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  <TITLE>Definition of Instrumentation Functions</TITLE>
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<A NAME="11"><!-- Empty --></A>
<H2>11 Definition of Instrumentation Functions</H2>

<P>The section <STRONG>Definition of Instrumentation Functions</STRONG> describes
the user defined functions, which the agent calls at different times.

<A NAME="11.1"><!-- Empty --></A>
<H3>11.1 Variable Instrumentation</H3>

<P>For scalar variables, a function <CODE>f(Operation, ...)</CODE> must
be defined.


<P>The <CODE>Operation</CODE> can be <CODE>new</CODE>, <CODE>delete</CODE>,
<CODE>get</CODE>, <CODE>is_set_ok</CODE>, <CODE>set</CODE>, or <CODE>undo</CODE>.


<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 <A HREF="snmp_app_a.html">Appendix A</A> for a
description of error code conversions.

<A NAME="11.1.1"><!-- Empty --></A>
<H4>11.1.1 f(new [, ExtraArgs])</H4>

<P>The function <CODE>f(new [, ExtraArgs])</CODE> 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>This function is optional. The return value is discarded.
<A NAME="11.1.2"><!-- Empty --></A>
<H4>11.1.2 f(delete [, ExtraArgs])</H4>

<P>The function <CODE>f(delete [, ExtraArgs])</CODE> 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>This function is optional. The return value is discarded.
<A NAME="11.1.3"><!-- Empty --></A>
<H4>11.1.3 f(get [, ExtraArgs])
</H4>

<P>The function <CODE>f(get [, ExtraArgs])</CODE> is called when a
        get-request or a get-next
request refers to the variable.


<P>This function is mandatory.

<A NAME="11.1.3.1"><!-- Empty --></A>
<H5>11.1.3.1 Valid Return Values</H5>

<P>
<UL>

<LI>
<CODE>{value, Value}</CODE>. The <CODE>Value</CODE> must be of
         correct type, length and within ranges, otherwise
         <CODE>genErr</CODE> 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.
         
         
</LI>


<LI>
<CODE>{noValue, noSuchName}</CODE>(SNMPv1)
         
         
</LI>


<LI>
<CODE>{noValue, noSuchObject | noSuchInstance} </CODE>(SNMPv2)

         
</LI>


<LI>
<CODE>genErr</CODE>. 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 <CODE>{noValue, noSuchName}</CODE> or
         <CODE>{noValue, noSuchInstance}</CODE>.

        
</LI>


</UL>
<A NAME="11.1.4"><!-- Empty --></A>
<H4>11.1.4 f(is_set_ok, NewValue [, ExtraArgs])
</H4>

<P>The function <CODE>f(is_set_ok, NewValue [, ExtraArgs])</CODE> is
        called in phase one of the set-request
processing so that the new value can be checked for
inconsistencies.


<P><CODE>NewValue</CODE> 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>This function is optional.


<P>If this function is called, it will be called again, either
with <CODE>undo</CODE> or with <CODE>set</CODE> as first argument.

<A NAME="11.1.4.1"><!-- Empty --></A>
<H5>11.1.4.1 Valid return values</H5>

<P>
<UL>

<LI>
<CODE>noError</CODE>
         
         
</LI>


<LI>
<CODE>badValue | noSuchName | genErr</CODE>(SNMPv1)
         
         
</LI>


<LI>
<CODE>noAccess | noCreation | inconsistentValue |
         resourceUnavailable | inconsistentName | genErr</CODE>(SNMPv2)
        
</LI>


</UL>
<A NAME="11.1.5"><!-- Empty --></A>
<H4>11.1.5 f(undo, NewValue [, ExtraArgs])</H4>

<P>If an error occurred, this function is called after the
<CODE>is_set_ok</CODE> function is called. If <CODE>set</CODE> is called for
this object, <CODE>undo</CODE> is not called.


<P><CODE>NewValue</CODE> 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>This function is optional.

