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Subject: Re: [PATCH RFC 04/10] SUNRPC: Add common byte-swapped RPC header
 constants
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <20190204143239.GA15081@infradead.org>
Date:   Mon, 4 Feb 2019 09:56:20 -0500
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>, simo@redhat.com
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References: <20190201195538.11389.96106.stgit@manet.1015granger.net>
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 <20190204143239.GA15081@infradead.org>
To:     Christoph Hellwig <hch@infradead.org>
Sender: linux-nfs-owner@vger.kernel.org
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> On Feb 4, 2019, at 9:32 AM, Christoph Hellwig <hch@infradead.org> wrote:
> 
> On Mon, Feb 04, 2019 at 09:16:54AM -0500, Chuck Lever wrote:
>> They are. The problem is that we are byte-swapping the incoming wire
>> data and then comparing to CPU-endian constants in some hot paths.
>> It's better to leave the incoming data alone and compare to a pre-
>> byte-swapped constant. This patch adds some of these constants that
>> were missing, in preparation for fixing the hot paths.
>> 
>> That is apparently not clear from the patch description, so I will
>> endeavor to improve it.
> 
> Why do we need new enums / #defines for that?
> 
> Just replace:
> 
> 	if (beXX_to_cpu(pkt->field) == SOME_CONSTANT)
> 
> with
> 
> 	if (pkt->field == cpu_to_be32(SOME_CONSTANT))
> 
> and we are done.

True.


> The latter is a pretty common pattern through the kernel.

However the pattern in the NFS server and lockd is to define a
lower-case version of the same macro that is pre-byte-swapped.
I'm attempting to follow existing precedent in this area.

We already have, for example, in various sunrpc headers:

enum rpc_accept_stat {
        RPC_SUCCESS = 0,
        RPC_PROG_UNAVAIL = 1,
        RPC_PROG_MISMATCH = 2,
  ...
};

#define rpc_success             cpu_to_be32(RPC_SUCCESS)
#define rpc_prog_unavail        cpu_to_be32(RPC_PROG_UNAVAIL)
#define rpc_prog_mismatch       cpu_to_be32(RPC_PROG_MISMATCH)

Or, for NFS:

enum nfs_stat {
   ...
   NFSERR_SHARE_DENIED = 10015,
   ...
};

#define nfserr_share_denied cpu_to_be32(NFSERR_SHARE_DENIED)

There are some missing lower-case macros, which I am trying to
add to our existing collection before I rewrite the RPC header
encoding and decoding functions. So I'm adding:

+       rpc_gss_version = cpu_to_be32(RPC_GSS_VERSION),

+       rpc_call                = cpu_to_be32(RPC_CALL),
+       rpc_reply               = cpu_to_be32(RPC_REPLY),
+
+       rpc_msg_accepted        = cpu_to_be32(RPC_MSG_ACCEPTED),
+       rpc_msg_denied          = cpu_to_be32(RPC_MSG_DENIED),

Actually since we have decided not to use enum for these, this
smaller addition can simply be squashed into the later patches,
and I can drop this patch, which was intended as a clean-up but
now appears to be unnecessary.

--
Chuck Lever