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