linux-kernel - Re: inotify, new idea?

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Message-ID: <CAHO5Pa1hfp+uLiQ78-pn2RJ6SytSYqXTniyx3UvaTwU_=ECWjA@mail.gmail.com>
Date:	Mon, 21 Apr 2014 09:24:47 +0200
From:	Michael Kerrisk <mtk.manpages@...il.com>
To:	Richard Weinberger <richard.weinberger@...il.com>
Cc:	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>,
	Jos Huisken <jos.huisken@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Michael Kerrisk-manpages <mtk.manpages@...il.com>
Subject: Re: inotify, new idea?

On Mon, Apr 21, 2014 at 12:22 AM, Richard Weinberger
<richard.weinberger@...il.com> wrote:
> On Fri, Apr 18, 2014 at 6:15 AM, Michael Kerrisk <mtk.manpages@...il.com> wrote:
>> On Thu, Apr 17, 2014 at 11:28 PM, Lennart Sorensen
>> <lsorense@...lub.uwaterloo.ca> wrote:
>>> On Thu, Apr 17, 2014 at 11:00:37PM +0200, Jos Huisken wrote:
>>>> I was trying to maintain a local and remote directory in sync with
>>>> lsync, using inotify.
>>>> I happen to have >4M files and >400k directories... running over
>>>> /proc/sys/fs/inotify/max_user_watches
>>>
>>> Would fanotify perhaps be a better interface to use?
>>
>> (One of us is misunderstanding fanotify; it might be me.)
>>
>> Did you look at fanotify closely? I don't think it could be used for
>> this task -- does not notify linka dn unlink events, difficult to set
>> up recursive monitoring, etc.
>
> Does recursive monitoring even work with inotify?
> Last time I've tried it did failed as soon I did a mkdir -p a/b/c/d because
> mkdir() raced against the thread which installes the new watches.

As I understand it, you have to program to deal with the races (rescan
directories after adding watches). I recently did a lot of work
updating the inotify(7) man page to discuss all the issues that I know
of, and their remedies. If I missed anything, I'd appreciate a note on
it, so that it can be added. See
http://man7.org/linux/man-pages/man7/inotify.7.html#NOTES

Cheers,

Michael


-- 
Michael Kerrisk Linux man-pages maintainer;
http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface", http://blog.man7.org/
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