Re: [Qemu-devel] [RESEND PATCH 2/2] hostmem-file: add an attribute 'align' to set its alignment

[Marc-André Lureau]

Hi

On Fri, May 26, 2017 at 10:51 AM Haozhong Zhang <address@hidden>
wrote:

> On 05/26/17 06:39 +0000, Marc-André Lureau wrote:
> > Hi
> >
> > On Fri, May 26, 2017 at 6:34 AM Haozhong Zhang <address@hidden
> >
> > wrote:
> >
> > > file_ram_alloc() currently maps the backend file via mmap to a virtual
> > > address aligned to the value returned by qemu_fd_getpagesize(). When a
> > > DAX device (e.g. /dev/dax0.0) is used as the backend file, its kernel
> > > mmap implementation may require an alignment larger than what
> > > qemu_fd_get_pagesize() returns (e.g. 2MB vs. 4KB), and mmap may fail.
> > >
> >
> > How is the accepted value queried? Any chance to configure it
> > automatically?
>
> Take /dev/dax0.0 for example. The value can be read from
> /sys/class/dax/dax0.0/device/dax_region/align.
>

Should this work be left to management layer, or could qemu figure it out
by itself (using udev?)


> [..]
> > > +static void
> > >  file_backend_class_init(ObjectClass *oc, void *data)
> > >  {
> > >      HostMemoryBackendClass *bc = MEMORY_BACKEND_CLASS(oc);
> > > @@ -116,6 +151,10 @@ file_backend_class_init(ObjectClass *oc, void
> *data)
> > >      object_class_property_add_str(oc, "mem-path",
> > >          get_mem_path, set_mem_path,
> > >          &error_abort);
> > > +    object_class_property_add(oc, "align", "int",
> > >
> >
> > It would make sense to make it "size" instead of "int"
> >
>
> will change in the next version
>

thanks
-- 
Marc-André Lureau