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

[FUJITA Tomonori]

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.


> but that it does need to be fixed in
> order to properly support the QEMU-KVM SCSI-BSG MegaSAS SGL passthrough.
> This is the code that has been being going in parallel with the recent
> multi-fabric TCM_Loop Virtual SCSI LLD develpments for STGT, which can
> be found here to give more of an idea how BSG functions.
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