linux_kernel/include/linux/sem.h

#ifndef _LINUX_SEM_H
#define _LINUX_SEM_H

#include <linux/atomic.h>
#include <linux/rcupdate.h>
#include <linux/cache.h>
#include <linux/time64.h>
#include <uapi/linux/sem.h>

struct task_struct;

/* One semaphore structure for each semaphore in the system. */
struct sem {
	int	semval;		/* current value */
	/*
	 * PID of the process that last modified the semaphore. For
	 * Linux, specifically these are:
	 *  - semop
	 *  - semctl, via SETVAL and SETALL.
	 *  - at task exit when performing undo adjustments (see exit_sem).
	 */
	int	sempid;
	spinlock_t	lock;	/* spinlock for fine-grained semtimedop */
	struct list_head pending_alter; /* pending single-sop operations */
					/* that alter the semaphore */
	struct list_head pending_const; /* pending single-sop operations */
					/* that do not alter the semaphore*/
	time_t	sem_otime;	/* candidate for sem_otime */
} ____cacheline_aligned_in_smp;

/* One sem_array data structure for each set of semaphores in the system. */
struct sem_array {
	struct kern_ipc_perm	sem_perm;	/* permissions .. see ipc.h */
	time64_t		sem_ctime;	/* create/last semctl() time */
	struct list_head	pending_alter;	/* pending operations */
						/* that alter the array */
	struct list_head	pending_const;	/* pending complex operations */
						/* that do not alter semvals */
	struct list_head	list_id;	/* undo requests on this array */
	int			sem_nsems;	/* no. of semaphores in array */
	int			complex_count;	/* pending complex operations */
	unsigned int		use_global_lock;/* >0: global lock required */

	struct sem		sems[];
} __randomize_layout;

#ifdef CONFIG_SYSVIPC

struct sysv_sem {
	struct sem_undo_list *undo_list;
};

extern int copy_semundo(unsigned long clone_flags, struct task_struct *tsk);
extern void exit_sem(struct task_struct *tsk);

#else

struct sysv_sem {
	/* empty */
};

static inline int copy_semundo(unsigned long clone_flags, struct task_struct *tsk)
{
	return 0;
}

static inline void exit_sem(struct task_struct *tsk)
{
	return;
}
#endif

#endif /* _LINUX_SEM_H */