Re: [PATCH V2] libibumad: update umad_recv man page.

Hal Rosenstock
2012-07-06T19:41:20Z

On 7/6/2012 3:38 PM, Ira Weiny wrote:
> On Fri, 06 Jul 2012 15:32:51 -0400
> Hal Rosenstock <hal-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org> wrote:
>
>> On 7/6/2012 3:24 PM, Ira Weiny wrote:
>>> On Fri, 06 Jul 2012 14:34:24 -0400
>>> Hal Rosenstock <hal-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org> wrote:
>>>
>>>> On 7/3/2012 12:55 PM, Ira Weiny wrote:
>>>>>
>>>>> Document the umad_recv length parameter better.
>>>>>
>>>>> Changes since V1:
>>>>> add comments from Hal
>>>>>
>>>>> Signed-off-by: Ira Weiny <weiny2-i2BcT+NCU+M@public.gmane.org>
>>>>> ---
>>>>> man/umad_recv.3 | 18 +++++++++++++++++-
>>>>> 1 files changed, 17 insertions(+), 1 deletions(-)
>>>>>
>>>>> diff --git a/man/umad_recv.3 b/man/umad_recv.3
>>>>> index e1b2985..310d3d2 100644
>>>>> --- a/man/umad_recv.3
>>>>> +++ b/man/umad_recv.3
>>>>> @@ -27,10 +27,26 @@ A negative
>>>>> makes the function block until a packet is received. A
>>>>> .I timeout_ms\fR
>>>>> parameter of zero indicates a non blocking read.
>>>>> +
>>>>> +.B Note
>>>>> +.I length
>>>>> +is a pointer to the length of the
>>>>> +.B data
>>>>> +portion of the umad buffer. This means that
>>>>> +.I umad
>>>>> +should point to a buffer at least umad_size() +
> ^^^^^^
> must
>
> Oh, You mean must here?

Yes, if that's the direction you choose (must rather than should).

-- Hal

> Ira
>
>
>>>>> +.I *length
>>>>> +bytes long.
>>>>> +
>>>>> +.B Note also
>>>>> +that
>>>>> +.I *length\fR
>>>>> +must be >= 256 bytes.
>>>>
>>>> This seems somewhat redundant to me as just above it says "should point
>>>> to a bugger that's at least umad_size() + *length bytes long.
>>>>
>>>> Also, if this remains, should "must be" be "should be" ?
>>>
>>> I _guess_ it _could_ be less than 256.
>>
>> My only point here is that if it's less than 256 + header, then the
>> error is returned (and nothing useful can be done). To me, that makes it
>> a should rather than a must but just make the two lines consistent.
>> Roland does have this as a must in user_mad.txt kernel doc:
>> "The buffer passed to read() must be at least one struct ib_user_mad +
>> 256 bytes."
>>
>> -- Hal
>>
>>> However the specification states:
>>>
>>> "C13-3: The data payload (as used in Chapter 9: Transport Layer on page 233) for all MADs shall be exactly 256 bytes."
>>>
>>> Furthermore, the kernel checks to ensure that *length is > the first (or only) packet in the MAD transaction. While some Class/Attributes may allow for less "valid" data I'm not sure the kernel distinguishes that. Therefore, I think it is safer to just specify it. Don't you think?
>>
>>> Ira
>>>
>>>>
>>>>> +
>>>>> .SH "RETURN VALUE"
>>>>> .B umad_recv()
>>>>> returns non negative receiving agentid on success, and a negative value on error as follows:
>>>>> - -EINVAL invalid port handle or agentid
>>>>> + -EINVAL invalid port handle or agentid or *length is less than the minimum
>>>>
>>>> Rather than just minimum, minimum support length might be clearer.
>>>>
>>>> -- Hal
>>>>
>>>>> -EIO receive operation failed
>>>>> -EWOULDBLOCK non blocking read can't be fulfilled
>>>>> .SH "SEE ALSO"
>>>>
>>>
>>>
>>
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