On Thu, Nov 10, 2011 at 4:50 PM, sumeet gandhare <sumeetgandhare@gmail.com>wrote:
Hi All, I am trying to understand the scsi upper layer and middle layer code and found the function sd_prep_fn which seems to convert a request to a scsi command. I want to know when this function sd_prep_fn gets invoked.
It seems sd_probe_async invokes
blk_queue_prep_rq <http://lxr.linux.no/linux+*/+code=blk_queue_prep_rq>(sdp <http://lxr.linux.no/linux+*/+code=sdp>->request_queue <http://lxr.linux.no/linux+*/+code=request_queue>, sd_prep_fn <http://lxr.linux.no/linux+*/+code=sd_prep_fn>);
Further following code is invoking the prep_rq_fn
which is the blk_peek_request
http://lxr.linux.no/#linux+v3.1/block/blk-core.c#L1879 <http://lxr.linux.no/#linux+v3.1/block/blk-core.c%23L1879>
and blk_peek_request is getting invoked from
scsi_request_fn http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_lib.c#L1493 <http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_lib.c%23L1493>
scsi_request_fn is registered with the block layer as a request function at the following code
http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_lib.c#L1688 <http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_lib.c%23L1688>
And scsi_alloc_queue is invoked from scsi_alloc_sdev http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_scan.c#L238 <http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_scan.c%23L238>
scsi_alloc_sdev is invoked as a part of scsi lun discovery from lots of places
http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_scan.c#L1004 <http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_scan.c%23L1004>
http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_scan.c#L1306 <http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_scan.c%23L1306>
The confusion I have is that the sd.c upper layer driver has not registered for a request function using blk_init_queue
Any help would be appreciated.
Thanks Sumeet
_______________________________________________ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Hello Sumeet,
sd_prep_fn function is set to the request queue's prep_rq_fn member as you have mentioned. Now this function gets called in ret = q->prep_rq_fn(q, rq); in function blk_peek_request() which is called from scsi_request_fn() in file scsi_lib.c Regards, Rohan Puri