linux-kernel - Re: [patch 3/7] fs, notify: Add file handle entry into inotify_inode

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Date:	Wed, 14 Nov 2012 10:08:51 +0000
From:	Tvrtko Ursulin <tvrtko.ursulin@...lan.co.uk>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	James Bottomley <jbottomley@...allels.com>,
	Matthew Helsley <matt.helsley@...il.com>,
	aneesh.kumar@...ux.vnet.ibm.com, bfields@...ldses.org
Subject: Re: [patch 3/7] fs, notify: Add file handle entry into inotify_inode_mark

On Wednesday 14 November 2012 13:58:12 Cyrill Gorcunov wrote:
> On Wed, Nov 14, 2012 at 09:50:55AM +0000, Tvrtko Ursulin wrote:
> > > > You could not use a pointer and then allocate your buffers on the
> > > > check
> > > > point operation, freeing on restore?
> > > 
> > > The problem is not allocating the memory itself but rather the time when
> > > the information needed (ie the dentry) is available. The only moment
> > > when we can use dentry of the target file/directory is at
> > > inotify_new_watch, that's why i need to compose fhandle that early. At
> > > any later point we simply have no dentry to use.
> > 
> > But you do not fundamentally need the dentry to restore a watch, right?
> 
> dentry only needed to encode the file handle.
> 
> > Couldn't you restore, creating a new restore path if needed, using the
> > inode which is pinned anyway while the watch exists?
> 
> plain inode is not enough as far as i can tell, iow i don't see the way
> to restore path from inode solely. or there something i miss?

I don't know, as I said I was not following this at all until now. Just 
throwing in ideas.

I thought, since inotify does not use the path or dentry outside the system 
call at all, perhaps you need a different entry point allowing you to restore 
the watch using the inode or something. Assuming life time of objects and 
stuff in C&R world would allow you that. Since you don't need the full path, 
just something 64 bytes long, I assumed that could be the case.
 
Regards,

Tvrtko

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