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Date: Fri, 7 Dec 2007 01:52:15 -0800
From: "Jared Hulbert" <jaredeh@gmail.com>
To: carsteno@de.ibm.com
Subject: Re: [patch] ext2: xip check fix
Cc: "Rob Landley" <rob@landley.net>, "Nick Piggin" <npiggin@suse.de>,
       "Christian Borntraeger" <borntraeger@de.ibm.com>,
       "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
       linux-fsdevel@vger.kernel.org,
       "Eric W. Biederman" <ebiederm@xmission.com>,
       "Andrew Morton" <akpm@linux-foundation.org>,
       "Jens Axboe" <axboe@kernel.dk>
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> > I think so.  The filemap_xip.c functionality doesn't work for Flash
> > memory yet.  Flash memory doesn't have struct pages to back it up with
> > which this stuff depends on.
>
> Struct page is not the major issue. The primary problem is writing to
> the media (and I am not a flash expert at all, just relaying here):
> For some period of time, the flash memory is not usable and thus we
> need to make sure we can nuke the page table entries that we have in
> userland page tables. For that, we need a callback from the device so
> that it can ask to get its references back. Oh, and a put_xip_page
> counterpart to get_xip_page, so that the driver knows when it's safe
> to erase.

Well... That's the biggest/hardest problem, yes.  But not the first.
First we got to tackle the easy read only case, which doesn't require
any of that unpleasantness, yet which is used in a bunch of out of
tree hacks.