README for packagers of libfaketime

First, thank you for your efforts to make libfaketime packages available
on your platform / distribution!

libfaketime has tagged releases about once every 1-2 years, made available
through github.com/wolfcw/libfaketime, but usually it is also safe (i.e.,
stable) to use the latest HEAD of the master branch, which contains bug
fixes since the last tagged release.

You may want to familiarize yourself with the options you can set into
src/Makefile, but sane defaults for stable operations have been chosen.

Currently, libfaketime does not use autotools yet, so there is
_no_ ./configure step, but "make" and "make test" will work as expected.

For "make test", an optional environment variable FAKETIME_TESTLIB can
be set, pointing to the path and filename of the libfaketime library
to be used for tests; the default is "../src/libfaketime.so.1".


However, one problem makes it somewhat difficult to get libfaketime
working on different platforms:

libfaketime currently has the challenge that depending on the version
of glibc and the platform (e.g., x86_64 or aarch64) certain compiler
CFLAGS have to be set manually, as we have not yet found a way to
safely determine behavior at run-time automatically.

Please proceed as follows:

- run "make test". If everything runs through smoothly and you do not
  encounter any hangs or test failure reports, use the binaries as
  they are.

- If you encounter endless hangs during the CLOCK_REALTIME test,
  add -DFORCE_PTHREAD_NONVER to the CFLAGS.

- If you encounter endless hangs during the CLOCK_MONOTONIC test,
  add -DFORCE_MONOTONIC_FIX to the CFLAGS. If it works with that,
  it's fine, otherwise additionally use -DFORCE_PTHREAD_NONVER.

CFLAGS can also be passed through the FAKETIME_COMPILE_CFLAGS environment
variable, so for example

  FAKETIME_COMPILE_CFLAGS="-DFORCE_PTHREAD_NONVER" make test

would create the libfaketime binaries and run the tests with the
FORCE_PTHREAD_NONVER flag set in a single step. Likewise there is
FAKETIME_LINK_FLAGS.

Please do not use FORCE_MONOTONIC_FIX by default, as it would result
in incorrect operations on platforms that do not need it.

Our observations with a limited number of Linux distributions is that
libfaketime may require different compile flags per platform even
if the same distribution and glibc version is used across these
platforms.

As soon as we have found a reliable way to automatically choose the
correct compile-time flags, we will remove this burden from you as
packager for obvious reasons. Until then, please feel free to report
your experiences with different platforms and distribution versions
through the issue tracker on Github.

Again, thanks for your time and effort to make libfaketime available
easily for everyone else!