UCT/TCP: added reachability mode conf var to tcp_iface

[amastbaum]

What?

Added UCX_TCP_REACHABILITY_MODE config (default: route) to optionally allow all addresses without route checking when set to all. Solving bug: https://redmine.mellanox.com/issues/4659780

Summary by CodeRabbit

• New Features
  • Added a TCP "reachability mode" configuration with three options: route (default), all, and last.
  • Selecting "all" treats all network addresses as reachable; the chosen mode is exposed in configuration and applied at runtime to influence reachability checks.

[gleon99]

@shasson5 please look

[coderabbitai[bot]]

Walkthrough

Adds a configurable TCP interface reachability mode enum and wires it through the public config, initialization, and the reachability check so the iface can treat addresses as routability-checked or universally reachable.

Changes

Cohort / File(s)	Change Summary
Header: public types & config src/uct/tcp/tcp.h	Added typedef enum uct_tcp_reachability_mode_t { UCT_TCP_REACHABILITY_ROUTE, UCT_TCP_REACHABILITY_ALL, UCT_TCP_REACHABILITY_LAST }; added reachability_mode field to the iface config area and to uct_tcp_iface_config_t.
Implementation & config table src/uct/tcp/tcp_iface.c	Added const char *uct_tcp_reachability_modes[] string mapping and REACHABILITY_MODE config entry (default "route"); propagated reachability_mode from TL config into self->config; modified uct_tcp_iface_is_reachable_v2 to use uct_iface_scope_is_reachable when mode==ALL and to perform routability checks when mode==ROUTE.

Sequence Diagram(s)

sequenceDiagram
    participant Caller as reachability caller
    participant IFACE as TCP_IFACE\n(config.reachability_mode)
    participant SCOPE as ScopeChecker
    participant ROUTE as RoutabilityChecker

    Caller->>IFACE: uct_tcp_iface_is_reachable_v2(addr)
    alt config == ALL
        IFACE->>SCOPE: uct_iface_scope_is_reachable(addr)
        SCOPE-->>IFACE: reachable / not reachable
        IFACE-->>Caller: return result
    else config == ROUTE
        IFACE->>ROUTE: check address routability (if_nametoindex / name-index)
        ROUTE-->>IFACE: routable / not routable
        IFACE-->>Caller: return result
    end

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

• Pay attention to:
  • Correct enum ↔ string mapping and NUL termination of uct_tcp_reachability_modes[].
  • Config table entry syntax, default value, and how the enum is parsed.
  • Proper propagation of reachability_mode into self->config during init.
  • The conditional logic in uct_tcp_iface_is_reachable_v2 to ensure no regressions in routability checks.

Poem

🐰 I nibble configs, choose route or all,
A hop of enum, a tiny call,
From table into runtime I bound,
Scope or route — I check the ground,
TCP carrots scattered round.

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title accurately summarizes the main change: adding a reachability mode configuration variable to tcp_iface, which is directly reflected in the code additions across tcp.h and tcp_iface.c.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing touches

• [ ] 📝 Generate docstrings

🧪 Generate unit tests (beta)

• [ ] Create PR with unit tests
• [ ] Post copyable unit tests in a comment

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[shasson5]

BTW why is WIP label set?

[amastbaum]

BTW why is WIP label set? By mistake