[This is a revision of http://lkml.org/lkml/2009/11/2/442 ] This patch series implements support for building, loading, and unloading subsystems as modules, both within and outside the kernel source tree. It provides an interface cgroup_load_subsys() and cgroup_unload_subsys() which modular subsystems can use to register and depart during runtime. The net_cls classifier subsystem serves as the example for a subsystem which can be converted into a module using these changes. Additionally, support for subsystem dependencies is implemented with the new modular subsystem scenario in mind. Patch #1 sets up the subsys[] array so its contents can be dynamic as modules appear and (eventually) disappear. I introduce an rwsem called subsys_mutex to protect against concurrent loads/unloads/reads, and modify iterations over the array to handle when subsystems are absent. Patch #2 implements an interface for modules to load subsystems, called cgroup_load_subsys, similar to cgroup_init_subsys, and adds a module pointer in struct cgroup_subsys. Patch #3 modifies the net_cls subsystem, which already had some module declarations, to be configurable as a module, which also serves as a simple proof-of-concept. Patch #4 adds a mechanism for unloading modular subsystems, which includes a more advanced rework of the rudimentary reference counting introduced in patch 2. It also modifies the exitcall of net_cls to use this interface. Patch #5 implements support for subsystems to specify dependencies on other subsystems. It requires the subsystem to give a list of its dependencies in the form of a NULL-terminated array of strings, each being the name of a depended-upon subsystem, for reasons explained in the patch itself. Part of implementing patches 2 and 4 involved updating css pointers in each css_set when the module appears or leaves. In doing this, it was discovered that css_sets always remain linked to the dummy cgroup, regardless of whether or not any subsystems are actually bound to it (i.e., not mounted on an actual hierarchy). The subsystem loading and unloading code therefore should keep in mind the special cases where the added subsystem is the only one in the dummy cgroup (and therefore all css_sets need to be linked back into it) and where the removed subsys was the only one in the dummy cgroup (and therefore all css_sets should be unlinked from it) - however, as all css_sets always stay attached to the dummy cgroup anyway, these cases are ignored. Any fix that addresses this issue should also make sure these cases are addressed in the subsystem loading and unloading code. -- bblum _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers