4 #include <linux/rculist.h>
12 /* only valid to __task_pid_nr_ns() */
19 * A struct pid is the kernel's internal notion of a process identifier.
20 * It refers to individual tasks, process groups, and sessions. While
21 * there are processes attached to it the struct pid lives in a hash
22 * table, so it and then the processes that it refers to can be found
23 * quickly from the numeric pid value. The attached processes may be
24 * quickly accessed by following pointers from struct pid.
26 * Storing pid_t values in the kernel and referring to them later has a
27 * problem. The process originally with that pid may have exited and the
28 * pid allocator wrapped, and another process could have come along
29 * and been assigned that pid.
31 * Referring to user space processes by holding a reference to struct
32 * task_struct has a problem. When the user space process exits
33 * the now useless task_struct is still kept. A task_struct plus a
34 * stack consumes around 10K of low kernel memory. More precisely
35 * this is THREAD_SIZE + sizeof(struct task_struct). By comparison
36 * a struct pid is about 64 bytes.
38 * Holding a reference to struct pid solves both of these problems.
39 * It is small so holding a reference does not consume a lot of
40 * resources, and since a new struct pid is allocated when the numeric pid
41 * value is reused (when pids wrap around) we don't mistakenly refer to new
47 * struct upid is used to get the id of the struct pid, as it is
48 * seen in particular namespace. Later the struct pid is found with
49 * find_pid_ns() using the int nr and struct pid_namespace *ns.
53 /* Try to keep pid_chain in the same cacheline as nr for find_vpid */
55 struct pid_namespace
*ns
;
56 struct hlist_node pid_chain
;
63 /* lists of tasks that use this pid */
64 struct hlist_head tasks
[PIDTYPE_MAX
];
66 struct upid numbers
[1];
69 extern struct pid init_struct_pid
;
73 struct hlist_node node
;
77 static inline struct pid
*get_pid(struct pid
*pid
)
80 atomic_inc(&pid
->count
);
84 extern void put_pid(struct pid
*pid
);
85 extern struct task_struct
*pid_task(struct pid
*pid
, enum pid_type
);
86 extern struct task_struct
*get_pid_task(struct pid
*pid
, enum pid_type
);
88 extern struct pid
*get_task_pid(struct task_struct
*task
, enum pid_type type
);
91 * these helpers must be called with the tasklist_lock write-held.
93 extern void attach_pid(struct task_struct
*task
, enum pid_type
);
94 extern void detach_pid(struct task_struct
*task
, enum pid_type
);
95 extern void change_pid(struct task_struct
*task
, enum pid_type
,
97 extern void transfer_pid(struct task_struct
*old
, struct task_struct
*new,
100 struct pid_namespace
;
101 extern struct pid_namespace init_pid_ns
;
104 * look up a PID in the hash table. Must be called with the tasklist_lock
105 * or rcu_read_lock() held.
107 * find_pid_ns() finds the pid in the namespace specified
108 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
110 * see also find_task_by_vpid() set in include/linux/sched.h
112 extern struct pid
*find_pid_ns(int nr
, struct pid_namespace
*ns
);
113 extern struct pid
*find_vpid(int nr
);
116 * Lookup a PID in the hash table, and return with it's count elevated.
118 extern struct pid
*find_get_pid(int nr
);
119 extern struct pid
*find_ge_pid(int nr
, struct pid_namespace
*);
120 int next_pidmap(struct pid_namespace
*pid_ns
, unsigned int last
);
122 extern struct pid
*alloc_pid(struct pid_namespace
*ns
);
123 extern void free_pid(struct pid
*pid
);
124 extern void disable_pid_allocation(struct pid_namespace
*ns
);
127 * ns_of_pid() returns the pid namespace in which the specified pid was
131 * ns_of_pid() is expected to be called for a process (task) that has
132 * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
133 * is expected to be non-NULL. If @pid is NULL, caller should handle
134 * the resulting NULL pid-ns.
136 static inline struct pid_namespace
*ns_of_pid(struct pid
*pid
)
138 struct pid_namespace
*ns
= NULL
;
140 ns
= pid
->numbers
[pid
->level
].ns
;
145 * is_child_reaper returns true if the pid is the init process
146 * of the current namespace. As this one could be checked before
147 * pid_ns->child_reaper is assigned in copy_process, we check
148 * with the pid number.
150 static inline bool is_child_reaper(struct pid
*pid
)
152 return pid
->numbers
[pid
->level
].nr
== 1;
156 * the helpers to get the pid's id seen from different namespaces
158 * pid_nr() : global id, i.e. the id seen from the init namespace;
159 * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of
161 * pid_nr_ns() : id seen from the ns specified.
163 * see also task_xid_nr() etc in include/linux/sched.h
166 static inline pid_t
pid_nr(struct pid
*pid
)
170 nr
= pid
->numbers
[0].nr
;
174 pid_t
pid_nr_ns(struct pid
*pid
, struct pid_namespace
*ns
);
175 pid_t
pid_vnr(struct pid
*pid
);
177 #define do_each_pid_task(pid, type, task) \
180 hlist_for_each_entry_rcu((task), \
181 &(pid)->tasks[type], pids[type].node) {
184 * Both old and new leaders may be attached to
185 * the same pid in the middle of de_thread().
187 #define while_each_pid_task(pid, type, task) \
188 if (type == PIDTYPE_PID) \
193 #define do_each_pid_thread(pid, type, task) \
194 do_each_pid_task(pid, type, task) { \
195 struct task_struct *tg___ = task; \
196 for_each_thread(tg___, task) {
198 #define while_each_pid_thread(pid, type, task) \
201 } while_each_pid_task(pid, type, task)
202 #endif /* _LINUX_PID_H */