Added submodule contents into tree

externals/breakpad/docs/linux_core_handler.md

@@ -0,0 +1,39 @@
+# How To Use Breakpad As a Coredump Handler on Linux
+
+This document presents a way to use Breakpad in order to generate
+minidumps system wide on Linux.
+
+Please refer to [Linux starter guide](./linux_starter_guide.md) if
+instead you want to integrate breakpad into your application.
+
+## Motivation
+
+When working on an embedded system, disk and memory space is often
+limited and when a process crashes it must be restarted as soon as
+possible. Sometime saving a full coredump takes to much time or
+consumes too much space.
+
+## Breakpad Core Handler
+
+In such case the program `core_handler` can be use to generate
+minidumps instead of coredumps. `core_handler` reads the firsts
+sections of the coredump (where the various threads are described)
+generated by Linux from the standard input and then directly reads
+`/proc/<pid>/mem` to reconstruct the stacktraces.
+
+One can test it with:
+
+```
+# echo "|/usr/libexec/core_handler %P /var/lib/minidump/%e-%i.md" >
+                /proc/sys/kernel/core_pattern
+# echo 1 > /proc/sys/kernel/core_pipe_limit
+```
+
+Be aware that a real world integration would likely require further
+customization and so `core_handler` can be wrapped into a script (for
+example to change the permission of the minidump file or to signal the
+presence of the minidump to another service).
+
+Please refer to
+[core(5)](https://man7.org/linux/man-pages/man5/core.5.html) for more
+details.