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<title>Definition of Instrumentation Functions</title>
<prepared></prepared>
<responsible></responsible>
<docno></docno>
<approved></approved>
<checked></checked>
<date></date>
<rev></rev>
<file>snmp_def_instr_functions.xml</file>
</header>
<p>The section <em>Definition of Instrumentation Functions</em> describes
the user defined functions, which the agent calls at different times.
</p>
<section>
<title>Variable Instrumentation</title>
<p>For scalar variables, a function <c>f(Operation, ...)</c> must
be defined.
</p>
<p>The <c>Operation</c> can be <c>new</c>, <c>delete</c>,
<c>get</c>, <c>is_set_ok</c>, <c>set</c>, or <c>undo</c>.
</p>
<p>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 <seealso marker="snmp_app_a">Appendix A</seealso> for a
description of error code conversions.
</p>
<section>
<title>f(new [, ExtraArgs])</title>
<p>The function <c>f(new [, ExtraArgs])</c> is called for each
variable in the MIB when the
MIB is loaded into the agent. This makes it possible to perform
necessary initialization.
</p>
<p>This function is optional. The return value is discarded.</p>
</section>
<section>
<title>f(delete [, ExtraArgs])</title>
<p>The function <c>f(delete [, ExtraArgs])</c> 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.
</p>
<p>This function is optional. The return value is discarded.</p>
</section>
<section>
<title>f(get [, ExtraArgs])</title>
<p>The function <c>f(get [, ExtraArgs])</c> is called when a
get-request or a get-next
request refers to the variable.
</p>
<p>This function is mandatory.
</p>
<section>
<title>Valid Return Values</title>
<list type="bulleted">
<item><c>{value, Value}</c>. The <c>Value</c> must be of
correct type, length and within ranges, otherwise
<c>genErr</c> 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.
</item>
<item><c>{noValue, noSuchName}</c>(SNMPv1)
</item>
<item><c>{noValue, noSuchObject | noSuchInstance} </c>(SNMPv2)
</item>
<item><c>genErr</c>. 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 <c>{noValue, noSuchName}</c> or
<c>{noValue, noSuchInstance}</c>.
</item>
</list>
</section>
</section>
<section>
<title>f(is_set_ok, NewValue [, ExtraArgs])</title>
<p>The function <c>f(is_set_ok, NewValue [, ExtraArgs])</c> is
called in phase one of the set-request
processing so that the new value can be checked for
inconsistencies.
</p>
<p><c>NewValue</c> 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.
</p>
<p>This function is optional.
</p>
<p>If this function is called, it will be called again, either
with <c>undo</c> or with <c>set</c> as first argument.
</p>
<section>
<title>Valid return values</title>
<list type="bulleted">
<item><c>noError</c></item>
<item><c>badValue | noSuchName | genErr</c>(SNMPv1)
</item>
<item><c>noAccess | noCreation | inconsistentValue | resourceUnavailable | inconsistentName | genErr</c>(SNMPv2)</item>
</list>
</section>
</section>
<section>
<title>f(undo, NewValue [, ExtraArgs])</title>
<p>If an error occurred, this function is called after the
<c>is_set_ok</c> function is called. If <c>set</c> is called for
this object, <c>undo</c> is not called.
</p>
<p><c>NewValue</c> 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.
</p>
<p>This function is optional.
</p>
<section>
<title>Valid return values</title>
<list type="bulleted">
<item><c>noError</c></item>
<item><c>genErr</c>(SNMPv1)
</item>
<item><c>undoFailed | genErr</c>(SNMPv2)</item>
</list>
</section>
</section>
<section>
<title>f(set, NewValue [, ExtraArgs])</title>
<p>This function is called to perform the set in phase two of
the set-request processing. It is only called if the
corresponding <c>is_set_ok</c> function is present and returns
<c>noError</c>.
</p>
<p><c>NewValue</c> 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.
</p>
<p>This function is mandatory.
</p>
<section>
<title>Valid return values</title>
<list type="bulleted">
<item><c>noError</c></item>
<item><c>genErr</c>(SNMPv1)
</item>
<item><c>commitFailed | undoFailed | genErr</c>(SNMPv2)</item>
</list>
</section>
</section>
</section>
<section>
<title>Table Instrumentation</title>
<p>For tables, a <c>f(Operation, ...)</c> function should be
defined (the function shown is exemplified with <c>f</c>).
