Re: [Xen-devel] Question on xc_gnttab_map_grant_ref()

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

To expand:

I'm working towards a shared-memory NFS-style filesystem for Xen guests.  This 
will allow high-performance data sharing within one host.  This leverages 
direct memory sharing to maximise performance and make better use of the 
available RAM.

A bonus feature of this direct sharing approach is that applications running 
in different domains on the same host should be able to share memory by both 
using a simple mmap() call.  This avoids us having to introduce any new wacky 
semantics / exotic character devices; sharing should work similarly to the 
case of two applications in one domain.

Cheers,
Mark

On Thursday 03 November 2005 22:59, Christopher Clark wrote:
> The implementation is indeed incomplete and I agree that grant references
> are not the correct interface for the kernel to expose to user space.
> MarkW's mmap work-in-progress ought be far more suitable.
>
> The main use of xc_gnttab stuff has been for debugging new clients using
> the grant tables -- it's been handy to modify and read them from userspace
> to figure out what's going on, but clearly this isn't something you'd want
> in a production kernel, which is why it's disabled.
>
> Christopher
>
> On 11/3/05, King, Steven R <steven.r.king@xxxxxxxxx> wrote:
> > I've been looking at xc_gnttab stuff lately too and the current
> > implementation is incomplete. For example, I don't see a way to acquire
> > a grant reference from user space, so the xc_gnttab functions taking a
> > reference are unusable.
> >
> > IMO, grant references are kernel level implementation details that
> > should not be exposed to user-mode anyway. Instead, user-mode needs
> > IOCTLs to share pages with a remote domain and to map those shared pages
> > within the remote end. If the kernel implements this functionality with
> > grant tables, then great; in the future it may do something else. I
> > hope to have a patch to offer for this eventually.
> >
> > -steve
> >
> >
> > -----Original Message-----
> > From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> > [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of NAHieu
> > Sent: Thursday, November 03, 2005 4:53 AM
> > To: xen-devel
> > Subject: [Xen-devel] Question on xc_gnttab_map_grant_ref()
> >
> > Hi,
> >
> > I am writing a kermel module in DomU, and this module grants a page of
> > memory to Dom0. Then in Dom0 I try to grant_map it with
> > xc_gnttab_map_grant_ref()
> >
> > But this function requires a flag, and I don't know which option to give
> > it. I tried with either GNTMAP_application_map or
> > GTF_reading|GTF_writing, but I always got this error:
> >
> > ERROR: do_gnttab_op: HYPERVISOR_grant_table_op failed: -1
> >
> > Anybody please tell me how to use xc_gnttab_map_grant_ref() properly in
> > Dom0's userspace?
> >
> >
> > Many thanks.
> > Hieu
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel
> >
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> > Xen-devel@xxxxxxxxxxxxxxxxxxx
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