9 Definition of Instrumentation Functions
The section Definition of Instrumentation Functions describes the user defined functions, which the agent calls at different times.
9.1 Variable Instrumentation
For scalar variables, a function
f(Operation, ...)must be defined.The
Operationcan benew,delete,get,is_set_ok,set, orundo.In case of an error, all instrumentation functions may return either an SNMPv1 or an SNMPv2 error code. If it returns an SNMPv2 code, it is converted into an SNMPv1 code before it is sent to a SNMPv1 manager. It is recommended to use the SNMPv2 error codes for all instrumentation functions, as these provide more details. See Appendix A for a description of error code conversions.
9.1.1 f(new [, ExtraArgs])
The function
f(new [, ExtraArgs])is called for each variable in the MIB when the MIB is loaded into the agent. This makes it possible to perform necessary initialization.This function is optional. The return value is discarded.
9.1.2 f(delete [, ExtraArgs])
THE function
f(delete [, ExtraArgs])is called for each object in an MIB when the MIB is unloaded from the agent. This makes it possible to perform necessary clean-up.This function is optional. The return value is discarded.
9.1.3 f(get [, ExtraArgs])
ThE function
f(get [, ExtraArgs])is called when a get-request or a get-next request refers to the variable.9.1.3.1 Valid Return Values
{value, Value}. TheValuemust be of correct type, length and within ranges, otherwisegenErris returned in the response PDU. If the object is an enumerated integer, the symbolic enum value may be used as an atom. If the object is of type BITS, the return value shall be an integer or a list of bits that are set.
{noValue, noSuchName}(SNMPv1)
{noValue, noSuchObject | noSuchInstance}(SNMPv2)
genErr. Used if an error occured. Note, this should be an internal processing error, e.g. a caused by a programing fault somewhere. If the variable does not exist, use{noValue, noSuchName}or{noValue, noSuchInstance}.
9.1.4 f(is_set_ok, NewValue [, ExtraArgs])
ThE function
f(is_set_ok, NewValue [, ExtraArgs])is called in phase one of the set-request processing so that the new value can be checked for inconsistencies.
NewValueis guaranteed to be of the correct type, length and within ranges, as specified in the MIB. If the object is an enumerated integer or of type BITS, the integer value is used.This function is optional.
If this function is called, it will be called again, either with
undoor withsetas first argument.9.1.4.1 Valid return values
noError
badValue | noSuchName | genErr(SNMPv1)
noAccess | noCreation | inconsistentValue | resourceUnavailable | inconsistentName | genErr(SNMPv2)
9.1.5 f(undo, NewValue [, ExtraArgs])
If an error occurred, this function is called after the
is_set_okfunction is called. Ifsetis called for this object,undois not called.
NewValueis guaranteed to be of the correct type, length and within ranges, as specified in the MIB. If the object is an enumerated integer or of type BITS, the integer value is used.9.1.5.1 Valid return values
noError
genErr(SNMPv1)
undoFailed | genErr(SNMPv2)
9.1.6 f(set, NewValue [, ExtraArgs])
This function is called to perform the set in phase two of the set-request processing. It is only called if the corresponding
is_set_okfunction is present and returnsnoError.
NewValueis guaranteed to be of the correct type, length and within ranges, as specified in the MIB. If the object is an enumerated integer or of type BITS, the integer value is used.9.1.6.1 Valid return values
noError
genErr(SNMPv1)
commitFailed | undoFailed | genErr(SNMPv2)
9.2 Table Instrumentation
For tables, a
f(Operation, ...)function should be defined (the function shown is exemplified withf).The
Operationcan benew,delete,get,next,is_set_ok,undoorset.In case of an error, all instrumentation functions may return either an SNMPv1 or an SNMPv2 error code. If it returns an SNMPv2 code, it is converted into an SNMPv1 code before it is sent to a SNMPv1 manager. It is recommended to use the SNMPv2 error codes for all instrumentation functions, as these provide more details. See Appendix A for a description of error code conversions.
9.2.1 f(new [, ExtraArgs])
The function
f(new [, ExtraArgs])is called for each object in an MIB when the MIB is loaded into the agent. This makes it possible to perform the necessary initialization.This function is optional. The return value is discarded.
9.2.2 f(delete [, ExtraArgs])
The function
f(delete [, ExtraArgs])is called for each object in an MIB when the MIB is unloaded from the agent. This makes it possible to perform any necessary clean-up.This function is optional. The return value is discarded.
9.2.3 f(get, RowIndex, Cols [, ExtraArgs])
The function
f(get, RowIndex, Cols [, ExtraArgs])is called when a get-request refers to a table.9.2.3.1 Arguments
RowIndexis a list of integers which define the key values for the row. TheRowIndexis the list representation (list of integers) which follow theColsinteger in the OBJECT IDENTIFIER.
Colsis a list of integers which represent the column numbers. TheColsare sorted by increasing value and are guaranteed to be valid column numbers.
