rc-local-generator: add comment explaining the background of the generator

This is not obvious, hence it deserves some form of documentation.
However, it's also ultimately an implementation detail, hence let's not
add this to the man page, but as a code comment, that is visible right
at the top of source file.

Fixes: #10675

diff --git a/src/rc-local-generator/rc-local-generator.c b/src/rc-local-generator/rc-local-generator.c
index 44b2edec05de933e208a19f8ac362e189c2f47d9..ba5e336a34f615a87cf4c9bfe4efd49396a56924 100644 (file)
--- a/src/rc-local-generator/rc-local-generator.c
+++ b/src/rc-local-generator/rc-local-generator.c
@@ -11,6 +11,12 @@
 
 static const char *arg_dest = "/tmp";
 
+/* So you are reading this, and might wonder: why is this implemented as a generator rather than as a plain, statically
+ * enabled service that carries appropriate ConditionFileIsExecutable= lines? The answer is this: conditions bypass
+ * execution of a service's binary, but they have no influence on unit dependencies. Thus, a service that is
+ * conditioned out will still act as synchronization point in the dependency tree, and we'd rather not have that for
+ * these two legacy scripts. */
+
 static int add_symlink(const char *service, const char *where) {
         const char *from, *to;
         int r;