linux-kernel - Re: [PATCH] bsg : Add support for io vectors in bsg

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Date:	Thu, 10 Jan 2008 16:33:07 -0600
From:	Mark Rustad <mrustad@...il.com>
To:	Pete Wyckoff <pw@....edu>
Cc:	James Bottomley <James.Bottomley@...senPartnership.com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>, tomof@....org,
	deepakrc@...il.com, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bsg : Add support for io vectors in bsg

On Jan 10, 2008, at 3:46 PM, Pete Wyckoff wrote:

> I'm fine with read/write, except Tomo is against handling iovecs
> because of the compat complexity with struct iovec being different
> on 32- vs 64-bit.  There is a standard way to do "compat" ioctl that
> hides this handling in a different file (not bsg.c), which is the
> only reason I'm even considering these ioctls.  I don't care about
> compat setups per se.

That is what I was thinking. Is it really necessary to support  
something like bsg for 32 on 64 bit? Yes, it is a userspace interface,  
but it isn't the kind of thing that normal user programs would use. It  
is a new interface for newly-written programs and I would expect those  
to be native. At least it doesn't strike me as overly-restrictive for  
that to be the case for this kind of interface.

> Is there another async I/O mechanism?  Userspace builds the CDBs,
> just needs some way to drop them in SCSI ML.  BSG is almost perfect
> for this, but doesn't do iovec, leading to lots of memcpy.


Precisely.

-- 
Mark Rustad, MRustad@...il.com


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