Re: [Qemu-devel] [PATCH v2 3/9] xen: introduce the header file for the Xen 9pfs transport protocol

[Stefano Stabellini <sstabellini@kernel.org>]

On Wed, 15 Mar 2017, Greg Kurz wrote:
> On Mon, 13 Mar 2017 16:55:54 -0700
> Stefano Stabellini <sstabellini@kernel.org> wrote:
> 
> > It uses the new ring.h macros to declare rings and interfaces.
> > 
> > Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
> > CC: anthony.perard@citrix.com
> > CC: jgross@suse.com
> > ---
> >  hw/9pfs/xen_9pfs.h | 20 ++++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> >  create mode 100644 hw/9pfs/xen_9pfs.h
> > 
> 
> This header file has only one user: please move its content to
> hw/9pfs/xen-9p-backend.c (except the 9P header structure, see
> below).

OK, I can do that. There is going to be a very similar header in the Xen
tree under xen/include/public/io
(http://marc.info/?l=xen-devel&m=148952997709142), but from QEMU point
of view, it makes sense to fold it in xen-9p-backend.c.


> > diff --git a/hw/9pfs/xen_9pfs.h b/hw/9pfs/xen_9pfs.h
> > new file mode 100644
> > index 0000000..c4e8901
> > --- /dev/null
> > +++ b/hw/9pfs/xen_9pfs.h
> > @@ -0,0 +1,20 @@
> > +#ifndef XEN_9PFS_H
> > +#define XEN_9PFS_H
> > +
> > +#include "hw/xen/io/ring.h"
> > +#include <xen/io/protocols.h>
> > +
> > +struct xen_9pfs_header {
> > +	uint32_t size;
> > +	uint8_t id;
> > +	uint16_t tag;
> > +
> > +	/* uint8_t sdata[]; */
> 
> This doesn't seem useful.

I'll remove


> > +} __attribute__((packed));
> > +
> 
> A few remarks:
> - this is a 9P message header actually, which is also used with virtio,
> - QEMU coding style requires a typedef in CamelCase,
> - the 9P protocol explicitely uses little-endian ordering. Since we
>   don't have endian-specific types, it makes sense to indicate that
>   when naming the fields.
> - we have a QEMU_PACKED macro which seems to be used a lot more than
>   the gcc syntax
> 
> Please define a new type in hw/9pfs/9p.h and use it in both transports.
> Something like:
> 
> typedef struct {
>     uint32_t size_le;
>     uint8_t id;
>     uint16_t tag_le;
> } QEMU_PACKED P9MsgHeader;

OK


> > +#define PAGE_SHIFT XC_PAGE_SHIFT
> 
> I don't see any user for this in hw/9pfs/xen-9p-backend.c

PAGE_SHIFT is used by the macros below, but the original Xen headers
don't have the PAGE_SHIFT definition, so, for the sake of keeping the
two in sync, I didn't add it there.


> > +#define XEN_9PFS_RING_ORDER 6
> > +#define XEN_9PFS_RING_SIZE  XEN_FLEX_RING_SIZE(XEN_9PFS_RING_ORDER)
> > +DEFINE_XEN_FLEX_RING_AND_INTF(xen_9pfs);
> > +
> > +#endif