What is the purpose of CAP_LARGE_READX?

[Jeremy Allison]

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.

Jeremy.