Mike Christie wrote: > James Smart wrote: >> Mike Christie wrote: >>> For the tasks you want to do for the fc class is performance critical? >> No, it should not be. >> >>> If not, you could do what the iscsi class (for the netdev people this is >>> drivers/scsi/scsi_transport_iscsi.c) does and just suffer a couple >>> copies. For iscsi we do this in userspace to send down a login pdu: >>> >>> /* >>> * xmitbuf is a buffer that is large enough for the iscsi_event, >>> * iscsi pdu (hdr_size) and iscsi pdu data (data_size) >>> */ >> Well, the real difference is that the payload of the "message" is actually >> the payload of the SCSI command or ELS/CT Request. Thus, the payload may > > I am not sure I follow. For iscsi, everything after the iscsi_event > struct can be the iscsi request that is to be transmitted. The payload > will not normally be Mbytes but it is not a couple if bytes. > >> range in size from a few hundred bytes to several kbytes (> 1 page) to >> Mbyte's in size. Rather than buffer all of this, and push it over the >> socket, >> thus the extra copies - it would best to have the LLDD simply DMA the >> payload like on a typical SCSI command. Additionally, there will be >> response data that can be several kbytes in length. >> > > Once you have got the buffer to the class, the class can create a > scatterlist to DMA from for the LLD. I thought. iscsi does not do this > just because it is software right now. For qla4xxx we do not need > something like what you are talking about (see below for what I was > thinking about for the initiators). If you are saying the extra step of > the copy is plain dumb, I agree, but this happens (you have to suffer > some copy and cannot do dio) for sg io as well in some cases. I think > for the sg driver the copy_*_user is the default. > > Instead of netlink for scsi commands and transport requests.... > > For scsi commands could we just use sg io, or is there something special > about the command you want to send? If you can use sg io for scsi > commands, maybe for transport level requests (in my example iscsi pdu) > we could modify something like sg/bsg/block layer scsi_ioctl.c to send > down transport requests to the classes and encapsulate them in some new > struct transport_requests or use the existing struct request but do that > thing people keep taling about using the request/request_queue for > message passing.
And just to be complete, the problem with this is that it is tied to the request queue and so you cannot just send a transport level request unless it is tied to the device. But for the target stuff we added a request queue to the host so we could inject requests (the idea was to send down those magic message requests) at a higher level. To be able to use that for sg io though it would require some more code and magic as you know. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
