MIB_API(3) Net-SNMP MIB_API(3)
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_vari-
able, 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
int add_mibdir(const char *dirname);
int add_module_replacement(const char *old_module, const char *new_module, const char *tag, int len);
struct tree *read_module(const char *name);
struct tree *read_mib(const char *filename);
struct tree *read_all_mibs(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
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 net-
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);
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
init_mib_internals sets up the internal structures, preparatory to reading in MIB modules. It should be called after all calls to add_mib-
dir, 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 recom-
mended 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
It can also be used to handle errors in the module identifiers used in MIB import clauses (such as referring to RFC1213 instead of
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.
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 buf-
fer. 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_real-
loc_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 display-
ing 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).
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.
4.2 Berkeley Distribution 06 Mar 2002 MIB_API(3)