man/read_config.3.def

.TH READ_CONFIG 3 "02 Mar 1999"
.UC 5
.SH NAME
register_config_handler, register_premib_handler
unregister_config_handler, register_mib_handlers, read_configs,
read_premib_configs, config_perror, config_pwarn - read_config functions
.SH SYNOPSIS
.B #include <read_config.h>
.PP
.B struct config_line *
.br
.B "  register_config_handler(char *filePrefix, char *token,"
.br
.B "            void (*parser)(char *, char *) handler, "
.br
.B "            void (*releaser) (void) freefunc,"
.br
.B "            char *usageLine)"
.PP
.B struct config_line *
.br
.B "  register_premib_handler(char *filePrefix, char *token,"
.br
.B "            void (*parser)(char *, char *) handler, "
.br
.B "            void (*releaser) (void) freefunc,"
.br
.B "            char *usageLine)"
.PP
.B struct config_line *
.br
.B "  snmpd_register_config_handler(char *token,"
.br
.B "            void (*parser)(char *, char *) handler, "
.br
.B "            void (*releaser) (void) freefunc,"
.br
.B "            char *usageLine)"
.PP
.B "void unregister_config_handler(char *filePrefix, "
.br
.B "            char *token)"
.PP
.B "void read_config_print_usage(char *lead)"
.PP
.B "void read_configs(void)"
.PP
.B "void read_premib_configs(void)"
.PP
.SH DESCRIPTION
The functions are a fairly extensible system of parsing various
configuration files at the run time of an application.  The
configuration file flow is broken into the following phases:
.RS
.PP
registration of handlers.
.PP
reading of the configuration files for pre-mib parsing requirements.
.PP
reading of the textual mib files.
.PP
reading of the configuration files for configuration directives.
.PP
optionally re-reading of the configuration files at a future date.
.RE
.PP
The idea is that the calling application is able to register
.I handlers
for certain
.I tokens
specified in certain types of
.I files.
The 
.B read_configs()
function can then be called to look for all the files that it has
registrations for, find the first word on each line, and pass the
remainder to the appropriately registered handler.
.SH Token Handlers
.PP
Handler functions should be of the following type:
.PP
.RS
void handler(char *token, char *line);
.RE
.PP
The function will be called with two arguments, the first being the
token that triggered the call to this function (which would be one of
the tokens that the function had been registered for), and the second
being the remainder of the configuration file line beyond the white
space following the token.
.SH Resource Freeing Handlers
.PP
If the read_config configuration system is called a second time to
re-read the configuration files, the optional second handler 
.I freefunc
will be called, if registered as non-NULL, to free any resources and
reset its notions to defaults before the config handlers are called
again.  It is not called with any arguments.
.SH Registering A Handler
.IP register_config_handler()
The handler above could then be registered for the configuration file
.I snmp.conf,
with the token
.I genericToken
and the help string (discussed later)
.I ARG1 ARG2
using the following call to the 
.B register_config_handler()
function:
.PP
.RS
.RS
register_config_handler("snmp", "genericToken", handler, NULL, "ARG1 ARG2");
.RE
.RE
.IP
This would register the
.B handler()
function so that it will get called every time the first word in the 
.I snmp.conf
configuration file(s) matches "genericToken" (see 
.B read_configs() 
below).
.IP register_premib_handler()
The 
.B register_premib_handler()
function works identically to the 
.B register_config_handler()
function but is intended for config file tokens that need to be read
in before the textual mibs are read in, probably because they will be
used to configure the mib parser.  It is rarely the case that anything 
but the snmp library itself should need to use this function.
.IP snmpd_register_config_handler()
This function performs exactly the same job as the
.B register_config_handler()
function, but doesn't require the file type argument (which is filled
in by the snmpd agent).  It is intended that mib modules written for
the agent use this function instead of the 
.B register_config_handler()
function directly to allow the agent to have more control over which
files the mib modules will read (which should be the 
.I snmpd.conf
files).
.IP unregister_config_handler()
Removes the registered configuration handler for the
.I filePrefix
and
.I token
.IP 
.SH Help Strings
.PP
The
.I usageLine
token passed to the register_config_handler(), and similar calls, is
used to display help information when the
.B read_config_print_usage()
function is called.  This function is used by all of the applications
when the 
.B -H
flag is passed to the command line.  It prints a summary of all of the 
configuration file lines, and the associated files, that the
configuration system understands.  The usageLine parameter should be a 
list of arguments expected after the token, and not a lengthy
description (which should go into a manual page instead).  The
.I lead
prefix will be prepended to each line that the function prints to
stderr, where it displays its output.
.PP
The
.B init_snmp()
function should be called before the
.B read_config_print_usage()
function is called, so that the library can register its configuration 
file directives as well for the 
.B read_config_print_usage()
function to display.
.SH Reading Configuration Files
.IP init_snmp()
The 
.B init_snmp()
function call should be called after registrations to appropriately
register parser configuration tokens, parse the configuration file
tokens registered with
.B register_premib_handler(),
read in the textual mib files using
.B init_mib(),
and finally parse the configuration file tokens registered with 
.B register_config_handler().  
.PP
If the 
.B init_snmp()
function is used, none of the following functions need to be called by 
the application:
.PP
.IP register_mib_handlers()
The snmp library's routine to register it's configuration file
handlers.
.IP read_premib_configs()
The routine that parses the configuration files for tokens registered
to be dealt with before the textual mibs are read in.  See 
.B read_configs()
below.
.IP read_configs()
Reads all the configuration files it can find in the 
.I SNMPCONFPATH
environment variable (or its default value) for tokens and
appropriately calls the handlers registered to it, or prints a
"Unknown token" warning message.  It looks for any file that it has
previously received a registration request for.
.SH Configuration Files Read
.PP
The configuration files read are found by using the colon separated
.I SNMPCONFPATH
environment variable (or its default value, which will be
DATADIR/snmp, followed by LIBDIR/snmp, followed by $HOME/.snmp) and
reading in the files found that match both the prefix registered and
the two suffixes
.I .conf
and
.I .local.conf.
The idea behind the two different suffixes is that the first file can
be rdisted across a large number of machines and the second file can
be used to configure local settings for one particular machine.  They
do not need to be present, and will only be read if found.
.SH Error Handling Functions
.PP
The two functions
.B config_pwarn()
and
.B config_perror()
both take an error string as an argument and print it to stderr along
with the file and line number that caused the error.  A call to the
second function will also force read_configs() to eventually return
with an error code indicating to it's calling function that it should
abort the operation of the application.
.SH "ENVIRONMENT VARIABLES"
.TP 10
SNMPCONFPATH
A colon separated list of directories to search for configuration
files in.
Default: DATADIR/snmp:LIBDIR/snmp:$HOME/.snmp
.SH "SEE ALSO"
mib_api(3), snmp_api(3)
.\" Local Variables:
.\"  mode: nroff
.\" End: