Variable Instrumentation
For scalar variables, a function f(Operation, ...) must
be defined.
The Operation can be new, delete,
get, is_set_ok, set, or undo.
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.
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.
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.
f(get [, ExtraArgs])
The function f(get [, ExtraArgs]) is called when a
get-request or a get-next
request refers to the variable.
This function is mandatory.
Valid Return Values
- {value, Value}. The Value must be of
correct type, length and within ranges, otherwise
genErr is 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 occurred. 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}.
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.
NewValue is 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 undo or with set as first argument.
Valid return values
- noError
- badValue | noSuchName | genErr(SNMPv1)
- noAccess | noCreation | inconsistentValue | resourceUnavailable | inconsistentName | genErr(SNMPv2)
f(undo, NewValue [, ExtraArgs])
If an error occurred, this function is called after the
is_set_ok function is called. If set is called for
this object, undo is not called.
NewValue is 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.
Valid return values
- noError
- genErr(SNMPv1)
- undoFailed | genErr(SNMPv2)
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_ok function is present and returns
noError.
NewValue is 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 mandatory.
Valid return values
- noError
- genErr(SNMPv1)
- commitFailed | undoFailed | genErr(SNMPv2)
Table Instrumentation
For tables, a f(Operation, ...) function should be
defined (the function shown is exemplified with f).
The Operation can be new, delete,
get, next, is_set_ok, undo or
set.
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.
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.
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.
f(get, RowIndex, Cols [, ExtraArgs])
The function f(get, RowIndex, Cols [, ExtraArgs]) is
called when a get-request refers to a table.
This function is mandatory.
Arguments
- RowIndex is a list of integers which define the
key values for the row. The RowIndex is the list
representation (list of integers) which follow the
Cols integer in the OBJECT IDENTIFIER.
- Cols is a list of integers which represent the
column numbers. The Cols are sorted by increasing
value and are guaranteed to be valid column numbers.
Valid Return Values
-
A list with as many elements as the Cols list,
where each element is the value of the corresponding
column. Each element can be:
- {value, Value}. The Value must be of
correct type, length and within ranges, otherwise
genErr is 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 occurred. 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}.
f(get_next, RowIndex, Cols [, ExtraArgs])
The function f(get_next, RowIndex, Cols [, ExtraArgs]) is
called when a get-next- or a
get-bulk-request refers to the table.
The RowIndex argument may refer to an existing row or a
non-existing row, or it may be unspecified. The Cols list
may refer to inaccessible columns or non-existing columns. For
each column in the Cols list, the corresponding next
instance is determined, and the last part of its OBJECT
IDENTIFIER and its value is returned.
This function is mandatory.
Arguments
- RowIndex is a list of integers (possibly empty)
that defines the key values for a row. The RowIndex
is the list representation (list of integers), which follow
the Cols integer in the OBJECT IDENTIFIER.
- Cols is a list of integers, greater than or
equal to zero, which represents the column numbers.
Valid Return Values
-
A list with as many elements as the Cols list
Each element can be:
- {NextOid, NextValue}, where NextOid
is 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.
NextValue is the value of this element.
- endOfTable if there are no accessible
elements after this one.
- {genErr, Column} where Column denotes
the column that caused the error. Column must be
one of the columns in the Cols list. 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 (or
endOfTable).
f(is_set_ok, RowIndex, Cols [, ExtraArgs])
The function 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 with set as first argument.
This function is optional.
Arguments
- RowIndex is a list of integers which define the
key values for the row. The RowIndex is the list
representation (list of integers) which follow the
Cols integer in the OBJECT IDENTIFIER.
- Cols is a list of {Column, NewValue},
where Column is an integer, and NewValue is
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 by Column (increasing) and
each Column is guaranteed to be a valid column
number.
Valid Return Values
- {noError, 0}
- {Error, Column}, where Error is the same
as for is_set_ok for variables, and Column
denotes the faulty column. Column must be one of the
columns in the Cols list.
f(undo, RowIndex, Cols [, ExtraArgs])
If an error occurs, The function
f(undo, RowIndex, Cols [, ExtraArgs]) is called after the
is_set_ok function. If set is called for this
object, undo is not called.
This function is optional.
Arguments
- RowIndex is a list of integers which define the
key values for the row. The RowIndex is the list
representation (list of integers) which follow the
Cols integer in the OBJECT IDENTIFIER.
- Cols is a list of {Column, NewValue},
where Column is an integer, and NewValue is
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 by Column (increasing) and
each Column is guaranteed to be a valid column
number.
Valid Return Values
- {noError, 0}
- {Error, Column} where Error is the same
as for undo for variables, and Column denotes
the faulty column. Column must be one of the columns
in the Cols list.
f(set, RowIndex, Cols [, ExtraArgs])
The function 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
corresponding is_set_ok function did not exist, or
returned {noError, 0}.
This function is mandatory.
Arguments
- RowIndex is a list of integers that define the
key values for the row. The RowIndex is the list
representation (list of integers) which follow the
Cols integer in the OBJECT IDENTIFIER.
- Cols is a list of {Column, NewValue},
where Column is an integer, and NewValue is
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 by Column (increasing) and
each Column is guaranteed to be a valid column
number.
Valid Return Values
- {noError, 0}
- {Error, Column} where Error is the same
as set for variables, and Column denotes
the faulty column. Column must be one of the columns
in the Cols list.