Matthew Wilcox from Oracle, known for creating the nvme driver (NVM Express) and the mechanism for direct access to the DAX FS, suggested removing the ReiserFS file system from the Linux kernel, similar to the once removed obsolete ext and xiafs FS, or shortening the code ReiserFS, leaving only read-only support.
The reason for the removal was additional difficulties with upgrading the kernel infrastructure, caused by the fact that specifically for ReiserFS, developers are forced to leave the deprecated AOP_FLAG_CONT_EXPAND flag handler in the kernel, since ReiserFS remains the only file system that uses this flag in the write_begin function. At the same time, the last fix in the ReiserFS code is dated 2019, and it is not clear how much this FS is in demand at all and whether they continue to use it.
Jan KΓ‘ra of SUSE agreed that ReiserFS is on its way to obsolescence, but it's unclear if it's obsolete enough to be removed from the kernel. According to Jan, ReiserFS continues to ship with openSUSE and SLES, but the user base for the filesystem is small and shrinking. For enterprise users, ReiserFS support in SUSE was discontinued 3-4 years ago, and the ReiserFS module is not bundled with the kernel by default. As an option, Ian suggested that we start displaying a deprecation warning when mounting ReiserFS partitions and consider this file system ready for removal if no one will let us know about the desire to continue using this file system within a year or two.
Eduard Shishkin, who maintains the ReiserFS file system, joined the discussion and provided a patch that removes the use of the AOP_FLAG_CONT_EXPAND flag from the ReiserFS code. Matthew Wilcox accepted the patch into his branch. Thus, the reason for the removal has been eliminated, and the issue of excluding ReiserFS from the kernel can be considered postponed for quite a long time.
It will not be possible to completely discard the issue of obsolescence of ReiserFS due to the work on the exclusion from the kernel of file systems with an unresolved problem of 2038. For example, for this reason, a schedule has already been prepared for removing the fourth version of the XFS file system format from the kernel (the new XFS format was proposed in the 5.10 kernel and shifted the time counter overflow to 2468). XFS v4 build will be disabled by default in 2025 and code removed in 2030). A similar schedule is proposed for ReiserFS, providing at least five years for migration to other file systems or a modified metadata format.
Source: opennet.ru