canonical
Add support for virtiofsd cache mode via `io.cache` setting
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- [x] I have searched existing issues to check if an issue already exists for my feature request.
Is your feature request related to a problem? Please describe.
LXD currently starts virtiofsd using the equivalent of the --cache auto option.
This allows executing commands from the share, and is a reasonable default for concurrently sharing of a filesystem with multiple instances.
However it is not as safe & coherent as --cache never, which also prevents executing from the shared filesystem (for strong coherence).
It would be good to default to --cache never in order to be safe/correct by default, and allow admins to control the level of performance vs coherency risk they are willing to take.
Incus has a PR that adds support for configuring some of this via io.cache setting:
https://github.com/lxc/incus/pull/951
However it lacks the ability to use --cache auto, and because it defaults to --cache never, it is not possible to use --allow-mmap to support executing commands from that filesystem.
It also doesn't use the --writeback option in unsafe mode which we could consider.
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