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

[David Holmes]

On Thu, 22 Aug 2024 18:36:39 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 the addition of a stub routine in os_posix.cpp and a Windows implementation of realpath(), using Windows _fullpath().
> 
> This PR depends on #20597 in that it removes the need for one #ifdef in that PR.  Because of that, this PR will be modified when and if #20597 is integrated.
> 
> Please note that guidelines for doing this appear in src/hotspot/share/runtime/os.hpp

This is okay in principle but a few changes can be made.

Also it seems that none of the callers of `realpath` ever check `errno` so I think that can be removed.

Thanks

src/hotspot/os/posix/os_posix.cpp line 896:

> 894: char* os::realpath(const char* filename, char* outbuf, size_t outbuflen) {
> 895:   return os::Posix::realpath(filename, outbuf, outbuflen);
> 896: }

We don't need `os::Posix::realpath` any more - just rename it to `os::realpath`.

src/hotspot/os/windows/os_windows.cpp line 5319:

> 5317: 
> 5318: char* os::realpath(const char* filename, char* outbuf, size_t outbuflen) {
> 5319:   return os::win32::realpath(filename, outbuf, outbuflen);

Again you don't need the indirection here.

src/hotspot/os/windows/os_windows.cpp line 5344:

> 5342:     // In this case, use the user provided buffer but at least check whether _fullpath caused
> 5343:     // a memory overwrite.
> 5344:     if (errno == EINVAL) {

There is nothing to indicate that `_fullpath` can ever set `EINVAL` it is only specified to return null on error. This code should not check errno but can just re-try with the user-supplied buffer.

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Changes requested by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20683#pullrequestreview-2267709458
PR Review Comment: https://git.openjdk.org/jdk/pull/20683#discussion_r1735587113
PR Review Comment: https://git.openjdk.org/jdk/pull/20683#discussion_r1735588758
PR Review Comment: https://git.openjdk.org/jdk/pull/20683#discussion_r1735593867