This patch re-introduces blktap support to libxl. Unlike earlier versions, it does not link against any blktap library. libxl changes are needed to write to the vbd3 backend XenStore nodes.
blktap has three components. tapdisk is a daemon implementing the disk IO, NBD (Network Block Device), and Xen PV interfaces. tap-ctl is a tool to control tapdisks - creating, starting, stopping and freeing. tapback manages the XenStore operations and instructs tapdisk to connect. It is notable that tapdisk performs the grant and event channel ops, but doesn't interact with XenStore. tapback performs XenStore operations and notifies tapdisks of values and changes. The flow is: libxl writes to the "vbd3" XenStore nodes and runs the block-tap script. The block-tap script runs tap-ctl to create a tapdisk instance as the physical device. tapback then sees the tapdisk and instructs the tapdisk to connect up the PV blkif interface. This is expected to work without the kernel blktap driver, so the block-tap script is modified accordingly to write the UNIX NBD path. (It works with the kernel blktap driver as well - upstream blktap hasn't removed the blktap driver requirement yet - https://github.com/xapi-project/blktap/pull/364) An example command to attach a vhd: xl block-attach vm 'vdev=xvdf,backendtype=tap,format=vhd,target=/srv/target.vhd' VHD support is important for OpenXT since there are lots of existing VHDs which still need supporting. tapdisk also supports encrypted VHDs which is not available in QEMU. blktap's tapback needs minimal changes to work with libxl: https://github.com/xapi-project/blktap/pull/394 Jason Andryuk (4): block-common: Fix same_vm for no targets libxl: Add support for blktap vbd3 hotplug: Update block-tap libxl: Support blktap with HVM device model docs/man/xl-disk-configuration.5.pod.in | 4 +- tools/hotplug/Linux/block-common.sh | 8 +- tools/hotplug/Linux/block-tap | 162 ++++++++++++++++++++-- tools/libs/light/libxl_device.c | 14 +- tools/libs/light/libxl_disk.c | 37 +++-- tools/libs/light/libxl_dm.c | 1 - tools/libs/light/libxl_linux.c | 1 + tools/libs/light/libxl_types_internal.idl | 1 + tools/libs/light/libxl_utils.c | 2 + 9 files changed, 201 insertions(+), 29 deletions(-) -- 2.43.0
