Subject: Re: [patch] inotify 0.22
From: Dale Blount <linux-kernel@dale.us>
To: Robert Love <rml@novell.com>
Cc: John McCutchan <ttb@tentacle.dhs.org>, linux-kernel@vger.kernel.org
In-Reply-To: <1112644936.6736.7.camel@betsy>
References: <1112644936.6736.7.camel@betsy>
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Date: Mon, 04 Apr 2005 16:50:55 -0400
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> inotify is intended to correct the deficiencies of dnotify, particularly
> its inability to scale and its terrible user interface:
> 
>         * dnotify requires the opening of one fd per each directory
>           that you intend to watch. This quickly results in too many
>           open files and pins removable media, preventing unmount.
>         * dnotify is directory-based. You only learn about changes to
>           directories. Sure, a change to a file in a directory affects
>           the directory, but you are then forced to keep a cache of
>           stat structures.
>         * dnotify's interface to user-space is awful.  Signals?
> 
> inotify provides a more usable, simple, powerful solution to file change
> notification:
> 
>         * inotify's interface is a device node, not SIGIO.  You open a 
>           single fd to the device node, which is select()-able.
>         * inotify has an event that says "the filesystem that the item
>           you were watching is on was unmounted."
>         * inotify can watch directories or files.
> 

Robert and others,

Will inotify watch directories recursively?  A quick browse through the
source doesn't look like it, but I very well could be wrong.  Last I
checked, dnotify did not either.  I am looking for a way to synchronize
files in as-real-as-possible-time when they are modified.  The ideal
implementation would be a kernel "hook" like d/inotify and a client
application that watches changes and copies them to a remote server for
redundancy purposes.   A scheduled rsync works decently, but has a lag
time of 2-3 (or more) hours on certain files on a large filesystem.
Will inotify work for this, or does someone else have another
recommended solution to the problem?

Thanks,

Dale

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