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_pid */ 52 int nr; 53 struct pid_namespace *ns; 54 struct hlist_node pid_chain; 55 }; 56 57 struct pid 58 { 59 atomic_t count; 60 /* lists of tasks that use this pid */ 61 struct hlist_head tasks[PIDTYPE_MAX]; 62 struct rcu_head rcu; 63 int level; 64 struct upid numbers[1]; 65 }; 66 67 extern struct pid init_struct_pid; 68 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 FASTCALL(put_pid(struct pid *pid)); 83 extern struct task_struct *FASTCALL(pid_task(struct pid *pid, enum pid_type)); 84 extern struct task_struct *FASTCALL(get_pid_task(struct pid *pid, 85 enum pid_type)); 86 87 extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type); 88 89 /* 90 * attach_pid() and detach_pid() must be called with the tasklist_lock 91 * write-held. 92 */ 93 extern int FASTCALL(attach_pid(struct task_struct *task, 94 enum pid_type type, struct pid *pid)); 95 extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type)); 96 extern void FASTCALL(transfer_pid(struct task_struct *old, 97 struct task_struct *new, enum pid_type)); 98 99 struct pid_namespace; 100 extern struct pid_namespace init_pid_ns; 101 102 /* 103 * look up a PID in the hash table. Must be called with the tasklist_lock 104 * or rcu_read_lock() held. 105 * 106 * find_pid_ns() finds the pid in the namespace specified 107 * find_pid() find the pid by its global id, i.e. in the init namespace 108 * find_vpid() finr the pid by its virtual id, i.e. in the current namespace 109 * 110 * see also find_task_by_pid() set in include/linux/sched.h 111 */ 112 extern struct pid *FASTCALL(find_pid_ns(int nr, struct pid_namespace *ns)); 113 extern struct pid *find_vpid(int nr); 114 extern struct pid *find_pid(int nr); 115 116 /* 117 * Lookup a PID in the hash table, and return with it's count elevated. 118 */ 119 extern struct pid *find_get_pid(int nr); 120 extern struct pid *find_ge_pid(int nr, struct pid_namespace *); 121 122 extern struct pid *alloc_pid(struct pid_namespace *ns); 123 extern void FASTCALL(free_pid(struct pid *pid)); 124 extern void zap_pid_ns_processes(struct pid_namespace *pid_ns); 125 126 /* 127 * the helpers to get the pid's id seen from different namespaces 128 * 129 * pid_nr() : global id, i.e. the id seen from the init namespace; 130 * pid_vnr() : virtual id, i.e. the id seen from the namespace this pid 131 * belongs to. this only makes sence when called in the 132 * context of the task that belongs to the same namespace; 133 * pid_nr_ns() : id seen from the ns specified. 134 * 135 * see also task_xid_nr() etc in include/linux/sched.h 136 */ 137 138 static inline pid_t pid_nr(struct pid *pid) 139 { 140 pid_t nr = 0; 141 if (pid) 142 nr = pid->numbers[0].nr; 143 return nr; 144 } 145 146 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns); 147 148 static inline pid_t pid_vnr(struct pid *pid) 149 { 150 pid_t nr = 0; 151 if (pid) 152 nr = pid->numbers[pid->level].nr; 153 return nr; 154 } 155 156 #define do_each_pid_task(pid, type, task) \ 157 do { \ 158 struct hlist_node *pos___; \ 159 if (pid != NULL) \ 160 hlist_for_each_entry_rcu((task), pos___, \ 161 &pid->tasks[type], pids[type].node) { 162 163 #define while_each_pid_task(pid, type, task) \ 164 } \ 165 } while (0) 166 167 #endif /* _LINUX_PID_H */ 168