Date: Thu, 14 Nov 2013 14:35:24 -0500
From: "J. Bruce Fields" <bfields@fieldses.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-nfs@vger.kernel.org
Subject: Re: sharing protocol defintions between client and server?
Message-ID: <20131114193524.GD21152@fieldses.org>
References: <20131113162116.GA14577@infradead.org>
 <20131114150546.GA21152@fieldses.org>
 <20131114164046.GA32275@infradead.org>
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On Thu, Nov 14, 2013 at 08:40:46AM -0800, Christoph Hellwig wrote:
> On Thu, Nov 14, 2013 at 10:05:46AM -0500, J. Bruce Fields wrote:
> > On Wed, Nov 13, 2013 at 08:21:16AM -0800, Christoph Hellwig wrote:
> > > >From a lot of the recent work it seems like there's basically no
> > > sharing of protocol definitions between the Linux NFS client and
> > > server, which seems fairly annoying to me.
> > 
> > What are you thinking of exactly?
> > 
> > I suspect that there could be more sharing.
> 
> To make it easy I'll just quote from the SEEK patches.
> 
> client:
> 
> +struct nfs42_seek_args {
> +	struct nfs4_sequence_args	seq_args;
> +
> +	struct nfs_fh			*sa_fh;
> +	nfs4_stateid			*sa_stateid;
> +	u64				sa_offset;
> +	u32				sa_what;
> +};
> +
> +struct nfs42_seek_res {
> +	struct nfs4_sequence_res	seq_res;
> +	unsigned int			status;
> +
> +	u32	sr_eof;
> +	u32	sr_whence;
> +	u64	sr_offset;
> +	u64	sr_length;
> +	u32	sr_allocated;
> +};
> +#endif
> 
> server:
> 
> +struct nfsd4_seek {
> +	/* request */
> +	stateid_t	seek_stateid;
> +	loff_t		seek_offset;
> +	u32		seek_whence;
> +
> +	/* response */
> +	u64		seek_pos;
> +	u32		seek_eof;
> +	u64		seek_length;
> +	u32		seek_allocated;
> +};
> 
> note that a lot of server operations also seem to have separate
> args and result substrutures.  In general I'd love to have one
> structure for the actual on-the wire operation in a header, and then
> client and server could build in-memory versions around them.
> 
> Of course just generating those from the XDR would be even better.

Sometimes a lot of those fields are unused.  And we can currently do
things like read/write directly from/to the data structures these are
eventually going to end up in.

So in theory the existing code might be more efficient.

In practice I don't know if it is.  And it'd be nice to be able to
autogenerate huge swaths of boring code.

--b.

> Maybe I'll play around with doing a krpcgen that we can initially
> just use for producing the structures, for which it should be
> pretty clear benefit.  If we're lucky we might be to also move
> some marshalling/unmarshalling over to it later.
> --
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