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

[Greg Kurz <groug@xxxxxxxx>]

On Mon, 13 Mar 2017 16:55:54 -0700
Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:

> It uses the new ring.h macros to declare rings and interfaces.
> 
> Signed-off-by: Stefano Stabellini <stefano@xxxxxxxxxxx>
> CC: anthony.perard@xxxxxxxxxx
> CC: jgross@xxxxxxxx
> ---
>  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).

> 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.

> +} __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;

> +#define PAGE_SHIFT XC_PAGE_SHIFT

I don't see any user for this in hw/9pfs/xen-9p-backend.c

> +#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

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