Date: Wed, 9 Mar 2005 11:53:48 -0800
From: Andrew Morton <akpm@osdl.org>
To: suparna@in.ibm.com
Cc: pbadari@us.ibm.com, daniel@osdl.org, sebastien.dugue@bull.net,
       linux-aio@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] 2.6.10 -  direct-io async short read bug
Message-Id: <20050309115348.2b86b765.akpm@osdl.org>
In-Reply-To: <20050309152047.GA4588@in.ibm.com>
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Suparna Bhattacharya <suparna@in.ibm.com> wrote:
>
>  > 	Solaris, which does forcedirectio as a mount option, actually
>  > will do buffered I/O on the trailing part.  Consider it like a bounce
>  > buffer.  That way they don't DMA the trailing data and succeed the I/O.
>  > The I/O returns actual bytes till EOF, just like read(2) is supposed to.
>  > 	Either this or a fully DMA'd number 4 is really what we should
>  > do.  If security can only be solved via a bounce buffer, who cares?  If
>  > the user created themselves a non-aligned file to open O_DIRECT, that's
>  > their problem if the last part-sector is negligably slower.
> 
>  If writes/truncates take care of zeroing out the rest of the sector
>  on disk, might we still be OK without having to do the bounce buffer
>  thing ?

We can probably rely on the rest of the sector outside i_size being zeroed
anyway.  Because if it contains non-zero gunk then the fs already has a
problem, and the user can get at that gunk with an expanding truncate and
mmap() anyway.


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