Re: [Xen-users] Shared memory between DomU's

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Sat, 2015-04-04 at 13:46 +0300, ××× ×××××××× wrote:
> Hi,
> Thank you very much for the answer.
> Unfortunately i haven't made much of a progress.
> Can you  please recall from what Xen version libvchan shipped with?

Looks like it was in Xen 4.2 onwards.

It's possible that distros haven't packaged it though, in which case you
can probably extract it from the relevant Xen release and build just
that library yourself.

> Is there a standalone version for installing it in case it doesn't
> shipped with my Xen?

Not AFAIK.

> Im not really sure who should i use it on other VM's expect Dom0.
> what are the right steps?
> where should i create the grant page? 
> how does The Cross Domain Vm's would know about it?
> Is there a guide that i can use?

There's not much in the way of docs for vchan (already noted in our docs
day TODO list, so I shan't add it again), there's some stuff in the list
archives e.g.
http://xen.1045712.n5.nabble.com/Using-libvchan-library-td5720867.html
which has some examples and references to the example applications in
the xen code base which includes the library headers etc which have a
small amount of extra stuff.

> As you all probably understood i am pretty new with Xen and with
> sharing memory in it.

You should be able to find some descriptions of the underlying sharing
mechanisms used by vchan in the Xen wiki and source documentation, but
you probably don't need to really get too deep since vchan is supposed
to save you having to know about it too much.

Ian.

> I will much appriate any help.
> Thanks,
> Eli.
> 
> 
> 
> 2015-03-30 12:05 GMT+03:00 Ian Campbell <ian.campbell@xxxxxxxxxx>:
>         On Sun, 2015-03-29 at 18:54 +0300, ××× ×××××××× wrote:
>         > Hello
>         >
>         > i want two distinct process both DomU's to be able the read
>         or write
>         > in a share memory.
>         >
>         > Many post are talking about granting permissions or grant
>         table.
>         >
>         > I'm sorry if my question is a bit stupid. Where would i
>         start to be
>         > able the test those grant permission?
>         > Should i need to write an external program or should i
>         modify some Xen
>         > source codes?
>         >
>         > I really have no idea about where to start.
>         > I'll sincerely appreciate any idea. Even one stating where
>         to start.
>         
>         
>         libvchan (shipped with Xen for a couple of versions) is
>         designed to make
>         it easier to setup a shared memory ring between two userspace
>         processes.
>         Even if you don't need the byte-stream it supplies it serves
>         as an
>         example of how one goes about doing this sort of thing.
>         
>         You wont need to modify any Xen source code, but you will need
>         to make
>         sure you have a kernel in each guest with the appropriate
>         grant table
>         and event channel drivers enabled. IIRC libvchan relies on
>         gntdev,
>         gntalloc and evtchn drivers.
>         
>         Ian.
>         
> 
> 



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