cregit-Linux how code gets into the kernel

Release 4.12 include/linux/pid.h

Directory: include/linux
#ifndef _LINUX_PID_H

#define _LINUX_PID_H

#include <linux/rculist.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 referring 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 (when pids wrap around) we don't mistakenly refer to new
 * processes.
 */


/*
 * struct upid is used to get the id of the struct pid, as it is
 * seen in particular namespace. Later the struct pid is found with
 * find_pid_ns() using the int nr and struct pid_namespace *ns.
 */


struct upid {
	/* Try to keep pid_chain in the same cacheline as nr for find_vpid */
	
int nr;
	
struct pid_namespace *ns;
	
struct hlist_node pid_chain;
};


struct pid
{
	
atomic_t count;
	
unsigned int level;
	/* lists of tasks that use this pid */
	
struct hlist_head tasks[PIDTYPE_MAX];
	
struct rcu_head rcu;
	
struct upid numbers[1];
};

extern struct pid init_struct_pid;


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; }

Contributors

PersonTokensPropCommitsCommitProp
Eric W. Biedermann2793.10%150.00%
Ingo Molnar26.90%150.00%
Total29100.00%2100.00%

extern void put_pid(struct pid *pid); extern struct task_struct *pid_task(struct pid *pid, enum pid_type); extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type); extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type); /* * these helpers must be called with the tasklist_lock write-held. */ extern void attach_pid(struct task_struct *task, enum pid_type); extern void detach_pid(struct task_struct *task, enum pid_type); extern void change_pid(struct task_struct *task, enum pid_type, struct pid *pid); extern void transfer_pid(struct task_struct *old, struct task_struct *new, enum pid_type); struct pid_namespace; extern struct pid_namespace init_pid_ns; /* * look up a PID in the hash table. Must be called with the tasklist_lock * or rcu_read_lock() held. * * find_pid_ns() finds the pid in the namespace specified * find_vpid() finds the pid by its virtual id, i.e. in the current namespace * * see also find_task_by_vpid() set in include/linux/sched.h */ extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns); extern struct pid *find_vpid(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 *find_ge_pid(int nr, struct pid_namespace *); int next_pidmap(struct pid_namespace *pid_ns, unsigned int last); extern struct pid *alloc_pid(struct pid_namespace *ns); extern void free_pid(struct pid *pid); extern void disable_pid_allocation(struct pid_namespace *ns); /* * ns_of_pid() returns the pid namespace in which the specified pid was * allocated. * * NOTE: * ns_of_pid() is expected to be called for a process (task) that has * an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid * is expected to be non-NULL. If @pid is NULL, caller should handle * the resulting NULL pid-ns. */
static inline struct pid_namespace *ns_of_pid(struct pid *pid) { struct pid_namespace *ns = NULL; if (pid) ns = pid->numbers[pid->level].ns; return ns; }

Contributors

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Eric W. Biedermann41100.00%1100.00%
Total41100.00%1100.00%

/* * is_child_reaper returns true if the pid is the init process * of the current namespace. As this one could be checked before * pid_ns->child_reaper is assigned in copy_process, we check * with the pid number. */
static inline bool is_child_reaper(struct pid *pid) { return pid->numbers[pid->level].nr == 1; }

Contributors

PersonTokensPropCommitsCommitProp
Eric W. Biedermann26100.00%1100.00%
Total26100.00%1100.00%

/* * the helpers to get the pid's id seen from different namespaces * * pid_nr() : global id, i.e. the id seen from the init namespace; * pid_vnr() : virtual id, i.e. the id seen from the pid namespace of * current. * pid_nr_ns() : id seen from the ns specified. * * see also task_xid_nr() etc in include/linux/sched.h */
static inline pid_t pid_nr(struct pid *pid) { pid_t nr = 0; if (pid) nr = pid->numbers[0].nr; return nr; }

Contributors

PersonTokensPropCommitsCommitProp
Eric W. Biedermann2468.57%150.00%
Pavel Emelyanov1131.43%150.00%
Total35100.00%2100.00%

pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns); pid_t pid_vnr(struct pid *pid); #define do_each_pid_task(pid, type, task) \ do { \ if ((pid) != NULL) \ hlist_for_each_entry_rcu((task), \ &(pid)->tasks[type], pids[type].node) { /* * Both old and new leaders may be attached to * the same pid in the middle of de_thread(). */ #define while_each_pid_task(pid, type, task) \ if (type == PIDTYPE_PID) \ break; \ } \ } while (0) #define do_each_pid_thread(pid, type, task) \ do_each_pid_task(pid, type, task) { \ struct task_struct *tg___ = task; \ for_each_thread(tg___, task) { #define while_each_pid_thread(pid, type, task) \ } \ task = tg___; \ } while_each_pid_task(pid, type, task) #endif /* _LINUX_PID_H */

Overall Contributors

PersonTokensPropCommitsCommitProp
Eric W. Biedermann24146.08%928.12%
Pavel Emelyanov7313.96%618.75%
Harvey Harrison6111.66%13.12%
Ingo Molnar489.18%39.38%
Oleg Nesterov387.27%412.50%
Sukadev Bhattiprolu305.74%26.25%
Ken Chen224.21%13.12%
Richard Kennedy40.76%13.12%
Tetsuo Handa20.38%13.12%
Linus Torvalds10.19%13.12%
Lucas De Marchi10.19%13.12%
Sisir Koppaka10.19%13.12%
Sasha Levin10.19%13.12%
Total523100.00%32100.00%
Directory: include/linux
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