read_module_node (3) - Linux Manuals
NAME
init_mib, add_mibdir, init_mib_internals, add_module_replacement, read_module, read_mib, read_all_mibs, read_objid, read_module_node, get_module_node, snmp_set_mib_warnings, snmp_set_save_descriptions, shutdown_mib, print_mib, print_variable, fprint_variable, snprint_variable, sprint_realloc_variable, print_value, fprint_value, snprint_value, sprint_realloc_value, print_objid, fprint_objid, snprint_objid, sprint_realloc_objid, print_description, fprint_description - mib_api functions
SYNOPSIS
#include <net-snmp/mib_api.h>
void init_mib(void);
int add_mibdir(const char *dirname);
int add_module_replacement(const char *old_module, const char *new_module, const char *tag, int len);
void init_mib_internals(void);
struct tree *read_module(const char *name);
struct tree *read_mib(const char *filename);
struct tree *read_all_mibs(void);
void shutdown_mib(void);
void print_mib(FILE *fp);
int read_objid(const char *input, oid *output, size_t *out_len);
int get_module_node(const char *name, const char *module, oid *objid, size_t *objidlen);
void print_variable(const oid *objid, size_t objidlen, const netsnmp_variable_list *variable);
void fprint_variable(FILE *fp, const oid *objid, size_t objidlen, const netsnmp_variable_list *variable);
int snprint_variable(char *buf, size_t len, const oid *objid, size_t objidlen, const netsnmp_variable_list *variable);
int sprint_realloc_variable(u_char **buf, size_t *buf_len, size_t *out_len, int allow_realloc, const oid *objid, size_t objidlen, const netsnmp_variable_list *variable);
void print_value(oid *objid, size_t objidlen, const netsnmp_variable_list *variable)
void fprint_value(FILE *fp, const oid *objid, size_t objidlen, const netsnmp_variable_list *variable);
int snprint_value(char *buf, size_t len, const oid *objid, size_t objidlen, const netsnmp_variable_list *variable);
int sprint_realloc_value(u_char **buf, size_t *buf_len, size_t *out_len, int allow_realloc, const oid *objid, size_t objidlen, const netsnmp_variable_list *variable);
void print_objid(const oid *objid, size_t objidlen);
void fprint_objid(FILE *fp, const oid *objid, size_t objidlen);
int snprint_objid(char *buf, size_t len, const oid *objid, size_t objidlen);
int sprint_realloc_objid(u_char **buf, size_t *buf_len, size_t *out_len, int allow_realloc, const oid *objid, size_t objidlen);
void print_description(oid *objid, size_t objidlen, int width);
void fprint_description(FILE *fp, const oid *objid, size_t objidlen, int width);
void snmp_set_mib_warnings(int level);
void snmp_set_save_descriptions(int save);
DESCRIPTION
The functions dealing with MIB modules fall into four groups. Those dealing with initialisation and shutdown, those that read in and parse MIB files, those that search the MIB tree, and various output routines.Initialisation and Shutdown
init_mib is a convenience function that handles all calls to add_mibdir, read_module and read_mib for standard applications. It should be called before any other routine that manipulates or accesses the MIB tree. This routine sets up various internal structures, as well as reading in the default MIB modules, as detailed below.add_mibdir is used to define the range of directory locations which are searched for files containing MIB modules (one module per file). By default, this will be set to the directory /usr/share/mibs but this can be overridden by setting the environment variable MIBDIRS to a (colon-separated) list of directories to search. Note that this does not actually load the MIB modules located in that directory, but is an initialisation step to make them available. This function returns a count of files found in the directory, or a -1 if there is an error.
init_mib_internals sets up the internal structures, preparatory to reading in MIB modules. It should be called after all calls to add_mibdir, and before and calls to read_module. This is called automatically if init_mib is used.
shutdown_mib will clear the information that was gathered by read_module, add_mibdir and add_module_replacement. It is strongly recommended that one does not invoke shutdown_mib while there are SNMP sessions being actively managed.
Reading and Parsing MIBs
add_module_replacement can be used to allow new MIB modules to obsolete older ones, without needing to amend the imports clauses of other modules. It takes the names of the old and new modules, together with an indication of which portions of the old module are affected.-
tag len load the new module when: NULL 0 always (the old module is a strict subset of the new) name 0 for the given tag only name non-0 for any identifier with this prefix
read_module
locates and parses the module specified, together with any modules
that it imports from, and adds the contents of these modules to the
active MIB tree. Note that
add_mibdir
must first be called to add the directory containing the file with the
module definition, if this is not in the standard path.
