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
km...@cs.ubc.ca
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