pkg/endpoint: make state synchronization atomic #32439
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BPF regeneration writes state into a new temporary directory. Once it has succeeded we need to swap the old and new directory. This is currently achieved by "backing up" the current state by renaming the directory. This code has a bunch of corner cases around cleaning up old directories and so on which are necessary since the synchronization isn't truly atomic. Instead, use the RENAME_EXCHANGE flag to atomically exchange the two existing directories. Also use hard links to retain existing state so that killing the agent during a synchronization doesn't lead to corruption. Signed-off-by: Lorenz Bauer <[email protected]>
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Endpoint regeneration goes to a lot of trouble to keep track of whether the on-disk state has changed, only to avoid doing a couple of readdir syscalls. The behaviour was added in commit f6c4385 ("pkg/endpoint: Keep BPF object files if compilation is skipped.") and the message does not indicate that performance was of particular concern. Do the safe thing and always perform the state copy. Signed-off-by: Lorenz Bauer <[email protected]>
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pkg/endpoint: make state synchronization atomic
pkg/endpoint: always copy existing state during synchronization
This is a pre-requisite to a large PR in which I'm reshuffling how the loader does Endpoint templating. The second commit in this PR makes that easier.