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

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Message-ID: <alpine.DEB.2.10.1703061334520.17906@sstabellini-ThinkPad-X260>
Date:   Mon, 6 Mar 2017 13:36:17 -0800 (PST)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
cc:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        Stefano Stabellini <stefano@...reto.com>,
        konrad.wilk@...cle.com, jgross@...e.com
Subject: Re: [PATCH 2/7] xen: introduce the header file for the Xen 9pfs
 transport protocol

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
>