</p>
<p>The <c>Operation</c> can be <c>new</c>, <c>delete</c>,
<c>get</c>, <c>next</c>, <c>is_set_ok</c>, <c>undo</c> or
<c>set</c>.
</p>
<p>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 <seealso marker="snmp_app_a">Appendix A</seealso> for a
description of error code conversions.</p>
<section>
<title>f(new [, ExtraArgs])</title>
<p>The function <c>f(new [, ExtraArgs])</c> 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.
</p>
<p>This function is optional. The return value is discarded.</p>
</section>
<section>
<title>f(delete [, ExtraArgs])</title>
<p>The function <c>f(delete [, ExtraArgs])</c> 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.
</p>
<p>This function is optional. The return value is discarded.</p>
</section>
<section>
<title>f(get, RowIndex, Cols [, ExtraArgs])</title>
<p>The function <c>f(get, RowIndex, Cols [, ExtraArgs])</c> is
called when a get-request refers to a table.
</p>
<p>This function is mandatory.
</p>
<section>
<title>Arguments</title>
<list type="bulleted">
<item><c>RowIndex</c> is a list of integers which define the
key values for the row. The <c>RowIndex</c> is the list
representation (list of integers) which follow the
<c>Cols</c> integer in the OBJECT IDENTIFIER.
</item>
<item><c>Cols</c> is a list of integers which represent the
column numbers. The <c>Cols</c> are sorted by increasing
value and are guaranteed to be valid column numbers.</item>
</list>
</section>
<section>
<title>Valid Return Values</title>
<list type="bulleted">
<item>
<p>A list with as many elements as the <c>Cols</c> list,
where each element is the value of the corresponding
column. Each element can be:</p>
<list type="bulleted">
<item><c>{value, Value}</c>. The <c>Value</c> must be of
correct type, length and within ranges, otherwise
<c>genErr</c> 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.
</item>
<item><c>{noValue, noSuchName}</c>(SNMPv1)
</item>
<item><c>{noValue, noSuchObject | noSuchInstance}</c>(SNMPv2)
</item>
</list>
</item>
<item><c>{noValue, Error}</c>. If the row does not exist,
because all columns have <c>{noValue, Error}</c>), the
single tuple <c>{noValue, Error}</c> can be returned.
This is a shorthand for a list with all elements
<c>{noValue, Error}</c>.
</item>
<item><c>genErr</c>. 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 <c>{noValue, noSuchName}</c> or
<c>{noValue, noSuchInstance}</c>.
</item>
</list>
</section>
</section>
<section>
<title>f(get_next, RowIndex, Cols [, ExtraArgs])</title>
<p>The function <c>f(get_next, RowIndex, Cols [, ExtraArgs])</c> is
called when a get-next- or a
get-bulk-request refers to the table.
</p>
<p>The <c>RowIndex</c> argument may refer to an existing row or a
non-existing row, or it may be unspecified. The <c>Cols</c> list
may refer to inaccessible columns or non-existing columns. For
each column in the <c>Cols</c> list, the corresponding next
instance is determined, and the last part of its OBJECT
IDENTIFIER and its value is returned.
</p>
<p>This function is mandatory.
</p>
<section>
<title>Arguments</title>
<list type="bulleted">
<item><c>RowIndex</c> is a list of integers (possibly empty)
that defines the key values for a row. The <c>RowIndex</c>
is the list representation (list of integers), which follow
the <c>Cols</c> integer in the OBJECT IDENTIFIER.
</item>
<item><c>Cols</c> is a list of integers, greater than or
equal to zero, which represents the column numbers.</item>
</list>
</section>
<section>
<title>Valid Return Values</title>
<list type="bulleted">
<item>
<p>A list with as many elements as the <c>Cols</c> list
Each element can be:</p>
<list type="bulleted">
<item><c>{NextOid, NextValue}</c>, where <c>NextOid</c>
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.
<c>NextValue</c> is the value of this element.
</item>
<item><c>endOfTable</c> if there are no accessible
elements after this one.
