[pve-devel] checking output of storage plugin API - volume_rollback_is_possible(..., blockers)

[Fabian Grünbichler]

> Andrei Perapiolkin via pve-devel <pve-devel at lists.proxmox.com> hat am 14.05.2025 14:44 CEST geschrieben:

> Hi,
> 
> I'm trying to test specific aspects of the storage plugin API,
> and I'm not sure how to verify whether my function 
> volume_rollback_is_possible
> correctly sets up the blockers list.
> 
> I've checked REST API documentation:
> https://pve.proxmox.com/pve-docs/api-viewer/index.html#/nodes/{node}/qemu/{vmid}/snapshot/{snapname}/rollback
> 
> CLI tool:
> qm rollback
> 
> But I couldn't find where the list of blockers is returned or printed.

the $blockers parameter is currently only passed in replication contexts:

https://git.proxmox.com/?p=pve-guest-common.git;a=blob;f=src/PVE/AbstractConfig.pm;h=3d4fcbbf98553b1f4edc8f59307daae1cf1b8a2f;hb=HEAD#l1051

the expected behaviour is to
- fill $blockers with the snapshot names preventing the rollback, if there are any
- to die with an error message if rollback is not possible

the caller can then decide if they want to pass a $blockers reference, and upon
catching the error, inspect it to give a nicer error message.

you can see how the 'zfs' plugin handles it (the only one supporting replication
at the moment):

https://git.proxmox.com/?p=pve-storage.git;a=blob;f=src/PVE/Storage/ZFSPoolPlugin.pm;h=26fb0a4237e5c1013ebfa85ca2cc072c57d2c36f;hb=HEAD#l502

and model your implementation after its behaviour (of course, whether rolling
back is limited to the most recent snapshot like it is with ZFS is up to you
and your storage ;))

> Are there any posts, guides, or documentation on how to test blockers or 
> other return values from storage plugins?

out of interest - is your plugin publicly available?