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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 #include <linux/wait.h>
  7 #include <linux/refcount.h>
  8 
  9 enum pid_type
 10 {
 11         PIDTYPE_PID,
 12         PIDTYPE_TGID,
 13         PIDTYPE_PGID,
 14         PIDTYPE_SID,
 15         PIDTYPE_MAX,
 16 };
 17 
 18 /*
 19  * What is struct pid?
 20  *
 21  * A struct pid is the kernel's internal notion of a process identifier.
 22  * It refers to individual tasks, process groups, and sessions.  While
 23  * there are processes attached to it the struct pid lives in a hash
 24  * table, so it and then the processes that it refers to can be found
 25  * quickly from the numeric pid value.  The attached processes may be
 26  * quickly accessed by following pointers from struct pid.
 27  *
 28  * Storing pid_t values in the kernel and referring to them later has a
 29  * problem.  The process originally with that pid may have exited and the
 30  * pid allocator wrapped, and another process could have come along
 31  * and been assigned that pid.
 32  *
 33  * Referring to user space processes by holding a reference to struct
 34  * task_struct has a problem.  When the user space process exits
 35  * the now useless task_struct is still kept.  A task_struct plus a
 36  * stack consumes around 10K of low kernel memory.  More precisely
 37  * this is THREAD_SIZE + sizeof(struct task_struct).  By comparison
 38  * a struct pid is about 64 bytes.
 39  *
 40  * Holding a reference to struct pid solves both of these problems.
 41  * It is small so holding a reference does not consume a lot of
 42  * resources, and since a new struct pid is allocated when the numeric pid
 43  * value is reused (when pids wrap around) we don't mistakenly refer to new
 44  * processes.
 45  */
 46 
 47 
 48 /*
 49  * struct upid is used to get the id of the struct pid, as it is
 50  * seen in particular namespace. Later the struct pid is found with
 51  * find_pid_ns() using the int nr and struct pid_namespace *ns.
 52  */
 53 
 54 struct upid {
 55         int nr;
 56         struct pid_namespace *ns;
 57 };
 58 
 59 struct pid
 60 {
 61         refcount_t count;
 62         unsigned int level;
 63         /* lists of tasks that use this pid */
 64         struct hlist_head tasks[PIDTYPE_MAX];
 65         /* wait queue for pidfd notifications */
 66         wait_queue_head_t wait_pidfd;
 67         struct rcu_head rcu;
 68         struct upid numbers[1];
 69 };
 70 
 71 extern struct pid init_struct_pid;
 72 
 73 extern const struct file_operations pidfd_fops;
 74 
 75 struct file;
 76 
 77 extern struct pid *pidfd_pid(const struct file *file);
 78 
 79 static inline struct pid *get_pid(struct pid *pid)
 80 {
 81         if (pid)
 82                 refcount_inc(&pid->count);
 83         return pid;
 84 }
 85 
 86 extern void put_pid(struct pid *pid);
 87 extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
 88 static inline bool pid_has_task(struct pid *pid, enum pid_type type)
 89 {
 90         return !hlist_empty(&pid->tasks[type]);
 91 }
 92 extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
 93 
 94 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
 95 
 96 /*
 97  * these helpers must be called with the tasklist_lock write-held.
 98  */
 99 extern void attach_pid(struct task_struct *task, enum pid_type);
100 extern void detach_pid(struct task_struct *task, enum pid_type);
101 extern void change_pid(struct task_struct *task, enum pid_type,
102                         struct pid *pid);
103 extern void transfer_pid(struct task_struct *old, struct task_struct *new,
104                          enum pid_type);
105 
106 struct pid_namespace;
107 extern struct pid_namespace init_pid_ns;
108 
109 /*
110  * look up a PID in the hash table. Must be called with the tasklist_lock
111  * or rcu_read_lock() held.
112  *
113  * find_pid_ns() finds the pid in the namespace specified
114  * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
115  *
116  * see also find_task_by_vpid() set in include/linux/sched.h
117  */
118 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
119 extern struct pid *find_vpid(int nr);
120 
121 /*
122  * Lookup a PID in the hash table, and return with it's count elevated.
123  */
124 extern struct pid *find_get_pid(int nr);
125 extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
126 
127 extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
128                              size_t set_tid_size);
129 extern void free_pid(struct pid *pid);
130 extern void disable_pid_allocation(struct pid_namespace *ns);
131 
132 /*
133  * ns_of_pid() returns the pid namespace in which the specified pid was
134  * allocated.
135  *
136  * NOTE:
137  *      ns_of_pid() is expected to be called for a process (task) that has
138  *      an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
139  *      is expected to be non-NULL. If @pid is NULL, caller should handle
140  *      the resulting NULL pid-ns.
141  */
142 static inline struct pid_namespace *ns_of_pid(struct pid *pid)
143 {
144         struct pid_namespace *ns = NULL;
145         if (pid)
146                 ns = pid->numbers[pid->level].ns;
147         return ns;
148 }
149 
150 /*
151  * is_child_reaper returns true if the pid is the init process
152  * of the current namespace. As this one could be checked before
153  * pid_ns->child_reaper is assigned in copy_process, we check
154  * with the pid number.
155  */
156 static inline bool is_child_reaper(struct pid *pid)
157 {
158         return pid->numbers[pid->level].nr == 1;
159 }
160 
161 /*
162  * the helpers to get the pid's id seen from different namespaces
163  *
164  * pid_nr()    : global id, i.e. the id seen from the init namespace;
165  * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
166  *               current.
167  * pid_nr_ns() : id seen from the ns specified.
168  *
169  * see also task_xid_nr() etc in include/linux/sched.h
170  */
171 
172 static inline pid_t pid_nr(struct pid *pid)
173 {
174         pid_t nr = 0;
175         if (pid)
176                 nr = pid->numbers[0].nr;
177         return nr;
178 }
179 
180 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
181 pid_t pid_vnr(struct pid *pid);
182 
183 #define do_each_pid_task(pid, type, task)                               \
184         do {                                                            \
185                 if ((pid) != NULL)                                      \
186                         hlist_for_each_entry_rcu((task),                \
187                                 &(pid)->tasks[type], pid_links[type]) {
188 
189                         /*
190                          * Both old and new leaders may be attached to
191                          * the same pid in the middle of de_thread().
192                          */
193 #define while_each_pid_task(pid, type, task)                            \
194                                 if (type == PIDTYPE_PID)                \
195                                         break;                          \
196                         }                                               \
197         } while (0)
198 
199 #define do_each_pid_thread(pid, type, task)                             \
200         do_each_pid_task(pid, type, task) {                             \
201                 struct task_struct *tg___ = task;                       \
202                 for_each_thread(tg___, task) {
203 
204 #define while_each_pid_thread(pid, type, task)                          \
205                 }                                                       \
206                 task = tg___;                                           \
207         } while_each_pid_task(pid, type, task)
208 #endif /* _LINUX_PID_H */
209 

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