v4.19.13 snapshot.
diff --git a/include/linux/pid.h b/include/linux/pid.h
new file mode 100644
index 0000000..14a9a39
--- /dev/null
+++ b/include/linux/pid.h
@@ -0,0 +1,194 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_PID_H
+#define _LINUX_PID_H
+
+#include <linux/rculist.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
+{
+ atomic_t count;
+ unsigned int level;
+ /* lists of tasks that use this pid */
+ struct hlist_head tasks[PIDTYPE_MAX];
+ struct rcu_head rcu;
+ struct upid numbers[1];
+};
+
+extern struct pid init_struct_pid;
+
+static inline struct pid *get_pid(struct pid *pid)
+{
+ if (pid)
+ atomic_inc(&pid->count);
+ return pid;
+}
+
+extern void put_pid(struct pid *pid);
+extern struct task_struct *pid_task(struct pid *pid, enum pid_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 transfer_pid(struct task_struct *old, struct task_struct *new,
+ enum pid_type);
+
+struct pid_namespace;
+extern struct pid_namespace init_pid_ns;
+
+/*
+ * 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 *);
+int next_pidmap(struct pid_namespace *pid_ns, unsigned int last);
+
+extern struct pid *alloc_pid(struct pid_namespace *ns);
+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 */