Re: O_DIRECT fails in some kernel and FS

[Jeff Garzik <jgarzik@mandrakesoft.com>]

Andi Kleen wrote:
> 
> Jeff Garzik <garzik@havoc.gtf.org> writes:
> 
> > On Sat, Feb 02, 2002 at 02:16:41PM -0600, Stephen Lord wrote:
> > > Can't you fall back to buffered I/O for the tail? OK it complicates the
> > > code, probably a lot, but it keeps things sane from the user's point of
> > > view.
> >
> > For O_DIRECT, IMHO you should fail not fallback.  You're simply lying
> > to the underlying program otherwise.
> 
> It's just impossible to write a tail which is smaller than a disk block
> without another buffer.

I argue, for reiserfs:

For O_DIRECT writes, the preferred behavior is to write disk blocks
obtained through the normal methods (get_block, etc.), and fully support
inodes for which file tails do not exist.

For O_DIRECT reads, if the data is determined to be in a file tail,
->direct_IO should either (a) fail or (b) dump the file tail to a normal
disk block before performing ->direct_IO.

-- 
Jeff Garzik      | "I went through my candy like hot oatmeal
Building 1024    |  through an internally-buttered weasel."
MandrakeSoft     |             - goats.com