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. - 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
