Emergency patching of OTP modules

The purpose of this directory is to hold patches for OTP modules. The patch files are generated using git diff, e.g.

Usage

git diff OTP-20.1 -- lib/mnesia/src/mnesia_index.erl > $OTP_PATCHES/20.1/mnesia_index.erl.patch

Patch files are stored in version-specific subdirectories. In each such subdirectory, a versions.eterm file contains patterns identifying which OTP application versions are compatible with the patches.

The versions.eterm file is read with file:consult/1, and shall contain {AppName, BaseNameRegexp} tuples. For example:

{mnesia, "mnesia-4\\.15\\.[123]"}.

which matches mnesia versions "4.15.1", "4.15.2" and "4.15.3".

The compile script will test each subdirectory, and pick the first one for which all application patterns match. It will then copy the relevant source files from the current OTP to the otp_patches directory, apply the patches and compile the result into otp_patches/ebin. This directory will then be copied into the release and pre-pended to the code path of the system.

rebar3 hook

In the rebar.config file, the patch compilation can be specified as a pre_hook, e.g.

{pre_hooks, [{compile, "escript ./otp_patches/compile.escript"},
             ...]}.

Compile options

Currently, files are compiled with debug_info and include paths to thesrc/ and include/ directories of the source file's application. More compile options, and support for specifying options per-application or per-module may have to be added later.