3. In-memory File System

A virtual in-memory file system is made available to ZeroVM by the ZeroVM RunTime environment (ZRT). Writes which occur at runtime are completely thrown away. The only way to persistently write data is to map a file in the virtual file system to a file or other device on the host operating system. This is accomplished by the use of channels.

Arbitrary file hierarchies can be loaded into a ZeroVM instance by mounting tar archives as disk images. This is necessary particularly in the case of the ZeroVM Python interpreter port, which requires not only a cross-compiled Python interpreter executable but also the Python standard library packages and modules; these files must accessible for Python programs to run inside ZeroVM. Any tarball can be mounted to the virtual file system, and multiple images can be mounted simultaneously. Each tarball is mounted by defining a channel, just as with any other file. (Note that there is a limit <zerovm-manifest-channel-max> to the number of channels per instance.)