more modular consumables description

[guillomovitch]

See agent PR #660 for original discussion

[g-bougard]

Hi,
on the agent side we are looking for the "MAX" value and we just put a value as a percentage. In that case we may not set "UNIT". So I think the spec should clarify that point or a <MAX>100</MAX> for example may be added. So I'm not sure what's the best: leaving <UNIT/> empty or add a <MAX/> node.
The point is also would the plugin (or users) prefer to know the usage in percent or the unit and the max possible absolute value ?

[guillomovitch]

on the agent side we are looking for the "MAX" value and we just put a value as a percentage

Only if maximum value is available, otherwise current value is used, with a unit. Keeping the same behaviour with the new specification would produce the following results:

1. <value>95</value><unit>%</unit>
2. <value>95</value><unit>cm</unit>

As an alternative, this computation could be made server-side by transmitting raw values, ie:

1. <current>95</current><max>100</max>
2. <current>95</current><unit>cm</unit>

[g-bougard]

My thought about <MAX/> was more to handle cases where MAX <> 100 and UNIT <> '%'. I agree MAX could be optional if unit is %.
So I would update the spec like this:

...
              <!ELEMENT UNIT (#PCDATA)>
              <!-- use MAX if available and UNIT <> % -->
              <!ELEMENT MAX (#PCDATA)>

[guillomovitch]

use MAX if available and UNIT <> %

I'm not sure to follow you here, as this double condition doesn't match current agent behaviour.

If a value is available for max OID (.1.3.6.1.2.1.43.11.1.1.8.1), the agent currently assumes the current consumable level is a fraction ($current * 100 / $max), and ignores the unit OID (.1.3.6.1.2.1.43.11.1.1.7.1) value, which doesn't include '%' anyway AFAIK.

Consider two different consumables, with the following SNMP values:

consumableA:

• current: 50
• max: 100
• unit: whatever

consumableB:

• current: 50
• max: -2
• unit: 16

With the current agent behaviour, the consumable A should be reported either by forging a value for unit, to make interpretation easier:

<consumable>
  <current_value>50</current_value>
  <unit>%</unit>
</consumable>

Let's call this scenario A.

Or not reporting unit at all, and let the information consumer deduce it's a computed fraction:

<consumable>
  <current_value>50</current_value>
</consumable>

Let's call this scenario B.

However, if we change the agent behaviour to report raw values directly, it seems safer to not report the unit at all, ie:

<consumable>
  <current_value>50</current_value>
  <max_value>100</max_value>
</consumable>

Let's call this scenario C.

In all case, consumable B would be reported as:

<consumable>
  <current_value>50</current_value>
  <unit>cm</unit>
</consumable>

[g-bougard]

I agree with you. Maybe a more appropriate comment would be:

<!-- use MAX if available, or assume it's 100 when UNIT is not set -->