Link phosphor-hostlogger and bmcweb

[Artem Senichev]

On Tue, May 25, 2021 at 11:51:44PM -0700, Nan Zhou wrote:
> > > 3. zlib_file.xpp, zlib_exception.xpp:
> > > will be removed or slightly changed; we can potentially use the linux
> > > logrotate which has built-in compression and file rotation (in this case
> > > these compression utilities will be removed).
> > > The latest log file isn't compressed any more. History log files are
> > > still compressed.
> > Just curious, how are you going to remove the oldest messages from the
> > latest file in runtime? You are not going to rewrite the entire file on
> > every input character, are you?
> 
> The following is my current idea: we will rename the latest file to
> something else and notify the writer (hostlogger) to close its old file
> descriptor and open a new one (should be doable via linux logrotate and
> inotify or some signal handlers, as logrotate is able to send some signals
> to hostlogger if a rotation is performed). The writer keeps appending logs
> most of the time using the same fd unless the latest file is rotated. This
> should be better than truncating the file where the reader (BMCWeb) won't
> have race conditions (it might read old snapshots but it is not a big deal
> in our case).

Currently we can keep the last N lines of the host's output, the oldest
messages are removed. It is easy to implement with a buffer in memory.
But how are you going to get rid of the old lines if you write data directly
to the log file?
Rotation will not help you with that (we actually don't need to store such old
logs).

-- 
Regards,
Artem Senichev
Software Engineer, YADRO.