For information about the C library API, it is recommended to consult the documentation that ships with the library installation on your development machine. On a Fedora / RHEL distro, this will typically be found in the following directory (once the ‘libosinfo-devel’ RPM is installed):

/usr/share/gtk-doc/html/Libosinfo/index.html

This is directly viewable in a web browser, but if running the GNOME desktop, can also be accessed by launching the ‘devhelp‘ program from your shell / desktop and selecting the Libosinfo library.

For those wishing to access the Libosinfo API from Python, there are some online docs that are generated from the GObject Introspection metadata:

http://lazka.github.io/pgi-docs/#Libosinfo-1.0

Finally, the raw introspection data and or C headers files can also be browsed to see what APIs are exposed from the C library

/usr/share/gir-1.0/Libosinfo-1.0.gir
/usr/include/libosinfo-1.0/