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