Re: [RFC] changes to buffer.c (was Test12 ll_rw_block error)

From: Chris Mason <mason@suse.com>
To: Alexander Viro <viro@math.psu.edu>
Cc: "Stephen C. Tweedie" <sct@redhat.com>,
	Marcelo Tosatti <marcelo@conectiva.com.br>,
	Linus Torvalds <torvalds@transmeta.com>,
	Russell Cattelan <cattelan@thebarn.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC] changes to buffer.c (was Test12 ll_rw_block error)
Date: Fri, 22 Dec 2000 08:49:09 -0500	[thread overview]
Message-ID: <232360000.977492949@coffee> (raw)
In-Reply-To: <Pine.GSO.4.21.0012212048210.5877-100000@weyl.math.psu.edu>

On Thursday, December 21, 2000 20:54:09 -0500 Alexander Viro <viro@math.psu.edu> wrote:

> 
> 
> On Thu, 21 Dec 2000, Chris Mason wrote:
> 
>> Obvious bug, block_write_full_page zeros out the bits past the end of 
>> file every time.  This should not be needed for normal file writes.
> 
> Unfortunately, it _is_ needed for pageout path. mmap() the last page
> of file. Dirty the data past the EOF (MMU will not catch that access).
> Let the pageout send the page to disk. You don't want to have the data
> past EOF end up on the backstore.
> 

Sorry, I wasn't very clear.  I'd like to find a way to just do the memset in the one case it is needed (a real writepage), and not do it when we are using writepage just to flush dirty buffers.  I don't see how to do it though, without making a new flush operation.  That would also solve my concerns about the change in writepage semantics (even though every FS I could find in the kernel tree was using block_write_full_page). 

thanks,
Chris

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