s4-dsdb: Reduce calls to the ldb layer by reloading less often

[Samba.git] / prog_guide4.txt

THIS IS INCOMPLETE! I'M ONLY COMMITING IT IN ORDER TO SOLICIT COMMENTS
FROM A FEW PEOPLE. DON'T TAKE THIS AS THE FINAL VERSION YET.


Samba4 Programming Guide
========================

.. contents::

The internals of Samba4 are quite different from previous versions of
Samba, so even if you are an experienced Samba developer please take
the time to read through this document.

This document will explain both the broad structure of Samba4, and
some of the common coding elements such as memory management and
dealing with macros.


Coding Style
------------

In past versions of Samba we have basically let each programmer choose
their own programming style. Unfortunately the result has often been
that code that other members of the team find difficult to read. For
Samba version 4 I would like to standardise on a common coding style
to make the whole tree more readable. For those of you who are
horrified at the idea of having to learn a new style, I can assure you
that it isn't as painful as you might think. I was forced to adopt a
new style when I started working on the Linux kernel, and after some
initial pain found it quite easy.

That said, I don't want to invent a new style, instead I would like to
adopt the style used by the Linux kernel. It is a widely used style
with plenty of support tools available. See Documentation/CodingStyle
in the Linux source tree. This is the style that I have used to write
all of the core infrastructure for Samba4 and I think that we should
continue with that style.

I also think that we should most definately *not* adopt an automatic
reformatting system in cvs (or whatever other source code system we
end up using in the future). Such automatic formatters are, in my
experience, incredibly error prone and don't understand the necessary
exceptions. I don't mind if people use automated tools to reformat
their own code before they commit it, but please do not run such
automated tools on large slabs of existing code without being willing
to spend a *lot* of time hand checking the results.

Finally, I think that for code that is parsing or formatting protocol
packets the code layout should strongly reflect the packet
format. That means ordring the code so that it parses in the same
order as the packet is stored on the wire (where possible) and using
white space to align packet offsets so that a reader can immediately
map any line of the code to the corresponding place in the packet.


Static and Global Data
----------------------

The basic rule is "avoid static and global data like the plague". What
do I mean by static data? The way to tell if you have static data in a
file is to use the "size" utility in Linux. For example if we run::

  size libcli/raw/*.o

in Samba4 then you get the following::

   text    data     bss     dec     hex filename
   2015       0       0    2015     7df libcli/raw/clikrb5.o
    202       0       0     202      ca libcli/raw/clioplock.o
     35       0       0      35      23 libcli/raw/clirewrite.o
   3891       0       0    3891     f33 libcli/raw/clisession.o
    869       0       0     869     365 libcli/raw/clisocket.o
   4962       0       0    4962    1362 libcli/raw/clispnego.o
   1223       0       0    1223     4c7 libcli/raw/clitransport.o
   2294       0       0    2294     8f6 libcli/raw/clitree.o
   1081       0       0    1081     439 libcli/raw/raweas.o
   6765       0       0    6765    1a6d libcli/raw/rawfile.o
   6824       0       0    6824    1aa8 libcli/raw/rawfileinfo.o
   2944       0       0    2944     b80 libcli/raw/rawfsinfo.o
    541       0       0     541     21d libcli/raw/rawioctl.o
   1728       0       0    1728     6c0 libcli/raw/rawnegotiate.o
    723       0       0     723     2d3 libcli/raw/rawnotify.o
   3779       0       0    3779     ec3 libcli/raw/rawreadwrite.o
   6597       0       0    6597    19c5 libcli/raw/rawrequest.o
   5580       0       0    5580    15cc libcli/raw/rawsearch.o
   3034       0       0    3034     bda libcli/raw/rawsetfileinfo.o
   5187       0       0    5187    1443 libcli/raw/rawtrans.o
   2033       0       0    2033     7f1 libcli/raw/smb_signing.o

notice that the "data" and "bss" columns are all zero? That is
good. If there are any non-zero values in data or bss then that
indicates static data and is bad (as a rule of thumb).

