[patch]: optimization for findfirst when in case-sensitive mode

[Matt Mitchell]

Jeremy (and all),

Here is a first crack at a patch implementing an optimization where, 
given that

- the connection is case-sensitive
- the request is not for a wildcard
- the client is doing a FINDFIRST (i.e. is looking for a particular file)

the smbd process will not perform a potentially costly OpenDir but 
instead will just use the SMB_VFS_STAT's answer to determine whether or 
not the file exists.

I originally implemented the patch against 3.0.8 (said patch is also 
attached) but reworked it against HEAD.

The populate_lanman2_dir_entry function (which was needed to avoid the 
OpenDir in get_lanman2_dir_entry) should be generalized and shared among 
the other functions that return lanman dir information.  I did not 
undertake this for this patch, rather thinking that I would like 
feedback first.

The motivation behind this patch was to eliminate the unnecessary 
readdirs when the server is in case-sensitive mode.  Our particular 
problem was in migrating huge directories (100ks of files) from Win to 
Linux, and it happens that our app enforces case sensitivity anyway, so 
we don't need it.  The old algorithm slows proportionally to the number 
of files in a directory; this will run as fast as the underlying vfs stat.

Any comments or slams appreciated.  Yes, it is a hack.


-m