Missed a fair bit of this thread when it was first sent, bad mail filter I think (or pebkac). * FUJITA Tomonori (fujita.tomonori@xxxxxxxxxxxxx) wrote: > From: Vladislav Bolkhovitin <vst@xxxxxxxx> > Subject: Re: [Stgt-devel] Question for pass-through target design > Date: Mon, 07 May 2007 18:24:44 +0400 > > > FUJITA Tomonori wrote: > > >>>>It looks like the pass-through target support is currently broken, at > > >>>>least as I've checked for ibmvstgt, but I think it's a general problem. > > >>>>I wanted to check my assumptions and get ideas. > > >>> > > >>>Yeah, unfortunately, it works only with the iSCSI target driver (which > > >>>runs in user space). > > >>> > > >>> > > >>> > > >>>>The code isn't allocating any memory to pass along to the sg code to store > > >>>>the result of a read or data for a write. Currently, dxferp for sg_io_hdr > > >>>>or dout_xferp/din_xferp for sg_io_v4 are assigned to the value of uaddr, > > >>>>which is set to 0 in kern_queue_cmd. With the pointer set to NULL, > > >>>>the pass-through target isn't going to function. Even if we had memory > > >>>>allocated, there isn't a means of getting data to be written via sg down > > >>>>this code path. > > >>>> > > >>>>What ideas are there as to how the data will get to user-space so that > > >>>>we can use sg? > > >>> > > >>>For kernel-space drivers, we don't need to go to user-space. We can do > > >>>the pass-through in kernel space. I talked with James about this last > > >>>year and he said that if the code is implemented cleanly, he would > > >>>merges it into mainline. > > >> > > >>We already have a pass-through in the kernel space for > > >>kernel space drivers. It is the scsi_tgt* code. > > > > > > > > > Could you elaborate more? > > > > > > What I meant that is that the kernel tgt code (scsi_tgt*) receives > > > SCSI commands from one lld and send them to another lld instead of > > > sending them to user space. > > > > Although the approach of passing SCSI commands from a target LLD to an > > initiator one without any significant interventions from the target > > software looks to be nice and simple, you should realize how limited, > > unsafe and illegal it is, since it badly violates SCSI specs. > > I think that 'implemented cleanly' means that one scsi_host is assigned > to only one initiator. Vladislav listed a number of issues that are inherent in an implementation that does not have a 1:1 relationship of initiators to targets. The vscsi architecture defines the 1:1 relationship; it's imposible to have more than one initiator per target. Are there any barriers that we will need to address if this were the case? Regards, Rob Jennings - 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
