RFR: 8343417: (fs) BasicFileAttributeView.setTimes uses microsecond precision with NOFOLLOW_LINKS [v2]

[Brian Burkhalter]

On Tue, 5 Nov 2024 18:39:09 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8343417: Make Java method utimensat() signature match that of the corresponding system call
>
> src/java.base/unix/classes/sun/nio/fs/UnixFileAttributeViews.java line 88:
> 
>> 86:                         useLutimes = lutimesSupported();
>> 87:                 }
>> 88:                 if (!useUtimensat && !useLutimes) {
> 
> Changing the utimesat method to match the sys call is good. Now I wonder if we go further and use fd from openForAttribtueAccess(false) with utimesat. That would remove the window between the lstat and  utimesat(AT_FDCWD...) where the file may be replaced.

Indeed UnixFileAttributes.get calls lstat. Calling symlink.openForAttributeAccess(false) however yields

java.nio.file.FileSystemException: symlink: No such file or directory or unable to access attributes of symbolic link

According to [symlink(7)](https://www.man7.org/linux/man-pages/man7/symlink.7.html):

The last access and last modification timestamps of a symbolic link can be changed using utimensat(2) or lutimes(3).

It looks like futimens will not work with a symlink's fd so that utimensat is necessary here to obtain nsec precision. I don't see a way to close the window between lstat and utimensat, which anyway was already there for the lutimes case.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21886#discussion_r1829937573