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#ifndef _LINUX_PID_H
#define _LINUX_PID_H
#include <linux/rcupdate.h>
enum pid_type
{
PIDTYPE_PID,
PIDTYPE_PGID,
PIDTYPE_SID,
PIDTYPE_MAX
};
/*
* 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 refering 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 we don't mistakenly refer to new processes.
*/
struct pid
{
atomic_t count;
/* Try to keep pid_chain in the same cacheline as nr for find_pid */
int nr;
struct hlist_node pid_chain;
/* lists of tasks that use this pid */
struct hlist_head tasks[PIDTYPE_MAX];
struct rcu_head rcu;
};
struct pid_link
{
struct hlist_node node;
struct pid *pid;
};
static inline struct pid *get_pid(struct pid *pid)
{
if (pid)
atomic_inc(&pid->count);
return pid;
}
extern void FASTCALL(put_pid(struct pid *pid));
extern struct task_struct *FASTCALL(pid_task(struct pid *pid, enum pid_type));
extern struct task_struct *FASTCALL(get_pid_task(struct pid *pid,
enum pid_type));
/*
* attach_pid() and detach_pid() must be called with the tasklist_lock
* write-held.
*/
extern int FASTCALL(attach_pid(struct task_struct *task,
enum pid_type type, int nr));
extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
/*
* look up a PID in the hash table. Must be called with the tasklist_lock
* or rcu_read_lock() held.
*/
extern struct pid *FASTCALL(find_pid(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 *alloc_pid(void);
extern void FASTCALL(free_pid(struct pid *pid));
#define pid_next(task, type) \
((task)->pids[(type)].node.next)
#define pid_next_task(task, type) \
hlist_entry(pid_next(task, type), struct task_struct, \
pids[(type)].node)
/* We could use hlist_for_each_entry_rcu here but it takes more arguments
* than the do_each_task_pid/while_each_task_pid. So we roll our own
* to preserve the existing interface.
*/
#define do_each_task_pid(who, type, task) \
if ((task = find_task_by_pid_type(type, who))) { \
prefetch(pid_next(task, type)); \
do {
#define while_each_task_pid(who, type, task) \
} while (pid_next(task, type) && ({ \
task = pid_next_task(task, type); \
rcu_dereference(task); \
prefetch(pid_next(task, type)); \
1; }) ); \
}
#endif /* _LINUX_PID_H */
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