Re: Fatal crash on xen4.2 HVM + qemu-xen dm + NFS

[Ian Campbell <Ian.Campbell@citrix.com>]

On Tue, 2013-01-22 at 13:02 +0000, Alex Bligh wrote:
> Ian,
> 
> --On 22 January 2013 10:05:16 +0000 Ian Campbell <Ian.Campbell@citrix.com> 
> wrote:
> 
> > I've never looked inside xen_qdisk so I can't really advise, but that
> > sound broadly correct, except you'd want to use gnttab_copy not mmap
> > +memcpy. e.g. (totally making up the API because I'm too lazy to go
> > look):
> > 	buffer = malloc(SIZE)
> > 	if (writing)
> > 		gnttab_copy_from(buffer, gntref, size)
> >
> > 	io->buffer = buffer
> > 	submit(io)
> > ... wait for completion:
> > 	if (reading)
> > 		gnttab_copy_to(...)
> > 	free(io->buffer)
> >
> > Hopefully you get the idea ;-) Sounds like before the ... goes in
> > ioreq_map and after the ... goes in ioreq_unmap.
> 
> Thanks. If the O_DIRECT thing doesn't fix it, I'll take a look again.
> My initial analysis was that a copy interface wasn't available through
> xc_ type functions.

I think the underlying /dev/xen/gntdev thing does, but you may need to
plumb it through libxc.

Ian.