[BUG] Using inotify on /proc/partitoins

[BUG] Using inotify on /proc/partitoins

[majianpeng]

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Hi all,
     I wanted to monitor /proc/partitions using inotify.Although now i know it can't catch the event of write.
But for read,it can't catch. The code is:
int main()
{
	int fd = inotify_init();
	int wd;
	char buff[4096];
	int ret;
	if (fd < 0)
		perror("inotify_init error\n");

	wd = inotify_add_watch(fd, "/proc/partitions", IN_ACCESS);
	if (wd < 0)
		perror("inotify_add_watch error\n");

	
	ret = read(fd, buff, 4096);
	if (ret < 0)
		perror("read error\n");
	else
		printf("buff %s\n", buff);
	return 0;
}

But when i call 'cat /proc/partitions',the program can't return.
So i added some message in kernel in order to find the reason.
In procfs for some files, the inode used this method to alloc.
proc_lookup-->proc_lookup_de--->proc_get_inode-->new_inode_pseudo
In new_inode_pseudo, it will alloc new inode so every open-operation procfs will alloc new inode.
So inotify can't work.

I think it should add a flag which indicate file can't support inotify.Although  there are a few files in procfs.


Thanks!
Jianpeng
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Re: [BUG] Using inotify on /proc/partitoins

[Al Viro]

On Fri, Jun 14, 2013 at 09:26:49AM +0800, majianpeng wrote:
> Hi all,
>      I wanted to monitor /proc/partitions using inotify.


That, indeed, is a bug.  Easily fixed - don't do that.

> But when i call 'cat /proc/partitions',the program can't return.
> So i added some message in kernel in order to find the reason.
> In procfs for some files, the inode used this method to alloc.
> proc_lookup-->proc_lookup_de--->proc_get_inode-->new_inode_pseudo
> In new_inode_pseudo, it will alloc new inode so every open-operation procfs will alloc new inode.
> So inotify can't work.

Of course, it can't work.  Inotify if a kludge that kinda-sorta works
for local disk-backed filesystems, if you do not mind a pile of races.
For anything else it's completely worthless.