Lets compare that result to the equivalent in Samba3::

   text    data     bss     dec     hex filename
   3978       0       0    3978     f8a libsmb/asn1.o
  18963       0     288   19251    4b33 libsmb/cliconnect.o
   2815       0    1024    3839     eff libsmb/clidgram.o
   4038       0       0    4038     fc6 libsmb/clientgen.o
   3337     664     256    4257    10a1 libsmb/clierror.o
  10043       0       0   10043    273b libsmb/clifile.o
    332       0       0     332     14c libsmb/clifsinfo.o
    166       0       0     166      a6 libsmb/clikrb5.o
   5212       0       0    5212    145c libsmb/clilist.o
   1367       0       0    1367     557 libsmb/climessage.o
    259       0       0     259     103 libsmb/clioplock.o
   1584       0       0    1584     630 libsmb/cliprint.o
   7565       0     256    7821    1e8d libsmb/cliquota.o
   7694       0       0    7694    1e0e libsmb/clirap.o
  27440       0       0   27440    6b30 libsmb/clirap2.o
   2905       0       0    2905     b59 libsmb/clireadwrite.o
   1698       0       0    1698     6a2 libsmb/clisecdesc.o
   5517       0       0    5517    158d libsmb/clispnego.o
    485       0       0     485     1e5 libsmb/clistr.o
   8449       0       0    8449    2101 libsmb/clitrans.o
   2053       0       4    2057     809 libsmb/conncache.o
   3041       0     256    3297     ce1 libsmb/credentials.o
   1261       0    1024    2285     8ed libsmb/doserr.o
  14560       0       0   14560    38e0 libsmb/errormap.o
   3645       0       0    3645     e3d libsmb/namecache.o
  16815       0       8   16823    41b7 libsmb/namequery.o
   1626       0       0    1626     65a libsmb/namequery_dc.o
  14301       0    1076   15377    3c11 libsmb/nmblib.o
  24516       0    2048   26564    67c4 libsmb/nterr.o
   8661       0       8    8669    21dd libsmb/ntlmssp.o
   3188       0       0    3188     c74 libsmb/ntlmssp_parse.o
   4945       0       0    4945    1351 libsmb/ntlmssp_sign.o
   1303       0       0    1303     517 libsmb/passchange.o
   1221       0       0    1221     4c5 libsmb/pwd_cache.o
   2475       0       4    2479     9af libsmb/samlogon_cache.o
  10768      32       0   10800    2a30 libsmb/smb_signing.o
   4524       0      16    4540    11bc libsmb/smbdes.o
   5708       0       0    5708    164c libsmb/smbencrypt.o
   7049       0    3072   10121    2789 libsmb/smberr.o
   2995       0       0    2995     bb3 libsmb/spnego.o
   3186       0       0    3186     c72 libsmb/trustdom_cache.o
   1742       0       0    1742     6ce libsmb/trusts_util.o
    918       0      28     946     3b2 libsmb/unexpected.o

notice all of the non-zero data and bss elements? Every bit of that
data is a bug waiting to happen.

Static data is evil as it has the following consequences:
- it makes code much less likely to be thread-safe
- it makes code much less likely to be recursion-safe
- it leads to subtle side effects when the same code is called from multiple places
- doesn't play well with shared libraries or plugins

Static data is particularly evil in library code (such as our internal
smb and rpc libraries). If you can get rid of all static data in
libraries then you can make some fairly strong guarantees about the
behaviour of functions in that library, which really helps.

Of course, it is possible to write code that uses static data and is
safe, it's just much harder to do that than just avoid static data in
the first place. We have been tripped up countless times by subtle
bugs in Samba due to the use of static data, so I think it is time to
start avoiding it in new code. Much of the core infrastructure of
Samba4 was specifically written to avoid static data, so I'm going to
be really annoyed if everyone starts adding lots of static data back
in.

