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182 lines
4.6 KiB
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182 lines
4.6 KiB
Plaintext
Chris Hertel, Samba Team
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November 1997
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This is a quick overview of the lexical analysis, syntax, and semantics
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of the smb.conf file.
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Lexical Analysis:
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Basically, the file is processed on a line by line basis. There are
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four types of lines that are recognized by the lexical analyzer
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(params.c):
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Blank lines - Lines containing only whitespace.
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Comment lines - Lines beginning with either a semi-colon or a
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pound sign (';' or '#').
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Section header lines - Lines beginning with an open square bracket
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('[').
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Parameter lines - Lines beginning with any other character.
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(The default line type.)
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The first two are handled exclusively by the lexical analyzer, which
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ignores them. The latter two line types are scanned for
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- Section names
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- Parameter names
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- Parameter values
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These are the only tokens passed to the parameter loader
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(loadparm.c). Parameter names and values are divided from one
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another by an equal sign: '='.
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Handling of Whitespace:
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Whitespace is defined as all characters recognized by the isspace()
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function (see ctype(3C)) except for the newline character ('\n')
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The newline is excluded because it identifies the end of the line.
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- The lexical analyzer scans past white space at the beginning of a
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line.
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- Section and parameter names may contain internal white space. All
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whitespace within a name is compressed to a single space character.
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- Internal whitespace within a parameter value is kept verbatim with
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the exception of carriage return characters ('\r'), all of which
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are removed.
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- Leading and trailing whitespace is removed from names and values.
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Handling of Line Continuation:
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Long section header and parameter lines may be extended across
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multiple lines by use of the backslash character ('\\'). Line
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continuation is ignored for blank and comment lines.
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If the last (non-whitespace) character within a section header or on
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a parameter line is a backslash, then the next line will be
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(logically) concatonated with the current line by the lexical
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analyzer. For example:
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param name = parameter value string \
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with line continuation.
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Would be read as
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param name = parameter value string with line continuation.
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Note that there are five spaces following the word 'string',
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representing the one space between 'string' and '\\' in the top
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line, plus the four preceeding the word 'with' in the second line.
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(Yes, I'm counting the indentation.)
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Line continuation characters are ignored on blank lines and at the end
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of comments. They are *only* recognized within section and parameter
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lines.
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Line Continuation Quirks:
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Note the following example:
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param name = parameter value string \
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\
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with line continuation.
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The middle line is *not* parsed as a blank line because it is first
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concatonated with the top line. The result is
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param name = parameter value string with line continuation.
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The same is true for comment lines.
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param name = parameter value string \
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; comment \
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with a comment.
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This becomes:
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param name = parameter value string ; comment with a comment.
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On a section header line, the closing bracket (']') is considered a
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terminating character, and the rest of the line is ignored. The lines
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[ section name ] garbage \
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param name = value
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are read as
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[section name]
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param name = value
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Syntax:
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The syntax of the smb.conf file is as follows:
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<file> :== { <section> } EOF
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<section> :== <section header> { <parameter line> }
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<section header> :== '[' NAME ']'
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<parameter line> :== NAME '=' VALUE NL
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Basically, this means that
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- a file is made up of zero or more sections, and is terminated by
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an EOF (we knew that).
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- A section is made up of a section header followed by zero or more
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parameter lines.
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- A section header is identified by an opening bracket and
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terminated by the closing bracket. The enclosed NAME identifies
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the section.
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- A parameter line is divided into a NAME and a VALUE. The *first*
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equal sign on the line separates the NAME from the VALUE. The
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VALUE is terminated by a newline character (NL = '\n').
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About params.c:
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The parsing of the config file is a bit unusual if you are used to
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lex, yacc, bison, etc. Both lexical analysis (scanning) and parsing
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are performed by params.c. Values are loaded via callbacks to
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loadparm.c.
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