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From: Karol Mroz (kmroz_at_[hidden])
Date: 2007-07-02 17:12:11


I've noticed the varying headers depending on transmit protocols but was
unaware that you couldn't access the message tag from within the BTL.
Well then, that answers that :) Thanks for the info.

George Bosilca wrote:
> Karol,
>
> There is no way to know the MPI tag at the BTL level. The BTL is
> protocol agnostic, it only moves bytes around (BTL = Byte Transport
> Layer). Moreover, the BTLs can be (and are) used by different PML,
> each of them supporting a different protocol.
>
> Now, let talk specifically about the OB1 PML. The first X bytes
> contain a message header, but this message header differ based on the
> protocol used to transmit the message. There are multiple protocols:
> eager, send/recv, RDMA. If you look in ompi/mca/pml/ob1/pml_ob1_hdr.h
> you will see the different types of headers used by the OB1 PML.
> However, do not use this file in the BTL, as the BTL is PML agnostic.
>
> Thanks,
> george.
>
> On Jul 2, 2007, at 4:56 PM, Karol Mroz wrote:
>
>> Good morning everyone. I had a question about obtaining the message tag
>> from the iovec array in mca_btl_sctp_frag_t* frag from within the
>> mca_btl_tcp_frag_send() function. If I understand correctly, the first X
>> bytes in the first iovec entry contain message header information in the
>> form of an mca_pml_ob1_match_hdr_t struct that contains a hdr_tag field.
>> When I extract this, I get a number that resembles an address.
>> Dereferencing this gives, from what I can tell, an incorrect value and
>> passing the value into ntohl() etc brings me no closer. There is
>> probably something basic I'm overlooking... any help would be
>> appreciated.
>>
>> Thanks,
>> Karol
>>
>> --Karol Mroz
>> kmroz_at_[hidden]
>>
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-- 
Karol Mroz
kmroz_at_[hidden]