[Xen-devel] Re: [5 Patches] Synchronize blktap with citrix blktap2.

[Dutch Meyer <dmeyer@xxxxxxxxx>]

I've been reminded that the ioemu patch to update the blktap dependencies 
in that repo is still necessary.  It is available here:
http://www.cs.ubc.ca/~dmeyer/blktap2/tools_ioemu_dir_use_blktap_old.patch

--Dutch

On Thu, 26 Mar 2009, Dutch Meyer wrote:

> Fixed a few issues, particularly on 64bit builds.  Updated to build with most 
> recent xen-unstable (19426).
> Kernel Changes:
> www.cs.ubc.ca/~dmeyer/blktap2/kernel_patches.tgz
>
> Dom0 userspace Changes:
> www.cs.ubc.ca/~dmeyer/blktap2/userspace_patches.tgz
>
> --Dutch
>
> On Wed, 18 Feb 2009, Dutch Meyer wrote:
>
> > This is an updated patch set to the one I posted a few months back.
> >
> > These patches contain a completely rewritten blktap implementation
> > and are an open source release of what Citrix intends to use in future
> > releases of XenServer.  They contain a number of bug fixes from my
> > previous patchset.
> >
> > They also contain Citrix's implementation of the VHD image format.  VHD is 
> > what XenServer uses to store file-based images, and this code is 
> > considerably more robust and efficient than the qcow implementation that 
> > is in the tree today.
> > Benefits to blktap2 over the old version of blktap:
> >
> > * Isolation from xenstore - Blktap devices are now created directly on
> >  the linux dom0 command line, rather than being spawned in response
> >  to XenStore events.  This is handy for debugging, makes blktap
> >  generally easier to work with, and is a step toward a generic
> >  user-level block device implementation that is not Xen-specific.
> >
> > * Improved tapdisk infrastructure: simpler request forwarding, new
> >  request scheduler, request merging, more efficient use of AIO.
> >
> > * Improved tapdisk error handling and memory management.  No
> >  allocations on the block data path, IO retry logic to protect guests
> >  transient block device failures.  This has been tested and is known
> >  to work on weird environments such as NFS soft mounts.
> >
> > * Pause and snapshot of live virtual disks (see xmsnap script).
> >
> > * VHD support.  The VHD code in this release has been rigorously
> >  tested, and represents a very mature implementation of the VHD image
> >  format.
> >
> > * No more duplication of mechanism with blkback.  The blktap kernel
> >  module has changed dramatically from the original blktap.  Blkback
> >  is now always used to talk to Xen guests, blktap just presents a
> >  Linux gendisk that blkback can export.  This is done while
> >  preserving the zero-copy data path from domU to physical device.
> >
> > These patches deprecate the old blktap code, which can hopefully be
> > removed from the tree completely at some point in the future.
> >
> > Signed-off-by: Jake Wires <jake.wires@xxxxxxxxxx>, Dutch Meyer
> > <dmeyer@xxxxxxxxx>
> >
> > Two blktap Patches (the xen tree):
> > http://www.cs.ubc.ca/~dmeyer/blktap2/01-deprecate-blktap
> > http://www.cs.ubc.ca/~dmeyer/blktap2/02-add-blktap2
> >
> > And 3 kernel module patches (the linux tree):
> > http://www.cs.ubc.ca/~dmeyer/blktap2/01-blktap-patch
> > http://www.cs.ubc.ca/~dmeyer/blktap2/02-blkback-pagemap-patch
> > http://www.cs.ubc.ca/~dmeyer/blktap2/03-blktap2-patch
> >
> > In addition to the above patches, the (external) ioemu git repository 
> > currently has some very heavy dependencies on blktap, and does not like 
> > the change of the blktap directory name to deprecate that code.  The 
> > following patch needs to be applied to fix ioemu:
> > http://www.cs.ubc.ca/~dmeyer/blktap2/tools_ioemu_dir_use_blktap_old.patch
> >
> > Ideally we can come up with a better integration between blktap2 and ioemu 
> > than what is currently in place with the old tapdisk code.  For instance, 
> > blktap2 makes it possible to just treat the tapdisk-based devices as raw 
> > devices for qemu, severing these (now unnecessary) dependencies.
> > --Dutch
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