RFR: 8272554: Add help message about the named pipe support of UL.

[David Holmes]

On Fri, 20 Aug 2021 22:52:05 GMT, Xin Liu <xliu at openjdk.org> wrote:

> This patch adds a help message about the named pipe support of the Unified Logging to -Xlog:help and manpage.
> 
> For -Xlog:help, here is the new help message:
> 
> Available log outputs:
>  stdout/stderr
>  file=<filename>
>   If the filename contains %p and/or %t, they will expand to the JVM's PID and startup timestamp, respectively. The filename can be a named pipe when log rotation is disabled.  
> 
> 
> Here is the new manpage content.
> 
>  When using file=filename, specifying %p and/or %t in the file name expands to the JVM's PID and startup timestamp, respectively.  You can also configure text files to handle file rotation based on file size and a number of files to rotate.  For example, to rotate the log file every 10 MB and  keep  5
>  files  in rotation, specify the options filesize=10M, filecount=5.  The target size of the files isn't guaranteed to be exact, it's just an approximate value.  Files are rotated by default with up to 5 rotated files of target size 20 MB, unless configured otherwise.  Specifying filecount=0 means that
>  the log file shouldn't be rotated.  The filename can be a named pipe when log rotation is disabled.  There's a possibility of the pre-existing log file getting overwritten.

Hi Xin,

I'm opening up the discussion to hotspot-dev as all the teams use UL. I'm not at all sure this is the right way to introduce the ability to use named pipes here. I'd probably prefer to see something under the "file=" section to expand on what kinds of "file" are supported; then the other sections would list any constraints in relation to the different kinds of "file".

The problem with any kind of documentation change like this is that when people examine the documentation they always tend to find more problems with it, and containing the scope of the change can be a challenge.

Thanks,
David

-------------

PR: https://git.openjdk.java.net/jdk/pull/5205