120 lines
3.3 KiB
C
120 lines
3.3 KiB
C
#ifndef _LINUX_PID_H
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#define _LINUX_PID_H
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#include <linux/rcupdate.h>
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enum pid_type
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{
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PIDTYPE_PID,
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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 refering 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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struct pid
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{
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atomic_t count;
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/* Try to keep pid_chain in the same cacheline as nr for find_pid */
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int nr;
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struct hlist_node pid_chain;
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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 rcu_head rcu;
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};
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struct pid_link
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{
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struct hlist_node node;
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struct pid *pid;
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};
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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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atomic_inc(&pid->count);
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return pid;
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}
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extern void FASTCALL(put_pid(struct pid *pid));
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extern struct task_struct *FASTCALL(pid_task(struct pid *pid, enum pid_type));
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extern struct task_struct *FASTCALL(get_pid_task(struct pid *pid,
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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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* attach_pid() and detach_pid() must be called with the tasklist_lock
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* write-held.
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*/
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extern int FASTCALL(attach_pid(struct task_struct *task,
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enum pid_type type, int nr));
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extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
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extern void FASTCALL(transfer_pid(struct task_struct *old,
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struct task_struct *new, enum pid_type));
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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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extern struct pid *FASTCALL(find_pid(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);
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extern struct pid *alloc_pid(void);
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extern void FASTCALL(free_pid(struct pid *pid));
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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->nr;
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return nr;
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}
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#define do_each_pid_task(pid, type, task) \
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do { \
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struct hlist_node *pos___; \
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if (pid != NULL) \
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hlist_for_each_entry_rcu((task), pos___, \
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&pid->tasks[type], pids[type].node) {
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#define while_each_pid_task(pid, type, task) \
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} \
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} while (0)
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#endif /* _LINUX_PID_H */
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