Re: [Xen-devel] [PATCH 2/7] xen: introduce the header file for the Xen 9pfs transport protocol

2017-03-06 Thread Boris Ostrovsky 
On 03/06/2017 04:36 PM, Stefano Stabellini wrote:
> On Mon, 6 Mar 2017, Boris Ostrovsky wrote:
>>> +   uint32_t size;
>>> +   uint8_t id;
>>> +   uint16_t tag;
>> I realize that this is in the spec now and it's probably too late to ask
>> this question but wouldn't it be better if id and tag were swapped? No
>> need to pack and potentially faster access to tag.
> I cannot do anything about it: that struct is defined by the 9pfs
> specification (not the Xen spec, the general 9pfs spec). See:

Oh, I thought it was Xen-specific (because it's described in
9pfs.markdown). Nevermind then.

-boris

>
> https://www.usenix.org/legacy/event/usenix05/tech/freenix/full_papers/hensbergen/hensbergen.pdf
>
>>> +} __attribute__((packed));
>>> +
>>> +#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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Re: [Xen-devel] [PATCH 2/7] xen: introduce the header file for the Xen 9pfs transport protocol

2017-03-06 Thread Stefano Stabellini 
On Mon, 6 Mar 2017, Boris Ostrovsky wrote:
> > +   uint32_t size;
> > +   uint8_t id;
> > +   uint16_t tag;
> 
> I realize that this is in the spec now and it's probably too late to ask
> this question but wouldn't it be better if id and tag were swapped? No
> need to pack and potentially faster access to tag.

I cannot do anything about it: that struct is defined by the 9pfs
specification (not the Xen spec, the general 9pfs spec). See:

https://www.usenix.org/legacy/event/usenix05/tech/freenix/full_papers/hensbergen/hensbergen.pdf

> > +} __attribute__((packed));
> > +
> > +#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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Re: [Xen-devel] [PATCH 2/7] xen: introduce the header file for the Xen 9pfs transport protocol

2017-03-06 Thread Boris Ostrovsky 

> +struct xen_9pfs_header {
> + uint32_t size;
> + uint8_t id;
> + uint16_t tag;

I realize that this is in the spec now and it's probably too late to ask
this question but wouldn't it be better if id and tag were swapped? No
need to pack and potentially faster access to tag.

-boris

> +} __attribute__((packed));
> +
> +#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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