RFR: 8298730: Refactor subsystem_file_line_contents and add docs and tests [v2]

[Johan Sjölen]

On Wed, 14 Dec 2022 13:56:33 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> test/hotspot/gtest/os/linux/test_cgroupSubsystem_linux.cpp line 137:
>> 
>>> 135:   err = subsystem_file_line_contents(&my_controller, test_file, "foo", "%s", &s);
>>> 136:   EXPECT_EQ(err, 0);
>>> 137:   EXPECT_STREQ(s, "1");
>> 
>> We should have a test where the separator isn't a single space, like `\t` instead. See https://github.com/jerboaa/jdk/commit/8ab1009a18a95510504f70d8a02c822083fdffd1 That's when those tests currently fail. Like I said previously it would also be good to have a test similar to how `CgroupV2Subsystem::cpu_period()` uses it. Like 
>> https://github.com/jerboaa/jdk/commit/4d562f08952e17f9137c0da74a3bb587c8539713
>
> I realize you wanted to include this as a separate RFE, but it doesn't make much sense as those additional case are (to me) the bare minimum to have in order to ensure we don't regress.

I absolutely think that these sorts of test can be added in this RFE, I didn't respond because I wanted clarity in the question of handling tabs or not first.

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PR: https://git.openjdk.org/jdk/pull/11667