Re: [PATCH 13/15] SUNRPC: RPC buffer size estimates are too large

["J. Bruce Fields" <bfields@fieldses.org>]

On Wed, Jan 24, 2007 at 02:20:20PM -0500, Chuck Lever wrote:
> The RPC buffer size estimation logic in net/sunrpc/clnt.c always
> significantly overestimates the requirements for the buffer size.
> A little instrumentation demonstrated that in fact rpc_malloc was never
> allocating the buffer from the mempool, but almost always called kmalloc.
> 
> To compute the size of the RPC buffer more precisely, split p_bufsiz into
> two fields; one for the argument size, and one for the result size.
> 
> So now we will compute the sum of the exact call and reply header sizes,
> and split the RPC buffer precisely between the two.  That should keep
> almost all RPC buffers within the 2KiB buffer mempool limit.

One other worry: after this patch, as I understand it, a small mistake
in any of the definitions of the *_sz macros could allow a buffer
overflow that RPC_SLACK_SPACE previously prevented.

Those definitions are all handwritten, and I'd be suprised if there
aren't at least a few minor errors.

I'd certainly rather have these calculations be exact than depend on
this big RPC_SLACK_SPACE fudge factor, but is there some way we could
verify those macros first?

--b.

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