(unknown)

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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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

--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html

Hi all:
read Neil Brown's mail, I modified the function:

char buff[4096] = {0};
	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",fds[0].revents);
		read(fd,buff,4096);
		memset(buff ,0,4096);
	}
	close(fd);

I add read command and confirm read end of file /proc/mdstat. But this fution also to find only one event.

poll will only block again after you read to the end of the file (and thus observe any change), and then seek back to the start.