On Fri, May 10, 2024 at 04:21:28AM GMT, Valerii Chernous wrote:
Cc: xe-linux-external@xxxxxxxxx Cc: Valerii Chernous <vchernou@xxxxxxxxx> Signed-off-by: Valerii Chernous <vchernou@xxxxxxxxx> --- 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
well... this kind of explains the what, but still no clue on why. If multiple different modules are providing the same symbol, then they are doing things wrong. If there are multiple variants of the same module (again, is this about external modules?), then I see no advantage to delay the decisions from depmod-time to modprobe-time. Just setup your depmod.d configuration. Also end users have not visibility on a README.deps.alternatives.txt file. Documentation in kmod is kept on man pages. Lucas De Marchi
-- 2.35.6
