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authorAlexander Bokovoy <ab@samba.org>2003-04-30 21:17:53 +0000
committerAlexander Bokovoy <ab@samba.org>2003-04-30 21:17:53 +0000
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+<chapter id="internals">
+<chapterinfo>
+ <author>
+ <firstname>David</firstname><surname>Chappell</surname>
+ <affiliation>
+ <address><email>David.Chappell@mail.trincoll.edu</email></address>
+ </affiliation>
+ </author>
+ <pubdate>8 May 1996</pubdate>
+</chapterinfo>
+
+<title>Samba Internals</title>
+
+<sect1>
+<title>Character Handling</title>
+<para>
+This section describes character set handling in Samba, as implemented in
+Samba 3.0 and above
+</para>
+
+<para>
+In the past Samba had very ad-hoc character set handling. Scattered
+throughout the code were numerous calls which converted particular
+strings to/from DOS codepages. The problem is that there was no way of
+telling if a particular char* is in dos codepage or unix
+codepage. This led to a nightmare of code that tried to cope with
+particular cases without handlingt the general case.
+</para>
+</sect1>
+
+<sect1>
+<title>The new functions</title>
+
+<para>
+The new system works like this:
+</para>
+
+<orderedlist>
+<listitem><para>
+ all char* strings inside Samba are "unix" strings. These are
+ multi-byte strings that are in the charset defined by the "unix
+ charset" option in smb.conf.
+</para></listitem>
+
+<listitem><para>
+ there is no single fixed character set for unix strings, but any
+ character set that is used does need the following properties:
+ </para>
+ <orderedlist>
+
+ <listitem><para>
+ must not contain NULLs except for termination
+ </para></listitem>
+
+ <listitem><para>
+ must be 7-bit compatible with C strings, so that a constant
+ string or character in C will be byte-for-byte identical to the
+ equivalent string in the chosen character set.
+ </para></listitem>
+
+ <listitem><para>
+ when you uppercase or lowercase a string it does not become
+ longer than the original string
+ </para></listitem>
+
+ <listitem><para>
+ must be able to correctly hold all characters that your client
+ will throw at it
+ </para></listitem>
+ </orderedlist>
+
+ <para>
+ For example, UTF-8 is fine, and most multi-byte asian character sets
+ are fine, but UCS2 could not be used for unix strings as they
+ contain nulls.
+ </para>
+</listitem>
+
+<listitem><para>
+ when you need to put a string into a buffer that will be sent on the
+ wire, or you need a string in a character set format that is
+ compatible with the clients character set then you need to use a
+ pull_ or push_ function. The pull_ functions pull a string from a
+ wire buffer into a (multi-byte) unix string. The push_ functions
+ push a string out to a wire buffer.
+</para></listitem>
+
+<listitem><para>
+ the two main pull_ and push_ functions you need to understand are
+ pull_string and push_string. These functions take a base pointer
+ that should point at the start of the SMB packet that the string is
+ in. The functions will check the flags field in this packet to
+ automatically determine if the packet is marked as a unicode packet,
+ and they will choose whether to use unicode for this string based on
+ that flag. You may also force this decision using the STR_UNICODE or
+ STR_ASCII flags. For use in smbd/ and libsmb/ there are wrapper
+ functions clistr_ and srvstr_ that call the pull_/push_ functions
+ with the appropriate first argument.
+ </para>
+
+ <para>
+ You may also call the pull_ascii/pull_ucs2 or push_ascii/push_ucs2
+ functions if you know that a particular string is ascii or
+ unicode. There are also a number of other convenience functions in
+ charcnv.c that call the pull_/push_ functions with particularly
+ common arguments, such as pull_ascii_pstring()
+ </para>
+</listitem>
+
+<listitem><para>
+ The biggest thing to remember is that internal (unix) strings in Samba
+ may now contain multi-byte characters. This means you cannot assume
+ that characters are always 1 byte long. Often this means that you will
+ have to convert strings to ucs2 and back again in order to do some
+ (seemingly) simple task. For examples of how to do this see functions
+ like strchr_m(). I know this is very slow, and we will eventually
+ speed it up but right now we want this stuff correct not fast.
+</para></listitem>
+
+<listitem><para>
+ all lp_ functions now return unix strings. The magic "DOS" flag on
+ parameters is gone.
+</para></listitem>
+
+<listitem><para>
+ all vfs functions take unix strings. Don't convert when passing to them
+</para></listitem>
+
+</orderedlist>
+
+</sect1>
+
+<sect1>
+<title>Macros in byteorder.h</title>
+
+<para>
+This section describes the macros defined in byteorder.h. These macros
+are used extensively in the Samba code.
+</para>
+
+<sect2>
+<title>CVAL(buf,pos)</title>
+
+<para>
+returns the byte at offset pos within buffer buf as an unsigned character.
+</para>
+</sect2>
+
+<sect2>
+<title>PVAL(buf,pos)</title>
+<para>returns the value of CVAL(buf,pos) cast to type unsigned integer.</para>
+</sect2>
+
+<sect2>
+<title>SCVAL(buf,pos,val)</title>
+<para>sets the byte at offset pos within buffer buf to value val.</para>
+</sect2>
+
+<sect2>
+<title>SVAL(buf,pos)</title>
+<para>
+ 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".
