READ_CONFIG(3) Net-SNMP READ_CONFIG(3)NAME
register_config_handler, register_premib_handler unregister_config_han‐
dler, register_mib_handlers, read_configs, read_premib_configs, con‐
fig_perror, config_pwarn - read_config functions
SYNOPSIS
#include <net-snmp/config_api.h>
struct config_line *
register_config_handler(const char *filePrefix,
const char *token,
void (*parser)(const char *, char *),
void (*releaser)(void),
const char *usageLine);
struct config_line *
register_premib_handler(const char *filePrefix,
const char *token,
void (*parser)(const char *, char *),
void (*releaser)(void),
const char *usageLine);
void unregister_config_handler(const char *filePrefix,
const char *token);
struct config_line *
register_app_config_handler(const char *token,
void (*parser)(const char *, char *),
void (*releaser)(void),
const char *usageLine);
struct config_line *
register_app_premib_handler(const char *token,
void (*parser)(const char *, char *),
void (*releaser)(void),
const char *usageLine);
void unregister_app_config_handler(const char *token);
void read_config_print_usage(char *lead);
void read_configs(void);
void read_premib_configs(void);
void config_pwarn(const char *string);
void config_perror(const char *string);
DESCRIPTION
The functions are a fairly extensible system of parsing various config‐
uration files at the run time of an application. The configuration
file flow is broken into the following phases:
1. Registration of handlers.
2. Reading of the configuration files for pre-MIB parsing require‐
ments.
3. Reading and parsing of the textual MIB files.
4. Reading of the configuration files for configuration direc‐
tives.
5. Optionally re-reading the configuration files at a future date.
The idea is that the calling application is able to register handlers
for certain tokens specified in certain types of files. The read_con‐
figs() 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.
TOKEN HANDLERS
Handler functions should have the following signature:
void handler(const char *token, char *line);
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.
RESOURCE FREEING HANDLERS
If the parameter releaser passed to register_config_handler is non-
NULL, then the function specified is called if and when the configura‐
tion files are re-read. This function should free any resources allo‐
cated by the token handler function and reset its notion of the config‐
uration to its default. The token handler function will then be called
again. No arguments are passed to the resource freeing handler.
REGISTERING A HANDLERregister_config_handler()
The handler() function above could be registered for the config‐
uration file snmp.conf, with the token genericToken and the help
string (discussed later) "ARG1 [ARG2]" using the following call
to the register_config_handler() function:
register_config_handler("snmp", "genericToken", handler,
NULL, "ARG1 [ARG2]");
This would register the handler() function so that it will get
called every time the first word of a line in the snmp.conf con‐
figuration file(s) matches "genericToken" (see read_configs()
below).
register_premib_handler()
The register_premib_handler() function works identically to the
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.
unregister_config_handler()
Removes the registered configuration handler for the filePrefix
and token.
register_app_config_handler()register_app_premib_handler()unregister_app_config_handler()
These functions are analagous to register_config_handler(), reg‐
ister_premib_handler() and unregister_config_handler() but don't
require the file type argument (which is filled in by the appli‐
cation). It is intended that MIB modules written for the agent
use these functions to allow the agent to have more control over
which configuration files are read (typically the snmpd.conf
files).
HELP STRINGS
The usageLine parameter passed to register_config_handler() and similar
calls, is used to display help information when the read_con‐
fig_print_usage() function is called. This function is used by all of
the applications when the -H flag is passed on the command line. It
prints a summary of all of the configuration file lines, and the asso‐
ciated 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 lead prefix will be prepended to each line that the function prints
to stderr, where it displays its output.
The init_snmp() function should be called before the read_con‐
fig_print_usage() function is called, so that the library can register
its configuration file directives as well for the read_con‐
fig_print_usage() function to display.
READING CONFIGURATION FILESinit_snmp()
Once the relevant configuration token parsers have been regis‐
tered, init_snmp() should be called. It will parse the configu‐
ration file tokens registered with register_premib_handler(),
read in the textual MIB files using init_mib(), and finally
parse the configuration file tokens registered with regis‐
ter_config_handler().
If the init_snmp() function is used, none of the following functions
need to be called by the application:
register_mib_handlers()
The SNMP library's routine to register its configuration file
handlers.
read_premib_configs()
The routine that parses the configuration files for tokens reg‐
istered to be dealt with before the textual MIBs are read in.
See read_configs() below.
read_configs()
Reads all the configuration files it can find in the SNMPCONF‐
PATH 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.
CONFIGURATION FILES READ
The configuration files read are found by using the colon separated
SNMPCONFPATH environment variable (or its default value, which will be
/usr/etc/snmp, followed by /etc/net-snmp/snmp, followed by
/usr/lib/snmp, followed by $HOME/.snmp) and reading in the files found
that match both the prefix registered and the two suffixes .conf and
.local.conf. The idea behind the two different suffixes is that the
first file can be shared (via rdist or an NFS mount) across a large
number of machines and the second file can be used to configure local
settings for one particular machine. They do not need to be present,
and will only be read if found.
ERROR HANDLING FUNCTIONS
The two functions config_pwarn() and config_perror() both take an error
string as an argument and print it to stderr along with the file and
line number that caused the error. A call to the second function will
also force read_configs() to eventually return with an error code indi‐
cating to it's calling function that it should abort the operation of
the application.
ENVIRONMENT VARIABLES
SNMPCONFPATH
A colon separated list of directories to search for configu‐
ration files in. Default: /usr/etc/snmp:/etc/net-
snmp/snmp:/usr/lib/snmp:$HOME/.snmp
SEE ALSOmib_api(3), snmp_api(3)ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌────────────────────┬─────────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼─────────────────────────────────┤
│Availability │ system/management/snmp/net-snmp │
├────────────────────┼─────────────────────────────────┤
│Interface Stability │ Volatile │
└────────────────────┴─────────────────────────────────┘
NOTES
Source for net-snmp is available on http://opensolaris.org.
4.2 Berkeley Distribution 07 Mar 2002 READ_CONFIG(3)
