RFR: 8327410: Add hostname option for UL file names [v3]

[David Holmes]

On Fri, 8 Mar 2024 15:26:21 GMT, Fredrik Bredberg <fbredberg at openjdk.org> wrote:

>> Added %hn as way to make the Unified Logging file name include the host name.
>> This is done in line with the already existing %p for pid, and %t for time stamp.
>> 
>> Also the %hn decorator is already used to prepend the host name to each log line. See: The [JDK-8148219](https://bugs.openjdk.org/browse/JDK-8148219).
>> 
>> Example: `java -Xlog:gc+init:file=frbr_%hn.%p.%t.log -version`
>> 
>> Tested tier1-tier5.
>
> Fredrik Bredberg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update after review

src/hotspot/share/logging/logFileOutput.cpp line 400:

> 398:   if (pid != nullptr) {
> 399:     result_len -= strlen(PidFilenamePlaceholder);
> 400:     result_len += strlen(pid_string);

We should cache the `strlen` values here and elsewhere so that we don't have to keep recalculating it when doing the actual `strcmp` and `strcpy` later on.

src/hotspot/share/logging/logFileOutput.cpp line 408:

> 406:   if (hostname != nullptr) {
> 407:     if (!os::get_host_name(hostname_string, sizeof(hostname_string))) {
> 408:       int res = jio_snprintf(hostname_string, sizeof(hostname_string), "%s", HostnameFilenamePlaceholder);

This seems overkill just to write `%hn` into `hostname_string`. And on error shouldn't we just replace the `%hn` with e.g. `unknown-host`?

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

PR Review Comment: https://git.openjdk.org/jdk/pull/18153#discussion_r1520889582
PR Review Comment: https://git.openjdk.org/jdk/pull/18153#discussion_r1520886154