Re: File change notification

[Michael Clark <michael@metaparadigm.com>]

On 01/01/04 02:48, Rüdiger Klaehn wrote:
> Javier Fernandez-Ivern wrote:
> 
>> Rüdiger Klaehn wrote:
>>
>>> I have been wondering for some time why there is no decent file 
>>> change notification mechanism in linux. Is there some deep 
>>> philosophical reason for this, or is it just that nobody has found 
>>> the time to implement it? If it is the latter, I am willing to 
>>> implement it as long there is a chance to get this accepted into the 
>>> mainstream kernel.
>>
>>
>>
>> Well, there's fam.  But AFAIK that's all done in user space, and your 
>> approach would be significantly more efficient (as a matter of fact, 
>> fam could be modified to use your change device as a first level of 
>> notification.)
>>
> Fam is a user space library that has some nice features such as network 
> transparent change notification. It currently uses the dnotify mechanism 
> if the underlying kernel supports it, but as I mentioned the dnotify 
> mechanism requires an open file handle and works only for single 
> directories. If the underlying os does not support dnotify, fam resorts 
> to polling for file changes (yuk!).

Have you had a look at dazuko. It provides a consistent file access
notification mechanism (and also intervention for denying access) across
linux and freebsd. It is currently being used by various on-access
virus scanners. It is under active development and supports 2.6 (and 2.4)

http://www.dazuko.org/about.shtml

Seems like a good idea. I've always thought it would be nice to use
something like this to maintain a dynamic locatedb (among many other
potential uses).

~mc