Linux 5.18's NFSD Adds Support For NFSv4 Birth Time File Attribute

Chuck Lever III has submitted the NFSD file-system server changes for the in-development Linux 5.18 kernel with a few interesting changes in tow.

First up with the NFSD changes for Linux 5.18 is support for the NFSv4 birth time file attribute. The "birth time" file attribute with NFSv4 is for exposing the file creation time. This NFSD support will work atop modern Linux file-systems supporting the statx "btime" timestamp for exposing file creation time rather than only the time the file was last modified.

This has been made possible on Linux since a few years ago with the statx system call for being able to expose more file attributes. Most Linux file-systems these days can now support the file creation time attribute and has also been seeing support for making use of that extended metadata by Linux user-space. Now with Linux 5.18, NFSD will expose the NFSv4 "birth time" when on a supported file-system.

The Linux NFS client code has already supported making use of this NFSv4 attribute when exposed from the server.

In addition to the birth time file attribute, Linux 5.18 makes NFSD always build NFSv3 support unconditionally. Linux to this point has always made NFSv2 unconditional and then spinning NFSv3 out as a build option with CONFIG_NFSD_V3. But with plans to eventually deprecate NFSv2 and remove that code later, the developers are now making NFSv3 "always supported" to help in easing that eventual transition.

NFSD for Linux 5.18 also has some performance optimizations and other improvements. See this pull request for the details with these patches that have already landed into mainline.