What is the purpose of CAP_LARGE_READX?

[Andrew Bartlett]

On Thu, 2013-01-17 at 13:54 -0800, Jeremy Allison wrote:
> On Fri, Jan 18, 2013 at 08:44:42AM +1100, Andrew Bartlett wrote:
> > I'm chasing a bug where a MacOSX client asks for 64k of data, we ignore
> > the high bits, and return 0 bytes.  The client then writes a 64k zero
> > page locally. 
> > 
> > The formal bug report will follow once I clear the details with the
> > reporter, but it raised in my head some 'meta' questions.
> > 
> > What is the purpose of CAP_LARGE_READX?  The Samba smbd file server only
> > mentions it to claim support for it in negprot, but does not use it in
> > reply.c since
> > https://git.samba.org/?p=samba.git;a=commitdiff;h=f8c26c16b82989e002b839fc9eba6386fc036f6a
> > 
> > I would say 'so, we should not advertise it', but the trace I've been
> > given of Win2008R2 also claims the same flag, but that patch claims it
> > also isn't supported.
> > 
> > If the only way to do large reads and writes with SMB1 is via the unix
> > extensions, what is the purpose of the capability flag?
> 
> Was created to allow implementations to do unix extensions without
> having to allow large readX or large writeX calls (there's also a
> CAP_LARGE_WRITEX). As we're the only server who ever implemented
> the unix extensions they appear synonomous, but they're not.

I guess what I'm puzzled at is windows advertising it, but not honouring
it, or getting a closer idea what's really going on.

Andrew Bartlett

-- 
Andrew Bartlett                                http://samba.org/~abartlet/
Authentication Developer, Samba Team           http://samba.org