[stgt] RFC [patch] README.passthrough v1 (2nd send)

[Nicholas A. Bellinger]

On Thu, 2010-08-19 at 23:03 +0900, FUJITA Tomonori wrote:
> On Wed, 18 Aug 2010 18:01:37 -0700
> "Nicholas A. Bellinger" <nab at linux-iscsi.org> wrote:
> 
> > BSG exposes more raw functionality (but certaily not all) of the modern
> > Linux Block layer code.  This includes the ability to do BIDI commands
> > and support for legacy SG_IO ioctls in block/bsg.c:bsg_ioctl().
> > 
> > Note that not all of the the structure members in struct sg_io_v4 can
> > safely be used with current mainline code.  For example, having a 32-bit
> > userspace passing up 32-bit pointers currently need a patch to require
> > proper conversion to 64-bit struct scatterlist memory.  The first half
> > of this patch is here:
> > 
> > http://groups.google.com/group/linux-iscsi-target-dev/browse_thread/thread/6b9f8a08f78067dc/6330a5897203854a?lnk=gst&q=BSG#6330a5897203854a
> > 
> > This issue came up again between Tomo-san and myself last week, and we
> > agreed that the patch to make 32-bit user + 64-bit kernel work with BSG
> > scatterlists would not be pretty,
> 
> Sorry, we agreed about it? I'm not sure about. I really want to avoid
> the compat code for bsg read/write interface.
> 
> I just want to say, bsg doesn't support such configuration and use
> 64-bit user space.
> 
> 

Hmmm, then it must have been Dr. Hannes..  ;)

The bigger issue for BSG is wrt to QEMUSGList when we are forced to use
non-contigious physical memory, instead of the (always?) contigious
memory that STGT is assigning to struct sg_io_v4->d[out,in]_xferp, and
in usr/bs_sg.c:bs_bsg_cmd_submit().

Since 64-bit kernel / 32-bit userspace for QEMU-KVM BSG is still broken
with the above patch to block/bsg.c that allows QEMU-KVM BSG to function
on 64-bit kernel / userspace.   I think this particular issue does need
to be addressed for those users, even if it is just a temporary measure
that we removed at some point in the future.

Best,

--nab


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