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This directory holds the implementation of individual MIB groups.
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Currently, this contains the eight MIB-2 groups, plus a basic template
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for new MIB groups (examples/example.c and examples/example.h)
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Additionally, you may wish to check out the 'mib2c' perl script in the
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SRCDIR/local directory that can convert a written mib into C template
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files for use with this package as mib modules.
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Each group consists of two files:
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examples/example.h: interface information
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- declaration of the initialisation function 'init_example'
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- declaration of the function(s) for retrieving variable
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information 'var_example'
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- declaration of the function(s) for setting variable
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information (if appropriate)
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- declaration of the function(s) for parsing the snmpd.conf file
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- a call to config_parse_dot_conf() to explain to the .conf
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parser which tokens we want to parse.
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- definitions of the MIB group 'magic numbers'
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declarations of the 'public' functions
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- a list of the variables in the group, including
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type information, mapping between magic numbers
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and OID sub-identifiers within the group,
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accessibility information, and the relevant
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function for retrieving this variable's value.
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They *must* be listed in the mib-descending order.
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- a call to 'config_load_mib', identifying the location of
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this MIB group within the general MIB structure.
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- a call to 'config_require' to identify any other files
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that are required by the implementation of this group.
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(these last three are only visible within the 'glue' file 'snmp_vars.c'
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(if at all), but are declared here for ease of maintainance)
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examples/example.c: implementation code
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(can be non-existant if only the .h file is needed)
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- a list of kernel information needed to report
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- an initialisation function (optional)
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- a routine to parse an snmpd.conf line.
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- a routine to free resources from above and return to
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- 'header' function(s) to map the OID requested
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to the next appropriate OID
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(and similar system-independent setup)
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- function(s) (possibly system-specific) to
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determine and return the value of the
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- (optionally) functions used to set values
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- other functions used internally
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To implement a new MIB group, copy the two files 'example.c'
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and 'example.h' to appropriate new files ({MODULENAME}.c and {MODULENAME}.h),
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and edit them as follows:
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globally change "example" to the new module name
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and update the initial comment.
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replace the EXAMPLE* defines with the list of
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variables within this new group
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fill in the 'MODULENAME_variables' structure with these
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new variables, updating the type, accessibility
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and sub-identifier information as appropriate.
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replace 'variableN' with the maximum size of the
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returned OID (omitting the group prefix).
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For non-table values, this will probably be one
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greater than the length of the sub-identifier.
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update or remove the 'config_parse_dot_conf' call if
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you need to handle lines in the snmpd.conf files.
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update the 'config_load_mib' call with the appropriate
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location within the global MIB structure, and
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its length (note that 'MIB' has length 6)
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provide a suitable 'config_require' call if this
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code uses routines from any other files within
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the 'mibgroup' directory (such as 'util_funcs.c')
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globally change "example" to the new module name
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and update the initial comment.
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replace the 'MODULENAME_nl' name list with any necessary
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kernel variables, and update the associated #define's
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replace the name length definition within the 'header'
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function with the length of the requesting OID
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(i.e. the sum of the lengths given in the subtree
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definition, and the variable structure above).
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replace the basic 'switch' structure within the
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'var_MODULENAME' function with the necessary code
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to calculate the required information.
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(plus any other internal functions as needed).
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It will then be necessary to (re-)run the configure script with the
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--with-mib-modules="MODULENAME"
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(where MODULENAME matches the name of the .c/.h file pair exactly).
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Note that if anything in the config_* macros changes, or the init function
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is added or removed, then the configure script will need to be re-run.
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agent/mibgroup/README
