podman events duplicates events after rotation

[mgjm]

Issue Description

When the libpod events file gets rotated in libpod/events/logfile.go, the log file gets truncated by discarding the older half of all events.

But the podman events command reads all events again after a log rotation has occurred.

Therefore, the newer half of the logs (which is not discarded) is printed again.

Steps to reproduce the issue

Steps to reproduce the issue

1. Set events_logfile_max_size = "4k" in the [engine] section in the containers.conf file
2. Watch the events with podman events
3. In another terminal: Generate some events (e.g. podman run --rm hello-world)

Describe the results you received

After the second or third podman run invocation, the file gets rotated and some events, which have already been printed, get printed again.

Describe the results you expected

Each event should be printed exactly once. Even after rotating the events file.

podman info output

podman version 4.3.1, alpine 3.17, x86_64

Podman in a container

No

Privileged Or Rootless

None

Upstream Latest Release

No

Additional environment details

No response

Additional information

No response

[Luap99]

@vrothberg PTAL

[vrothberg]

I started working on it and found a solution. Writing tests at this moment.

[mgjm]

@vrothberg Awesome, I know it's still a WIP, but just a heads up: the inode number doesn't have to change, if the file isn't renamed, there's os.Create as a fallback, so it just truncates the existing file.

[vrothberg]

@vrothberg Awesome, I know it's still a WIP, but just a heads up: the inode number doesn't have to change, if the file isn't renamed, there's os.Create as a fallback, so it just truncates the existing file.

Thanks for checking, @mgjm!

What's happening during rotation is that a new tempfile is created with the rotated content. Then it's getting renamed to the previous path.

After that, the inode number of the previous path should be changed, shouldn't it?

[vrothberg]

Rename logic can be found here https://github.com/containers/podman/blob/main/libpod/events/logfile.go#L239

[mgjm]

That's the normal operation, but if the temp file is created in a different file system there is a fallback to use os.Create:
libpod/events/logfile.go#L329-L353

[vrothberg]

Nice catch, thank you! Note that I will be largely out of office next week; just in case you wonder about the progress.