  We introduce the Software Heritage filesystem (SwhFS), a user-space
filesystem that integrates large-scale open source software archival with
development workflows. SwhFS provides a POSIX filesystem view of Software
Heritage, the largest public archive of software source code and version
control system (VCS) development history.Using SwhFS, developers can quickly
"checkout" any of the 2 billion commits archived by Software Heritage, even
after they disappear from their previous known location and without incurring
the performance cost of repository cloning. SwhFS works across unrelated
repositories and different VCS technologies. Other source code artifacts
archived by Software Heritage-individual source code files and trees, releases,
and branches-can also be accessed using common programming tools and custom
scripts, as if they were locally available.A screencast of SwhFS is available
online at dx.doi.org/10.5281/zenodo.4531411.
