RE: plugin reentrant?

[Anthony Galica <anthony.galica@hitachivantara.com>]

Thanks, Fabian. 

This is more or less what I expected (cross process execution concurrency, but not in-process concurrency), but obviously there are different considerations so I wanted to make sure.

As to the PS: We are developing a custom plugin, but at the moment I can't share much about it!

Thanks again,
Anthony


-----Original Message-----
From: Fabian Grünbichler <f.gruenbichler@proxmox.com> 
Sent: Wednesday, June 17, 2026 11:43 PM
To: Anthony Galica <anthony.galica@hitachivantara.com>; pve-devel@lists.proxmox.com
Subject: Re: plugin reentrant?

***** EXTERNAL EMAIL *****

On June 17, 2026 9:45 pm, Anthony Galica wrote:
> Hi Everyone,
>
> Is a proxmox plugin reentrant in that will it simultaneously send two or more requests to the same instance of the running script?

There can be more than one *process* calling into storage plugin perl code at the same time - API requests are processed concurrently, including long-running tasks executed in their own worker process, and CLI tools can also call into plugin code via PVE::Storage.

For some code paths, there will be a mutual exclusion mechanism in effect via pmxcfs cluster-wide locking for shared storages, and node-local locking for local storages.

Those mostly cover code paths related to allocating or freeing volumes.

> Does the answer differ for the same storage pool vs. different storage pools?

Currently, the locking done by PVE is per storage plugin instance (which is normally one pool/export/directory/.. ). We have discussed allowing storage plugins to mark themselves as not requiring such a coarse lock, in which case we would instead lock the (storage plugin instance, VMID) tuple - but that is not yet implemented.

If you have different locking requirements, you can of course implement your own locking inside your plugin on top of what PVE does - but please be careful to not cause accidental deadlocks.

Hope this helps - please reach out if you have more questions!
Fabian

P.s. if you are developing your own custom storage plugin, we'd be interested to know about it!