Log package: support logging to file

[caitong93]

/kind feature

[kdada]

Please implement it and file a PR.

[gaocegege]

Hi, I am a student from Shanghai Jiao Tong University and will be a Caiclouder in the next year. I am interested in the project :-) I am glad to implement the feature as my first contribution when I am free in the next month.

While, I have a question about our logger package. There are many libraries about loggers then I am not sure why we implemented the std logger on our own. Is there any thing I missed about it? I'd appreciate it if you could resolve my doubts.

[kdada]

Actually the biggest problem is there are so many log libraries. So we implement a common log interface (glog-like) to constraint our codes. Then you can replace the implementation of logger with any other packages which you like.

In the other hand, Nirvana should have its own log packages for common usages. e.g. std, file.

[kdada]

@gaocegege go ahead. You can write your design doc in this issue.

[volgariver6]

@gaocegege hello，what is the status of this issue?

[kdada]

@lauber00 There is no implementation of file logger now. If you could implement it, we'll very appreciate it.

[gaocegege]

/assign