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

From: Badari Pulavarty
Date: Wed Mar 09 2005 - 16:45:28 EST

On Wed, 2005-03-09 at 11:53, Andrew Morton wrote:
> Suparna Bhattacharya <suparna@xxxxxxxxxx> 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.

Rest of the sector or rest of the block ? Are you implying that, we
already do this, so there is no problem reading beyond EOF to user
buffer ? Or we need to zero out the userbuffer beyond EOF ?


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