It has been seen that for some network mac drivers (i.e. lan78xx) the related module for the phy is loaded dynamically depending on the current hardware. In this case, the associated phy is read using mdio bus and then the associated phy module is loaded during runtime (kernel function phy_request_driver_module). However, no software dependency is defined, so the user tools will no be able to get this dependency. For example, if dracut is used and the hardware is present, lan78xx will be included but no phy module will be added, and in the next restart the device will not work from boot because no related phy will be found during initramfs stage. In order to solve this, we could define a normal 'pre' software dependency in lan78xx module with all the possible phy modules (there may be some), but proceeding in that way, all the possible phy modules would be loaded while only one is necessary. The idea is to create a new type of dependency, that we are going to call 'weak' to be used only by the user tools that need to detect this situation. In that way, for example, dracut could check the 'weak' dependency of the modules involved in order to install these dependencies in initramfs too. That is, for the commented lan78xx module, defining the 'weak' dependency with the possible phy modules list, only the necessary phy would be loaded on demand keeping the same behavior, but all the possible phy modules would be available from initramfs. The 'weak' dependency support has been included in kmod: https://github.com/kmod-project/kmod/commit/05828b4a6e9327a63ef94df544a042b5e9ce4fe7 But, take into account that this can only be used if depmod is new enough. If it isn't, depmod will have the same behavior as always (keeping backward compatibility) and the information for the 'weak' dependency will not be provided. Signed-off-by: Jose Ignacio Tornos Martinez <jtornosm@xxxxxxxxxx> --- V2 -> V3: - Include note about backward compatibility. - Balance the /* and */. V1 -> V2: - Include reference to 'weak' dependency support in kmod. include/linux/module.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/linux/module.h b/include/linux/module.h index 1153b0d99a80..2a056017df5b 100644 --- a/include/linux/module.h +++ b/include/linux/module.h @@ -173,6 +173,12 @@ extern void cleanup_module(void); */ #define MODULE_SOFTDEP(_softdep) MODULE_INFO(softdep, _softdep) +/* + * Weak module dependencies. See man modprobe.d for details. + * Example: MODULE_WEAKDEP("module-foo") + */ +#define MODULE_WEAKDEP(_weakdep) MODULE_INFO(weakdep, _weakdep) + /* * MODULE_FILE is used for generating modules.builtin * So, make it no-op when this is being built as a module -- 2.44.0