So, how do we avoid static data? The basic method is to use context
pointers. When reading the Samba4 code you will notice that just about
every function takes a pointer to a context structure as its first
argument. Any data that the function needs that isn't an explicit
argument to the function can be found by traversing that context. 

Note that this includes all of the little caches that we have lying
all over the code in Samba3. I'm referring to the ones that generally
have a "static int initialised" and then some static string or integer
that remembers the last return value of the function. Get rid of them!
If you are *REALLY* absolutely completely certain that your personal
favourite mini-cache is needed then you should do it properly by
putting it into the appropriate context rather than doing it the lazy
way by putting it inside the target function. I would suggest however
that the vast majority of those little caches are useless - don't
stick it in unless you have really firm benchmarking results that show
that it is needed and helps by a significant amount.

Note that Samba4 is not yet completely clean of static data like
this. I've gotten the smbd/ directory down to 24 bytes of static data,
and libcli/raw/ down to zero. I've also gotten the ntvfs layer and all
backends down to just 8 bytes in ntvfs_base.c. The rest still needs
some more work.

Also note that truly constant data is OK, and will not in fact show up
in the data and bss columns in "size" anyway (it will be included in
"text"). So you can have constant tables of protocol data.


How to use talloc
-----------------

Please see the separate document, lib/talloc/talloc_guide.txt
You _must_ read this if you want to program in Samba4.


Interface Structures
--------------------

One of the biggest changes in Samba4 is the universal use of interface
structures. Go take a look through libcli/raw/interfaces.h now to get
an idea of what I am talking about.

In Samba3 many of the core wire structures in the SMB protocol were
never explicitly defined in Samba. Instead, our parse and generation
functions just worked directly with wire buffers. The biggest problem
with this is that is tied our parse code with our "business logic"
much too closely, which meant the code got extremely confusing to
read.

In Samba4 we have explicitly defined interface structures for
everything in the protocol. When we receive a buffer we always parse
it completely into one of these structures, then we pass a pointer to
that structure to a backend handler. What we must *not* do is make any
decisions about the data inside the parse functions. That is critical
as different backends will need different portions of the data. This
leads to a golden rule for Samba4:

  "don't design interfaces that lose information"

In Samba3 our backends often received "condensed" versions of the
information sent from clients, but this inevitably meant that some
backends could not get at the data they needed to do what they wanted,
so from now on we should expose the backends to all of the available
information and let them choose which bits they want.

Ok, so now some of you will be thinking "this sounds just like our
msrpc code from Samba3", and while to some extent this is true there
are extremely important differences in the approach that are worth
pointing out.

In the Samba3 msrpc code we used explicit parse structures for all
msrpc functions. The problem is that we didn't just put all of the
real variables in these structures, we also put in all the artifacts
as well. A good example is the security descriptor strucrure that
looks like this in Samba3::

        typedef struct security_descriptor_info
        {
                uint16 revision; 
                uint16 type;    

                uint32 off_owner_sid;
                uint32 off_grp_sid;
                uint32 off_sacl;
                uint32 off_dacl;

                SEC_ACL *dacl;
                SEC_ACL *sacl;
                DOM_SID *owner_sid; 
                DOM_SID *grp_sid;
        } SEC_DESC;

The problem with this structure is all the off_* variables. Those are
not part of the interface, and do not appear in any real descriptions
of Microsoft security descriptors. They are parsing artifacts
generated by the IDL compiler that Microsoft use. That doesn't mean
they aren't needed on the wire - indeed they are as they tell the
parser where to find the following four variables, but they should
*NOT* be in the interface structure.

In Samba3 there were unwritten rules about which variables in a
structure a high level caller has to fill in and which ones are filled
in by the marshalling code. In Samba4 those rules are gone, because
the redundent artifact variables are gone. The high level caller just
sets up the real variables and the marshalling code worries about
generating the right offsets.