+</para>
+</sect2>
+
+<sect2>
+<title>IVAL(buf,pos)</title>
+<para>returns the value of the unsigned 32 bit little-endian integer at offset
+pos within buffer buf.</para>
+</sect2>
+
+<sect2>
+<title>SVALS(buf,pos)</title>
+<para>returns the value of the signed short (16 bit) little-endian integer at
+offset pos within buffer buf.</para>
+</sect2>
+
+<sect2>
+<title>IVALS(buf,pos)</title>
+<para>returns the value of the signed 32 bit little-endian integer at offset pos
+within buffer buf.</para>
+</sect2>
+
+<sect2>
+<title>SSVAL(buf,pos,val)</title>
+<para>sets the unsigned short (16 bit) little-endian integer at offset pos within
+buffer buf to value val.</para>
+</sect2>
+
+<sect2>
+<title>SIVAL(buf,pos,val)</title>
+<para>sets the unsigned 32 bit little-endian integer at offset pos within buffer
+buf to the value val.</para>
+</sect2>
+
+<sect2>
+<title>SSVALS(buf,pos,val)</title>
+<para>sets the short (16 bit) signed little-endian integer at offset pos within
+buffer buf to the value val.</para>
+</sect2>
+
+<sect2>
+<title>SIVALS(buf,pos,val)</title>
+<para>sets the signed 32 bit little-endian integer at offset pos withing buffer
+buf to the value val.</para>
+</sect2>
+
+<sect2>
+<title>RSVAL(buf,pos)</title>
+<para>returns the value of the unsigned short (16 bit) big-endian integer at
+offset pos within buffer buf.</para>
+</sect2>
+
+<sect2>
+<title>RIVAL(buf,pos)</title>
+<para>returns the value of the unsigned 32 bit big-endian integer at offset
+pos within buffer buf.</para>
+</sect2>
+
+<sect2>
+<title>RSSVAL(buf,pos,val)</title>
+<para>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".</para>
+</sect2>
+
+<sect2>
+<title>RSIVAL(buf,pos,val)</title>
+<para>sets the value of the unsigned 32 bit big-endian integer at offset
+pos within buffer buf to value val.</para>
+</sect2>
+
+</sect1>
+
+
+<sect1>
+<title>LAN Manager Samba API</title>
+
+<para>
+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.
+</para>
+
+<para>
+<programlisting>
+call_api(int prcnt, int drcnt, int mprcnt, int mdrcnt,
+ char *param, char *data, char **rparam, char **rdata);
+</programlisting>
+</para>
+
+<para>
+This function is defined in client.c. It uses an SMB transaction to call a
+remote api.
+</para>
+
+<sect2>
+<title>Parameters</title>
+
+<para>The parameters are as follows:</para>
+
+<orderedlist>
+<listitem><para>
+ prcnt: the number of bytes of parameters begin sent.
+</para></listitem>
+<listitem><para>
+ drcnt: the number of bytes of data begin sent.
+</para></listitem>
+<listitem><para>
+ mprcnt: the maximum number of bytes of parameters which should be returned
+</para></listitem>
+<listitem><para>
+ mdrcnt: the maximum number of bytes of data which should be returned
+</para></listitem>
+<listitem><para>
+ param: a pointer to the parameters to be sent.
+</para></listitem>
+<listitem><para>
+ data: a pointer to the data to be sent.
+</para></listitem>
+<listitem><para>
+ 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.
+</para></listitem>
+<listitem><para>
+ 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.
+</para></listitem>
+</orderedlist>
+
+<para>
+These are the parameters which you ought to send, in the order of their
+appearance in the parameter block:
+</para>
+
+<orderedlist>
+
+<listitem><para>
+An unsigned 16 bit integer API number. You should set this value with
+SSVAL(). I do not know where these numbers are described.
+</para></listitem>
+
+<listitem><para>
+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 ommited. This string is based uppon the API function as described
+in the manual, not the data which is actually passed.
+</para></listitem>
+
+<listitem><para>
+An ASCIIZ string describing the data structure which ought to be returned.
+</para></listitem>
+
+<listitem><para>
+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.
+</para></listitem>
+
+<listitem><para>
+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().
+</para></listitem>
+
+<listitem><para>
+An ASCIIZ string describing substructures which should be returned. If no
+substructures apply, this string is of zero length.
+</para></listitem>
+
+</orderedlist>
+
+<para>
+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.
+</para>
+
+</sect2>
+
+<sect2>
+<title>Return value</title>
+
+<para>
+The returned parameters (pointed to by rparam), in their order of appearance
+are:</para>
+
+<orderedlist>
+
+<listitem><para>
+An unsigned 16 bit integer which contains the API function's return code.
+This value should be read with SVAL().
+</para></listitem>
+
+<listitem><para>
+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.
+</para></listitem>
+
+<listitem><para>
+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.
+</para></listitem>
+</orderedlist>
+
+<para>
+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)".
+</para>
+
+<para>
+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.
+</para>
+
+<para>
+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.
+</para>
+
+<para>
+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.
+</para>
+
+</sect2>
+</sect1>
+
+<sect1>
+<title>Code character table</title>
+<para>
+Certain data structures are described by means of ASCIIz strings containing
+code characters. These are the code characters:
+</para>
+
+<orderedlist>
+<listitem><para>
+W a type byte little-endian unsigned integer
+</para></listitem>
+<listitem><para>
+N a count of substructures which follow
+</para></listitem>
+<listitem><para>
+D a four byte little-endian unsigned integer
+</para></listitem>
+<listitem><para>
+B a byte (with optional count expressed as trailing ASCII digits)
+</para></listitem>
+<listitem><para>
+z a four byte offset to a NULL terminated string
+</para></listitem>
+<listitem><para>
+l a four byte offset to non-string user data
+</para></listitem>
+<listitem><para>
+b an offset to data (with count expressed as trailing ASCII digits)
+</para></listitem>
+<listitem><para>
+r pointer to returned data buffer???
+</para></listitem>
+<listitem><para>
+L length in bytes of returned data buffer???
+</para></listitem>
+<listitem><para>
+h number of bytes of information available???
+</para></listitem>
+</orderedlist>
+
+</sect1>
+</chapter>