Re: [Scst-devel] Passing iovec instead of pbuf

[Vladislav B. <vs...@vl...>]

Uri Yanai, on 10/20/2010 07:26 PM wrote:
> Hi Vlad
> 
> If I decide to use the SCST SGV cache (setting SCST_USER_MEM_REUSE_AL)
> and lets suppose I receive a SCSI write command.
> How will SCST_USER_EXEC subcommand work with IO transfer bigger then
> cache page/cluster size?
> It can't break it down into smaller commands, can it ?     

What do you mean?

> Thanks 
> Uri
> 
> -----Original Message-----
> From: Vladislav Bolkhovitin [mailto:vs...@vl...] 
> Sent: Tuesday, October 19, 2010 11:44 PM
> To: Uri Yanai
> Cc: scs...@li...; Dorit Halsadi
> Subject: Re: [Scst-devel] Passing iovec instead of pbuf
> 
> Hi,
> 
> Uri Yanai, on 10/19/2010 07:11 PM wrote:
>> Hi
>>
>> We are writing a SCST user space device handler and we don't want to
> use
>> SCST memory reuse, instead we would like to use our pre allocated
>> memory pool.
>>
>> In cases where the SCSI command needs data transfer, the user space
>> handler should be prepared to allocate the data buffer with
>>
>> size alloc_len that could be bigger then the size of our basic memory
>> pool unit, In this case we would like to fulfill the request returning
>> an array of buffers similar to iovec  in readv/writev methods.
>>
>> My questions.
>>
>> 1.       Is this in the SCST roadmap?
> 
> No
> 
>> 2.       If not in the roadmap, and an implementation is offered will
>> the SCST adopt it?
> 
> Yes (if done properly, of course)
> 
>> 3.       Can we handle this problem differently?   
> 
> Most likely. Have you looked at sgv_single_alloc_pages option of struct
> scst_user_dev_desc and SCST_USER_PREALLOC_BUFFER IOCTL? Why not just
> preallocate the buffers you need in the SGV cache in the shared mode?
> 
> Vlad
> 
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