[RFC] Example multi-bindable subsystem: a per-cgroup notes field As an example of a multiply-bindable subsystem, this patch introduces the "info" subsystem, which provides a single file, "info.notes", in which user-space middleware can store an arbitrary (up to one page) string representing configuration data about that cgroup. This reduces the need to keep additional state outside the cgroup filesystem.
TODO: a single page is somewhat limiting - the file limit should be userspace-configurable, and the system should store large notes in a vector of pages (to avoid trying to kmalloc() an excessively large chunk of memory. (Or maybe just use vmalloc()) Signed-off-by: Paul Menage <[email protected]> --- include/linux/cgroup_subsys.h | 6 +++ init/Kconfig | 8 ++++ kernel/Makefile | 1 kernel/info_cgroup.c | 93 +++++++++++++++++++++++++++++++++++++++++ 4 files changed, 108 insertions(+), 0 deletions(-) create mode 100644 kernel/info_cgroup.c diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h index f78605e..5dfea38 100644 --- a/include/linux/cgroup_subsys.h +++ b/include/linux/cgroup_subsys.h @@ -60,3 +60,9 @@ SUBSYS(net_cls) #endif /* */ + +#ifdef CONFIG_CGROUP_INFO +MULTI_SUBSYS(info) +#endif + +/* */ diff --git a/init/Kconfig b/init/Kconfig index fd5e3be..018601b 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -604,6 +604,14 @@ config CGROUP_MEM_RES_CTLR_SWAP there will be no overhead from this. Even when you set this config=y, if boot option "noswapaccount" is set, swap will not be accounted. +config CGROUP_INFO + bool "Simple application-specific info cgroup subsystem + help + Provides a simple cgroups subsystem with an "info.notes" + field, which can be used by middleware to store + application-specific configuration data about a cgroup. Can + be mounted on multiple hierarchies at once. + endif # CGROUPS config MM_OWNER diff --git a/kernel/Makefile b/kernel/Makefile index bdc528f..782752f 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -60,6 +60,7 @@ obj-$(CONFIG_CGROUPS) += cgroup.o obj-$(CONFIG_CGROUP_FREEZER) += cgroup_freezer.o obj-$(CONFIG_CPUSETS) += cpuset.o obj-$(CONFIG_CGROUP_NS) += ns_cgroup.o +obj-$(CONFIG_CGROUP_INFO) += info_cgroup.o obj-$(CONFIG_UTS_NS) += utsname.o obj-$(CONFIG_USER_NS) += user_namespace.o obj-$(CONFIG_PID_NS) += pid_namespace.o diff --git a/kernel/info_cgroup.c b/kernel/info_cgroup.c new file mode 100644 index 0000000..b8fdb37 --- /dev/null +++ b/kernel/info_cgroup.c @@ -0,0 +1,93 @@ +/* + * info_cgroup.c - simple cgroup providing a "notes" field + */ + +#include "linux/cgroup.h" +#include "linux/err.h" +#include "linux/seq_file.h" + +#define MAX_NOTES_LEN PAGE_SIZE + +struct info_cgroup { + struct cgroup_subsys_state css; + const char *notes; + spinlock_t lock; +}; + +static inline struct info_cgroup *cg_info(struct cgroup *cg) +{ + return container_of(cgroup_subsys_state(cg, info_subsys_id), + struct info_cgroup, css); +} + +static struct cgroup_subsys_state *info_create(struct cgroup_subsys *ss, + struct cgroup *cg) +{ + struct info_cgroup *info = kzalloc(sizeof(*info), GFP_KERNEL); + if (!info) + return ERR_PTR(-ENOMEM); + spin_lock_init(&info->lock); + return &info->css; +} + +static void info_destroy(struct cgroup_subsys *ss, struct cgroup *cont) +{ + struct info_cgroup *css = cg_info(cont); + kfree(css->notes); + kfree(css); +} + +static int info_read(struct cgroup *cont, + struct cftype *cft, + struct seq_file *seq) +{ + struct info_cgroup *css = cg_info(cont); + spin_lock(&css->lock); + if (css->notes) + seq_puts(seq, css->notes); + spin_unlock(&css->lock); + return 0; +} + +static int info_write(struct cgroup *cont, + struct cftype *cft, + const char *str) { + struct info_cgroup *css = cg_info(cont); + if (*str) { + if (strlen(str) > MAX_NOTES_LEN) + return -ENOSPC; + str = kstrdup(str, GFP_KERNEL); + if (!str) + return -ENOMEM; + } else { + str = NULL; + } + + spin_lock(&css->lock); + kfree(css->notes); + css->notes = str; + spin_unlock(&css->lock); + return 0; +} + +static struct cftype info_files[] = { + { + .name = "notes", + .read_seq_string = info_read, + .write_string = info_write, + }, +}; + +static int info_populate(struct cgroup_subsys *ss, struct cgroup *cont) +{ + return cgroup_add_files(cont, ss, info_files, + ARRAY_SIZE(info_files)); +} + +struct cgroup_subsys info_subsys = { + .name = "info", + .create = info_create, + .destroy = info_destroy, + .populate = info_populate, + .subsys_id = info_subsys_id, +}; _______________________________________________ Containers mailing list [email protected] https://lists.linux-foundation.org/mailman/listinfo/containers _______________________________________________ Devel mailing list [email protected] https://openvz.org/mailman/listinfo/devel
