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TOMOYO Linux Cross Reference
Linux/include/linux/pid.h

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  1 #ifndef _LINUX_PID_H
  2 #define _LINUX_PID_H
  3 
  4 #include <linux/rcupdate.h>
  5 
  6 enum pid_type
  7 {
  8         PIDTYPE_PID,
  9         PIDTYPE_PGID,
 10         PIDTYPE_SID,
 11         PIDTYPE_MAX
 12 };
 13 
 14 /*
 15  * What is struct pid?
 16  *
 17  * A struct pid is the kernel's internal notion of a process identifier.
 18  * It refers to individual tasks, process groups, and sessions.  While
 19  * there are processes attached to it the struct pid lives in a hash
 20  * table, so it and then the processes that it refers to can be found
 21  * quickly from the numeric pid value.  The attached processes may be
 22  * quickly accessed by following pointers from struct pid.
 23  *
 24  * Storing pid_t values in the kernel and referring to them later has a
 25  * problem.  The process originally with that pid may have exited and the
 26  * pid allocator wrapped, and another process could have come along
 27  * and been assigned that pid.
 28  *
 29  * Referring to user space processes by holding a reference to struct
 30  * task_struct has a problem.  When the user space process exits
 31  * the now useless task_struct is still kept.  A task_struct plus a
 32  * stack consumes around 10K of low kernel memory.  More precisely
 33  * this is THREAD_SIZE + sizeof(struct task_struct).  By comparison
 34  * a struct pid is about 64 bytes.
 35  *
 36  * Holding a reference to struct pid solves both of these problems.
 37  * It is small so holding a reference does not consume a lot of
 38  * resources, and since a new struct pid is allocated when the numeric pid
 39  * value is reused (when pids wrap around) we don't mistakenly refer to new
 40  * processes.
 41  */
 42 
 43 
 44 /*
 45  * struct upid is used to get the id of the struct pid, as it is
 46  * seen in particular namespace. Later the struct pid is found with
 47  * find_pid_ns() using the int nr and struct pid_namespace *ns.
 48  */
 49 
 50 struct upid {
 51         /* Try to keep pid_chain in the same cacheline as nr for find_vpid */
 52         int nr;
 53         struct pid_namespace *ns;
 54         struct hlist_node pid_chain;
 55 };
 56 
 57 struct pid
 58 {
 59         atomic_t count;
 60         unsigned int level;
 61         /* lists of tasks that use this pid */
 62         struct hlist_head tasks[PIDTYPE_MAX];
 63         struct rcu_head rcu;
 64         struct upid numbers[1];
 65 };
 66 
 67 extern struct pid init_struct_pid;
 68 
 69 struct pid_link
 70 {
 71         struct hlist_node node;
 72         struct pid *pid;
 73 };
 74 
 75 static inline struct pid *get_pid(struct pid *pid)
 76 {
 77         if (pid)
 78                 atomic_inc(&pid->count);
 79         return pid;
 80 }
 81 
 82 extern void put_pid(struct pid *pid);
 83 extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
 84 extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
 85 
 86 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
 87 
 88 /*
 89  * these helpers must be called with the tasklist_lock write-held.
 90  */
 91 extern void attach_pid(struct task_struct *task, enum pid_type);
 92 extern void detach_pid(struct task_struct *task, enum pid_type);
 93 extern void change_pid(struct task_struct *task, enum pid_type,
 94                         struct pid *pid);
 95 extern void transfer_pid(struct task_struct *old, struct task_struct *new,
 96                          enum pid_type);
 97 
 98 struct pid_namespace;
 99 extern struct pid_namespace init_pid_ns;
100 
101 /*
102  * look up a PID in the hash table. Must be called with the tasklist_lock
103  * or rcu_read_lock() held.
104  *
105  * find_pid_ns() finds the pid in the namespace specified
106  * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
107  *
108  * see also find_task_by_vpid() set in include/linux/sched.h
109  */
110 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
111 extern struct pid *find_vpid(int nr);
112 
113 /*
114  * Lookup a PID in the hash table, and return with it's count elevated.
115  */
116 extern struct pid *find_get_pid(int nr);
117 extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
118 int next_pidmap(struct pid_namespace *pid_ns, unsigned int last);
119 
120 extern struct pid *alloc_pid(struct pid_namespace *ns);
121 extern void free_pid(struct pid *pid);
122 extern void disable_pid_allocation(struct pid_namespace *ns);
123 
124 /*
125  * ns_of_pid() returns the pid namespace in which the specified pid was
126  * allocated.
127  *
128  * NOTE:
129  *      ns_of_pid() is expected to be called for a process (task) that has
130  *      an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
131  *      is expected to be non-NULL. If @pid is NULL, caller should handle
132  *      the resulting NULL pid-ns.
133  */
134 static inline struct pid_namespace *ns_of_pid(struct pid *pid)
135 {
136         struct pid_namespace *ns = NULL;
137         if (pid)
138                 ns = pid->numbers[pid->level].ns;
139         return ns;
140 }
141 
142 /*
143  * is_child_reaper returns true if the pid is the init process
144  * of the current namespace. As this one could be checked before
145  * pid_ns->child_reaper is assigned in copy_process, we check
146  * with the pid number.
147  */
148 static inline bool is_child_reaper(struct pid *pid)
149 {
150         return pid->numbers[pid->level].nr == 1;
151 }
152 
153 /*
154  * the helpers to get the pid's id seen from different namespaces
155  *
156  * pid_nr()    : global id, i.e. the id seen from the init namespace;
157  * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
158  *               current.
159  * pid_nr_ns() : id seen from the ns specified.
160  *
161  * see also task_xid_nr() etc in include/linux/sched.h
162  */
163 
164 static inline pid_t pid_nr(struct pid *pid)
165 {
166         pid_t nr = 0;
167         if (pid)
168                 nr = pid->numbers[0].nr;
169         return nr;
170 }
171 
172 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
173 pid_t pid_vnr(struct pid *pid);
174 
175 #define do_each_pid_task(pid, type, task)                               \
176         do {                                                            \
177                 if ((pid) != NULL)                                      \
178                         hlist_for_each_entry_rcu((task),                \
179                                 &(pid)->tasks[type], pids[type].node) {
180 
181                         /*
182                          * Both old and new leaders may be attached to
183                          * the same pid in the middle of de_thread().
184                          */
185 #define while_each_pid_task(pid, type, task)                            \
186                                 if (type == PIDTYPE_PID)                \
187                                         break;                          \
188                         }                                               \
189         } while (0)
190 
191 #define do_each_pid_thread(pid, type, task)                             \
192         do_each_pid_task(pid, type, task) {                             \
193                 struct task_struct *tg___ = task;                       \
194                 do {
195 
196 #define while_each_pid_thread(pid, type, task)                          \
197                 } while_each_thread(tg___, task);                       \
198                 task = tg___;                                           \
199         } while_each_pid_task(pid, type, task)
200 #endif /* _LINUX_PID_H */
201 

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