Vladislav Bolkhovitin wrote: > Boaz Harrosh wrote: >> Vladislav Bolkhovitin wrote: >>> Boaz Harrosh wrote: >>>> Vladislav Bolkhovitin wrote: >>>>> Christoph Hellwig wrote: >>>>>> On Fri, May 02, 2008 at 05:53:22PM +0200, Bart Van Assche wrote: >>>>>>> Regarding scsi_execute_async(): I didn't know that this API is on its >>>>>>> way out. What will it be replaced by, and when ? >>>>>> blk_execute_rq/blk_execute_rq_nowait plus the block level helpers built >>>>>> ontop to build requests. >>>>> scsi_execute_async() is already a nice and simple helper function on top >>>>> blk_execute_rq_nowait(). What's the point then to remove it? Do you >>>>> consider that exposing scsi_execute_async() internals to its users is >>>>> better? >>>>> >>>> The problem with it is the use of sg list to *hack* in bio's. Which totally >>>> ignores/duplicates block layer mechanisms. There is pending a large patchset >>>> that removes the use of scsi_execute_async from sg/sr and friends to use blk_map_* >>>> members and directly call blk_execute_*. The original patchset was written by >>>> Mike Christie but is now brought up to date by Tomo. It should be submitted soon I think. >>>> If you need good example of usage check out bsg.c it maps user-space data in all kind >>>> of combinations. If you have kernel space memory it is even simpler. >>> Thanks for pointing on it. But it still remained unclear for me what's >>> the point in the scsi_execute_async() removal. Function >>> scsi_req_map_sg() looks pretty simple and straightforward, so I don't >>> see how the overall code can be simplified. >>> >> Well No, scsi_req_map_sg() is a complete hack. If you have user memory >> or kernel memory you better go through blk_map_* which will take care of >> device masks, alignment and all, where here the ULD does that. So you have >> 2 places of waisted code both at ULD to build the SG right, and here to >> translate SG to BIO. Where at block layer you have one function call. >> Try it out you see that not using scsi_execute_async() is much more simple >> at ULD then using it. >> If you do mmap then Tomo has code for block layer to support that. > > Seems, I'm starting understanding you. You mean that all ULDs (User > Level Devices, i.e. sg, st, etc.) deal with user supplied buffers, i.e. > pointers to virtually continuous memory, which at the moment it has to > convert to SG vector, which then will be translated to BIOs for the > corresponding LDD by scsi_execute_async() (and then back to SG vector on > the queuecommand() time). So, it will be simpler to supply that buffer > pointer directly to block functions. Correct? > > But the problem is that in SCST in each data transfer 2 LDDs > participate: one target and one backstorage (initiator). And the target > LDD deals with SG vectors only. So, SCST never deals with buffers, it > always deals with SG vectors and pass them between target LDDs and > backstorage as necessary. Where is that SG coming from? is it from Network stack? or is it an SG prepared by scsi-ml with call to blk_rq_map_sg()? > > Thus, looks like for SCST in the pass-through mode there is no > alternative to scsi_execute_async(). > Tomo what do you think is it logical to add a blk function that will accept an SG list and map it to a request. Like, for example, an SG from Network? opposite of what blk_rq_map_sg does. > Thanks, > Vlad > Boaz -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
