From mboxrd@z Thu Jan  1 00:00:00 1970
From: Shaya Potter <spotter@cs.columbia.edu>
Subject: Re: which dentry a page belongs to
Date: Fri, 23 Apr 2004 18:26:52 -0400
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To: Jamie Lokier <jamie@shareable.org>
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On Fri, 2004-04-23 at 22:37 +0100, Jamie Lokier wrote:
> Shaya Potter wrote:
> > right, I know i can do that (or on lookup(), or on open() ) but that
> > basically limits me to a open/close transaction for versioning.  Can't
> > ioctl the fs, and cause all future writes to be in a new version.
> 
> "all future writes" is not very well defined with shared writable mappings.
> 
> Imagine this:
> 
>     1. program write to a page, dirty bit is set in pte
> 
> [6 weeks later...]
> 
>     2. you do the ioctl
>     3. your writepage gets called
> 
> Now you will store an update for a change which happened 6 weeks
> before you called the ioctl().  Is that what you really wanted?
> Perhaps it is.

OK, great example, now I see the problem which can't be easily solved.

update-data
ioctl
update-data
writepage()

writepage can't differentiate b/w data b4 and data after, so only way to
do it would be to force a sync b4 ioctl is called, which I would think
(perhaps wrong) should write out all the data to disk.  But unsure if
prorgramatically able to really test to see if it worked or not.

shaya