</item>
</list>
</item>
<item><c>{genErr, Column}</c> where <c>Column</c> denotes
the column that caused the error. <c>Column</c> must be
one of the columns in the <c>Cols</c> 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
<c>endOfTable</c>).
</item>
</list>
</section>
</section>
<section>
<title>f(is_set_ok, RowIndex, Cols [, ExtraArgs])</title>
<p>The function <c>f(is_set_ok, RowIndex, Cols [, ExtraArgs])</c>
is called in phase one of the set-request
processing so that new values can be checked for
inconsistencies.
</p>
<p>If the function is called, it will be called again with
<c>undo</c>, or with <c>set</c> as first argument.
</p>
<p>This function is optional.
</p>
<section>
<title>Arguments</title>
<list type="bulleted">
<item><c>RowIndex</c> is a list of integers which define the
key values for the row. The <c>RowIndex</c> is the list
representation (list of integers) which follow the
<c>Cols</c> integer in the OBJECT IDENTIFIER.
</item>
<item><c>Cols</c> is a list of <c>{Column, NewValue}</c>,
where <c>Column</c> is an integer, and <c>NewValue</c> 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 <c>Column</c> (increasing) and
each <c>Column</c> is guaranteed to be a valid column
number.</item>
</list>
</section>
<section>
<title>Valid Return Values</title>
<list type="bulleted">
<item><c>{noError, 0}</c></item>
<item><c>{Error, Column}</c>, where <c>Error</c> is the same
as for <c>is_set_ok</c> for variables, and <c>Column</c>
denotes the faulty column. <c>Column</c> must be one of the
columns in the <c>Cols</c> list.</item>
</list>
</section>
</section>
<section>
<title>f(undo, RowIndex, Cols [, ExtraArgs])</title>
<p>If an error occurs, The function
<c>f(undo, RowIndex, Cols [, ExtraArgs])</c> is called after the
<c>is_set_ok</c> function. If <c>set</c> is called for this
object, <c>undo</c> is not called.
</p>
<p>This function is optional.
</p>
<section>
<title>Arguments</title>
<list type="bulleted">
<item><c>RowIndex</c> is a list of integers which define the
key values for the row. The <c>RowIndex</c> is the list
representation (list of integers) which follow the
<c>Cols</c> integer in the OBJECT IDENTIFIER.
</item>
<item><c>Cols</c> is a list of <c>{Column, NewValue}</c>,
where <c>Column</c> is an integer, and <c>NewValue</c> 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 <c>Column</c> (increasing) and
each <c>Column</c> is guaranteed to be a valid column
number.
</item>
</list>
</section>
<section>
<title>Valid Return Values</title>
<list type="bulleted">
<item><c>{noError, 0}</c></item>
<item><c>{Error, Column}</c> where <c>Error</c> is the same
as for <c>undo</c> for variables, and <c>Column</c> denotes
the faulty column. <c>Column</c> must be one of the columns
in the <c>Cols</c> list.
</item>
</list>
</section>
</section>
<section>
<title>f(set, RowIndex, Cols [, ExtraArgs])</title>
<p>The function <c>f(set, RowIndex, Cols [, ExtraArgs])</c> is
called to perform the set in phase two of
the set-request processing. It is only called if the
corresponding <c>is_set_ok</c> function did not exist, or
returned <c>{noError, 0}</c>.
</p>
<p>This function is mandatory.
</p>
<section>
<title>Arguments</title>
<list type="bulleted">
<item><c>RowIndex</c> is a list of integers that define the
key values for the row. The <c>RowIndex</c> is the list
representation (list of integers) which follow the
<c>Cols</c> integer in the OBJECT IDENTIFIER.
</item>
<item><c>Cols</c> is a list of <c>{Column, NewValue}</c>,
where <c>Column</c> is an integer, and <c>NewValue</c> 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 <c>Column</c> (increasing) and
each <c>Column</c> is guaranteed to be a valid column
number.
</item>
</list>
</section>
<section>
<title>Valid Return Values</title>
<list type="bulleted">
<item><c>{noError, 0}</c></item>
<item><c>{Error, Column}</c> where <c>Error</c> is the same
as <c>set</c> for variables, and <c>Column</c> denotes
the faulty column. <c>Column</c> must be one of the columns
in the <c>Cols</c> list.</item>
</list>
</section>
</section>
</section>
</chapter>
