ocaml-unix-errno provides
an errno variant similar to Unix.error but including POSIX 2008,
Linux, OS X, and FreeBSD constructors. A macro definition type, defns
is also provided in order to transport a specific errno-integer map as
is the case with FUSE or 9p2000.u. The types and their functions reside
in Errno and are independent of any Unix bindings. This makes the
library's types usable from MirageOS on top of Xen. Errno_unix
provides maps to and from Unix.error, the present host's errno map, an
errno exception Error, and higher-order errno checking functions.

The executable errno-map will output a tab-delimited map from errno
macro name to integer. This map can then be read back using the function
Errno.defns_of_string.