linux-kernel - Re: [RFC 00/26] VFS based Union Mount (V2)

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Date:	Mon, 30 Jul 2007 21:23:24 +0300
From:	Al Boldi <a1426z@...ab.com>
To:	Jan Blunck <jblunck@...e.de>
Cc:	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 00/26] VFS based Union Mount (V2)

Jan Blunck wrote:
> Here is another post of the VFS based union mount implementation. Unlike
> the traditional mount which hides the contents of the mount point, union
> mounts present the merged view of the mount point and the mounted
> filesytem.

Great!

> Recent changes:
> - brand new union structure no longer tied to the dentryn, now works with
> bind mounts
> - generic part of the whiteout patches extracted
> - introduces MS_WHITEOUT to make the white-out patches independant of the
>   union-mount stuff
> - uses a singleton whiteout inode for the tmpfs filesystem (I need to fix
> this for ext2/3, too)
> - renaming files on unions uses copyup now

I wonder if this copyup functionality could be generalized to induce CoW when 
modifying hard-linked files.  Does that sound feasible?

> - rewrote the union mount debugging code: it is now debugfs/relay based.
> - random cleanups
>
> I'm able to compile the kernel with this patches applied on a  3 layer
> union mount with the seperate layers bind mounted to different locations.
> I haven't done any performance tests since I think there is a more
> important topic ahead: better readdir() support.

What about the umount oops?  Did that get fixed?

> This series is against 2.6.22-rc6-mm1.

Things as big and important like this should probably also be diff'd against 
mainline, to increase testing input.


Thanks!

--
Al

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