[MODALTS v0.1 4/4] add modules deps alternatives description

[Valerii Chernous <vchernou@cisco.com>]

Cc: xe-linux-external@cisco.com
Cc: Valerii Chernous <vchernou@cisco.com>
Signed-off-by: Valerii Chernous <vchernou@cisco.com>
---
 README.deps.alternatives.txt | 40 ++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 README.deps.alternatives.txt

diff --git a/README.deps.alternatives.txt b/README.deps.alternatives.txt
new file mode 100644
index 0000000..9ad3ce5
--- /dev/null
+++ b/README.deps.alternatives.txt
@@ -0,0 +1,40 @@
+Modules alternatives feature allow to calculate dependency alternatives
+during build time and aviod to regenerate modules db into runtime
+
+To enable deps alternatives calculation use "-D" flag with depmod,
+it will create indexes modules.alternatives and modules.alternatives.bin
+This indexes will be used by modprobe in runtime
+By default modprobe will load first(primary/major) dependency from list
+If it required to load alternative module, it should be done manually before
+loading main modules set.
+For example systemd service that detect platform type can load required platform
+modules and after it run main device initialization
+In case when alternative module loaded, modprobe detect this and skip to load primary
+dependency
+
+modules deps alternatives generation basic algorithm description
+1. Load modules information(imported/exported symbols)
+2. Find depended symbol alternatives(create list available symbols
+   alternatives instead of storing last one)
+3. Choise primary/major alternative per depended symbol correspond to
+   build time dependency(build time deps getting from module info section)
+4. Create a list of dependency modules alternatives correspond to next rule:
+4.1 All modules alternatives for module dependency should provide all symbols
+    from primary/major dependency module
+5 Store modules alternatives index(modules.alternatives) as key:value where
+key is a pair depended#_#primary_depency,
+value is list of all modules that provide all symbols from primary_depency
+for depended module
+
+Note:
+Current implementation/algorithm doesn't cover variant where requred symbols
+from primary deps provided by more that one modules. Exporting all symbols in
+alternative depency that used by depended module from primary_depency is
+mandatory!
+
+Note:
+modules.dep index different for standard/basic and modules alternatives algorithms
+modules.dep for modules alternatives algorithm contain only direct dependencies and
+full dependency list will be calculated into runtime correspond to preferred alternative.
+modules.dep for standard/basic algorithm contain full dependency list for module and
+can't be changed during runtime without rebuild database via depmod
-- 
2.35.6