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Diffstat (limited to 'include/linux/pid.h')
| -rw-r--r-- | include/linux/pid.h | 202 |
1 files changed, 202 insertions, 0 deletions
diff --git a/include/linux/pid.h b/include/linux/pid.h new file mode 100644 index 00000000..b152d44f --- /dev/null +++ b/include/linux/pid.h @@ -0,0 +1,202 @@ +#ifndef _LINUX_PID_H +#define _LINUX_PID_H + +#include <linux/rcupdate.h> + +enum pid_type +{ + PIDTYPE_PID, + PIDTYPE_PGID, + PIDTYPE_SID, + PIDTYPE_MAX +}; + +/* + * What is struct pid? + * + * A struct pid is the kernel's internal notion of a process identifier. + * It refers to individual tasks, process groups, and sessions. While + * there are processes attached to it the struct pid lives in a hash + * table, so it and then the processes that it refers to can be found + * quickly from the numeric pid value. The attached processes may be + * quickly accessed by following pointers from struct pid. + * + * Storing pid_t values in the kernel and referring to them later has a + * problem. The process originally with that pid may have exited and the + * pid allocator wrapped, and another process could have come along + * and been assigned that pid. + * + * Referring to user space processes by holding a reference to struct + * task_struct has a problem. When the user space process exits + * the now useless task_struct is still kept. A task_struct plus a + * stack consumes around 10K of low kernel memory. More precisely + * this is THREAD_SIZE + sizeof(struct task_struct). By comparison + * a struct pid is about 64 bytes. + * + * Holding a reference to struct pid solves both of these problems. + * It is small so holding a reference does not consume a lot of + * resources, and since a new struct pid is allocated when the numeric pid + * value is reused (when pids wrap around) we don't mistakenly refer to new + * processes. + */ + + +/* + * struct upid is used to get the id of the struct pid, as it is + * seen in particular namespace. Later the struct pid is found with + * find_pid_ns() using the int nr and struct pid_namespace *ns. + */ + +struct upid { + /* Try to keep pid_chain in the same cacheline as nr for find_vpid */ + int nr; + struct pid_namespace *ns; + struct hlist_node pid_chain; +}; + +struct pid +{ + atomic_t count; + unsigned int level; + /* lists of tasks that use this pid */ + struct hlist_head tasks[PIDTYPE_MAX]; + struct rcu_head rcu; + struct upid numbers[1]; +}; + +extern struct pid init_struct_pid; + +struct pid_link +{ + struct hlist_node node; + struct pid *pid; +}; + +static inline struct pid *get_pid(struct pid *pid) +{ + if (pid) + atomic_inc(&pid->count); + return pid; +} + +extern void put_pid(struct pid *pid); +extern struct task_struct *pid_task(struct pid *pid, enum pid_type); +extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type); + +extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type); + +/* + * attach_pid() and detach_pid() must be called with the tasklist_lock + * write-held. + */ +extern void attach_pid(struct task_struct *task, enum pid_type type, + struct pid *pid); +extern void detach_pid(struct task_struct *task, enum pid_type); +extern void change_pid(struct task_struct *task, enum pid_type, + struct pid *pid); +extern void transfer_pid(struct task_struct *old, struct task_struct *new, + enum pid_type); + +struct pid_namespace; +extern struct pid_namespace init_pid_ns; + +/* + * look up a PID in the hash table. Must be called with the tasklist_lock + * or rcu_read_lock() held. + * + * find_pid_ns() finds the pid in the namespace specified + * find_vpid() finds the pid by its virtual id, i.e. in the current namespace + * + * see also find_task_by_vpid() set in include/linux/sched.h + */ +extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns); +extern struct pid *find_vpid(int nr); + +/* + * Lookup a PID in the hash table, and return with it's count elevated. + */ +extern struct pid *find_get_pid(int nr); +extern struct pid *find_ge_pid(int nr, struct pid_namespace *); +int next_pidmap(struct pid_namespace *pid_ns, unsigned int last); + +extern struct pid *alloc_pid(struct pid_namespace *ns); +extern void free_pid(struct pid *pid); + +/* + * ns_of_pid() returns the pid namespace in which the specified pid was + * allocated. + * + * NOTE: + * ns_of_pid() is expected to be called for a process (task) that has + * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid + * is expected to be non-NULL. If @pid is NULL, caller should handle + * the resulting NULL pid-ns. + */ +static inline struct pid_namespace *ns_of_pid(struct pid *pid) +{ + struct pid_namespace *ns = NULL; + if (pid) + ns = pid->numbers[pid->level].ns; + return ns; +} + +/* + * is_child_reaper returns true if the pid is the init process + * of the current namespace. As this one could be checked before + * pid_ns->child_reaper is assigned in copy_process, we check + * with the pid number. + */ +static inline bool is_child_reaper(struct pid *pid) +{ + return pid->numbers[pid->level].nr == 1; +} + +/* + * the helpers to get the pid's id seen from different namespaces + * + * pid_nr() : global id, i.e. the id seen from the init namespace; + * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of + * current. + * pid_nr_ns() : id seen from the ns specified. + * + * see also task_xid_nr() etc in include/linux/sched.h + */ + +static inline pid_t pid_nr(struct pid *pid) +{ + pid_t nr = 0; + if (pid) + nr = pid->numbers[0].nr; + return nr; +} + +pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns); +pid_t pid_vnr(struct pid *pid); + +#define do_each_pid_task(pid, type, task) \ + do { \ + struct hlist_node *pos___; \ + if ((pid) != NULL) \ + hlist_for_each_entry_rcu((task), pos___, \ + &(pid)->tasks[type], pids[type].node) { + + /* + * Both old and new leaders may be attached to + * the same pid in the middle of de_thread(). + */ +#define while_each_pid_task(pid, type, task) \ + if (type == PIDTYPE_PID) \ + break; \ + } \ + } while (0) + +#define do_each_pid_thread(pid, type, task) \ + do_each_pid_task(pid, type, task) { \ + struct task_struct *tg___ = task; \ + do { + +#define while_each_pid_thread(pid, type, task) \ + } while_each_thread(tg___, task); \ + task = tg___; \ + } while_each_pid_task(pid, type, task) +#endif /* _LINUX_PID_H */ |