The section Definition of Instrumentation Functions describes the user defined functions, which the agent calls at different times.
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.
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.
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.
The function f(get [, ExtraArgs])
is called when a
get-request or a get-next
request refers to the variable.
{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 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}
.
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.
noError
badValue | noSuchName | genErr
(SNMPv1)
noAccess | noCreation | inconsistentValue |
resourceUnavailable | inconsistentName | genErr
(SNMPv2)
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.
noError
genErr
(SNMPv1)
undoFailed | genErr
(SNMPv2)
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.
noError
genErr
(SNMPv1)
commitFailed | undoFailed | genErr
(SNMPv2)
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.
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.
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.
The function f(get, RowIndex, Cols [, ExtraArgs])
is
called when a get-request refers to a table.
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.
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 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}
.
The fumction 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 unaccessible 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.
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.
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
).
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 with set
as first argument.
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.
{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.
If an error occurs, The fumction
f(undo, RowIndex, Cols [, ExtraArgs])
is called after the
is_set_ok
function. If set
is called for this
object, undo
is not called.
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.
{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.
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
corresponding is_set_ok
function did not exist, or
returned {noError, 0}
.
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.
{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.