libkmod: expand the deprecated/0xB007FA57 comment

Provide a summary how the magic and version fields have evolved. It
serves as better reference than the current "deprecated versions" note.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://github.com/kmod-project/kmod/pull/256
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>

diff --git a/libkmod/libkmod-index.c b/libkmod/libkmod-index.c
index 19d4cc3f1feef21d5cf7a900afbcf0aa5bde14e5..40199a54d699a5b44fbe406364411d017f114214 100644 (file)
--- a/libkmod/libkmod-index.c
+++ b/libkmod/libkmod-index.c
@@ -27,7 +27,13 @@
  * Integers are stored as 32 bit unsigned in "network" order, i.e. MSB first.
  * All files start with a magic number.
  *
- * Magic spells "BOOTFAST". Deprecated versions encoded it as 0xB007FA57.
+ * Magic spells "BOOTFAST", where the exact encoding varies across versions.
+ *
+ * The original implementation in modutils/module-init-tools used 0xB007FA57, but also
+ * lacked the version fields. Thus later on, with module-init-tools commit 44d7ac4
+ * ("add versioning to the binary module files"), the encoding was changed to 0xB007F457
+ * (A -> 4) and the version fields were introduced. Shortly afterwards the format was
+ * changed in backwards incompatible way and the major version was bumped to 2.
  *
  * We use a version string to keep track of changes to the binary format.
  * This is stored in the form: INDEX_MAJOR (hi) INDEX_MINOR (lo) just in