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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_TGID,
 11         PIDTYPE_PGID,
 12         PIDTYPE_SID,
 13         PIDTYPE_MAX,
 14 };
 15 
 16 /*
 17  * What is struct pid?
 18  *
 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.
 25  *
 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.
 30  *
 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.
 37  *
 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
 42  * processes.
 43  */
 44 
 45 
 46 /*
 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.
 50  */
 51 
 52 struct upid {
 53         int nr;
 54         struct pid_namespace *ns;
 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 static inline struct pid *get_pid(struct pid *pid)
 70 {
 71         if (pid)
 72                 atomic_inc(&pid->count);
 73         return pid;
 74 }
 75 
 76 extern void put_pid(struct pid *pid);
 77 extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
 78 extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
 79 
 80 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
 81 
 82 /*
 83  * these helpers must be called with the tasklist_lock write-held.
 84  */
 85 extern void attach_pid(struct task_struct *task, enum pid_type);
 86 extern void detach_pid(struct task_struct *task, enum pid_type);
 87 extern void change_pid(struct task_struct *task, enum pid_type,
 88                         struct pid *pid);
 89 extern void transfer_pid(struct task_struct *old, struct task_struct *new,
 90                          enum pid_type);
 91 
 92 struct pid_namespace;
 93 extern struct pid_namespace init_pid_ns;
 94 
 95 /*
 96  * look up a PID in the hash table. Must be called with the tasklist_lock
 97  * or rcu_read_lock() held.
 98  *
 99  * find_pid_ns() finds the pid in the namespace specified
100  * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
101  *
102  * see also find_task_by_vpid() set in include/linux/sched.h
103  */
104 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
105 extern struct pid *find_vpid(int nr);
106 
107 /*
108  * Lookup a PID in the hash table, and return with it's count elevated.
109  */
110 extern struct pid *find_get_pid(int nr);
111 extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
112 
113 extern struct pid *alloc_pid(struct pid_namespace *ns);
114 extern void free_pid(struct pid *pid);
115 extern void disable_pid_allocation(struct pid_namespace *ns);
116 
117 /*
118  * ns_of_pid() returns the pid namespace in which the specified pid was
119  * allocated.
120  *
121  * NOTE:
122  *      ns_of_pid() is expected to be called for a process (task) that has
123  *      an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
124  *      is expected to be non-NULL. If @pid is NULL, caller should handle
125  *      the resulting NULL pid-ns.
126  */
127 static inline struct pid_namespace *ns_of_pid(struct pid *pid)
128 {
129         struct pid_namespace *ns = NULL;
130         if (pid)
131                 ns = pid->numbers[pid->level].ns;
132         return ns;
133 }
134 
135 /*
136  * is_child_reaper returns true if the pid is the init process
137  * of the current namespace. As this one could be checked before
138  * pid_ns->child_reaper is assigned in copy_process, we check
139  * with the pid number.
140  */
141 static inline bool is_child_reaper(struct pid *pid)
142 {
143         return pid->numbers[pid->level].nr == 1;
144 }
145 
146 /*
147  * the helpers to get the pid's id seen from different namespaces
148  *
149  * pid_nr()    : global id, i.e. the id seen from the init namespace;
150  * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
151  *               current.
152  * pid_nr_ns() : id seen from the ns specified.
153  *
154  * see also task_xid_nr() etc in include/linux/sched.h
155  */
156 
157 static inline pid_t pid_nr(struct pid *pid)
158 {
159         pid_t nr = 0;
160         if (pid)
161                 nr = pid->numbers[0].nr;
162         return nr;
163 }
164 
165 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
166 pid_t pid_vnr(struct pid *pid);
167 
168 #define do_each_pid_task(pid, type, task)                               \
169         do {                                                            \
170                 if ((pid) != NULL)                                      \
171                         hlist_for_each_entry_rcu((task),                \
172                                 &(pid)->tasks[type], pid_links[type]) {
173 
174                         /*
175                          * Both old and new leaders may be attached to
176                          * the same pid in the middle of de_thread().
177                          */
178 #define while_each_pid_task(pid, type, task)                            \
179                                 if (type == PIDTYPE_PID)                \
180                                         break;                          \
181                         }                                               \
182         } while (0)
183 
184 #define do_each_pid_thread(pid, type, task)                             \
185         do_each_pid_task(pid, type, task) {                             \
186                 struct task_struct *tg___ = task;                       \
187                 for_each_thread(tg___, task) {
188 
189 #define while_each_pid_thread(pid, type, task)                          \
190                 }                                                       \
191                 task = tg___;                                           \
192         } while_each_pid_task(pid, type, task)
193 #endif /* _LINUX_PID_H */
194 

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