landlock: Test trace path output boundaries

Use focused KUnit tests to exercise the renderer's internal boundary and
composition contracts with synthetic scratch states, including both
sibling-helpe

landlock: Test trace path output boundaries

Use focused KUnit tests to exercise the renderer's internal boundary and
composition contracts with synthetic scratch states, including both
sibling-helper evaluation orders. Check the exact output and
reservation boundaries, including a four-byte octal escape accepted at
exact capacity and rejected one byte short. Also verify an unchanged
cursor on failure, that bracketed process names and embedded NUL bytes
remain data, and that input ellipsis bytes are escaped rather than
mistaken for the raw truncation marker.

The composition test requires generic trace output helpers. Enable
CONFIG_FTRACE and CONFIG_SCHED_TRACER because the latter selects the
otherwise-hidden CONFIG_TRACING support required by
trace_print_flags_seq().

Use kselftests to exercise the complete tracefs path for both affected
filesystem events. A valid path containing 2640 spaces exceeds the
scratch output budget. Require its escaped prefix to end in the raw
UTF-8 ellipsis while access_rights and blockers remain intact.

This division keeps the exact safety contract compiler-independent while
proving that real tracepoints preserve their surrounding symbolic
fields. The end-to-end assertions fail after a full fix revert with
both GCC and Clang, while the composition KUnit test fails if the
scratch reserve is removed.

Cc: Günther Noack <gnoack@google.com>
Link: https://patch.msgid.link/20260907154401.124362-2-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>

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selftests/landlock: Add filesystem tracepoint tests

Add filesystem-specific trace tests in a dedicated file, following the
audit-test pattern of living alongside each subsystem's functional
tests.

selftests/landlock: Add filesystem tracepoint tests

Add filesystem-specific trace tests in a dedicated file, following the
audit-test pattern of living alongside each subsystem's functional
tests.

trace_fs_test.c verifies that the add_rule_fs, check_rule_fs, and
deny_access_fs events fire with the correct fields on matching rules and
denied accesses, that check_rule_fs does not fire for unhandled access
types, and that no event fires without a sandbox. A denial covered by a
quiet rule still emits a deny_access_fs event but with logged=0, the
same suppression verdict audit applies; because that verdict must not
depend on CONFIG_AUDIT, the test also runs under a tracepoints-only
build.

Add trace_layout1 fixture tests in fs_test.c that reuse the layout1
hierarchy to verify the per-layer grants field: field values, multi-rule
pathwalk short-circuit, request intersection, the optional truncate
right surfacing in the request and grants, and an empty grants set from
a rule that grants none of the requested rights.

Cc: Günther Noack <gnoack@google.com>
Cc: Tingmao Wang <m@maowtm.org>
Link: https://patch.msgid.link/20260811094338.288094-16-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>

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