[PATCH] staging: lustre: Fix unneeded byte-ordering cast

[PATCH] staging: lustre: Fix unneeded byte-ordering cast

[Justin Skists]

Fix sparse warning:

  CHECK   drivers/staging//lustre/lnet/lnet/acceptor.c
drivers/staging//lustre/lnet/lnet/acceptor.c:243:30: warning: cast to
restricted __le32

LNET_PROTO_TCP_MAGIC, as a define, is already CPU byte-ordered when
compared to 'magic', so no need for a cast.

Signed-off-by: Justin Skists <j.skists@gmail.com>
---
 drivers/staging/lustre/lnet/lnet/acceptor.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/lustre/lnet/lnet/acceptor.c b/drivers/staging/lustre/lnet/lnet/acceptor.c
index fb478e20e204..13e981781b9a 100644
--- a/drivers/staging/lustre/lnet/lnet/acceptor.c
+++ b/drivers/staging/lustre/lnet/lnet/acceptor.c
@@ -240,7 +240,7 @@ lnet_accept(struct socket *sock, __u32 magic)
 			return -EPROTO;
 		}
 
-		if (magic == le32_to_cpu(LNET_PROTO_TCP_MAGIC))
+		if (magic == LNET_PROTO_TCP_MAGIC)
 			str = "'old' socknal/tcpnal";
 		else
 			str = "unrecognised";
-- 
2.16.2

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Re: [PATCH] staging: lustre: Fix unneeded byte-ordering cast

[NeilBrown]

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On Sat, Mar 17 2018, Justin Skists wrote:

> Fix sparse warning:
>
>   CHECK   drivers/staging//lustre/lnet/lnet/acceptor.c
> drivers/staging//lustre/lnet/lnet/acceptor.c:243:30: warning: cast to
> restricted __le32
>
> LNET_PROTO_TCP_MAGIC, as a define, is already CPU byte-ordered when
> compared to 'magic', so no need for a cast.
>
> Signed-off-by: Justin Skists <j.skists@gmail.com>
> ---
>  drivers/staging/lustre/lnet/lnet/acceptor.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/staging/lustre/lnet/lnet/acceptor.c b/drivers/staging/lustre/lnet/lnet/acceptor.c
> index fb478e20e204..13e981781b9a 100644
> --- a/drivers/staging/lustre/lnet/lnet/acceptor.c
> +++ b/drivers/staging/lustre/lnet/lnet/acceptor.c
> @@ -240,7 +240,7 @@ lnet_accept(struct socket *sock, __u32 magic)
>  			return -EPROTO;
>  		}
>  
> -		if (magic == le32_to_cpu(LNET_PROTO_TCP_MAGIC))
> +		if (magic == LNET_PROTO_TCP_MAGIC)
>  			str = "'old' socknal/tcpnal";
>  		else
>  			str = "unrecognised";

This code is almost completely irrelevant (it just choose which error
message to use when failing), but we may as well get it right and I
cannot see why your change is a fix.

"magic" was passed as an argument from lnet_acceptor() to lnet_accept(),
and lnet_acceptor() got it by reading bytes off the network with
lnet_sock_read().
My knowledge is far from complete, but from what I've seen, lustre sends
data in host-byte-order on the sender, and expects the receiver to
determine which byte-order that is (often by looking at a "magic" word
like this) and do any byte-swap that is necessary.

While I agree that LNET_PROTO_TCP_MAGIC is in host-byte-order so calling
le32_to_cpu() on it makes no sense, I don't agree that "magic" is also
host byte-ordered.

I suspect a more correct fix would be to use
  lnet_accept_magic(magic, LNET_PROTO_TCP_MAGIC)
as the condition of the if().  This is consistent with other code that
tests magic, and it is consistent with the general understanding that
"magic" should be in host-byte-order for the peer which sent the
message.
  
Could you resubmit with that change?

Thanks,
NeilBrown

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Re: [PATCH] staging: lustre: Fix unneeded byte-ordering cast

[Justin Skists]

On 20 March 2018 at 01:06, NeilBrown <neilb@suse.com> wrote:
> On Sat, Mar 17 2018, Justin Skists wrote:
>
>> Fix sparse warning:
>>
>>   CHECK   drivers/staging//lustre/lnet/lnet/acceptor.c
>> drivers/staging//lustre/lnet/lnet/acceptor.c:243:30: warning: cast to
>> restricted __le32
>>
>> LNET_PROTO_TCP_MAGIC, as a define, is already CPU byte-ordered when
>> compared to 'magic', so no need for a cast.
>>
>> Signed-off-by: Justin Skists <j.skists@gmail.com>
>> ---
>>  drivers/staging/lustre/lnet/lnet/acceptor.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/staging/lustre/lnet/lnet/acceptor.c b/drivers/staging/lustre/lnet/lnet/acceptor.c
>> index fb478e20e204..13e981781b9a 100644
>> --- a/drivers/staging/lustre/lnet/lnet/acceptor.c
>> +++ b/drivers/staging/lustre/lnet/lnet/acceptor.c
>> @@ -240,7 +240,7 @@ lnet_accept(struct socket *sock, __u32 magic)
>>                       return -EPROTO;
>>               }
>>
>> -             if (magic == le32_to_cpu(LNET_PROTO_TCP_MAGIC))
>> +             if (magic == LNET_PROTO_TCP_MAGIC)
>>                       str = "'old' socknal/tcpnal";
>>               else
>>                       str = "unrecognised";
>
> This code is almost completely irrelevant (it just choose which error
> message to use when failing), but we may as well get it right and I
> cannot see why your change is a fix.

I admit that the change is trivial, and, in hindsight, the word fix is
a little "strong".
The rationale was that the if-statement, as it was, probably wouldn't work as
intented on big-endian systems.

I chose this sparse warning to test the waters, as it was an isolated change,
before I thought about proposing a bigger change: There are quite a few
sparse warning in regards to struct lnet_hdr with regards to __u32 vs. __le32
(etc.) restricted castings.

> I suspect a more correct fix would be to use
>   lnet_accept_magic(magic, LNET_PROTO_TCP_MAGIC)
> as the condition of the if().  This is consistent with other code that
> tests magic, and it is consistent with the general understanding that
> "magic" should be in host-byte-order for the peer which sent the
> message.
>
> Could you resubmit with that change?

I agree that your suggestion is a much better fix.

As Greg has already accepted the patch in question into staging-next,
would the correct course of action be for me to submit a new patch with a
"fixes" tag based on staging-next? Or would Greg prefer to drop the
previous one for a fresh v2?

Regards,
Justin.
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