[Stgt-devel] User-mode iSER
Thu Aug 3 00:33:02 CEST 2006
From: Tom Tucker <tom at opengridcomputing.com>
Subject: Re: [Stgt-devel] User-mode iSER
Date: Wed, 02 Aug 2006 10:58:40 -0500
> On Wed, 2006-08-02 at 07:21 +0900, FUJITA Tomonori wrote:
> > >
> > > Also, won't a user-mode approach support virtual target devices more
> > > easily?
> > There's no difference. Note that we try to push a small portion of the
> > iSCSI tcp driver into kernel (iSCSI protocol processing). Both
> > approaches perform SCSI protocol processing, I/O in user space.
> > I think that you can easily implement any kind of vitalization, device
> > vitalization (like virtual tape library) and backing vitalization
> > (snapshot, encryption, compression, etc) in user space with both
> > approaches.
> Yes, I think this is true, in the current design, the target device I/O
> is done in user space, so adding a new device type to trunk/usr is just
> as easy. The event that initiates this I/O though comes from the kernel
> over a netlink socket.
We don't use netlink because it turned out that we cannot pass
user-space pointers via netlik due to its philosophy.
The pathch to replace netlink is at:
The reason why we cannot netlink is at:
> Moving this all to user-space "might" make this perform better and
> simplify the architecture.
> Do you think this is true or does it create as many problems as it
I'm not sure. That might be true if we think about only target drivers
that can be implemented in user-space (iSCSI tcp for generic NICs,
iSER), but we also need to support target drivers that needs in-kernel
Anyway, as I said in the first mail, we don't know where iSCSI tcp for
generic NICs and iSER drivers live. So just wait for few days.
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