Re: [PATCH] 2.6.10 - direct-io async short read bug

[Andrew Morton <akpm@osdl.org>]

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.