[PROPOSAL] extend UNIX_INFO2 to flag extended access controls (take 2)

[James Peach]

Hi all,

This is a modified version of my earlier proposal,
	<http://marc.info/?l=samba-technical&m=120103599815292&w=2>

I think that this version clarifies my intent and solves the backwards  
compatibility /versioning problem.

1. The Problem

The fundamental problem is that a SMB client that uses UNIX_INFO2  
isn't able to use the Permissions field to evaluate access(2) if the  
server implements a permissions model that goes beyond the basic Unix  
permissions bits.

However, even when the server implements an extended permissions  
model, most files residing on the server do not have extended  
permission applied to them.

If the Unix permissions are the only access control on the file, then  
the client can accurately handle access(2) calls without making  
further round trips to the server (as long as it is prepared to live  
with the race condition).

2. The Proposal
#define UNIX_NO_EXTENDED_PERMISSIONS (1<<63)
The server MAY set the UNIX_NO_EXTENDED_PERMISSIONS bit in the  
UNIX_INFO2 Permissions field if this field completely describes the  
permissions of the file.
That is, if the server sets this bit, it is indicating to the client  
that the file has no access control other than the Unix permissions  
bits described in the SNIA QUERY_FILE_UNIX_BASIC documentation.
3. Compatibility
Existing servers that support the Unix extensions leave the  
UNIX_NO_EXTENDED_PERMISSIONS clear, indicating that there MAY be an  
extended permissions model in use. In this case, clients SHOULD uses  
their existing strategies for presenting permissions to the user and  
for evaluating access(2).