qos: T4248: Allow to remove the only rule from the qos class (backport #3316)

[mergify]

Change Summary

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://vyos.dev/T4248

Related PR(s)

Component(s) name

Proposed changes

How to test

single rule:

set qos interface eth0 egress qos-shaper-eth0
set qos policy shaper qos-shaper-eth0 bandwidth 10mbit
set qos policy shaper qos-shaper-eth0 default bandwidth 100mbit
set qos policy shaper qos-shaper-eth0 default burst 100
set qos policy shaper qos-shaper-eth0 class 30 bandwidth 50mbit
set qos policy shaper qos-shaper-eth0 class 30 ceiling 5mbit
set qos policy shaper qos-shaper-eth0 class 30 match ADDRESS30 ip source address 10.1.1.0/24
set qos policy shaper qos-shaper-eth0 class 30 priority 5
set qos policy shaper qos-shaper-eth0 class 30 queue-type fair-queue
commit
del qos policy shaper qos-shaper-eth0 class 30 match ADDRESS30 ip source address 10.1.1.0/24
commit

two rules:

conf
set qos interface eth1 egress MY-HTB
set qos policy shaper MY-HTB default bandwidth '10mbit'
set qos policy shaper MY-HTB class 40 bandwidth '90%'
set qos policy shaper MY-HTB class 40 ceiling '100%'
set qos policy shaper MY-HTB class 40 match ADDRESS40 ip source address '10.2.1.0/24'
set qos policy shaper MY-HTB class 40 match ADDRESS40 ip dscp CS4
set qos policy shaper MY-HTB class 40 priority '5'
set qos policy shaper MY-HTB class 40 queue-type 'fair-queue'
commit
del qos policy shaper MY-HTB class 40 match ADDRESS40 ip source address '10.2.1.0/24'
commit
del qos policy shaper MY-HTB class 40 match ADDRESS40 ip dscp CS4
commit

Smoketest result

vyos@vyos:~$ python3 /usr/libexec/vyos/tests/smoke/cli/test_qos.py 
test_01_cake (__main__.TestQoS.test_01_cake) ... ok
test_02_drop_tail (__main__.TestQoS.test_02_drop_tail) ... 
Selected QoS policy "qos-policy-eth0" does not exist!

ok
test_03_fair_queue (__main__.TestQoS.test_03_fair_queue) ... 
Selected QoS policy "qos-policy-eth0" does not exist!

ok
test_04_fq_codel (__main__.TestQoS.test_04_fq_codel) ... 
Selected QoS policy "qos-policy-eth0" does not exist!

ok
test_05_limiter (__main__.TestQoS.test_05_limiter) ... 
Selected QoS policy "qos-policy-eth0" does not exist!

ok
test_06_network_emulator (__main__.TestQoS.test_06_network_emulator) ... 
Selected QoS policy "qos-policy-eth0" does not exist!

ok
test_07_priority_queue (__main__.TestQoS.test_07_priority_queue) ... 
Selected QoS policy "qos-policy-eth0" does not exist!

ok
test_08_random_detect (__main__.TestQoS.test_08_random_detect) ... skipped 'tc returns invalid JSON here - needs iproute2 fix'
test_09_rate_control (__main__.TestQoS.test_09_rate_control) ... 
Selected QoS policy "qos-policy-eth0" does not exist!

ok
test_10_round_robin (__main__.TestQoS.test_10_round_robin) ... 
Selected QoS policy "qos-policy-eth0" does not exist!

ok
test_11_shaper (__main__.TestQoS.test_11_shaper) ... ok
test_12_shaper_with_red_queue (__main__.TestQoS.test_12_shaper_with_red_queue) ... ok
test_13_shaper_delete_only_rule (__main__.TestQoS.test_13_shaper_delete_only_rule) ... ok

----------------------------------------------------------------------
Ran 13 tests in 41.900s

OK (skipped=1)

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

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This is an automatic backport of pull request #3316 done by [Mergify](https://mergify.com).