1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef _LINUX_PID_H 3 #define _LINUX_PID_H 4 5 #include <linux/pid_types.h> 6 #include <linux/rculist.h> 7 #include <linux/refcount.h> 8 #include <linux/wait.h> 9 10 /* 11 * What is struct pid? 12 * 13 * A struct pid is the kernel's internal notion of a process identifier. 14 * It refers to individual tasks, process groups, and sessions. While 15 * there are processes attached to it the struct pid lives in a hash 16 * table, so it and then the processes that it refers to can be found 17 * quickly from the numeric pid value. The attached processes may be 18 * quickly accessed by following pointers from struct pid. 19 * 20 * Storing pid_t values in the kernel and referring to them later has a 21 * problem. The process originally with that pid may have exited and the 22 * pid allocator wrapped, and another process could have come along 23 * and been assigned that pid. 24 * 25 * Referring to user space processes by holding a reference to struct 26 * task_struct has a problem. When the user space process exits 27 * the now useless task_struct is still kept. A task_struct plus a 28 * stack consumes around 10K of low kernel memory. More precisely 29 * this is THREAD_SIZE + sizeof(struct task_struct). By comparison 30 * a struct pid is about 64 bytes. 31 * 32 * Holding a reference to struct pid solves both of these problems. 33 * It is small so holding a reference does not consume a lot of 34 * resources, and since a new struct pid is allocated when the numeric pid 35 * value is reused (when pids wrap around) we don't mistakenly refer to new 36 * processes. 37 */ 38 39 40 /* 41 * struct upid is used to get the id of the struct pid, as it is 42 * seen in particular namespace. Later the struct pid is found with 43 * find_pid_ns() using the int nr and struct pid_namespace *ns. 44 */ 45 46 struct upid { 47 int nr; 48 struct pid_namespace *ns; 49 }; 50 51 struct pid 52 { 53 refcount_t count; 54 unsigned int level; 55 spinlock_t lock; 56 /* lists of tasks that use this pid */ 57 struct hlist_head tasks[PIDTYPE_MAX]; 58 struct hlist_head inodes; 59 /* wait queue for pidfd notifications */ 60 wait_queue_head_t wait_pidfd; 61 struct rcu_head rcu; 62 struct upid numbers[]; 63 }; 64 65 extern struct pid init_struct_pid; 66 67 extern const struct file_operations pidfd_fops; 68 69 struct file; 70 71 extern struct pid *pidfd_pid(const struct file *file); 72 struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags); 73 struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags); 74 int pidfd_create(struct pid *pid, unsigned int flags); 75 int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret); 76 77 static inline struct pid *get_pid(struct pid *pid) 78 { 79 if (pid) 80 refcount_inc(&pid->count); 81 return pid; 82 } 83 84 extern void put_pid(struct pid *pid); 85 extern struct task_struct *pid_task(struct pid *pid, enum pid_type); 86 static inline bool pid_has_task(struct pid *pid, enum pid_type type) 87 { 88 return !hlist_empty(&pid->tasks[type]); 89 } 90 extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type); 91 92 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type); 93 94 /* 95 * these helpers must be called with the tasklist_lock write-held. 96 */ 97 extern void attach_pid(struct task_struct *task, enum pid_type); 98 extern void detach_pid(struct task_struct *task, enum pid_type); 99 extern void change_pid(struct task_struct *task, enum pid_type, 100 struct pid *pid); 101 extern void exchange_tids(struct task_struct *task, struct task_struct *old); 102 extern void transfer_pid(struct task_struct *old, struct task_struct *new, 103 enum pid_type); 104 105 extern int pid_max; 106 extern int pid_max_min, pid_max_max; 107 108 /* 109 * look up a PID in the hash table. Must be called with the tasklist_lock 110 * or rcu_read_lock() held. 111 * 112 * find_pid_ns() finds the pid in the namespace specified 113 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace 114 * 115 * see also find_task_by_vpid() set in include/linux/sched.h 116 */ 117 extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns); 118 extern struct pid *find_vpid(int nr); 119 120 /* 121 * Lookup a PID in the hash table, and return with it's count elevated. 122 */ 123 extern struct pid *find_get_pid(int nr); 124 extern struct pid *find_ge_pid(int nr, struct pid_namespace *); 125 126 extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid, 127 size_t set_tid_size); 128 extern void free_pid(struct pid *pid); 129 extern void disable_pid_allocation(struct pid_namespace *ns); 130 131 /* 132 * ns_of_pid() returns the pid namespace in which the specified pid was 133 * allocated. 134 * 135 * NOTE: 136 * ns_of_pid() is expected to be called for a process (task) that has 137 * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid 138 * is expected to be non-NULL. If @pid is NULL, caller should handle 139 * the resulting NULL pid-ns. 140 */ 141 static inline struct pid_namespace *ns_of_pid(struct pid *pid) 142 { 143 struct pid_namespace *ns = NULL; 144 if (pid) 145 ns = pid->numbers[pid->level].ns; 146 return ns; 147 } 148 149 /* 150 * is_child_reaper returns true if the pid is the init process 151 * of the current namespace. As this one could be checked before 152 * pid_ns->child_reaper is assigned in copy_process, we check 153 * with the pid number. 154 */ 155 static inline bool is_child_reaper(struct pid *pid) 156 { 157 return pid->numbers[pid->level].nr == 1; 158 } 159 160 /* 161 * the helpers to get the pid's id seen from different namespaces 162 * 163 * pid_nr() : global id, i.e. the id seen from the init namespace; 164 * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of 165 * current. 166 * pid_nr_ns() : id seen from the ns specified. 167 * 168 * see also task_xid_nr() etc in include/linux/sched.h 169 */ 170 171 static inline pid_t pid_nr(struct pid *pid) 172 { 173 pid_t nr = 0; 174 if (pid) 175 nr = pid->numbers[0].nr; 176 return nr; 177 } 178 179 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns); 180 pid_t pid_vnr(struct pid *pid); 181 182 #define do_each_pid_task(pid, type, task) \ 183 do { \ 184 if ((pid) != NULL) \ 185 hlist_for_each_entry_rcu((task), \ 186 &(pid)->tasks[type], pid_links[type]) { 187 188 /* 189 * Both old and new leaders may be attached to 190 * the same pid in the middle of de_thread(). 191 */ 192 #define while_each_pid_task(pid, type, task) \ 193 if (type == PIDTYPE_PID) \ 194 break; \ 195 } \ 196 } while (0) 197 198 #define do_each_pid_thread(pid, type, task) \ 199 do_each_pid_task(pid, type, task) { \ 200 struct task_struct *tg___ = task; \ 201 for_each_thread(tg___, task) { 202 203 #define while_each_pid_thread(pid, type, task) \ 204 } \ 205 task = tg___; \ 206 } while_each_pid_task(pid, type, task) 207 #endif /* _LINUX_PID_H */ 208