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

From: Andrew Morton
Date: Wed Mar 09 2005 - 15:26:45 EST

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.

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