| /* SPDX-License-Identifier: GPL-2.0 */ |
| #ifndef _LINUX_PID_H |
| #define _LINUX_PID_H |
| |
| #include <linux/rculist.h> |
| #include <linux/wait.h> |
| #include <linux/refcount.h> |
| |
| enum pid_type |
| { |
| PIDTYPE_PID, |
| PIDTYPE_TGID, |
| PIDTYPE_PGID, |
| PIDTYPE_SID, |
| PIDTYPE_MAX, |
| }; |
| |
| /* |
| * What is struct pid? |
| * |
| * A struct pid is the kernel's internal notion of a process identifier. |
| * It refers to individual tasks, process groups, and sessions. While |
| * there are processes attached to it the struct pid lives in a hash |
| * table, so it and then the processes that it refers to can be found |
| * quickly from the numeric pid value. The attached processes may be |
| * quickly accessed by following pointers from struct pid. |
| * |
| * Storing pid_t values in the kernel and referring to them later has a |
| * problem. The process originally with that pid may have exited and the |
| * pid allocator wrapped, and another process could have come along |
| * and been assigned that pid. |
| * |
| * Referring to user space processes by holding a reference to struct |
| * task_struct has a problem. When the user space process exits |
| * the now useless task_struct is still kept. A task_struct plus a |
| * stack consumes around 10K of low kernel memory. More precisely |
| * this is THREAD_SIZE + sizeof(struct task_struct). By comparison |
| * a struct pid is about 64 bytes. |
| * |
| * Holding a reference to struct pid solves both of these problems. |
| * It is small so holding a reference does not consume a lot of |
| * resources, and since a new struct pid is allocated when the numeric pid |
| * value is reused (when pids wrap around) we don't mistakenly refer to new |
| * processes. |
| */ |
| |
| |
| /* |
| * struct upid is used to get the id of the struct pid, as it is |
| * seen in particular namespace. Later the struct pid is found with |
| * find_pid_ns() using the int nr and struct pid_namespace *ns. |
| */ |
| |
| struct upid { |
| int nr; |
| struct pid_namespace *ns; |
| }; |
| |
| struct pid |
| { |
| refcount_t count; |
| unsigned int level; |
| spinlock_t lock; |
| /* lists of tasks that use this pid */ |
| struct hlist_head tasks[PIDTYPE_MAX]; |
| struct hlist_head inodes; |
| /* wait queue for pidfd notifications */ |
| wait_queue_head_t wait_pidfd; |
| struct rcu_head rcu; |
| struct upid numbers[1]; |
| }; |
| |
| extern struct pid init_struct_pid; |
| |
| extern const struct file_operations pidfd_fops; |
| |
| struct file; |
| |
| extern struct pid *pidfd_pid(const struct file *file); |
| struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags); |
| struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags); |
| int pidfd_create(struct pid *pid, unsigned int flags); |
| |
| static inline struct pid *get_pid(struct pid *pid) |
| { |
| if (pid) |
| refcount_inc(&pid->count); |
| return pid; |
| } |
| |
| extern void put_pid(struct pid *pid); |
| extern struct task_struct *pid_task(struct pid *pid, enum pid_type); |
| static inline bool pid_has_task(struct pid *pid, enum pid_type type) |
| { |
| return !hlist_empty(&pid->tasks[type]); |
| } |
| extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type); |
| |
| extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type); |
| |
| /* |
| * these helpers must be called with the tasklist_lock write-held. |
| */ |
| extern void attach_pid(struct task_struct *task, enum pid_type); |
| extern void detach_pid(struct task_struct *task, enum pid_type); |
| extern void change_pid(struct task_struct *task, enum pid_type, |
| struct pid *pid); |
| extern void exchange_tids(struct task_struct *task, struct task_struct *old); |
| extern void transfer_pid(struct task_struct *old, struct task_struct *new, |
| enum pid_type); |
| |
| struct pid_namespace; |
| extern struct pid_namespace init_pid_ns; |
| |
| extern int pid_max; |
| extern int pid_max_min, pid_max_max; |
| |
| /* |
| * look up a PID in the hash table. Must be called with the tasklist_lock |
| * or rcu_read_lock() held. |
| * |
| * find_pid_ns() finds the pid in the namespace specified |
| * find_vpid() finds the pid by its virtual id, i.e. in the current namespace |
| * |
| * see also find_task_by_vpid() set in include/linux/sched.h |
| */ |
| extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns); |
| extern struct pid *find_vpid(int nr); |
| |
| /* |
| * Lookup a PID in the hash table, and return with it's count elevated. |
| */ |
| extern struct pid *find_get_pid(int nr); |
| extern struct pid *find_ge_pid(int nr, struct pid_namespace *); |
| |
| extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid, |
| size_t set_tid_size); |
| extern void free_pid(struct pid *pid); |
| extern void disable_pid_allocation(struct pid_namespace *ns); |
| |
| /* |
| * ns_of_pid() returns the pid namespace in which the specified pid was |
| * allocated. |
| * |
| * NOTE: |
| * ns_of_pid() is expected to be called for a process (task) that has |
| * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid |
| * is expected to be non-NULL. If @pid is NULL, caller should handle |
| * the resulting NULL pid-ns. |
| */ |
| static inline struct pid_namespace *ns_of_pid(struct pid *pid) |
| { |
| struct pid_namespace *ns = NULL; |
| if (pid) |
| ns = pid->numbers[pid->level].ns; |
| return ns; |
| } |
| |
| /* |
| * is_child_reaper returns true if the pid is the init process |
| * of the current namespace. As this one could be checked before |
| * pid_ns->child_reaper is assigned in copy_process, we check |
| * with the pid number. |
| */ |
| static inline bool is_child_reaper(struct pid *pid) |
| { |
| return pid->numbers[pid->level].nr == 1; |
| } |
| |
| /* |
| * the helpers to get the pid's id seen from different namespaces |
| * |
| * pid_nr() : global id, i.e. the id seen from the init namespace; |
| * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of |
| * current. |
| * pid_nr_ns() : id seen from the ns specified. |
| * |
| * see also task_xid_nr() etc in include/linux/sched.h |
| */ |
| |
| static inline pid_t pid_nr(struct pid *pid) |
| { |
| pid_t nr = 0; |
| if (pid) |
| nr = pid->numbers[0].nr; |
| return nr; |
| } |
| |
| pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns); |
| pid_t pid_vnr(struct pid *pid); |
| |
| #define do_each_pid_task(pid, type, task) \ |
| do { \ |
| if ((pid) != NULL) \ |
| hlist_for_each_entry_rcu((task), \ |
| &(pid)->tasks[type], pid_links[type]) { |
| |
| /* |
| * Both old and new leaders may be attached to |
| * the same pid in the middle of de_thread(). |
| */ |
| #define while_each_pid_task(pid, type, task) \ |
| if (type == PIDTYPE_PID) \ |
| break; \ |
| } \ |
| } while (0) |
| |
| #define do_each_pid_thread(pid, type, task) \ |
| do_each_pid_task(pid, type, task) { \ |
| struct task_struct *tg___ = task; \ |
| for_each_thread(tg___, task) { |
| |
| #define while_each_pid_thread(pid, type, task) \ |
| } \ |
| task = tg___; \ |
| } while_each_pid_task(pid, type, task) |
| #endif /* _LINUX_PID_H */ |