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 spinlock_t lock; 64 /* lists of tasks that use this pid */ 65 struct hlist_head tasks[PIDTYPE_MAX]; 66 struct hlist_head inodes; 67 /* wait queue for pidfd notifications */ 68 wait_queue_head_t wait_pidfd; 69 struct rcu_head rcu; 70 struct upid numbers[1]; 71 }; 72 73 extern struct pid init_struct_pid; 74 75 extern const struct file_operations pidfd_fops; 76 77 struct file; 78 79 extern struct pid *pidfd_pid(const struct file *file); 80 struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags); 81 struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags); 82 int pidfd_create(struct pid *pid, unsigned int flags); 83 84 static inline struct pid *get_pid(struct pid *pid) 85 { 86 if (pid) 87 refcount_inc(&pid->count); 88 return pid; 89 } 90 91 extern void put_pid(struct pid *pid); 92 extern struct task_struct *pid_task(struct pid *pid, enum pid_type); 93 static inline bool pid_has_task(struct pid *pid, enum pid_type type) 94 { 95 return !hlist_empty(&pid->tasks[type]); 96 } 97 extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type); 98 99 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type); 100 101 /* 102 * these helpers must be called with the tasklist_lock write-held. 103 */ 104 extern void attach_pid(struct task_struct *task, enum pid_type); 105 extern void detach_pid(struct task_struct *task, enum pid_type); 106 extern void change_pid(struct task_struct *task, enum pid_type, 107 struct pid *pid); 108 extern void exchange_tids(struct task_struct *task, struct task_struct *old); 109 extern void transfer_pid(struct task_struct *old, struct task_struct *new, 110 enum pid_type); 111 112 struct pid_namespace; 113 extern struct pid_namespace init_pid_ns; 114 115 extern int pid_max; 116 extern int pid_max_min, pid_max_max; 117 118 /* 119 * look up a PID in the hash table. Must be called with the tasklist_lock 120 * or rcu_read_lock() held. 121 * 122 * find_pid_ns() finds the pid in the namespace specified 123 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace 124 * 125 * see also find_task_by_vpid() set in include/linux/sched.h 126 */ 127 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns); 128 extern struct pid *find_vpid(int nr); 129 130 /* 131 * Lookup a PID in the hash table, and return with it's count elevated. 132 */ 133 extern struct pid *find_get_pid(int nr); 134 extern struct pid *find_ge_pid(int nr, struct pid_namespace *); 135 136 extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid, 137 size_t set_tid_size); 138 extern void free_pid(struct pid *pid); 139 extern void disable_pid_allocation(struct pid_namespace *ns); 140 141 /* 142 * ns_of_pid() returns the pid namespace in which the specified pid was 143 * allocated. 144 * 145 * NOTE: 146 * ns_of_pid() is expected to be called for a process (task) that has 147 * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid 148 * is expected to be non-NULL. If @pid is NULL, caller should handle 149 * the resulting NULL pid-ns. 150 */ 151 static inline struct pid_namespace *ns_of_pid(struct pid *pid) 152 { 153 struct pid_namespace *ns = NULL; 154 if (pid) 155 ns = pid->numbers[pid->level].ns; 156 return ns; 157 } 158 159 /* 160 * is_child_reaper returns true if the pid is the init process 161 * of the current namespace. As this one could be checked before 162 * pid_ns->child_reaper is assigned in copy_process, we check 163 * with the pid number. 164 */ 165 static inline bool is_child_reaper(struct pid *pid) 166 { 167 return pid->numbers[pid->level].nr == 1; 168 } 169 170 /* 171 * the helpers to get the pid's id seen from different namespaces 172 * 173 * pid_nr() : global id, i.e. the id seen from the init namespace; 174 * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of 175 * current. 176 * pid_nr_ns() : id seen from the ns specified. 177 * 178 * see also task_xid_nr() etc in include/linux/sched.h 179 */ 180 181 static inline pid_t pid_nr(struct pid *pid) 182 { 183 pid_t nr = 0; 184 if (pid) 185 nr = pid->numbers[0].nr; 186 return nr; 187 } 188 189 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns); 190 pid_t pid_vnr(struct pid *pid); 191 192 #define do_each_pid_task(pid, type, task) \ 193 do { \ 194 if ((pid) != NULL) \ 195 hlist_for_each_entry_rcu((task), \ 196 &(pid)->tasks[type], pid_links[type]) { 197 198 /* 199 * Both old and new leaders may be attached to 200 * the same pid in the middle of de_thread(). 201 */ 202 #define while_each_pid_task(pid, type, task) \ 203 if (type == PIDTYPE_PID) \ 204 break; \ 205 } \ 206 } while (0) 207 208 #define do_each_pid_thread(pid, type, task) \ 209 do_each_pid_task(pid, type, task) { \ 210 struct task_struct *tg___ = task; \ 211 for_each_thread(tg___, task) { 212 213 #define while_each_pid_thread(pid, type, task) \ 214 } \ 215 task = tg___; \ 216 } while_each_pid_task(pid, type, task) 217 #endif /* _LINUX_PID_H */ 218