sd_prep_fn

[sumeet gandhare]

On Thu, Nov 10, 2011 at 9:23 PM, rohan puri <rohan.puri15 at gmail.com> wrote:

>
>
> On Thu, Nov 10, 2011 at 6:26 PM, sumeet gandhare <sumeetgandhare at gmail.com
> > wrote:
>
>>
>>
>> On Thu, Nov 10, 2011 at 6:13 PM, rohan puri <rohan.puri15 at gmail.com>wrote:
>>
>>>
>>>
>>> On Thu, Nov 10, 2011 at 4:50 PM, sumeet gandhare <
>>> sumeetgandhare at 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 at 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
>>>
>>
>> Hi Rohan,
>>  Thanks for your response and help.
>>  It seems there is scsi_prep_fn too. I thought the blk_peek_request()
>> invokes scsi_prep_fn and not sd_prep_fn.
>>
>> http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_lib.c#L1248<http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_lib.c%23L1248>
>>
>> scsi_prep_fn is registered here
>>
>> http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_lib.c#L1684<http://lxr.linux.no/#linux+v3.1/drivers/scsi/scsi_lib.c%23L1684>
>>
>>
>> Please could you confirm.
>>
>> Thanks
>> Sumeet
>>
>
> Whenever a new scsi device is attached sd_probe is called sd_async_probe()
> is the async part of sd_probe() So when this is called the prep_fn is set
> to sd_prep_fn and hence this will be called.
>
> sd_prep_fn is for scsi disk, similarly there is a function sr_prep_fn
> which gets called for scsi cd-rom.
>
> Regards,
> Rohan Puri
>
Hi Rohan,
  Thanks for the info. I am still not sure when does scsi_prep_fn gets
invoked.

Regards,
Sumeet
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