Re: [libvirt-users] Locking without virtlockd (nor sanlock)?

Il 03-01-2020 11:26 Daniel P. Berrangé ha scritto: > virtlockd also uses fcntl(), however, it doesn't have to acquire locks > on > the file/block device directly. It can use a look-aside file for > locking. > For example a path under /var/lib/libvirt/lock. This means that locks on > block devices for /dev/sda1 would be held as > /var/lib/libvirt/lock/$HASH(/dev/sda1) > > If you mount /var/lib/libvirt/lock on NFS, these locks now apply across > all machines which use the same block devices. This is useful when your > block device storage is network based (iSCSI, RBD, etc). Hi Daniel, if I understand the docs correctly, this locking scheme is really useful for raw block devices, right? Now that Qemu automatically locks file-based vdisks, what is the main advantage of virtlockd locking?

> There are some issues with libvirt's locking though where we haven't > always released/re-acquired locks at the correct time when dealing > with block jobs. As long as your not using snapshots, block rebase, > block mirror APIs, it'll be ok though. While I am not an heavy user of external snapshot and other block-related operation, I occasionally use them (and, in these cases, I found them very useful). Does it means that I should avoid relying on virtlockd for locking? Should I rely on Qemu locks only?