<A NAME="11.1.5.1"><!-- Empty --></A>
<H5>11.1.5.1 Valid return values</H5>

<P>
<UL>

<LI>
<CODE>noError</CODE>
         
         
</LI>


<LI>
<CODE>genErr</CODE>(SNMPv1)
         
         
</LI>


<LI>
<CODE>undoFailed | genErr</CODE>(SNMPv2)
        
</LI>


</UL>
<A NAME="11.1.6"><!-- Empty --></A>
<H4>11.1.6 f(set, NewValue [, ExtraArgs])
</H4>

<P>This function is called to perform the set in phase two of
the set-request processing. It is only called if the
corresponding <CODE>is_set_ok</CODE> function is present and returns
<CODE>noError</CODE>.


<P><CODE>NewValue</CODE> 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>This function is mandatory.

<A NAME="11.1.6.1"><!-- Empty --></A>
<H5>11.1.6.1 Valid return values
        </H5>

<P>
<UL>

<LI>
<CODE>noError</CODE>
         
         
</LI>


<LI>
<CODE>genErr</CODE>(SNMPv1)
         
         
</LI>


<LI>
<CODE>commitFailed | undoFailed | genErr</CODE>(SNMPv2)
        
</LI>


</UL>
<A NAME="11.2"><!-- Empty --></A>
<H3>11.2 Table Instrumentation</H3>

<P>For tables, a <CODE>f(Operation, ...)</CODE> function should be
defined (the function shown is exemplified with <CODE>f</CODE>).


<P>The <CODE>Operation</CODE> can be <CODE>new</CODE>, <CODE>delete</CODE>,
<CODE>get</CODE>, <CODE>next</CODE>, <CODE>is_set_ok</CODE>, <CODE>undo</CODE> or
<CODE>set</CODE>.


<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 <A HREF="snmp_app_a.html">Appendix A</A> for a
description of error code conversions.<A NAME="11.2.1"><!-- Empty --></A>
<H4>11.2.1 f(new [, ExtraArgs])</H4>

<P>The function <CODE>f(new [, ExtraArgs])</CODE> 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>This function is optional. The return value is discarded.
<A NAME="11.2.2"><!-- Empty --></A>
<H4>11.2.2 f(delete [, ExtraArgs])</H4>

<P>The function <CODE>f(delete [, ExtraArgs])</CODE> 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>This function is optional. The return value is discarded.
<A NAME="11.2.3"><!-- Empty --></A>
<H4>11.2.3 f(get, RowIndex, Cols [, ExtraArgs])</H4>

<P>The function <CODE>f(get, RowIndex, Cols [, ExtraArgs])</CODE> is
        called when a get-request refers to a table.


<P>This function is mandatory.

<A NAME="11.2.3.1"><!-- Empty --></A>
<H5>11.2.3.1 Arguments</H5>

<P>
<UL>

<LI>
<CODE>RowIndex</CODE> is a list of integers which define the
         key values for the row. The <CODE>RowIndex</CODE> is the list
         representation (list of integers) which follow the
         <CODE>Cols</CODE> integer in the OBJECT IDENTIFIER.
         
         
</LI>


<LI>
<CODE>Cols</CODE> is a list of integers which represent the
         column numbers. The <CODE>Cols</CODE> are sorted by increasing
         value and are guaranteed to be valid column numbers.
        
</LI>


</UL>
<A NAME="11.2.3.2"><!-- Empty --></A>
<H5>11.2.3.2 Valid Return Values</H5>

<P>
<UL>

<LI>
A list with as many elements as the <CODE>Cols</CODE> list,
         where each element is the value of the corresponding
         column. Each element can be:
         
         
<UL>

<LI>
<CODE>{value, Value}</CODE>. The <CODE>Value</CODE> must be of
                correct type, length and within ranges, otherwise
                <CODE>genErr</CODE> 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.
         
         
</LI>


<LI>
<CODE>{noValue, noSuchName}</CODE>(SNMPv1)
         
         
</LI>


<LI>
<CODE>{noValue, noSuchObject | noSuchInstance}</CODE>(SNMPv2)
                
         
</LI>


</UL>


         
</LI>


<LI>
<CODE>{noValue, Error}</CODE>. If the row does not exist,
         because all columns have <CODE>{noValue, Error}</CODE>), the
         single tuple <CODE>{noValue, Error}</CODE> can be returned.
         This is a shorthand for a list with all elements
         <CODE>{noValue, Error}</CODE>.