The same rule applies to strings. In many places in the SMB and MSRPC
protocols complex strings are used on the wire, with complex rules
about padding, format, alighment, termination etc. None of that
information is useful to a high level calling routine or to a backend - its 
all just so much wire fluff. So, in Samba4 these strings are
just "char \*" and are always in our internal multi-byte format (which
is usually UTF8). It is up to the parse functions to worry about
translating the format and getting the padding right.

The one exception to this is the use of the WIRE_STRING type, but that
has a very good justification in terms of regression testing. Go and
read the comment in smb_interfaces.h about that now.

So, here is another rule to code by. When writing an interface
structure think carefully about what variables in the structure can be
left out as they are redundent. If some length is effectively defined
twice on the wire then only put it once in the packet. If a length can
be inferred from a null termination then do that and leave the length
out of the structure completely. Don't put redundent stuff in
structures!


Async Design
------------

Samba4 has an asynchronous design. That affects *lots* of the code,
and the implications of the asynchronous design needs to be considered
just about everywhere.

The first aspect of the async design to look at is the SMB client
library. Lets take a look at the following three functions in
libcli/raw/rawfile.c::

        struct cli_request *smb_raw_seek_send(struct cli_tree *tree, struct smb_seek *parms);
        NTSTATUS smb_raw_seek_recv(struct cli_request *req, struct smb_seek *parms);
        NTSTATUS smb_raw_seek(struct cli_tree *tree, struct smb_seek *parms);

Go and read them now then come back.

Ok, first notice there there are 3 separate functions, whereas the
equivalent code in Samba3 had just one. Also note that the 3rd
function is extremely simple - its just a wrapper around calling the
first two in order.

The three separate functions are needed because we need to be able to
generate SMB calls asynchronously. The first call, which for smb calls
is always called smb_raw_XXXX_send(), constructs and sends a SMB
request and returns a "struct cli_request" which acts as a handle for
the request. The caller is then free to do lots of other calls if it
wants to, then when it is ready it can call the smb_raw_XXX_recv()
function to receive the reply.

If all you want is a synchronous call then call the 3rd interface, the
one called smb_raw_XXXX(). That just calls the first two in order, and
blocks waiting for the reply.

But what if you want to be called when the reply comes in? Yes, thats
possible. You can do things like this::

    struct cli_request *req;

    req = smb_raw_XXX_send(tree, params);

    req->async.fn = my_callback;
    req->async.private = my_private_data;

then in your callback function you can call the smb_raw_XXXX_recv()
function to receive the reply. Your callback will receive the "req"
pointer, which you can use to retrieve your private data from
req->async.private.

Then all you need to do is ensure that the main loop in the client
library gets called. You can either do that by polling the connection
using cli_transport_pending() and cli_request_receive_next() or you
can use transport->idle.func to setup an idle function handler to call
back to your main code. Either way, you can build a fully async
application.

In order to support all of this we have to make sure that when we
write a piece of library code (SMB, MSRPC etc) that we build the
separate _send() and _recv() functions. It really is worth the effort.

Now about async in smbd, a much more complex topic.

The SMB protocol is inherently async. Some functions (such as change
notify) often don't return for hours, while hundreds of other
functions pass through the socket. Take a look at the RAW-MUX test in
the Samba4 smbtorture to see some really extreme examples of the sort
of async operations that Windows supports. I particularly like the
open/open/close sequence where the 2nd open (which conflicts with the
first) succeeds because the subsequent close is answered out of order.

In Samba3 we handled this stuff very badly. We had awful "pending
request" queues that allocated full 128k packet buffers, and even with
all that crap we got the semantics wrong. In Samba4 I intend to make
sure we get this stuff right.

So, how do we do this? We now have an async interface between smbd and
the NTVFS backends. Whenever smbd calls into a backend the backend has
an option of answer the request in a synchronous fashion if it wants
to just like in Samba3, but it also has the option of answering the
request asynchronously. The only backend that currently does this is
the CIFS backend, but I hope the other backends will soon do this to.

