kernel/api: add debugfs interface for kernel API specifications

Add a debugfs interface, enabled by CONFIG_KAPI_SPEC_DEBUGFS, to expose
kernel API specifications at runtime. This allows tools and users to
query the complete API specifications through the debugfs filesystem.

The interface provides:
- /sys/kernel/debug/kapi/list - lists all available API specifications
- /sys/kernel/debug/kapi/specs/<name> - detailed info for each API
- /sys/kernel/debug/kapi/specs-json/<name> - the same spec as JSON

Each specification file includes:
- Function name, version, and descriptions
- Execution context requirements and flags
- Parameter details with types, flags, and constraints
- Return value specifications and success conditions
- Error codes with descriptions and conditions
- Locking requirements and constraints
- Signal handling specifications
- Examples and notes

This enables runtime introspection of kernel APIs for documentation
tools, static analyzers, and debugging purposes.

Assisted-by: LLM
Signed-off-by: Sasha Levin <sashal@kernel.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/kernel/api/Makefile b/kernel/api/Makefile
index 6e14ca243980..2e1c3555d5aa 100644
--- a/kernel/api/Makefile
+++ b/kernel/api/Makefile
@@ -6,5 +6,8 @@
 # Core API specification framework
 obj-y				+= kernel_api_spec.o
 
+# Debugfs interface for kernel API specs
+obj-$(CONFIG_KAPI_SPEC_DEBUGFS) += kapi_debugfs.o
+
 # KUnit tests
 obj-$(CONFIG_KAPI_KUNIT_TEST) += kapi_kunit.o