According md.c:
* We have a system wide 'event count' that is incremented
* on any 'interesting' event, and readers of /proc/mdstat
* can use 'poll' or 'select' to find out when the event
* count increases.
Events are:
* start array, stop array, error, add device, remove device,
* start build, activate spare
I wanted to monitor RAID5 events,so I writed a c-function:
int fd = open("/proc/mdstat",O_RDONLY);
if(fd < 0){
printf("open /proc/mdstat error:%s\n",strerror(errno));
return -errno;
}
struct pollfd fds[1];
int ret;
fds[0].fd = fd;
fds[0].events = POLLPRI;
while(1){
fds[0].fd = fd;
fds[0].events = POLLPRI;
ret = poll(fds,1,-1);
if(ret < 0){
printf("poll error:%s\n",strerror(errno));
break;
}else
printf("ret value=%d\n",ret);
}
close(fd);
But this function did not run like my thought.
After a raid event occured,the poll did not blocked,.The function only well at first.
I wrote anthoer function:
do{
int fd = open("/proc/mdstat",O_RDONLY);
if(fd < 0){
printf("open /proc/mdstat error:%s\n",strerror(errno));
return ;
}
struct pollfd fds;
memset(&fds,0, sizeof(struct pollfd));
fds.fd = fd;
fds.events = POLLPRI|POLLERR;
if(poll(&fds,1,-1) == -1){
printf("poll error:%s\n",strerror(errno));
break;
}
printf("return events:%d\n",fds.revents);
close(fd);
}while(1);
this function work well, can return when raid_event occured.
I read the source found:
static unsigned int mdstat_poll(struct file *filp, poll_table *wait)
{
struct seq_file *m = filp->private_data;
struct mdstat_info *mi = m->private;
int mask;
poll_wait(filp, &md_event_waiters, wait);
/* always allow read */
mask = POLLIN | POLLRDNORM;
if (mi->event != atomic_read(&md_event_count)){
mask |= POLLERR | POLLPRI;
}
return mask;
}
the mi->event assigned at function:md_seq_open.
When open /proc/mdstat,the mi->event = md_event_count, so the first poll blocked.
But after poll return,mi->event != md_event_count,so the rest poll must immediately return.
In second function,every time I opend /proc/mdstat,so mi->event = md_event_count, when blocked
2010-12-25
kernel.majianpeng
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