To make this work you need to do things like this in the backend::

  req->control_flags |= REQ_CONTROL_ASYNC;

that tells smbd that the backend has elected to reply later rather
than replying immediately. The backend must *only* do this if
req->async.send_fn is not NULL. If send_fn is NULL then it means that
the smbd front end cannot handle this function being replied to in an
async fashion.

If the backend does this then it is up to the backend to call
req->async.send_fn() when it is ready to reply. It the meantime smbd
puts the call on hold and goes back to answering other requests on the
socket.

Inside smbd you will find that there is code to support this. The most
obvious change is that smbd splits each SMB reply function into two
parts - just like the client library has a _send() and _recv()
function, so smbd has a _send() function and the parse function for
each SMB.

As an example go and have a look at reply_getatr_send() and
reply_getatr() in smb_server/smb/reply.c. Read them? Good.

Notice that reply_getatr() sets up the req->async structure to contain
the send function. Thats how the backend gets to do an async reply, it
calls this function when it is ready. Also notice that reply_getatr()
only does the parsing of the request, and does not do the reply
generation. That is done by the _send() function.


NTVFS
-----

One of the most noticeable changes in Samba4 is the introduction of
the NTVFS layer. This provided the initial motivation for the design
of Samba4 and in many ways lies at the heart of the design.

In Samba3 the main file serving process (smbd) combined the handling
of the SMB protocol with the mapping to POSIX semantics in the same
code. If you look in smbd/reply.c in Samba3 you see numerous places
where POSIX assumptions are mixed tightly with SMB parsing code. We
did have a VFS layer in Samba3, but it was a POSIX-like VFS layer, so
no matter how you wrote a plugin you could not bypass the POSIX
mapping decisions that had already been made before the VFS layer was
called.

In Samba4 things are quite different. All SMB parsing is performed in
the smbd front end, then fully parsed requests are passed to the NTVFS
backend. That backend makes any semantic mapping decisions and fills
in the 'out' portion of the request. The front end is then responsible
for putting those results into wire format and sending them to the
client.

Lets have a look at one of those request structures. Go and read the
definition of "union smb_write" and "enum write_level" in
libcli/raw/interfaces.h. (no, don't just skip reading it, really go
and read it. Yes, that means you!).

Notice the union? That's how Samba4 allows a single NTVFS backend
interface to handle the several different ways of doing a write
operation in the SMB protocol. Now lets look at one section of that
union::

        /* SMBwriteX interface */
        struct {
                enum smb_write_level level;
                struct {
                        union smb_handle file;
                        uint64_t offset;
                        uint16_t wmode;
                        uint16_t remaining;
                        uint32_t count;
                        const uint8_t *data;
                } in;
                struct {
                        uint32_t nwritten;
                        uint16_t remaining;
                } out;
        } writex, generic;

see the "in" and "out" sections? The "in" section is for parameters
that the SMB client sends on the wire as part of the request. The smbd
front end parse code parses the wire request and fills in all those
parameters. It then calls the NTVFS interface which looks like this::

  NTSTATUS (*write)(struct request_context *req, union smb_write *io);

and the NTVFS backend does the write request. The backend then fills
in the "out" section of the writex structure and gives the union back
to the front end (either by returning, or if done in an async fashion
then by calling the async send function. See the async discussion
elsewhere in this document).

The NTVFS backend knows which particular function is being requested
by looking at io->generic.level. Notice that this enum is also
repeated inside each of the sub-structures in the union, so the
backend could just as easily look at io->writex.level and would get
the same variable.

Notice also that some levels (such as splwrite) don't have an "out"
section. This happens because there is no return value apart from a
status code from those SMB calls.

So what about status codes? The status code is returned directly by
the backend NTVFS interface when the call is performed
synchronously. When performed asynchronously then the status code is
put into req->async.status before the req->async.send_fn() callback is
called.

