Add interface between cgroups subsystem management and module loading From: Ben Blum <[email protected]>
This patch implements rudimentary module-loading support for cgroups - namely, a cgroup_load_subsys (similar to cgroup_init_subsys) for use as a module initcall, and a struct module pointer in struct cgroup_subsys. Several functions that might be wanted by modules have had EXPORT_SYMBOL added to them, but it's unclear exactly which functions want it and which won't. Signed-off-by: Ben Blum <[email protected]> --- Documentation/cgroups/cgroups.txt | 3 + include/linux/cgroup.h | 4 + kernel/cgroup.c | 119 +++++++++++++++++++++++++++++++++++++ 3 files changed, 126 insertions(+), 0 deletions(-) diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt index 3df4b9a..dd0d6f1 100644 --- a/Documentation/cgroups/cgroups.txt +++ b/Documentation/cgroups/cgroups.txt @@ -492,6 +492,9 @@ Each subsystem should: - add an entry in linux/cgroup_subsys.h - define a cgroup_subsys object called <name>_subsys +If a subsystem can be compiled as a module, it should also have in its +module initcall a call to cgroup_load_subsys(). + Each subsystem may export the following methods. The only mandatory methods are create/destroy. Any others that are null are presumed to be successful no-ops. diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index d7f1545..c8474c4 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -38,6 +38,7 @@ extern void cgroup_fork_failed(struct task_struct *p, int run_callbacks, unsigned long clone_flags); extern int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry); +extern int cgroup_load_subsys(struct cgroup_subsys *ss); extern struct file_operations proc_cgroup_operations; @@ -477,6 +478,9 @@ struct cgroup_subsys { /* used when use_id == true */ struct idr idr; spinlock_t id_lock; + + /* should be defined only by modular subsystems */ + struct module *module; }; #define SUBSYS(_x) extern struct cgroup_subsys _x ## _subsys; diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 84448d0..858a786 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2492,6 +2492,7 @@ int cgroup_add_file(struct cgroup *cgrp, error = PTR_ERR(dentry); return error; } +EXPORT_SYMBOL_GPL(cgroup_add_file); int cgroup_add_files(struct cgroup *cgrp, struct cgroup_subsys *subsys, @@ -2506,6 +2507,7 @@ int cgroup_add_files(struct cgroup *cgrp, } return 0; } +EXPORT_SYMBOL_GPL(cgroup_add_files); /** * cgroup_task_count - count the number of tasks in a cgroup. @@ -3651,7 +3653,124 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss) mutex_init(&ss->hierarchy_mutex); lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key); ss->active = 1; + + /* this function shouldn't be used with modular subsystems, since they + * need to register a subsys_id, among other things */ + BUG_ON(ss->module); +} + +/** + * cgroup_load_subsys: load and register a modular subsystem at runtime + * @ss: the subsystem to load + * + * This function should be called in a modular subsystem's initcall. If the + * subsytem is built as a module, it will be assigned a new subsys_id and set + * up for use. If the subsystem is built-in anyway, work is delegated to the + * simpler cgroup_init_subsys. + */ +int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss) +{ + int i; + struct cgroup_subsys_state *css; + struct cg_cgroup_link *link; + + /* check name and function validity */ + if (ss->name == NULL || strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN || + ss->create == NULL || ss->destroy == NULL) + return -EINVAL; + + /* we don't support callbacks in modular subsystems. this check is + * before the ss->module check for consistency - a module that *could* + * be a module should still have no callbacks for consistency. */ + if (ss->fork || ss->exit) + return -EINVAL; + + /* an optionally modular subsystem is built-in: we want to do nothing, + * since cgroup_init_subsys will take care of it. */ + if (ss->module == NULL) { + /* sanity: ss->module NULL only if the subsys is built-in and + * appears in subsys[] already. */ + BUG_ON(ss->subsys_id >= CGROUP_BUILTIN_SUBSYS_COUNT); + BUG_ON(subsys[ss->subsys_id] != ss); + return 0; + } + + /* need to register a subsys id before anything else - for example, + * init_cgroup_css needs it. also, subsys_mutex needs to nest outside + * cgroup_mutex. */ + down_write(&subsys_mutex); + /* find the first empty slot in the array */ + for (i = CGROUP_BUILTIN_SUBSYS_COUNT; i < CGROUP_SUBSYS_COUNT; i++) { + if (subsys[i] == NULL) + break; + } + if (i == CGROUP_SUBSYS_COUNT) { + /* maximum number of subsystems already registered! */ + up_write(&subsys_mutex); + return -EBUSY; + } + /* assign ourselves the subsys_id */ + ss->subsys_id = i; + subsys[i] = ss; + + mutex_lock(&cgroup_mutex); + /* no ss->create seems to need anything important in the ss struct, so + * this can happen first (i.e. before the rootnode attachment). */ + css = ss->create(ss, dummytop); + if (IS_ERR(css)) { + /* failure case - need to deassign the subsys[] slot. */ + mutex_unlock(&cgroup_mutex); + subsys[i] = NULL; + up_write(&subsys_mutex); + return PTR_ERR(css); + } + + list_add(&ss->sibling, &rootnode.subsys_list); + ss->root = &rootnode; + + /* our new subsystem will be attached to the dummy hierarchy. */ + init_cgroup_css(css, ss, dummytop); + /* now we need to entangle the css into the existing css_sets. unlike + * in cgroup_init_subsys, there are now multiple css_sets, so each one + * will need a new pointer to it; done by iterating the css_set_table. + * furthermore, modifying the existing css_sets will corrupt the hash + * table state, so each changed css_set will need its hash recomputed. + * this is all done under the css_set_lock. */ + write_lock(&css_set_lock); + for (i = 0; i < CSS_SET_TABLE_SIZE; i++) { + struct css_set *cg; + struct hlist_node *node, *tmp; + struct hlist_head *bucket = &css_set_table[i], *new_bucket; + hlist_for_each_entry_safe(cg, node, tmp, bucket, hlist) { + /* skip entries that we already rehashed */ + if (cg->subsys[ss->subsys_id]) + continue; + /* remove existing entry */ + hlist_del(&cg->hlist); + /* set new value */ + cg->subsys[ss->subsys_id] = css; + /* recompute hash and restore entry */ + new_bucket = css_set_hash(cg->subsys); + hlist_add_head(&cg->hlist, new_bucket); + } + } + write_unlock(&css_set_lock); + + mutex_init(&ss->hierarchy_mutex); + lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key); + ss->active = 1; + + /* pin the subsystem's module so it doesn't go away. this shouldn't + * fail, since the module's initcall calls us. + * TODO: with module unloading, move this elsewhere */ + BUG_ON(!try_module_get(ss->module)); + + /* success! */ + mutex_unlock(&cgroup_mutex); + up_write(&subsys_mutex); + return 0; } +EXPORT_SYMBOL_GPL(cgroup_load_subsys); /** * cgroup_init_early - cgroup initialization at system boot _______________________________________________ Containers mailing list [email protected] https://lists.linux-foundation.org/mailman/listinfo/containers _______________________________________________ Devel mailing list [email protected] https://openvz.org/mailman/listinfo/devel