By default, the following MIB modules will be loaded: IP-MIB, IF-MIB,
TCP-MIB, UDP-MIB, SNMPv2-MIB, RFC1213-MIB, UCD-SNMP-MIB.
This can be overridden by setting the environment variable
MIBS
to a (colon-separated) list of modules to load.
If this variable starts with a plus character, then the specified modules
are added to the default list. Otherwise only those modules listed are
loaded (together with any others they import from).
If
MIBS
is set to
ALL,
read_all_mibs
is called to load all the MIB files found in all the specified
MIBDIRS.
read_mib
parses the file specified, together with any modules that it imports
from, and adds the contents to the active MIB tree. Such a file can
contain more then one module, though care must be taken that any
imports occur earlier in the file, if they are not to be read from the
installed modules. Note that the file specified does not need to be
in any of the directories initialised by
add_mibdir
(or the default setup), though any imported modules do.
The environment variable
MIBFILES
can be set to a (colon-separated) list of files containing MIBs to load.
read_objid takes a string containing a textual version of an object identifier (in either numeric or descriptor form), and transforms this into the corresponding list of sub-identifiers. This is returned in the output parameter, with the number of sub-identifiers returned via out_len. When called, out_len must hold the maximum length of the output array. If multiple object identifiers are being processed, then this length should be reset before each call. This function returns a value of 1 if it succeeds in parsing the string and 0 otherwise.
Searching the MIB Tree
get_module_node takes a descriptor and the name of a module, and returns the corresponding oid list, in the same way as read_objid above.If the module name is specified as "ANY", then this routine will assume that the descriptor given is unique within the tree, and will return the matching entry. If this assumption is invalid, then the behaviour as to which variable is returned is implementation dependent.
Output
print_mib will print out a representation of the currently active MIB tree to the specified FILE pointer.
print_variable
will take an object identifier (as returned by
read_objid
or
get_module_node)
and an instance of such a variable, and prints to the standard output
the textual form of the object identifier together with the value
of the variable.
fprint_variable
does the same, but prints to the FILE pointer specified by the initial
parameter.
snprint_variable
prints the same information into the buffer pointed to by
buf
which is of length
len
and returns either the number of characters printed, or -1 if the
buffer was not large enough. In the latter case,
buf
will typically contained a truncated version of the information (but
this behaviour is not guaranteed). This function replaces the
obsolete function
sprint_variable.
sprint_realloc_variable
is the low-level function used to implement all these functions. It
prints to a specified offset in a string buffer. The
buf
parameter points to a pointer to that buffer;
buf_len
points to a variable holding the current size of that buffer, and
out_len
points to a variable holding the offset to which to print.
out_len
will be updated to hold the offset of the character following the last
one added to the buffer. If
allow_realloc
is 1, the buffer will be dynamically expanded, as necessary, to hold
the output; the variables pointed to by
buf
and
buf_len
will be updated. If
allow_realloc
is 0, the buffer will not be dynamically expanded.
sprint_realloc_variable
returns 0 if
allow_realloc
is 1 and an attempt to allocate memory to expand the buffer fails, or
if
allow_realloc
is 0 and the output wouldn't fit in the buffer. Otherwise it returns
1. When using this function you should be careful to call
free(3)
on
*buf
when you have finished with it.
print_value, fprint_value, snprint_value and sprint_realloc_value do the same as the equivalent print_variable routines, but only displaying the value of the variable, without the corresponding object identifier.
print_objid, fprint_objid, snprint_objid, and sprint_realloc_objid take an object identifier (without an accompanying variable instance) and print out the textual representation.
print_description and fprint_description take an object identifier (as for print_objid above) and print out the associated DESCRIPTION clause. The width argument gives the number of subidentifiers of an OID, e.g., .1.3.6 is composed of 3 subidentifiers.
Note that there are no corresponding routines snprint_description or sprint_realloc_description. By default the parser does not save descriptions since they may be huge. In order to be able to print them, you must call snmp_set_save_descriptions(1).
In general the parser is silent about what strangenesses it sees in the MIB files. To get warnings reported, call snmp_set_mib_warnings with a level of 1 (or 2 for even more warnings).
ENVIRONMENT VARIABLES
- MIBDIRS
- A colon separated list of directories to search for MIB modules. Default: /usr/share/snmp/mibs
- MIBFILES
- A colon separated list of files to load. Default: (none)
- MIBS
- A colon separated list of MIB modules to load. Default: IP-MIB:IF-MIB:TCP-MIB:UDP-MIB:SNMPv2-MIB:RFC1213-MIB:UCD-SNMP-MIB.