Currently the most complete NTVFS backend is the CIFS backend. I don't
expect this backend will be used much in production, but it does
provide the ideal test case for our NTVFS design. As it offers the
full capabilities that are possible with a CIFS server we can be sure
that we don't have any gaping holes in our APIs, and that the front
end code is flexible enough to handle any advances in the NT style
feature sets of Unix filesystems that make come along.


Process Models
--------------

In Samba3 we supported just one process model. It just so happens that
the process model that Samba3 supported is the "right" one for most
users, but there are situations where this model wasn't ideal.

In Samba4 you can choose the smbd process model on the smbd command
line.


DCERPC binding strings
----------------------

When connecting to a dcerpc service you need to specify a binding
string.

The format is:

  TRANSPORT:host[flags]

where TRANSPORT is either ncacn_np for SMB or ncacn_ip_tcp for RPC/TCP

"host" is an IP or hostname or netbios name. If the binding string
identifies the server side of an endpoint, "host" may be an empty
string.

"flags" can include a SMB pipe name if using the ncacn_np transport or
a TCP port number if using the ncacn_ip_tcp transport, otherwise they
will be auto-determined.

other recognised flags are:

  sign      : enable ntlmssp signing
  seal      : enable ntlmssp sealing
  spnego    : use SPNEGO instead of NTLMSSP authentication
  krb5      : use KRB5 instead of NTLMSSP authentication
  connect   : enable rpc connect level auth (auth, but no sign or seal)
  validate  : enable the NDR validator
  print     : enable debugging of the packets
  bigendian : use bigendian RPC
  padcheck  : check reply data for non-zero pad bytes


Here are some examples:

   ncacn_np:myserver
   ncacn_np:myserver[samr]
   ncacn_np:myserver[\pipe\samr]
   ncacn_np:myserver[/pipe/samr]
   ncacn_np:myserver[samr,sign,print]
   ncacn_np:myserver[sign,spnego]
   ncacn_np:myserver[\pipe\samr,sign,seal,bigendian]
   ncacn_np:myserver[/pipe/samr,seal,validate]
   ncacn_np:
   ncacn_np:[/pipe/samr]
   ncacn_ip_tcp:myserver
   ncacn_ip_tcp:myserver[1024]
   ncacn_ip_tcp:myserver[sign,seal]
   ncacn_ip_tcp:myserver[spnego,seal]


IDEA: Maybe extend UNC names like this?

 smbclient //server/share
 smbclient //server/share[sign,seal,spnego]

DCERPC Handles
--------------
The various handles that are used in the RPC servers should be created and
fetch using the dcesrv_handle_* functions.

Use dcesrv_handle_new(struct dcesrv_connection \*, uint8 handle_type) to obtain
a new handle of the specified type. Handle types are unique within each
pipe.

The handle can later be fetched again using::

        struct dcesrv_handle *dcesrv_handle_fetch(struct dcesrv_connection *dce_conn, struct policy_handle *p, uint8 handle_type)

and destroyed by::

        dcesrv_handle_destroy(struct dcesrv_handle *).

User data should be stored in the 'data' member of the dcesrv_handle struct.


MSRPC
-----



 - ntvfs
 - testing
 - command line handling
 - libcli structure
 - posix reliance
 - uid/gid handling
 - process models
 - static data
 - msrpc


don't zero structures! avoid ZERO_STRUCT() and talloc_zero()


GMT vs TZ in printout of QFILEINFO timezones

put in full UNC path in tconx

test timezone handling by using a server in different zone from client

do {} while (0) system

NT_STATUS_IS_OK() is NOT the opposite of NT_STATUS_IS_ERR()

need to implement secondary parts of trans2 and nttrans in server and
client

document access_mask in openx reply

check all capabilities and flag1, flag2 fields (eg. EAs)

large files -> pass thru levels

setpathinfo is very fussy about null termination of the file name

the overwrite flag doesn't seem to work on setpathinfo RENAME_INFORMATION

END_OF_FILE_INFORMATION and ALLOCATION_INFORMATION don't seem to work
via setpathinfo

on w2k3 setpathinfo DISPOSITION_INFORMATION fails, but does have an
effect. It leaves the file with SHARING_VIOLATION.

