4 #include <linux/rcupdate.h>
18 * A struct pid is the kernel's internal notion of a process identifier.
19 * It refers to individual tasks, process groups, and sessions. While
20 * there are processes attached to it the struct pid lives in a hash
21 * table, so it and then the processes that it refers to can be found
22 * quickly from the numeric pid value. The attached processes may be
23 * quickly accessed by following pointers from struct pid.
25 * Storing pid_t values in the kernel and refering to them later has a
26 * problem. The process originally with that pid may have exited and the
27 * pid allocator wrapped, and another process could have come along
28 * and been assigned that pid.
30 * Referring to user space processes by holding a reference to struct
31 * task_struct has a problem. When the user space process exits
32 * the now useless task_struct is still kept. A task_struct plus a
33 * stack consumes around 10K of low kernel memory. More precisely
34 * this is THREAD_SIZE + sizeof(struct task_struct). By comparison
35 * a struct pid is about 64 bytes.
37 * Holding a reference to struct pid solves both of these problems.
38 * It is small so holding a reference does not consume a lot of
39 * resources, and since a new struct pid is allocated when the numeric pid
40 * value is reused (when pids wrap around) we don't mistakenly refer to new
47 /* Try to keep pid_chain in the same cacheline as nr for find_pid */
49 struct hlist_node pid_chain;
50 /* lists of tasks that use this pid */
51 struct hlist_head tasks[PIDTYPE_MAX];
57 struct hlist_node node;
61 static inline struct pid *get_pid(struct pid *pid)
64 atomic_inc(&pid->count);
68 extern void FASTCALL(put_pid(struct pid *pid));
69 extern struct task_struct *FASTCALL(pid_task(struct pid *pid, enum pid_type));
70 extern struct task_struct *FASTCALL(get_pid_task(struct pid *pid,
73 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
76 * attach_pid() and detach_pid() must be called with the tasklist_lock
79 extern int FASTCALL(attach_pid(struct task_struct *task,
80 enum pid_type type, int nr));
82 extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
83 extern void FASTCALL(transfer_pid(struct task_struct *old,
84 struct task_struct *new, enum pid_type));
87 * look up a PID in the hash table. Must be called with the tasklist_lock
88 * or rcu_read_lock() held.
90 extern struct pid *FASTCALL(find_pid(int nr));
93 * Lookup a PID in the hash table, and return with it's count elevated.
95 extern struct pid *find_get_pid(int nr);
96 extern struct pid *find_ge_pid(int nr);
98 extern struct pid *alloc_pid(void);
99 extern void FASTCALL(free_pid(struct pid *pid));
101 static inline pid_t pid_nr(struct pid *pid)
110 #define do_each_task_pid(who, type, task) \
112 struct hlist_node *pos___; \
113 struct pid *pid___ = find_pid(who); \
114 if (pid___ != NULL) \
115 hlist_for_each_entry_rcu((task), pos___, \
116 &pid___->tasks[type], pids[type].node) {
118 #define while_each_task_pid(who, type, task) \
123 #define do_each_pid_task(pid, type, task) \
125 struct hlist_node *pos___; \
127 hlist_for_each_entry_rcu((task), pos___, \
128 &pid->tasks[type], pids[type].node) \
129 if (vx_check((task)->xid, VS_ADMIN_P|VS_IDENT)) {
131 #define while_each_pid_task(pid, type, task) \
135 #endif /* _LINUX_PID_H */