         
</LI>


<LI>
<CODE>genErr</CODE>. 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 <CODE>{noValue, noSuchName}</CODE> or
         <CODE>{noValue, noSuchInstance}</CODE>.

        
</LI>


</UL>
<A NAME="11.2.4"><!-- Empty --></A>
<H4>11.2.4 f(get_next, RowIndex, Cols [, ExtraArgs])
</H4>

<P>The fumction <CODE>f(get_next, RowIndex, Cols [, ExtraArgs])</CODE> is 
        called when a get-next- or a
get-bulk-request refers to the table.


<P>The <CODE>RowIndex</CODE> argument may refer to an existing row or a
non-existing row, or it may be unspecified. The <CODE>Cols</CODE> list
may refer to unaccessible columns or non-existing columns. For
each column in the <CODE>Cols</CODE> list, the corresponding next
instance is determined, and the last part of its OBJECT
IDENTIFIER and its value is returned.


<P>This function is mandatory.

<A NAME="11.2.4.1"><!-- Empty --></A>
<H5>11.2.4.1 Arguments</H5>

<P>
<UL>

<LI>
<CODE>RowIndex</CODE> is a list of integers (possibly empty)
         that defines the key values for a row. The <CODE>RowIndex</CODE>
         is the list representation (list of integers), which follow
         the <CODE>Cols</CODE> integer in the OBJECT IDENTIFIER.
         
         
</LI>


<LI>
<CODE>Cols</CODE> is a list of integers, greater than or
         equal to zero, which represents the column numbers.
        
</LI>


</UL>
<A NAME="11.2.4.2"><!-- Empty --></A>
<H5>11.2.4.2 Valid Return Values</H5>

<P>
<UL>

<LI>
A list with as many elements as the <CODE>Cols</CODE> list
         Each element can be:
         
         
<UL>

<LI>
<CODE>{NextOid, NextValue}</CODE>, where <CODE>NextOid</CODE>
                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.
                <CODE>NextValue</CODE> is the value of this element.

         
</LI>


<LI>
<CODE>endOfTable</CODE> if there are no accessible
                elements after this one.

         
</LI>


</UL>


         
</LI>


<LI>
<CODE>{genErr, Column}</CODE> where <CODE>Column</CODE> denotes
         the column that caused the error. <CODE>Column</CODE> must be
         one of the columns in the <CODE>Cols</CODE> 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
         <CODE>endOfTable</CODE>). 

        
</LI>


</UL>
<A NAME="11.2.5"><!-- Empty --></A>
<H4>11.2.5 f(is_set_ok, RowIndex, Cols [, ExtraArgs])
</H4>

<P>The fumction <CODE>f(is_set_ok, RowIndex, Cols [, ExtraArgs])</CODE>
        is called in phase one of the set-request
processing so that new values can be checked for
inconsistencies.


<P>If the function is called, it will be called again with
<CODE>undo</CODE>, or with <CODE>set</CODE> as first argument.


<P>This function is optional.

<A NAME="11.2.5.1"><!-- Empty --></A>
<H5>11.2.5.1 Arguments</H5>

<P>
<UL>

<LI>
<CODE>RowIndex</CODE> is a list of integers which define the
         key values for the row. The <CODE>RowIndex</CODE> is the list
         representation (list of integers) which follow the
         <CODE>Cols</CODE> integer in the OBJECT IDENTIFIER.
         
         
</LI>


<LI>
<CODE>Cols</CODE> is a list of <CODE>{Column, NewValue}</CODE>,
         where <CODE>Column</CODE> is an integer, and <CODE>NewValue</CODE> 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 <CODE>Column</CODE> (increasing) and
         each <CODE>Column</CODE> is guaranteed to be a valid column
         number.
        
