Add trace level log support in containerd.

[Random-Liu]

Description

logrus doesn't support trace. But it is useful in general containerd/cri#548.

In https://github.com/containerd/cri-containerd/pull/547/files#diff-1135f265d25e96e557b8114567653176 we added the library to support Trace in cri-containerd.

Can we have this library in containerd? Or can we at least accept trace in log-level flag?

Steps to reproduce the issue:
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Describe the results you received:

Describe the results you expected:

Output of containerd --version:

(paste your output here)

[crosbymichael]

Why not just use debug level instead of adding more levels. we already have fatal, error, warn, info, and debug. I think we can find an existing one

[Random-Liu]

Here is our use case:

• One log level for normal production log output (corresponds to logrus info)
• One log level for test environment output (corresponds to logrus debug)
• One log level for actual debug, we don't want to log this in test environment, because they are too spammy. But we do want to be able to turn on those logs when we actually see a problem and try to debug. (corresponds to what? I think this is where trace is useful.)

Is there any other way to solve this? Or shouldn't we add "trace level" logs?

[crosbymichael]

So trace is a level below debug?

[mlaventure]

@crosbymichael that's how it is treated in other logging library. Usually the expectation is that that level will log every entry and exit within a function.

[crosbymichael]

ok, sounds good to me.

@stevvooe any thoughts ?

[stevvooe]

@crosbymichael Do we want to upstream the TraceLevel?

[crosbymichael]

That would be ideal

[Random-Liu]

@stevvooe This was proposed several times in logrus:

• Custom Log Levels sirupsen/logrus#463
• Add Trace level logging sirupsen/logrus#629
• Trace log level sirupsen/logrus#663

Even several PRs:

• Add trace log level  sirupsen/logrus#198
• Trace Support sirupsen/logrus#284
• Re-incorporating the trace logging originally written by Sean Berry. sirupsen/logrus#516
• Add Trace level logging sirupsen/logrus#643
• Add TRACE level logging. sirupsen/logrus#652

I just don't understand why they don't want it...

[stevvooe]

@Random-Liu I am a maintainer there...

I think the problem with sirupsen/logrus#652 is that it is not backwards compatible for those using the interface to define a logger type. I'll LGTM it and see if that is a concern.