Re: [Xen-users] blktap/blktap2

[Mike McClurg <mike.mcclurg@xxxxxxxxxx>]

On 29/07/11 03:54, Grant McWilliams wrote:
>
> What's the issue with blktap that precludes it from being added to the
> kernel?
>

Just to make sure there's no confusion, we're talking about blktap,
which is different from blkback/blkfront. Both blkback and blkfront are
included in the Linux kernel since 3.0.0. These are the drivers that
make paravirtualized IO possible, and are thus necessary for Xen PV domains.

blktap is used to provide a high performance disk IO interface to
virtual block devices (see http://wiki.xensource.com/xenwiki/blktap). It
could, in fact, be implemented completely in userspace, and not as a
kernel driver. For this reason, blktap is unlikely to ever be accepted
into the mainline Linux kernel. I'm not a kernel dev myself, so that's
the best I'll be able to do to explain why it's not going into mainline.

There is talk of refactoring blktap so that it actually does exist as
pure userspace code, and doesn't require a kernel module. I don't know
of any concrete plans to actually do this in the near future, since it
works just fine as an out-of-tree module, but in theory it would be
possible to move it to userspace.

Mike

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