> >> > >> > Karthik
> >> > >> >
> >> > >> >
> >> >
> >> > Best,
> >> > Karthik.
> >> >
> >>
> 
> 
>

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