Shared Memory Segment's Infomation

每個Segment的相關資料，都可以經由shmctl(segment_id, IPC_STAT, &shmbuffer)來取得

而shmbuffer是struct shmid_ds (在/usr/include/sys/shm.h中)，

裏面有些欄位來說明一下：

int shm_segsz: size of the shared memory

short shm_nattch: number of attaches to the segment

struct ipc_perm shm_perm:permission structure

而ipc_perm在/usr/include/sys/ipc.h中，裏面有些欄位是

unsigned short uid: identifier of the user of the segment

unsigned short mode : permission modes

key_t key(on linux is __key) : user-specified key identifier

下面是個簡單的實作範例：

#include 
#include 
#include 
#include 

int main(){
        int segment_id;
        struct shmid_ds shmbuffer;

        segment_id = shmget(IPC_PRIVATE, 4096, S_IRUSR | S_IWUSR);
        shmctl(segment_id, IPC_STAT, &shmbuffer);
        printf("Seg ID\tKey\tMode\tOwner\tSize\tAttaches\n");
        printf("%d\t%d\t%o\t%d\t%d\t%d\n", segment_id, shmbuffer.shm_perm.__key,
                shmbuffer.shm_perm.mode, shmbuffer.shm_perm.uid, shmbuffer.shm_segsz,
                shmbuffer.shm_nattch);
        shmctl(segment_id, IPC_RMID, NULL);
        return 0;
}

不過unix中有提供一個工具是ipcs就是類似這的output了，只是這裡寫的是極陽春版....