Re: [Virtio-fs] [PATCH] fuse: implement FUSE_INIT map_alignment field

[Vivek Goyal <vgoyal@redhat.com>]

On Mon, Jul 29, 2019 at 09:21:49AM +0100, Stefan Hajnoczi wrote:
> On Fri, Jul 26, 2019 at 04:39:41PM -0400, Vivek Goyal wrote:
> > On Fri, Jul 26, 2019 at 09:29:33AM +0100, Stefan Hajnoczi wrote:
> > > The device communicates FUSE_SETUPMAPPING/FUSE_REMOVMAPPING alignment
> > > constraints via the FUST_INIT map_alignment field.  Parse this field and
> > > ensure our DAX mappings meet the alignment constraints.
> > 
> > Hi Stefan,
> > 
> > To meet alignment constraints, we also need to make sure dax window
> > start/end address is 2MB aligned as well?
> 
> No, because the mmap on the host is independent of the guest virtual
> address at which the BAR is mapped inside the guest.
> 
> QEMU hw/virtio/vhost-user-fs.c:vuf_device_realize() mmaps the DAX window
> on the host side and that's where the mmap alignment requirement is in
> effect.

Ok.

What about checking alignment constratins on inarg.moffset and
inarg.foffset in fuse_setup_one_mapping().

Thanks
Vivek

> 
> The guest can map the DAX window at any address compatible with its own
> virtual memory constraints (i.e. page size).
> 
> Stefan