mc/vfs/samba/internals.doc

internals.txt, 8 May 1996
Written by David Chappell <David.Chappell@mail.trincoll.edu>.

This document describes some of the internal functions which must be
understood by anyone wishing to add features to Samba.





=============================================================================
This section describes the macros defined in byteorder.h.  These macros 
are used extensively in the Samba code.

-----------------------------------------------------------------------------
CVAL(buf,pos)

returns the byte at offset pos within buffer buf as an unsigned character.

-----------------------------------------------------------------------------
PVAL(buf,pos)

returns the value of CVAL(buf,pos) cast to type unsigned integer.

-----------------------------------------------------------------------------
SCVAL(buf,pos,val)

sets the byte at offset pos within buffer buf to value val.

-----------------------------------------------------------------------------
SVAL(buf,pos)

returns the value of the unsigned short (16 bit) little-endian integer at 
offset pos within buffer buf.  An integer of this type is sometimes
refered to as "USHORT".

-----------------------------------------------------------------------------
IVAL(buf,pos)

returns the value of the unsigned 32 bit little-endian integer at offset 
pos within buffer buf.

-----------------------------------------------------------------------------
SVALS(buf,pos)

returns the value of the signed short (16 bit) little-endian integer at 
offset pos within buffer buf.

-----------------------------------------------------------------------------
IVALS(buf,pos)

returns the value of the signed 32 bit little-endian integer at offset pos
within buffer buf.

-----------------------------------------------------------------------------
SSVAL(buf,pos,val)

sets the unsigned short (16 bit) little-endian integer at offset pos within 
buffer buf to value val.

-----------------------------------------------------------------------------
SIVAL(buf,pos,val)

sets the unsigned 32 bit little-endian integer at offset pos within buffer 
buf to the value val.

-----------------------------------------------------------------------------
SSVALS(buf,pos,val)

sets the short (16 bit) signed little-endian integer at offset pos within 
buffer buf to the value val.

-----------------------------------------------------------------------------
SIVALS(buf,pos,val)

sets the signed 32 bit little-endian integer at offset pos withing buffer
buf to the value val.

-----------------------------------------------------------------------------
RSVAL(buf,pos)

returns the value of the unsigned short (16 bit) big-endian integer at 
offset pos within buffer buf.

-----------------------------------------------------------------------------
RIVAL(buf,pos)

returns the value of the unsigned 32 bit big-endian integer at offset 
pos within buffer buf.

-----------------------------------------------------------------------------
RSSVAL(buf,pos,val)

sets the value of the unsigned short (16 bit) big-endian integer at 
offset pos within buffer buf to value val.
refered to as "USHORT".

-----------------------------------------------------------------------------
RSIVAL(buf,pos,val)

sets the value of the unsigned 32 bit big-endian integer at offset 
pos within buffer buf to value val.





=============================================================================
This section describes the functions need to make a LAN Manager RPC call.
This information had been obtained by examining the Samba code and the LAN
Manager 2.0 API documentation.  It should not be considered entirely
reliable.

-----------------------------------------------------------------------------
call_api(int prcnt, int drcnt, int mprcnt, int mdrcnt, 
	char *param, char *data, char **rparam, char **rdata);

This function is defined in client.c.  It uses an SMB transaction to call a
remote api.

The parameters are as follows:

prcnt:   the number of bytes of parameters begin sent.
drcnt:   the number of bytes of data begin sent.
mprcnt:  the maximum number of bytes of parameters which should be returned
mdrcnt:  the maximum number of bytes of data which should be returned
param:   a pointer to the parameters to be sent.
data:    a pointer to the data to be sent.
rparam:  a pointer to a pointer which will be set to point to the returned
	 paramters.  The caller of call_api() must deallocate this memory.
rdata:   a pointer to a pointer which will be set to point to the returned 
	 data.  The caller of call_api() must deallocate this memory.

-----------------------------------------------------------------------------
These are the parameters which you ought to send, in the order of their
appearance in the parameter block:

* An unsigned 16 bit integer API number.  You should set this value with
SSVAL().  I do not know where these numbers are described.

* An ASCIIZ string describing the parameters to the API function as defined
in the LAN Manager documentation.  The first parameter, which is the server
name, is omitted.  This string is based uppon the API function as described
in the manual, not the data which is actually passed.

* An ASCIIZ string describing the data structure which ought to be returned.

* Any parameters which appear in the function call, as defined in the LAN
Manager API documentation, after the "Server" and up to and including the
"uLevel" parameters.

* An unsigned 16 bit integer which gives the size in bytes of the buffer we
will use to receive the returned array of data structures.  Presumably this
should be the same as mdrcnt.  This value should be set with SSVAL().

* An ASCIIZ string describing substructures which should be returned.  If no 
substructures apply, this string is of zero length.

-----------------------------------------------------------------------------
The code in client.c always calls call_api() with no data.  It is unclear
when a non-zero length data buffer would be sent.

-----------------------------------------------------------------------------
The returned parameters (pointed to by rparam), in their order of appearance
are:

* An unsigned 16 bit integer which contains the API function's return code. 
This value should be read with SVAL().

* An adjustment which tells the amount by which pointers in the returned
data should be adjusted.  This value should be read with SVAL().  Basically, 
the address of the start of the returned data buffer should have the returned
pointer value added to it and then have this value subtracted from it in
order to obtain the currect offset into the returned data buffer.

* A count of the number of elements in the array of structures returned. 
It is also possible that this may sometimes be the number of bytes returned.

-----------------------------------------------------------------------------
When call_api() returns, rparam points to the returned parameters.  The
first if these is the result code.  It will be zero if the API call
suceeded.  This value by be read with "SVAL(rparam,0)".

The second parameter may be read as "SVAL(rparam,2)".  It is a 16 bit offset
which indicates what the base address of the returned data buffer was when
it was built on the server.  It should be used to correct pointer before
use.

The returned data buffer contains the array of returned data structures. 
Note that all pointers must be adjusted before use.  The function
fix_char_ptr() in client.c can be used for this purpose.

The third parameter (which may be read as "SVAL(rparam,4)") has something to
do with indicating the amount of data returned or possibly the amount of
data which can be returned if enough buffer space is allowed.

-----------------------------------------------------------------------------
Certain data structures are described by means of ASCIIz strings containing
code characters.  These are the code characters:

W	a type byte little-endian unsigned integer
N	a count of substructures which follow
D	a four byte little-endian unsigned integer
B	a byte (with optional count expressed as trailing ASCII digits)
z	a four byte offset to a NULL terminated string
l	a four byte offset to non-string user data
b	an offset to data (with count expressed as trailing ASCII digits)
r	pointer to returned data buffer???
L	length in bytes of returned data buffer???
h	number of bytes of information available???

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