Tapdisk control in userspace, a replacement for the original blktap2
control stack, which had to pass a kernel space interface based on
sysfs nodes.
All tapdisk processes listen for commands on a unix stream socket. The
control library supports scanning the socket namespace for running
tapdisks, VBD minors allocated, associated images and state inquiry.
Control operations include allocating/releasing devices, spawning
tapdisks, opening/closing images, attaching disk images to
devices. disk pause/resume operations and runtime switching of disk
images.
Signed-off-by: Jake Wires <jake.wires@citrix.com>
Signed-off-by: Daniel Stodden <daniel.stodden@citrix.com>
Stop coercing drivers/disktype code into the tool stack. Make both
blktapctrl and tap-ctl transfer type/path pairs as "<type>:<path>"
strings. Remove the message.disktype integer altogether.
Signed-off-by: Daniel Stodden <daniel.stodden@citrix.com>
Signed-off-by: Jake Wires <jake.wires@citrix.com>
Hide tapdisk support for different raw I/O interfaces behind a new
struct tio. Libaio remains to dominate the interface, requiring
everyone to dispatch iocb/ioevent structs.
Backends:
- lio: Kernel AIO via libaio.
- rwio: Canonical read/write() mode.
Misc:
- Fixes a bug in tapdisk-vbd which locks up the sync io mode.
- Wants a PERROR macro in blktaplib.h
- Removes dead code in qcow2raw to make it link again.
Signed-off-by: Daniel Stodden <daniel.stodden@citrix.com>
Signed-off-by: Jake Wires <jake.wires@citrix.com>
Move event callbacks registration into tapdisk-queue. This should also
obsoletes the dummy pollfd pipe in the synchronous I/O case.
Signed-off-by: Daniel Stodden <daniel.stodden@citrix.com>
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@citrix.com>
Signed-off-by: Dutch Meyer <dmeyer@cs.ubc.ca>
Keir Fraser