SYSTEM V SEMAPHORE

struct sem_array {
        struct kern_ipc_perm    ____cacheline_aligned_in_smp
                                sem_perm;       /* permissions .. see ipc.h */
        time_t                  sem_otime;      /* last semop time */
        time_t                  sem_ctime;      /* last change time */
        struct sem              *sem_base;      /* ptr to first semaphore in array */
        struct list_head        sem_pending;    /* pending operations to be processed */
        struct list_head        list_id;        /* undo requests on this array */
        int                     sem_nsems;      /* no. of semaphores in array */
        int                     complex_count;  /* pending complex operations */
};

struct sem {
        int     semval;         /* current value */
        int     sempid;         /* pid of last operation */
        struct list_head sem_pending; /* pending single-sop operations */
};