RFR: 8338851: Hoist os::Posix::realpath() to os::realpath() and implement on Windows [v13]

[David Holmes]

On Fri, 20 Sep 2024 13:14:54 GMT, Simon Tooke <stooke at openjdk.org> wrote:

>> This PR changes the status of realpath() from a Posix-specific API to a globally available API, i.e. adding it to the "Hotspot Porting API".  Code would refer to os::realpath() instead of os::Posix::realpath().
>> 
>> This requires a Windows implementation of realpath(), using Windows _fullpath(), and renaming os::Posix::realpath() to os::realpath().
>> 
>> The main difference between POSIX and Windows behaviour is that POSIX actually requires an existing accessible file, while Windows will happily work with made-up filenames.
>> 
>> Please note that guidelines for doing this appear in src/hotspot/share/runtime/os.hpp
>
> Simon Tooke has updated the pull request incrementally with one additional commit since the last revision:
> 
>   delete commented out code

Changes requested by dholmes (Reviewer).

test/hotspot/gtest/runtime/test_os.cpp line 434:

> 432: #if defined(_WINDOWS)
> 433:   EXPECT_TRUE(returnedBuffer == buffer);
> 434:   EXPECT_TRUE(errno == 0);

I thought we concluded you cannot guarantee that errno==0 after a successful call?

test/hotspot/gtest/runtime/test_os.cpp line 442:

> 440:   errno = 0;
> 441:   returnedBuffer = os::realpath(tmppath, buffer, MAX_PATH);
> 442:   EXPECT_TRUE(returnedBuffer != nullptr);

Why the change?

test/hotspot/gtest/runtime/test_os.cpp line 452:

> 450:   EXPECT_TRUE(returnedBuffer == nullptr);
> 451:   EXPECT_TRUE(errno == ENAMETOOLONG);
> 452: #endif

I think it would be better to increase the buffer size on macOS so this remains a positive test for all platforms.

test/hotspot/gtest/runtime/test_os.cpp line 460:

> 458: 
> 459:   /* the following tests cause an assert in fastdebug mode */
> 460:   DEBUG_ONLY(if (false)) {

Suggestion:

 #ifndef ASSERT

no need for a runtime check.

test/hotspot/gtest/runtime/test_os.cpp line 467:

> 465: 
> 466:     errno = 0;
> 467:     returnedBuffer = os::realpath(tmppath, buffer, sizeof(buffer));

This is still not an EINVAL case - the buffer should be null.
Suggestion:

    returnedBuffer = os::realpath(tmppath, nullptr, sizeof(buffer));

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

PR Review: https://git.openjdk.org/jdk/pull/20683#pullrequestreview-2321034429
PR Review Comment: https://git.openjdk.org/jdk/pull/20683#discussion_r1770713210
PR Review Comment: https://git.openjdk.org/jdk/pull/20683#discussion_r1770713938
PR Review Comment: https://git.openjdk.org/jdk/pull/20683#discussion_r1770716883
PR Review Comment: https://git.openjdk.org/jdk/pull/20683#discussion_r1770717314
PR Review Comment: https://git.openjdk.org/jdk/pull/20683#discussion_r1770717227