LCOV - code coverage report
Current view: top level - include/linux - pid.h (source / functions) Hit Total Coverage
Test: landlock.info Lines: 18 18 100.0 %
Date: 2021-04-22 12:43:58 Functions: 0 1 0.0 %

          Line data    Source code
       1             : /* SPDX-License-Identifier: GPL-2.0 */
       2             : #ifndef _LINUX_PID_H
       3             : #define _LINUX_PID_H
       4             : 
       5             : #include <linux/rculist.h>
       6             : #include <linux/wait.h>
       7             : #include <linux/refcount.h>
       8             : 
       9             : enum pid_type
      10             : {
      11             :         PIDTYPE_PID,
      12             :         PIDTYPE_TGID,
      13             :         PIDTYPE_PGID,
      14             :         PIDTYPE_SID,
      15             :         PIDTYPE_MAX,
      16             : };
      17             : 
      18             : /*
      19             :  * What is struct pid?
      20             :  *
      21             :  * A struct pid is the kernel's internal notion of a process identifier.
      22             :  * It refers to individual tasks, process groups, and sessions.  While
      23             :  * there are processes attached to it the struct pid lives in a hash
      24             :  * table, so it and then the processes that it refers to can be found
      25             :  * quickly from the numeric pid value.  The attached processes may be
      26             :  * quickly accessed by following pointers from struct pid.
      27             :  *
      28             :  * Storing pid_t values in the kernel and referring to them later has a
      29             :  * problem.  The process originally with that pid may have exited and the
      30             :  * pid allocator wrapped, and another process could have come along
      31             :  * and been assigned that pid.
      32             :  *
      33             :  * Referring to user space processes by holding a reference to struct
      34             :  * task_struct has a problem.  When the user space process exits
      35             :  * the now useless task_struct is still kept.  A task_struct plus a
      36             :  * stack consumes around 10K of low kernel memory.  More precisely
      37             :  * this is THREAD_SIZE + sizeof(struct task_struct).  By comparison
      38             :  * a struct pid is about 64 bytes.
      39             :  *
      40             :  * Holding a reference to struct pid solves both of these problems.
      41             :  * It is small so holding a reference does not consume a lot of
      42             :  * resources, and since a new struct pid is allocated when the numeric pid
      43             :  * value is reused (when pids wrap around) we don't mistakenly refer to new
      44             :  * processes.
      45             :  */
      46             : 
      47             : 
      48             : /*
      49             :  * struct upid is used to get the id of the struct pid, as it is
      50             :  * seen in particular namespace. Later the struct pid is found with
      51             :  * find_pid_ns() using the int nr and struct pid_namespace *ns.
      52             :  */
      53             : 
      54             : struct upid {
      55             :         int nr;
      56             :         struct pid_namespace *ns;
      57             : };
      58             : 
      59             : struct pid
      60             : {
      61             :         refcount_t count;
      62             :         unsigned int level;
      63             :         spinlock_t lock;
      64             :         /* lists of tasks that use this pid */
      65             :         struct hlist_head tasks[PIDTYPE_MAX];
      66             :         struct hlist_head inodes;
      67             :         /* wait queue for pidfd notifications */
      68             :         wait_queue_head_t wait_pidfd;
      69             :         struct rcu_head rcu;
      70             :         struct upid numbers[1];
      71             : };
      72             : 
      73             : extern struct pid init_struct_pid;
      74             : 
      75             : extern const struct file_operations pidfd_fops;
      76             : 
      77             : struct file;
      78             : 
      79             : extern struct pid *pidfd_pid(const struct file *file);
      80             : struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
      81             : 
      82        9802 : static inline struct pid *get_pid(struct pid *pid)
      83             : {
      84        9800 :         if (pid)
      85        7325 :                 refcount_inc(&pid->count);
      86        9802 :         return pid;
      87             : }
      88             : 
      89             : extern void put_pid(struct pid *pid);
      90             : extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
      91        7822 : static inline bool pid_has_task(struct pid *pid, enum pid_type type)
      92             : {
      93        7822 :         return !hlist_empty(&pid->tasks[type]);
      94             : }
      95             : extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
      96             : 
      97             : extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
      98             : 
      99             : /*
     100             :  * these helpers must be called with the tasklist_lock write-held.
