CP-49249: Implement SMAPIv3 CBT Forwarding #5675
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added 2 commits
June 5, 2024 10:36
Signed-off-by: Colin James <colin.barr@cloud.com>
Implements the changes required to forward CBT-related functionality to the SMAPIv3 storage plugins, which now support CBT for XFS and GFS2 storage repositories. The length of the changed blocks requested is hardcoded as a negative number, which is interpreted by the related plugins as requesting the changes for the entire length of the VDIs being compared. SMAPIv1 does not support this functionality but we retain it here with this behaviour in case we want to make the functionality explicit in future. Signed-off-by: Colin James <colin.barr@cloud.com>
psafont
approved these changes
Jun 6, 2024
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These changes populate the stubs in
xapi-storage-scriptwith the logic required for forwarding CBT-related functionality toxapi-storage-plugins. Specifically, it will enable changed block tracking between snapshot VDIs whose storage substrate is XFS (local) or GFS2 (pool-wide).This functionality has been tested and looks to be working (the primary logic is on the storage plugins side, not ours). This set of changes shouldn't cause any breakage as the SMAPIv3 plugins are meant to be guarded to not advertise this capability to XAPI.
The style of the changes is up for discussion. I'm not fond of much of the style in
xapi-storage-script; it nests monads in awkward ways (the kind of ways that motivate monad transformers in a language like Haskell) with undocumented details (e.g.Attached_SRsensures an SR's UUID string gets mapped to somewhere, typically/run/sr-mount/...- otherwise the associated python plugins can't resolve them). Furthermore, the changes predate OCaml's addition oflet-operators, so it's all very much infix monadic bind>>=everywhere. I don't like infix@@usage generally, as in my current commit, but it is a good visual marker.All that said: I'd rather not play more type tetris where it's unnecessary.
There exists another branch by psafont that cleans up a lot of
xapi-storage-script, so I'd push for those kind of sweeping changes in the long run rather than make isolated syntax changes ad nauseam.This PR also includes relevant lifecycle updates from previous stuff, so if any fixup commits are pushed on top, a selective squash should be done to preserve that history (no github merge strategies). Or, we could make a separate PR for the lifecycle change, then I'll rebase this onto the new master.