The design and implementation of the reiser4 file system
Many users like Linux not for its openness, stability and other important characteristics, but above all for its flexibility. In Linux, there is probably not a single component for which there does not exist an alternative. File systems are no exception... Today you will become acquainted with the reiser4 file system, this file system is written from scratch, although it inherited some features of its "ideological" predecessor – reiserfs.
As well as implementing the traditional Linux fs functions, reiser4 provides users with a number of additional features: transparent compression and encryption of files, full data journaling, as well as almost unlimited (with the help of plug-in architecture) extensibility, i.e. the ability to adapt to arbitrarily complex end user requirements.
In addition to the classic implementation of regular files (unix-file plugin), reiser4 offers another in which the file data is stored on disk in a compressed and (or) encrypted form (transparent compression/encryption). The cryptcompress plugin is responsible for this implementation. Its main idea is to perform compression and encryption immediately before flushing cached data to disk, while saving CPU resources in the case when the same data in memory is repeatedly modified by one or more processes. On modern machines equipped with fast processors and large amounts of RAM, data compression does not degrade, but on the contrary – increases the performance of the file system, because data conversion is performed relatively quickly, and the volume of disk traffic is reduced.
Each data transformation or conversion (compression, encryption, etc.) is performed by some algorithm that is present in reiser4 in the form of a corresponding plugin (the so-called transform plugin). It is worth noting the benefits of plug-in architecture, in which support for any desired compression or encryption algorithm is reduced to just writing and adding a standard plug-in of the appropriate type. Currently, transform-plugins are available for compression by the gzip1, lzo1, and Zstd (added on 2017-11-26) algorithms,...
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