Re: [libvirt] [PATCHv4 11/18] blockjob: support pivot operation on cancel

This is the bare minimum to end a copy job (of course, until a later patch adds the ability to start a copy job, this patch doesn't do much in isolation; I've just split the patches to ease the review).

This patch intentionally avoids SELinux, lock manager, and audit actions, saving that for a later patch that affects the overall lifecycle of a disk copy. In particular, I'm still fuzzy on the exact qemu error semantics, and whether I need to make more of an effort after a 'drive-reopen' fails. When a mirror job is started, cancelling the job safely reverts back to the source disk, regardless of whether the destination is in phase 1 (streaming, in which case the destination is worthless) or phase 2 (mirroring, in which case the destination is sync'd up to the source at the time of the cancel). Our existing code does just fine in either phase, other than some bookkeeping cleanup. Pivoting the job requires the use of the new 'drive-reopen' command. Here, failure of the command is potentially catastrophic to the domain, since it rips out the old disk before attempting to open the new one; if our recovery path of retrying the reopen on the original source disk also fails, the domain is hosed. If only qemu could get 'drive-reopen' inside 'transaction'... Interesting side note: while snapshot-create --disk-only creates a copy of the disk at a point in time by moving the domain on to a new file (the copy is the file now in the just-extended backing chain), blockjob --abort of a copy job creates a copy of the disk while keeping the domain on the original file. There may be potential improvements to the snapshot code to exploit block copy over multiple disks all at one point in time. And, if 'block_job_cancel' were made part of 'transaction', you could copy multiple disks at the same point in time without pausing the domain. This also implies we may want to add a --quiesce flag to the pivot operation, so that when breaking a mirror, the side of the mirror that we are abandoning is at least in a stable state with regards to guest I/O. * src/qemu/qemu_driver.c (qemuDomainBlockJobAbort): Accept new flag. (qemuDomainBlockPivot): New helper function. (qemuDomainBlockJobImpl): Implement it. --- src/qemu/qemu_driver.c | 115 +++++++++++++++++++++++++++++++++++++++++++++-- 1 files changed, 110 insertions(+), 5 deletions(-)