[stgt] [PATCH] [tgt]: Convert bs_sg to use BSG v4 interface

[Nicholas A. Bellinger]

On Wed, 2010-06-16 at 23:26 +0900, FUJITA Tomonori wrote:
> On Wed, 16 Jun 2010 01:05:28 -0700
> "Nicholas A. Bellinger" <nab at linux-iscsi.org> wrote:
> 
> > On Tue, 2010-06-15 at 23:59 +0900, FUJITA Tomonori wrote:
> > > On Tue, 15 Jun 2010 17:10:46 +0300
> > > "Alexander Nezhinsky" <alexandern at voltaire.com> wrote:
> > > 
> > > > > Alexander, I think that you added bs_sg.c. Dropping sg and supporting
> > > > > only bsg is ok for you? Or you still use this feature?
> > > > 
> > > > It is generally ok with me. 
> > > > 
> > > > I've used bs_sg mainly for some performance measurements.
> > > > As we had discussed once, it has a major drawback of not handling properly
> > > > cache_sync in some scenarios, because the pass-through mode is disabled. 
> > > > As far as i understand, the new implementation suffers from the same problem,
> > > > so it is subject to the same limitations and requires the same precautions.
> > > 
> > > I can't recall the discussion, but the new implementation passes
> > > though all the commands. So it can inform initiators of the cache mode
> > > properly and pass SYNC commands to the underlying devices properly.
> > > 
> > > 
> > > > The only other concern might be that if anybody uses bs_sg with real devices
> > > > then the bsg-based implementation may preclude using older kernels,
> > > > like 2.6.18 of RHEL5.x. 
> > > 
> > > Yeah, if there are someone who cares about sg support, supporting both
> > > bsg and sg is fine by me.
> > 
> > Hmmm, perhaps it still makes sense to support both bsg and sg following
> > the previous patch then..?
> > 
> > http://lists.wpkg.org/pipermail/stgt/2010-June/003766.html
> 
> Ok if you are really care about sg. But Seems that the above patch
> can't be applied to the current head. Can you send the updated patch?
> --

Hi Tomo-san,

Ok, I just resent the BSG support patch which keeps existing SG_IO code,
and adds a minor fix to chk_sg_device() in order determine mode based on
BSG major=254 instead of pathname.  After a few quick tests both modes
are now functioning as expected.

Also, I included another small patch to the legacy SG_IO I have been
testing to add struct sg_iovec usage support.  As we don't have a hard
requirement for non contigious memory in STGT backstores currently this
is obviously not a hard requirement, but may be useful later.

Best,

--nab


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