Artem Kachitchkine wrote:
>> There is one wrinkle however.  I may need to access the associated buf 
>> (bp) for a packet instead of passing it off for DMA.  This is necessary 
>> if the HBA has to fall back to PIO, or if the driver needs to "fake" a 
>> SCSI transaction.  The wrinkle here is that none of the entry points 
>> directly take a bp anymore.  Even tran_start() doesn't get the bp.
> 
> I'm confused. Or maybe you're confused... :) tran_init_pkt takes bp.

tran_setup_pkt (there is no scsi_tran_setup_pkt) is an optional HBA entry 
point, 
and doesn't take a bp.  The manpage doesn't make it very clear, but the code 
implies that if you have a tran_setup_pkt, you must not have a tran_init_pkt, 
that is, it ASSERT()s to that effect.  (the manpage merely says that 
tran_setup_pkt is an "alternative".)

but if you're using tran_setup_pkt instead of tran_init_pkt, it doesn't appear 
as though you get a bp, no, and I don't know what the answer is.

> E.g. scsa1394: we bp_mapin() in scsa1394_scsi_init_pkt() and save bp 
> pointer in the private command structure scsa1394_cmd_t, which in turn 
> hangs off of scsi_pkt->pkt_ha_private - which is how functions like 
> tran_start get to it. We bp_mapout() in scsa1394_scsi_destroy_pkt(). In 
> between, the driver simply references memory pointed by bp->b_un.b_addr.
> 
> -Artem
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