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

[Suparna Bhattacharya <suparna@in.ibm.com>]

On Tue, Mar 08, 2005 at 08:07:57PM -0800, Joel Becker wrote:
> On Tue, Mar 08, 2005 at 03:54:04PM -0800, Badari Pulavarty wrote:
> > > 1. return EINVAL if the DIO goes past EOF.
> > > 
> > > 2. truncate the request to file size (which is what your patch does)
> > >     and if it works, it works.
> > > 
> > > 3. truncate the request to a size that actually works - like a multiple
> > >     of 512.
> > > 
> > > 4. Do the full i/o since the user buffer is big enough, truncate the
> > >     result returned to file size (and clear out the user buffer where it
> > >     read past EOF).
> > > 
> > > Number 4 would make it easy on the user-level code, but AIO DIO might be
> > > a bit tricky and might be a security hole since the data would be dma'ed
> > > there and then cleared.  I need to look at the code some more.
> 
> 	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 ?

Regards
Suparna

> 
> -- 
> 
> Life's Little Instruction Book #3
> 
> 	"Watch a sunrise at least once a year."
> 
> Joel Becker
> Senior Member of Technical Staff
> Oracle
> E-mail: joel.becker@oracle.com
> Phone: (650) 506-8127
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-- 
Suparna Bhattacharya (suparna@in.ibm.com)
Linux Technology Center
IBM Software Lab, India