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 extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type); 89 90 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type); 91 92 /* 93 * these helpers must be called with the tasklist_lock write-held. 94 */ 95 extern void attach_pid(struct task_struct *task, enum pid_type); 96 extern void detach_pid(struct task_struct *task, enum pid_type); 97 extern void change_pid(struct task_struct *task, enum pid_type, 98 struct pid *pid); 99 extern void transfer_pid(struct task_struct *old, struct task_struct *new, 100 enum pid_type); 101 102 struct pid_namespace; 103 extern struct pid_namespace init_pid_ns; 104 105 /* 106 * look up a PID in the hash table. Must be called with the tasklist_lock 107 * or rcu_read_lock() held. 108 * 109 * find_pid_ns() finds the pid in the namespace specified 110 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace 111 * 112 * see also find_task_by_vpid() set in include/linux/sched.h 113 */ 114 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns); 115 extern struct pid *find_vpid(int nr); 116 117 /* 118 * Lookup a PID in the hash table, and return with it's count elevated. 119 */ 120 extern struct pid *find_get_pid(int nr); 121 extern struct pid *find_ge_pid(int nr, struct pid_namespace *); 122 123 extern struct pid *alloc_pid(struct pid_namespace *ns); 124 extern void free_pid(struct pid *pid); 125 extern void disable_pid_allocation(struct pid_namespace *ns); 126 127 /* 128 * ns_of_pid() returns the pid namespace in which the specified pid was 129 * allocated. 130 * 131 * NOTE: 132 * ns_of_pid() is expected to be called for a process (task) that has 133 * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid 134 * is expected to be non-NULL. If @pid is NULL, caller should handle 135 * the resulting NULL pid-ns. 136 */ 137 static inline struct pid_namespace *ns_of_pid(struct pid *pid) 138 { 139 struct pid_namespace *ns = NULL; 140 if (pid) 141 ns = pid->numbers[pid->level].ns; 142 return ns; 143 } 144 145 /* 146 * is_child_reaper returns true if the pid is the init process 147 * of the current namespace. As this one could be checked before 148 * pid_ns->child_reaper is assigned in copy_process, we check 149 * with the pid number. 150 */ 151 static inline bool is_child_reaper(struct pid *pid) 152 { 153 return pid->numbers[pid->level].nr == 1; 154 } 155 156 /* 157 * the helpers to get the pid's id seen from different namespaces 158 * 159 * pid_nr() : global id, i.e. the id seen from the init namespace; 160 * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of 161 * current. 162 * pid_nr_ns() : id seen from the ns specified. 163 * 164 * see also task_xid_nr() etc in include/linux/sched.h 165 */ 166 167 static inline pid_t pid_nr(struct pid *pid) 168 { 169 pid_t nr = 0; 170 if (pid) 171 nr = pid->numbers[0].nr; 172 return nr; 173 } 174 175 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns); 176 pid_t pid_vnr(struct pid *pid); 177 178 #define do_each_pid_task(pid, type, task) \ 179 do { \ 180 if ((pid) != NULL) \ 181 hlist_for_each_entry_rcu((task), \ 182 &(pid)->tasks[type], pid_links[type]) { 183 184 /* 185 * Both old and new leaders may be attached to 186 * the same pid in the middle of de_thread(). 187 */ 188 #define while_each_pid_task(pid, type, task) \ 189 if (type == PIDTYPE_PID) \ 190 break; \ 191 } \ 192 } while (0) 193 194 #define do_each_pid_thread(pid, type, task) \ 195 do_each_pid_task(pid, type, task) { \ 196 struct task_struct *tg___ = task; \ 197 for_each_thread(tg___, task) { 198 199 #define while_each_pid_thread(pid, type, task) \ 200 } \ 201 task = tg___; \ 202 } while_each_pid_task(pid, type, task) 203 #endif /* _LINUX_PID_H */ 204