linux-kernel - Re: No error when inotify_add

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Date:	Sat, 24 Nov 2007 20:11:45 +0000
From:	"Phil Endecott" <phil_wueww_endecott@...zphil.org>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	<linux-kernel@...r.kernel.org>
Subject: Re: No error when inotify_add_watch(/an/NFS/file)

J. Bruce Fields wrote:
> On Fri, Nov 23, 2007 at 11:20:55PM +0000, Phil Endecott wrote:
>> Dear Experts,
>>
>> NFS doesn't work with inotify (and it looks like it can't, certainly not 
>> before NFS v4.1).  However, if I give an NFS filename to 
>> inotify_add_watch(), I don't get an error.
>>
>> If it indicated an error in this case then I could easily fall back to some 
>> sort of polling.  Without an error, I need some other way to detect NFS 
>> (and any other non-inotify-compatible filesystems).
>>
>> Any thoughts?
>
> The one reason I can think of that you might want that behavior is if
> you know you only access a given piece of the filesystem from one client
> at a time, and you still want inotify to work in that situation.

That's a good point.

> (I'm assuming inotify still notifies you of changes that are made on the same
> client.)

A quick test suggest that it does.

> But maybe you could handle that case by allowing inotify_add_watch() in
> the case where the nfs filesystem was mounted with the "nolock" option,
> and failing it otherwise, and telling people to turn on nolock if
> they're sure they know what they're doing.

I'm not sure what your rationale for proposing that is, and I don't 
think it helps in my scenario; a user wants their inotify-using 
application to "just work", not to be told to "sudo re-mount".

I suppose that I just need some way to determine whether I will get 
all, some, or none of the events that I've asked for.

Phil.

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