on w2k3 trans2 setpathinfo with any invalid low numbered level causes
the file to get into a state where DELETE_PENDING is reported, and the
file cannot be deleted until you reboot

trans2 qpathinfo doesn't see the delete_pending flag correctly, but
qfileinfo does!

get rid of strtok

add programming documentation note about lp_set_cmdline()

need to add a wct checking function in all client parsing code,
similar to REQ_CHECK_WCT()

need to make sure that NTTIME is a round number of seconds when
converted from time_t

not using a zero next offset in SMB_FILE_STREAM_INFORMATION for last
entry causes explorer exception under win2000


if the server sets the session key the same for a second SMB socket as
an initial socket then the client will not re-authenticate, it will go
straight to a tconx, skipping session setup and will use all the
existing parameters! This allows two sockets with the same keys!?


removed blocking lock code, we now queue the whole request the same as
we queue any other pending request. This allows for things like a
close() while a pending blocking lock is being processed to operate
sanely.

disabled change notify code

disabled oplock code



MILESTONES
==========


client library and test code
----------------------------

  convert client library to new structure
  get smbtorture working
  get smbclient working
  expand client library for all requests
  write per-request test suite
  gentest randomised test suite
  separate client code as a library for non-Samba use

server code
-----------
  add remaining core SMB requests
  add IPC layer
  add nttrans layer
  add rpc layer
  fix auth models (share, server, rpc)
  get net command working
  connect CIFS backend to server level auth
  get nmbd working
  get winbindd working
  reconnect printing code
  restore removed smbd options
  add smb.conf macro substitution code
  add async backend notification 
  add generic timer event mechanism

clustering code
---------------

  write CIFS backend
  new server models (break 1-1)
  test clustered models
  add fulcrum statistics gathering

docs
----

  conference paper
  developer docs

svn instructions

Ideas
-----

 - store all config in config.ldb

 - load from smb.conf if modtime changes

 - dump full system config with ldbsearch

 - will need the ability to form a ldif difference file

 - advanced web admin via a web ldb editor

 - normal web admin via web forms -> ldif

 - config.ldb will replace smb.conf, secrets.tdb, shares.tdb etc

 - subsystems in smbd will load config parameters for a share
   using ldbsearch at tconx time

 - need a loadparm equivalent module that provides parameter defaults

 - start smbd like this:  "smbd -C tdb://etc/samba/config.ldb" or
   "smbd -C ldapi://var/run/ldapi"

 - write a tool that generates a template ldap schema from an existing
   ldb+tdb file

 - no need to HUP smbd to reload config

 - how to handle configuration comments? same problem as SWAT


BUGS:
  add a test case for last_entry_offset in trans2 find interfaces
  conn refused
  connect -> errno
  no 137 resolution not possible
  should not fallback to anon when pass supplied
  should check pass-thu cap bit, and skip lots of tests
  possibly allow the test suite to say "allow oversized replies" for trans2 and other calls
  handle servers that don't have the setattre call in torture
  add max file coponent length test and max path len test
  check for alloc failure in all core reply.c and trans2.c code where allocation size depends on client parameter

case-insenstive idea:
  all filenames on disk lowercase
  real case in extended attribute
  keep cache of what dirs are all lowercase
  when searching for name, don't search if dir is definately all lowercase
  when creating file, use dnotify to tell if someone else creates at
  same time

solve del *.* idea:
  make mangle cache dynamic size
  fill during a dir scan
  setup a timer
  destroy cache after 30 sec
  destroy if a 2nd dir scan happens on same dir