linux-kernel - Re: [PATCH 2/2] cifs: don't use __constant_cpu_to

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Date:   Fri, 15 Mar 2019 23:29:38 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     'Sergey Senozhatsky' <sergey.senozhatsky.work@...il.com>,
        Steve French <sfrench@...ba.org>,
        "linux-cifs@...r.kernel.org" <linux-cifs@...r.kernel.org>,
        "samba-technical@...ts.samba.org" <samba-technical@...ts.samba.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH 2/2] cifs: don't use __constant_cpu_to_le32()

On (03/15/19 12:31), David Laight wrote:
> From: Sergey Senozhatsky
> > 
> > cpu_to_le32() is capable enough to detect __builtin_constant_p()
> > and to use an appropriate compile time ___constant_swahb32()
> > function.
> > 
> > So we can use cpu_to_le32() instead of __constant_cpu_to_le32().
> 
> Unless any code tries to use them as case statement labels.

What is the problem?

For compile time constants cpu_to_le32() should do the same thing
as __constant_cpu_to_le32().

There seems a whole bunch of cpu_to_XX compile time constants which
are used in case statement labels

include/linux/sunrpc/xdr.h:#define      rpc_msg_accepted        cpu_to_be32(RPC_MSG_ACCEPTED)
include/linux/sunrpc/xdr.h:#define      rpc_success             cpu_to_be32(RPC_SUCCESS)
include/linux/sunrpc/xdr.h:#define      rpc_prog_unavail        cpu_to_be32(RPC_PROG_UNAVAIL)
include/linux/sunrpc/xdr.h:#define      rpc_prog_mismatch       cpu_to_be32(RPC_PROG_MISMATCH)
include/linux/sunrpc/xdr.h:#define      rpc_proc_unavail        cpu_to_be32(RPC_PROC_UNAVAIL)
include/linux/sunrpc/xdr.h:#define      rpc_garbage_args        cpu_to_be32(RPC_GARBAGE_ARGS)
include/linux/sunrpc/xdr.h:#define      rpc_system_err          cpu_to_be32(RPC_SYSTEM_ERR)
include/linux/sunrpc/xdr.h:#define      rpc_drop_reply          cpu_to_be32(RPC_DROP_REPLY)
include/linux/sunrpc/xdr.h:#define      rpc_mismatch            cpu_to_be32(RPC_MISMATCH)
include/linux/sunrpc/xdr.h:#define      rpc_auth_error          cpu_to_be32(RPC_AUTH_ERROR)
include/linux/sunrpc/xdr.h:#define      rpc_auth_ok             cpu_to_be32(RPC_AUTH_OK)
include/linux/sunrpc/xdr.h:#define      rpc_autherr_badcred     cpu_to_be32(RPC_AUTH_BADCRED)
include/linux/sunrpc/xdr.h:#define      rpc_autherr_rejectedcred cpu_to_be32(RPC_AUTH_REJECTEDCRED)
include/linux/sunrpc/xdr.h:#define      rpc_autherr_badverf     cpu_to_be32(RPC_AUTH_BADVERF)
include/linux/sunrpc/xdr.h:#define      rpc_autherr_rejectedverf cpu_to_be32(RPC_AUTH_REJECTEDVERF)
include/linux/sunrpc/xdr.h:#define      rpc_autherr_tooweak     cpu_to_be32(RPC_AUTH_TOOWEAK)


net/sunrpc/clnt.c

2479         switch (*p) {
2480         case rpc_success:
2481                 return 0;
2482         case rpc_prog_unavail:
2483                 trace_rpc__prog_unavail(task);
2484                 error = -EPFNOSUPPORT;
2485                 goto out_err;
2486         case rpc_prog_mismatch:
2487                 trace_rpc__prog_mismatch(task);
2488                 error = -EPROTONOSUPPORT;
2489                 goto out_err;
2490         case rpc_proc_unavail:
2491                 trace_rpc__proc_unavail(task);
2492                 error = -EOPNOTSUPP;
2493                 goto out_err;
2494         case rpc_garbage_args:
2495                 trace_rpc__garbage_args(task);
2496                 break;
2497         default:
2498                 trace_rpc__unparsable(task);
2499         }

	-ss