Re: NFSv4.2 READ_PLUS support?

On Mon, Aug 25, 2025 at 1:45 PM Dag-Erling Smørgrav <des@freebsd.org> wrote:
>
> "Rob Norris" <robn@despairlabs.com> writes:
> > Cedric Blancher <cedric.blancher@gmail.com> writes:
> > > Holes are not sequences of 0x00 bytes. Holes means "no data here". ZFS
> > > compression should preserve the sparse information, otherwise you turn
> > > ANY sequence of 0x00 bytes into holes,and that will break databases
> > > and other applications which depend on exactly that *precise*
> > > semantics.
> > This is the second time I've heard this on this list (previously[1]) but
> > I don't know what it's referring to.
>
> They made it up.

Nobody made that up. It's reality, even defined by POSIX, IETF NFS and
the UNIX greybeards, long ago

> A hole is just an optimization, and it is 100% up to
> the file system whether holes are created and where.  Any application
> that considers a hole to be semantically different from a sequence of
> zeroes is broken.

No, this is part of POSIX (e.g.
https://pubs.opengroup.org/onlinepubs/9799919799/ ff), *AND*
traditional UNIX filesystem behaviour.

As pointed out, changing hold to 0x00 bytes is bad, as it breaks
existing applications (usually databases and scientific applications),

Aurélien
-- 
Aurélien Couderc <aurelien.couderc2002@gmail.com>
Big Data/Data mining expert, chess enthusiast