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XML: generator should support override of variables
Closed, ResolvedPublicFEATURE REQUEST


All our interfaces have a default MTU of 1500 bytes. Some interfaces (PPPoE, L2TPv3, MACsec) do not have a default MTU of 1500 bytes, but as we inherit the XML definition we "pull-in" this invalid value.

The default value is later exchanged during runtime of the script here:

This simply "feels wrong" to change the value in the handler script. It would be nice to add an XML statement into stating:

#include <include/interface-mtu-68-1500.xml.i>
<leafNode name="mtu">

to override the default value with the correct one on this interface. This would mean "true inheritance" like in C++/Python.


Difficulty level
Unknown (require assessment)
Why the issue appeared?
Will be filled on close
Is it a breaking change?
Unspecified (possibly destroys the router)
Issue type
Internal change (not visible to end users)

Event Timeline

c-po triaged this task as Normal priority.Sep 20 2020, 6:48 PM
c-po created this task.
c-po added subscribers: dmbaturin, jestabro.
jestabro changed the task status from Open to Needs testing.EditedJan 19 2021, 8:32 PM

Preprocessing solution in testing here:

in response to the following constraints:
(1) Agreed that maintaining defaults in the conf_mode scripts feels incorrect, and defeats the purpose of the tag 'defaultValue'.
(2) Overriding of the tag within the XML must be processed before 'build-command-templates' is invoked, as the check against the schema will fail if more than one 'defaultValue' tag exists for a given path.
(3) Overriding of the tag within the XML must be processed after the preprocessing of the * files, for the obvious reason that all instances will not be collected until after that step.

Consequently, a script is provided to run at the outset of 'make interface_definitions' to process the XML to collect, replace, and remove the appropriate elements, with result the updated 'defaultValue' contents.

The script is a terse application of lxml's xpath capability. The link above includes the test case outlined in the description.

Two minor comments left out of the above:
(1) The script in question runs a check on all interface definitions, however, there is no measurable increase in compile time.
(2) lxml will escape characters '>', '<', however these are unescaped by build-command-templates, so the issue is mooted. One can see the single line changed in the XML by running the test case above; it is noted that some interface definitions already have a mixed use of, say, '>' and '&gt;'.

Will remove test case and rebase to create PR and merge for 1.4; will later backport to 1.3 pending any issue.

erkin set Issue type to Internal change (not visible to end users).Aug 29 2021, 12:58 PM
erkin removed a subscriber: Active contributors.