Filesystem API

A file system API is an application programming interface through which a utility or user program requests services of a file system. An operating system may provide abstractions for accessing different file systems transparently.

Some file system APIs may also include interfaces for maintenance operations, such as creating or initializing a file system, verifying the file system for integrity, and defragmentation.

Each operating system includes the APIs needed for the file systems it supports. Microsoft Windows has file system APIs for NTFS and several FAT file systems. Linux systems can include APIs for ext2, ext3, ReiserFS, and Btrfs to name a few.

Some early operating systems were capable of handling only tape and disk file systems. These provided the most basic of interfaces with:

More coordination such as device allocation and deallocation required the addition of:

As file systems provided more services, more interfaces were defined:

As additional file system types, hierarchy structure and supported media increased, additional features needed some specialized functions:

Multi-user systems required APIs for:

Writing user data to a file system is provided for use directly by the user program or the run-time library. The run-time library for some programming languages may provide type conversion, formatting and blocking. Some file systems provide identification of records by key and may include re-writing an existing record. This operation is sometimes called PUT or PUTX (if the record exists)

Reading user data, sometimes called GET, may include a direction (forward or reverse) or in the case of a keyed file system, a specific key. As with writing run-time libraries may intercede for the user program.

Positioning includes adjusting the location of the next record. This may include skipping forward or reverse as well as positioning to the beginning or end of the file.

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