</LI>


</UL>
<A NAME="11.2.5.2"><!-- Empty --></A>
<H5>11.2.5.2 Valid Return Values</H5>

<P>
<UL>

<LI>
<CODE>{noError, 0}</CODE>
         
         
</LI>


<LI>
<CODE>{Error, Column}</CODE>, where <CODE>Error</CODE> is the same
         as for <CODE>is_set_ok</CODE> for variables, and <CODE>Column</CODE>
         denotes the faulty column. <CODE>Column</CODE> must be one of the
         columns in the <CODE>Cols</CODE> list.
        
</LI>


</UL>
<A NAME="11.2.6"><!-- Empty --></A>
<H4>11.2.6 f(undo, RowIndex, Cols [, ExtraArgs])
</H4>

<P>If an error occurs, The fumction
        <CODE>f(undo, RowIndex, Cols [, ExtraArgs])</CODE> is called after the
<CODE>is_set_ok</CODE> function. If <CODE>set</CODE> is called for this
object, <CODE>undo</CODE> is not called.


<P>This function is optional.

<A NAME="11.2.6.1"><!-- Empty --></A>
<H5>11.2.6.1 Arguments</H5>

<P>
<UL>

<LI>
<CODE>RowIndex</CODE> is a list of integers which define the
         key values for the row. The <CODE>RowIndex</CODE> is the list
         representation (list of integers) which follow the
         <CODE>Cols</CODE> integer in the OBJECT IDENTIFIER.
         
         
</LI>


<LI>
<CODE>Cols</CODE> is a list of <CODE>{Column, NewValue}</CODE>,
         where <CODE>Column</CODE> is an integer, and <CODE>NewValue</CODE> 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 <CODE>Column</CODE> (increasing) and
         each <CODE>Column</CODE> is guaranteed to be a valid column
         number.

        
</LI>


</UL>
<A NAME="11.2.6.2"><!-- Empty --></A>
<H5>11.2.6.2 Valid Return Values</H5>

<P>
<UL>

<LI>
<CODE>{noError, 0}</CODE>
         
         
</LI>


<LI>
<CODE>{Error, Column}</CODE> where <CODE>Error</CODE> is the same
         as for <CODE>undo</CODE> for variables, and <CODE>Column</CODE> denotes
         the faulty column. <CODE>Column</CODE> must be one of the columns
         in the <CODE>Cols</CODE> list.

        
</LI>


</UL>
<A NAME="11.2.7"><!-- Empty --></A>
<H4>11.2.7 f(set, RowIndex, Cols [, ExtraArgs])
</H4>

<P>The fumction <CODE>f(set, RowIndex, Cols [, ExtraArgs])</CODE> is
        called to perform the set in phase two of
the set-request processing. It is only called if the
corresponding <CODE>is_set_ok</CODE> function did not exist, or
returned <CODE>{noError, 0}</CODE>.


<P>This functionn is mandatory.

<A NAME="11.2.7.1"><!-- Empty --></A>
<H5>11.2.7.1 Arguments</H5>

<P>
<UL>

<LI>
<CODE>RowIndex</CODE> is a list of integers that define the
         key values for the row. The <CODE>RowIndex</CODE> is the list
         representation (list of integers) which follow the
         <CODE>Cols</CODE> integer in the OBJECT IDENTIFIER.
         
         
</LI>


<LI>
<CODE>Cols</CODE> is a list of <CODE>{Column, NewValue}</CODE>,
         where <CODE>Column</CODE> is an integer, and <CODE>NewValue</CODE> 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 <CODE>Column</CODE> (increasing) and
         each <CODE>Column</CODE> is guaranteed to be a valid column
         number.

        
</LI>


</UL>
<A NAME="11.2.7.2"><!-- Empty --></A>
<H5>11.2.7.2 Valid Return Values</H5>

<P>
<UL>

<LI>
<CODE>{noError, 0}</CODE>
         
         
</LI>


<LI>
<CODE>{Error, Column}</CODE> where <CODE>Error</CODE> is the same
         as <CODE>set</CODE> for variables, and <CODE>Column</CODE> denotes
         the faulty column. <CODE>Column</CODE> must be one of the columns
         in the <CODE>Cols</CODE> list.
        
</LI>


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