Re: [PATCH] [Target_Core_Mod/pSCSI]: Add optional legacy scsi_execute_async() usage for Linux/SCSI passthrough

[Boaz Harrosh <bharrosh@panasas.com>]

On 04/21/2009 03:15 PM, Vladislav Bolkhovitin wrote:
> Boaz Harrosh, on 04/19/2009 02:56 PM wrote:
>> On 04/17/2009 04:09 AM, Nicholas A. Bellinger wrote:
> 
> [..]
> 
>> Are you aware that scsi_execute_async() has gone in 2.6.30-rc1?
>>
>> I'm not sure what would be the best alternative for you. I would say
>> a bio, but it is still being debated. Your current options are:
>>
>> 1. bio_alloc then loop () bio_add_pc_page, and finally blk_rq_append_bio
>>    (Which block people don't like)
>> 2. sglist => page-pointers-array translation and blk_rq_map_user with 
>>    struct rq_map_data mode. (not possible with all kind of sglists)
>> 2. sglist => iovec translation and blk_rq_map_user_iov()
>>    (Very very ugly mapping of pages to virtual pointers)
>>
>> I have a similar situation with my OSD code.
> 
> Do you have somewhere in it a need to run an arbitrary CDB with data 
> pages stored in an sglist? Is that code accepted in the mainline?
> 

No, I have a direct bio which comes from two sources.
1. A bio prepared by a filesystem to describe a write/read to a file (osd object)
2. A cloned bio that comes from a stacking block-device over osd-object.

So I do not have an sglist at all, anywhere in code.

> If yes, why not to resurrect the necessary bits of scsi_execute_async() 
> (option (1) above)? It was deleted, because in 2.6.30 there are no users 
> of it left, but if there are users (OSD), then why not to return it? 
> Seems nothing better for the sg->bio case can be invented.
> 

I hate scsi_execute_async() for lots of reasons, 
1. The cover-up of an historical abuse of sglists by sg/sr
2. Override of use_sg/data-pointer crap
3. What is data-format got to do with sync/async execution
4. the need of all that scsi_io_context and the re-invention
   of async_done API.
5. ...
Good riddence

But you might be looking into an API introduced by an RFC by
Tejun Heo in the form of blk_rq_map_kern_sgl() which should
be a more appropriate general API for your use.
(And is not directly usable for me in OSD)

> Vlad

Boaz