9.2.3.2 Valid Return Values
- A list with as many elements as the
Colslist, where each element is the value of the corresponding column. Each element can be:
{value, Value}. TheValuemust be of correct type, length and within ranges, otherwisegenErris returned in the response PDU. If the object is an enumerated integer, the symbolic enum value may be used (as an atom). If the object is of type BITS, the return value shall be an integer or a list of bits that are set.
{noValue, noSuchName}(SNMPv1)
{noValue, noSuchObject | noSuchInstance}(SNMPv2)
{noValue, Error}. If the row does not exist, because all columns have{noValue, Error}), the single tuple{noValue, Error}can be returned. This is a shorthand for a list with all elements{noValue, Error}.
genErr. Used if an error occured. Note that this should be an internal processing error, e.g. a caused by a programing fault somewhere. If some column does not exist, use{noValue, noSuchName}or{noValue, noSuchInstance}.
9.2.4 f(get_next, RowIndex, Cols [, ExtraArgs])
The fumction
f(get_next, RowIndex, Cols [, ExtraArgs])is called when a get-next- or a get-bulk-request refers to the table.The
RowIndexargument may refer to an existing row or a non-existing row, or it may be unspecified. TheColslist may refer to unaccessible columns or non-existing columns. For each column in theColslist, the corresponding next instance is determined, and the last part of its OBJECT IDENTIFIER and its value is returned.9.2.4.1 Arguments
RowIndexis a list of integers (possibly empty) that defines the key values for a row. TheRowIndexis the list representation (list of integers), which follow theColsinteger in the OBJECT IDENTIFIER.
Colsis a list of integers, greater than or equal to zero, which represents the column numbers.
9.2.4.2 Valid Return Values
- A list with as many elements as the
Colslist Each element can be:
{NextOid, NextValue}, whereNextOidis the lexicographic next OBJECT IDENTIFIER for the corresponding column. This should be specified as the OBJECT IDENTIFER part following the table entry. This means that the first integer is the column number and the rest is a specification of the keys.NextValueis the value of this element.
endOfTableif there are no accessible elements after this one.
{genErr, Column}whereColumndenotes the column that caused the error.Columnmust be one of the columns in theColslist. Note that this should be an internal processing error, e.g. a caused by a programing fault somewhere. If some column does not exist, you must return the next accessible element (orendOfTable).
9.2.5 f(is_set_ok, RowIndex, Cols [, ExtraArgs])
The fumction
f(is_set_ok, RowIndex, Cols [, ExtraArgs])is called in phase one of the set-request processing so that new values can be checked for inconsistencies.If the function is called, it will be called again with
undo, or withsetas first argument.9.2.5.1 Arguments
RowIndexis a list of integers which define the key values for the row. TheRowIndexis the list representation (list of integers) which follow theColsinteger in the OBJECT IDENTIFIER.
Colsis a list of{Column, NewValue}, whereColumnis an integer, andNewValueis guaranteed to be of the correct type, length and within ranges, as specified in the MIB. If the object is an enumerated integer or of type BITS, the integer value is used. The list is sorted byColumn(increasing) and eachColumnis guaranteed to be a valid column number.
9.2.5.2 Valid Return Values
{noError, 0}
{Error, Column}, whereErroris the same as foris_set_okfor variables, andColumndenotes the faulty column.Columnmust be one of the columns in theColslist.
9.2.6 f(undo, RowIndex, Cols [, ExtraArgs])
If an error occurs, The fumction
f(undo, RowIndex, Cols [, ExtraArgs])is called after theis_set_okfunction. Ifsetis called for this object,undois not called.9.2.6.1 Arguments
RowIndexis a list of integers which define the key values for the row. TheRowIndexis the list representation (list of integers) which follow theColsinteger in the OBJECT IDENTIFIER.
Colsis a list of{Column, NewValue}, whereColumnis an integer, andNewValueis guaranteed to be of the correct type, length and within ranges, as specified in the MIB. If the object is an enumerated integer or of type BITS, the integer value is used. The list is sorted byColumn(increasing) and eachColumnis guaranteed to be a valid column number.
9.2.6.2 Valid Return Values
{noError, 0}
{Error, Column}whereErroris the same as forundofor variables, andColumndenotes the faulty column.Columnmust be one of the columns in theColslist.
9.2.7 f(set, RowIndex, Cols [, ExtraArgs])
The fumction
f(set, RowIndex, Cols [, ExtraArgs])is called to perform the set in phase two of the set-request processing. It is only called if the correspondingis_set_okfunction did not exist, or returned{noError, 0}.9.2.7.1 Arguments
RowIndexis a list of integers that define the key values for the row. TheRowIndexis the list representation (list of integers) which follow theColsinteger in the OBJECT IDENTIFIER.
Colsis a list of{Column, NewValue}, whereColumnis an integer, andNewValueis guaranteed to be of the correct type, length and within ranges, as specified in the MIB. If the object is an enumerated integer or of type BITS, the integer value is used. The list is sorted byColumn(increasing) and eachColumnis guaranteed to be a valid column number.
9.2.7.2 Valid Return Values
{noError, 0}
{Error, Column}whereErroris the same assetfor variables, andColumndenotes the faulty column.Columnmust be one of the columns in theColslist.