feat: add SEG6_LOCAL_FLAVORS support for seg6local NEXT-CSID

[privateip]

Add the SEG6_LOCAL_FLAVORS attribute and its nested sub-attributes (SEG6_LOCAL_FLV_OPERATION, SEG6_LOCAL_FLV_LCBLOCK_BITS, SEG6_LOCAL_FLV_LCNODE_FN_BITS), introduced in Linux 6.1 (commit 848f3c0d47, "seg6: add support for the SRv6 End* flavors").

This exposes the NEXT-CSID flavor operation on SEG6LocalEncap, letting callers configure the locator-block and node-function bit lengths used for compressed SID (uSID/C-SID) behaviors, matching what iproute2 exposes as flavors next-csid lblen <n> nflen <n>.

Summary by CodeRabbit

• New Features

  • Added support for segment-routing “flavors” in local encapsulation handling, including encode/decode, equality checks, and expanded string output (operation plus bit-length parameters).
  • Extended available flavor-related constants and added a helper that renders flavor operation names, returning a fallback for unknown values.

• Tests

  • Added round-trip tests for multiple flavor configurations, including an unsupported operation, validating equality and string formatting.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 4eac43d2-c4fb-40db-9115-729a03ecbd73

📥 Commits

Reviewing files that changed from the base of the PR and between c286917 and 290b871.

📒 Files selected for processing (1)

• route_linux.go

🚧 Files skipped from review as they are similar to previous changes (1)

• route_linux.go

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📝 Walkthrough

Walkthrough

Adds SEG6_LOCAL_FLAVORS support across netlink constants, SEG6LocalEncap encoding/decoding and formatting, and test coverage for flavor round-tripping and string output.

Changes

SEG6 Local Flavors Support

Layer / File(s)	Summary
Flavor constants and string helper nl/seg6local_linux.go	Adds SEG6_LOCAL_COUNTERS, SEG6_LOCAL_FLAVORS, SEG6_LOCAL_FLV_* and SEG6_LOCAL_FLV_OP_* constants, plus SEG6LocalFlavorOperationString mapping operation codes to names.
SEG6LocalEncap Flavors field and encode/decode logic route_linux.go	Adds Flavors field and SEG6LocalFlavors type; Decode parses SEG6_LOCAL_FLAVORS sub-attributes; Encode serializes them when set.
String and Equal updates route_linux.go	String output includes a flavors segment; Equal comparison now covers the Flavors field.
Flavors test coverage route_test.go	Adds TestSEG6LocalEncapFlavors covering encode/decode round-trips, equality, and String formatting including an unknown-operation case.

Estimated code review effort: 2 (Simple) | ~15 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Caller
  participant SEG6LocalEncap
  participant nl as nl package

  Caller->>SEG6LocalEncap: Decode(attrs)
  SEG6LocalEncap->>nl: parse SEG6_LOCAL_FLAVORS sub-attrs
  nl-->>SEG6LocalEncap: Operation, LcBlockBits, LcNodeFnBits
  SEG6LocalEncap-->>Caller: Flavors populated

  Caller->>SEG6LocalEncap: Encode()
  SEG6LocalEncap->>nl: emit SEG6_LOCAL_FLAVORS attrs
  nl-->>Caller: encoded bytes

  Caller->>SEG6LocalEncap: String()
  SEG6LocalEncap->>nl: SEG6LocalFlavorOperationString(op)
  nl-->>SEG6LocalEncap: operation name
  SEG6LocalEncap-->>Caller: formatted string

Loading

Related PRs: None specified.

Suggested labels: enhancement, seg6

Suggested reviewers: vishvananda

Poem

A rabbit hops through netlink's maze,
Flavors added, bits ablaze,
NEXT-CSID whispers in the wire,
Encode, decode, never tire,
Tests confirm the paths are true,
Hop, hop, hooray — a feature new!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: adding SEG6_LOCAL_FLAVORS support for seg6local NEXT-CSID.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@route_linux.go`:
- Around line 356-373: The unknown-attribute error in the SEG6_LOCAL_FLAVORS
decode path is formatting the wrong value with %d, because flvAttr.Attr is a
syscall.RtAttr struct rather than the attribute type. Update the error
construction in the SEG6_LOCAL_FLAVORS case to report flvAttr.Attr.Type instead,
matching the intended behavior and avoiding confusing Len/Type output; use the
same pattern as the other SEG6_LOCAL_* decoding branches.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 9b4debca-a495-4d77-a39c-181b8a2932db

📥 Commits

Reviewing files that changed from the base of the PR and between 4e35dc9 and c286917.

📒 Files selected for processing (3)

• nl/seg6local_linux.go
• route_linux.go
• route_test.go