/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_PID_H
#define _LINUX_PID_H

#include <linux/pid_types.h>
#include <linux/rculist.h>
#include <linux/rcupdate.h>
#include <linux/refcount.h>
#include <linux/rhashtable-types.h>
#include <linux/sched.h>
#include <linux/wait.h>

/*
 * 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.
 */

#define RESERVED_PIDS 300

struct pidfs_attr;

struct upid {
        int nr;
        struct pid_namespace *ns;
};

struct pid {
        refcount_t count;
        unsigned int level;
        spinlock_t lock;
        struct {
                u64 ino;
                struct rhash_head pidfs_hash;
                struct dentry *stashed;
                struct pidfs_attr *attr;
        };
        /* 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[];
};

extern struct pid init_struct_pid;

struct file;

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_prepare(struct pid *pid, unsigned int flags, struct file **ret_file);
void do_notify_pidfd(struct task_struct *task);

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);
void detach_pid(struct pid **pids, struct task_struct *task, enum pid_type);
void change_pid(struct pid **pids, 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);

/*
 * 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);
void free_pids(struct pid **pids);
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)

static inline struct pid *task_pid(struct task_struct *task)
{
        return task->thread_pid;
}

/*
 * the helpers to get the task's different pids as they are seen
 * from various namespaces
 *
 * task_xid_nr()     : global id, i.e. the id seen from the init namespace;
 * task_xid_vnr()    : virtual id, i.e. the id seen from the pid namespace of
 *                     current.
 * task_xid_nr_ns()  : id seen from the ns specified;
 *
 * see also pid_nr() etc in include/linux/pid.h
 */
pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type, struct pid_namespace *ns);

static inline pid_t task_pid_nr(struct task_struct *tsk)
{
        return tsk->pid;
}

static inline pid_t task_pid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
{
        return __task_pid_nr_ns(tsk, PIDTYPE_PID, ns);
}

static inline pid_t task_pid_vnr(struct task_struct *tsk)
{
        return __task_pid_nr_ns(tsk, PIDTYPE_PID, NULL);
}


static inline pid_t task_tgid_nr(struct task_struct *tsk)
{
        return tsk->tgid;
}

/**
 * pid_alive - check that a task structure is not stale
 * @p: Task structure to be checked.
 *
 * Test if a process is not yet dead (at most zombie state)
 * If pid_alive fails, then pointers within the task structure
 * can be stale and must not be dereferenced.
 *
 * Return: 1 if the process is alive. 0 otherwise.
 */
static inline int pid_alive(const struct task_struct *p)
{
        return p->thread_pid != NULL;
}

static inline pid_t task_pgrp_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
{
        return __task_pid_nr_ns(tsk, PIDTYPE_PGID, ns);
}

static inline pid_t task_pgrp_vnr(struct task_struct *tsk)
{
        return __task_pid_nr_ns(tsk, PIDTYPE_PGID, NULL);
}


static inline pid_t task_session_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
{
        return __task_pid_nr_ns(tsk, PIDTYPE_SID, ns);
}

static inline pid_t task_session_vnr(struct task_struct *tsk)
{
        return __task_pid_nr_ns(tsk, PIDTYPE_SID, NULL);
}

static inline pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
{
        return __task_pid_nr_ns(tsk, PIDTYPE_TGID, ns);
}

static inline pid_t task_tgid_vnr(struct task_struct *tsk)
{
        return __task_pid_nr_ns(tsk, PIDTYPE_TGID, NULL);
}

static inline pid_t task_ppid_nr_ns(const struct task_struct *tsk, struct pid_namespace *ns)
{
        pid_t pid = 0;

        rcu_read_lock();
        if (pid_alive(tsk))
                pid = task_tgid_nr_ns(rcu_dereference(tsk->real_parent), ns);
        rcu_read_unlock();

        return pid;
}

static inline pid_t task_ppid_vnr(const struct task_struct *tsk)
{
        return task_ppid_nr_ns(tsk, NULL);
}

static inline pid_t task_ppid_nr(const struct task_struct *tsk)
{
        return task_ppid_nr_ns(tsk, &init_pid_ns);
}

/* Obsolete, do not use: */
static inline pid_t task_pgrp_nr(struct task_struct *tsk)
{
        return task_pgrp_nr_ns(tsk, &init_pid_ns);
}

/**
 * is_global_init - check if a task structure is init. Since init
 * is free to have sub-threads we need to check tgid.
 * @tsk: Task structure to be checked.
 *
 * Check if a task structure is the first user space task the kernel created.
 *
 * Return: 1 if the task structure is init. 0 otherwise.
 */
static inline int is_global_init(struct task_struct *tsk)
{
        return task_tgid_nr(tsk) == 1;
}

#endif /* _LINUX_PID_H */