File rotating handling testing / external modification handling

[Krisscut]

Hi !

For testing the file rotation, I used the dd command to artificially inflate the file size.
But I noticed despite that the file didn't rotate on next log being emitted.

Checking the code here:

supervisor/supervisor/loggers.py

Line 264 in 5732a41

if not (self.stream.tell() >= self.maxBytes):

I see it uses the tell function, but I guess it keeps the cursor at the location it emitted its previous log, without taking into account an eventual new log being written in the file externally.

What do you think of adding this for instance right before this check, so that we move the cursor at the end of the line ?

# Seek to end to ensure tell() reflects actual file size
# This handles cases where file was externally modified (e.g., with dd)
self.stream.seek(0, 2)  # SEEK_END

Thanks for reading me !

[justinpryzby]

Is there some reason to think that it's supported to write to the logfile from another tool ?
It seems to me that if you configure a logfile, supervisor owns that file, and editing the file outside of supervisor is a Bad Idea.
Maybe you're just interested in doing this to facilitate testing, in which case it's much easier to justify the patch (and +1 for better testing of log rotation).

[Krisscut]

Yes for my usecase this was indeed to facilitate testing of the configuration that I just did !