     101             :  */
     102             : extern void attach_pid(struct task_struct *task, enum pid_type);
     103             : extern void detach_pid(struct task_struct *task, enum pid_type);
     104             : extern void change_pid(struct task_struct *task, enum pid_type,
     105             :                         struct pid *pid);
     106             : extern void exchange_tids(struct task_struct *task, struct task_struct *old);
     107             : extern void transfer_pid(struct task_struct *old, struct task_struct *new,
     108             :                          enum pid_type);
     109             : 
     110             : struct pid_namespace;
     111             : extern struct pid_namespace init_pid_ns;
     112             : 
     113             : extern int pid_max;
     114             : extern int pid_max_min, pid_max_max;
     115             : 
     116             : /*
     117             :  * look up a PID in the hash table. Must be called with the tasklist_lock
     118             :  * or rcu_read_lock() held.
     119             :  *
     120             :  * find_pid_ns() finds the pid in the namespace specified
     121             :  * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
     122             :  *
     123             :  * see also find_task_by_vpid() set in include/linux/sched.h
     124             :  */
     125             : extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
     126             : extern struct pid *find_vpid(int nr);
     127             : 
     128             : /*
     129             :  * Lookup a PID in the hash table, and return with it's count elevated.
     130             :  */
     131             : extern struct pid *find_get_pid(int nr);
     132             : extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
     133             : 
     134             : extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
     135             :                              size_t set_tid_size);
     136             : extern void free_pid(struct pid *pid);
     137             : extern void disable_pid_allocation(struct pid_namespace *ns);
     138             : 
     139             : /*
     140             :  * ns_of_pid() returns the pid namespace in which the specified pid was
     141             :  * allocated.
     142             :  *
     143             :  * NOTE:
     144             :  *      ns_of_pid() is expected to be called for a process (task) that has
     145             :  *      an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
     146             :  *      is expected to be non-NULL. If @pid is NULL, caller should handle
     147             :  *      the resulting NULL pid-ns.
     148             :  */
     149       10710 : static inline struct pid_namespace *ns_of_pid(struct pid *pid)
     150             : {
     151       10710 :         struct pid_namespace *ns = NULL;
     152       10710 :         if (pid)
     153       10710 :                 ns = pid->numbers[pid->level].ns;
     154        4263 :         return ns;
     155             : }
     156             : 
     157             : /*
     158             :  * is_child_reaper returns true if the pid is the init process
     159             :  * of the current namespace. As this one could be checked before
     160             :  * pid_ns->child_reaper is assigned in copy_process, we check
     161             :  * with the pid number.
     162             :  */
     163         908 : static inline bool is_child_reaper(struct pid *pid)
     164             : {
     165         908 :         return pid->numbers[pid->level].nr == 1;
     166             : }
     167             : 
     168             : /*
     169             :  * the helpers to get the pid's id seen from different namespaces
     170             :  *
     171             :  * pid_nr()    : global id, i.e. the id seen from the init namespace;
     172             :  * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
     173             :  *               current.
     174             :  * pid_nr_ns() : id seen from the ns specified.
     175             :  *
     176             :  * see also task_xid_nr() etc in include/linux/sched.h
     177             :  */
     178             : 
     179         916 : static inline pid_t pid_nr(struct pid *pid)
     180             : {
     181         916 :         pid_t nr = 0;
     182         916 :         if (pid)
     183         916 :                 nr = pid->numbers[0].nr;
     184         916 :         return nr;
     185             : }
     186             : 
     187             : pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
     188             : pid_t pid_vnr(struct pid *pid);
     189             : 
     190             : #define do_each_pid_task(pid, type, task)                               \
     191             :         do {                                                            \
     192             :                 if ((pid) != NULL)                                      \
     193             :                         hlist_for_each_entry_rcu((task),                \
     194             :                                 &(pid)->tasks[type], pid_links[type]) {
     195             : 
     196             :                         /*
     197             :                          * Both old and new leaders may be attached to
     198             :                          * the same pid in the middle of de_thread().
     199             :                          */
     200             : #define while_each_pid_task(pid, type, task)                            \
     201             :                                 if (type == PIDTYPE_PID)                \
     202             :                                         break;                          \
     203             :                         }                                               \
     204             :         } while (0)
     205             : 
     206             : #define do_each_pid_thread(pid, type, task)                             \
     207             :         do_each_pid_task(pid, type, task) {                             \
     208             :                 struct task_struct *tg___ = task;                       \
     209             :                 for_each_thread(tg___, task) {
     210             : 
     211             : #define while_each_pid_thread(pid, type, task)                          \
     212             :                 }                                                       \
     213             :                 task = tg___;                                           \
     214             :         } while_each_pid_task(pid, type, task)
     215             : #endif /* _LINUX_PID_H */

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