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

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  1 /* SPDX-License-Identifier: GPL-2.0 */
  2 #ifndef _LINUX_PID_H
  3 #define _LINUX_PID_H
  4 
  5 #include <linux/rculist.h>
  6 
  7 enum pid_type
  8 {
  9         PIDTYPE_PID,
 10         PIDTYPE_PGID,
 11         PIDTYPE_SID,
 12         PIDTYPE_MAX,
 13         /* only valid to __task_pid_nr_ns() */
 14         __PIDTYPE_TGID
 15 };
 16 
 17 /*
 18  * What is struct pid?
 19  *
 20  * A struct pid is the kernel's internal notion of a process identifier.
 21  * It refers to individual tasks, process groups, and sessions.  While
 22  * there are processes attached to it the struct pid lives in a hash
 23  * table, so it and then the processes that it refers to can be found
 24  * quickly from the numeric pid value.  The attached processes may be
 25  * quickly accessed by following pointers from struct pid.
 26  *
 27  * Storing pid_t values in the kernel and referring to them later has a
 28  * problem.  The process originally with that pid may have exited and the
 29  * pid allocator wrapped, and another process could have come along
 30  * and been assigned that pid.
 31  *
 32  * Referring to user space processes by holding a reference to struct
 33  * task_struct has a problem.  When the user space process exits
 34  * the now useless task_struct is still kept.  A task_struct plus a
 35  * stack consumes around 10K of low kernel memory.  More precisely
 36  * this is THREAD_SIZE + sizeof(struct task_struct).  By comparison
 37  * a struct pid is about 64 bytes.
 38  *
 39  * Holding a reference to struct pid solves both of these problems.
 40  * It is small so holding a reference does not consume a lot of
 41  * resources, and since a new struct pid is allocated when the numeric pid
 42  * value is reused (when pids wrap around) we don't mistakenly refer to new
 43  * processes.
 44  */
 45 
 46 
 47 /*
 48  * struct upid is used to get the id of the struct pid, as it is
 49  * seen in particular namespace. Later the struct pid is found with
 50  * find_pid_ns() using the int nr and struct pid_namespace *ns.
 51  */
 52 
 53 struct upid {
 54         int nr;
 55         struct pid_namespace *ns;
 56 };
 57 
 58 struct pid
 59 {
 60         atomic_t count;
 61         unsigned int level;
 62         /* lists of tasks that use this pid */
 63         struct hlist_head tasks[PIDTYPE_MAX];
 64         struct rcu_head rcu;
 65         struct upid numbers[1];
 66 };
 67 
 68 extern struct pid init_struct_pid;
 69 
 70 struct pid_link
 71 {
 72         struct hlist_node node;
 73         struct pid *pid;
 74 };
 75 
 76 static inline struct pid *get_pid(struct pid *pid)
 77 {
 78         if (pid)
 79                 atomic_inc(&pid->count);
 80         return pid;
 81 }
 82 
 83 extern void put_pid(struct pid *pid);
 84 extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
 85 extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
 86 
 87 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
 88 
 89 /*
 90  * these helpers must be called with the tasklist_lock write-held.
 91  */
 92 extern void attach_pid(struct task_struct *task, enum pid_type);
 93 extern void detach_pid(struct task_struct *task, enum pid_type);
 94 extern void change_pid(struct task_struct *task, enum pid_type,
 95                         struct pid *pid);
 96 extern void transfer_pid(struct task_struct *old, struct task_struct *new,
 97                          enum pid_type);
 98 
 99 struct pid_namespace;
100 extern struct pid_namespace init_pid_ns;
101 
102 /*
103  * look up a PID in the hash table. Must be called with the tasklist_lock
104  * or rcu_read_lock() held.
105  *
106  * find_pid_ns() finds the pid in the namespace specified
107  * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
108  *
109  * see also find_task_by_vpid() set in include/linux/sched.h
110  */
111 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
112 extern struct pid *find_vpid(int nr);
113 
114 /*
115  * Lookup a PID in the hash table, and return with it's count elevated.
116  */
117 extern struct pid *find_get_pid(int nr);
118 extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
119 int next_pidmap(struct pid_namespace *pid_ns, unsigned int last);
120 
121 extern struct pid *alloc_pid(struct pid_namespace *ns);
122 extern void free_pid(struct pid *pid);
123 extern void disable_pid_allocation(struct pid_namespace *ns);
124 
125 /*
126  * ns_of_pid() returns the pid namespace in which the specified pid was
127  * allocated.
128  *
129  * NOTE:
130  *      ns_of_pid() is expected to be called for a process (task) that has
131  *      an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
132  *      is expected to be non-NULL. If @pid is NULL, caller should handle
133  *      the resulting NULL pid-ns.
134  */
135 static inline struct pid_namespace *ns_of_pid(struct pid *pid)
136 {
137         struct pid_namespace *ns = NULL;
138         if (pid)
139                 ns = pid->numbers[pid->level].ns;
140         return ns;
141 }
142 
143 /*
144  * is_child_reaper returns true if the pid is the init process
145  * of the current namespace. As this one could be checked before
146  * pid_ns->child_reaper is assigned in copy_process, we check
147  * with the pid number.
148  */
149 static inline bool is_child_reaper(struct pid *pid)
150 {
151         return pid->numbers[pid->level].nr == 1;
152 }
153 
154 /*
155  * the helpers to get the pid's id seen from different namespaces
156  *
157  * pid_nr()    : global id, i.e. the id seen from the init namespace;
158  * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
159  *               current.
160  * pid_nr_ns() : id seen from the ns specified.
161  *
162  * see also task_xid_nr() etc in include/linux/sched.h
163  */
164 
165 static inline pid_t pid_nr(struct pid *pid)
166 {
167         pid_t nr = 0;
168         if (pid)
169                 nr = pid->numbers[0].nr;
170         return nr;
171 }
172 
173 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
174 pid_t pid_vnr(struct pid *pid);
175 
176 #define do_each_pid_task(pid, type, task)                               \
177         do {                                                            \
178                 if ((pid) != NULL)                                      \
179                         hlist_for_each_entry_rcu((task),                \
180                                 &(pid)->tasks[type], pids[type].node) {
181 
182                         /*
183                          * Both old and new leaders may be attached to
184                          * the same pid in the middle of de_thread().
185                          */
186 #define while_each_pid_task(pid, type, task)                            \
187                                 if (type == PIDTYPE_PID)                \
188                                         break;                          \
189                         }                                               \
190         } while (0)
191 
192 #define do_each_pid_thread(pid, type, task)                             \
193         do_each_pid_task(pid, type, task) {                             \
194                 struct task_struct *tg___ = task;                       \
195                 for_each_thread(tg___, task) {
196 
197 #define while_each_pid_thread(pid, type, task)                          \
198                 }                                                       \
199                 task = tg___;                                           \
200         } while_each_pid_task(pid, type, task)
201 #endif /* _LINUX_PID_H */
202 

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