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#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 refering 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_pid */

        int nr;

        struct pid_namespace *ns;

        struct hlist_node pid_chain;

};

struct pid

{

        atomic_t count;

        /* lists of tasks that use this pid */

        struct hlist_head tasks[PIDTYPE_MAX];

        struct rcu_head rcu;

        int level;

        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 FASTCALL(put_pid(struct pid *pid));

extern struct task_struct *FASTCALL(pid_task(struct pid *pid, enum pid_type));

extern struct task_struct *FASTCALL(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 int FASTCALL(attach_pid(struct task_struct *task,

                                enum pid_type type, struct pid *pid));

extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));

extern void FASTCALL(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_pid() find the pid by its global id, i.e. in the init namespace

 * find_vpid() finr the pid by its virtual id, i.e. in the current namespace

 *

 * see also find_task_by_pid() set in include/linux/sched.h

 */

extern struct pid *FASTCALL(find_pid_ns(int nr, struct pid_namespace *ns));

extern struct pid *find_vpid(int nr);

extern struct pid *find_pid(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 *);

extern struct pid *alloc_pid(struct pid_namespace *ns);

extern void FASTCALL(free_pid(struct pid *pid));

extern void zap_pid_ns_processes(struct pid_namespace *pid_ns);

/*

 * 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 namespace this pid

 *               belongs to. this only makes sence when called in the

 *               context of the task that belongs to the same namespace;

 * 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);

static inline pid_t pid_vnr(struct pid *pid)

{

        pid_t nr = 0;

        if (pid)

                nr = pid->numbers[pid->level].nr;

        return nr;

}

#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) {

#define while_each_pid_task(pid, type, task)                            \

                        }                                               \

        } while (0)

#endif /* _LINUX_PID_H */