Cc: [email protected] Cc: Valerii Chernous <[email protected]> Signed-off-by: Valerii Chernous <[email protected]> --- 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
