On Mon, 2011-02-14 at 18:29 +0900, FUJITA Tomonori wrote: > On Mon, 14 Feb 2011 01:01:12 -0800 > "Nicholas A. Bellinger" <nab@xxxxxxxxxxxxxxx> wrote: > > > > btw, can we kill the non scatter/gather data path? I think that we > > > should always use the scatter/gather data transfer. > > > > Unfortuately it's not that easy. The main reason why CDB type > > SCF_SCSI_CONTROL_NONSG_IO_CDB was originally added (back in 2.2/2.4 > > days) was because certain LLDs had a problem with basic control CDBs > > using SGLs.. > > > > Obviously we are way past that point with drivers/scsi today, but the > > main reason today why SCF_SCSI_CONTROL_NONSG_IO_CDB still exists is > > because of CDB emulation for complex stuff in target_core_cdb.c. It has > > historically proven much easier to code complex CDB emulation using a > > contigious buffer, than with walking SGL formatted memory. > > > > Converting over the more complex CDB emulation stuff to SGLs would > > somewhat painful, at least without adding an extra location allocation + > > copy into SGLs (not a big deal for CONTROL CDB stuff), > > lib/scatterlist.c provides nice helper functions to copy data between > a linear buffer and an SG list. I think that at least, it's more clear > than now. > Yeah, I think this is going to make the most sense for a proper long term conversion and removal of SCF_SCSI_CONTROL_NONSG_IO_CDB. > > > or something else > > to obtain a virtually contigious buffer for building the emulated > > response. > > Hmm, I don't think that very large contiguous buffer for CONTROL CDB > so why can't we allocate a physically contiguous buffer for it? > Well, that depends what you consider large.. ;) > We could play with vmap for a virtually contiguous buffer but it adds > the complicated cache issue so I don't like that. Yes, most likely overkill I think.. Best Regards, --nab -- 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
