麻煩解釋一下 attach_shm()
void *attach_shm(int shmkey, int shmsize) {
void *shmptr;
int shmid;
char *empty_addr;
/* set up one page in-accessible -- jochang */
{
int fd = open("/dev/zero",O_RDONLY);
int size = ((shmsize + 4095) / 4096) * 4096;
munmap(
(empty_addr=mmap(0,4096+size,PROT_NONE,MAP_PRIVATE,fd,0))+4096
,size);
close(fd);
}
shmid = shmget(shmkey, shmsize, 0);
if(shmid < 0) {
shmid = shmget(shmkey, shmsize, IPC_CREAT | 0600);
if(shmid < 0)
attach_err(shmkey, "shmget");
shmptr = (void *)shmat(shmid, NULL, 0);
if(shmptr == (void *)-1)
attach_err(shmkey, "shmat");
} else {
shmptr = (void *)shmat(shmid, NULL, 0);
if(shmptr == (void *)-1)
attach_err(shmkey, "shmat");
}
/* unmap the page -- jochang */
{
munmap(empty_addr,4096);
}
return shmptr;
}
為什麼要 mmap ??
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 140.112.30.143