LCOV - code coverage report
Current view: top level - include/linux - pid.h (source / functions) Hit Total Coverage
Test: coverage.info Lines: 3 3 100.0 %
Date: 2017-01-25 Functions: 0 0 -

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

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