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 <[email protected]>
---
 Documentation/dev-tools/kernel-api-spec.rst |  82 ++-
 kernel/api/Kconfig                          |  20 +
 kernel/api/Makefile                         |   3 +
 kernel/api/kapi_debugfs.c                   | 553 ++++++++++++++++++++
 4 files changed, 641 insertions(+), 17 deletions(-)
 create mode 100644 kernel/api/kapi_debugfs.c

diff --git a/Documentation/dev-tools/kernel-api-spec.rst 
b/Documentation/dev-tools/kernel-api-spec.rst
index 03b32d3718c8e..fa8aabb92a503 100644
--- a/Documentation/dev-tools/kernel-api-spec.rst
+++ b/Documentation/dev-tools/kernel-api-spec.rst
@@ -262,6 +262,7 @@ Runtime validation is controlled by kernel configuration:
 
 1. Enable ``CONFIG_KAPI_SPEC`` to build the framework
 2. Enable ``CONFIG_KAPI_RUNTIME_CHECKS`` for runtime validation
+3. Optionally enable ``CONFIG_KAPI_SPEC_DEBUGFS`` for debugfs interface
 
 Validation Behavior
 -------------------
@@ -310,6 +311,68 @@ specification. Kerneldoc annotations cannot set it, so it 
is only available to a
     .constraint_type = KAPI_CONSTRAINT_CUSTOM,
     .validate = validate_buffer_size,
 
+DebugFS Interface
+=================
+
+The debugfs interface provides runtime access to API specifications:
+
+Directory Structure
+-------------------
+
+::
+
+    /sys/kernel/debug/kapi/
+    ├── list                     # Overview of all registered API specs
+    ├── specs/                   # Per-API specification files
+    │   ├── sys_open             # Human-readable spec for sys_open
+    │   ├── sys_close            # Human-readable spec for sys_close
+    │   ├── sys_read             # Human-readable spec for sys_read
+    │   ├── sys_write            # Human-readable spec for sys_write
+    │   └── sys_madvise          # Human-readable spec for sys_madvise
+    └── specs-json/              # Machine-readable counterpart of specs/
+        ├── sys_open             # JSON spec for sys_open
+        └── ...
+
+Usage Examples
+--------------
+
+List all available API specifications::
+
+    $ cat /sys/kernel/debug/kapi/list
+    Available Kernel API Specifications
+    ===================================
+
+    sys_open - Open or create a file
+    sys_close - Close a file descriptor
+    sys_read - Read data from a file descriptor
+    sys_write - Write data to a file descriptor
+    sys_madvise - Give advice about use of memory
+
+    Total: 5 specifications
+
+Query specific API::
+
+    $ cat /sys/kernel/debug/kapi/specs/sys_open
+    Kernel API Specification
+    ========================
+
+    Name: sys_open
+    Version: 1
+    Description: Open or create a file
+    ...
+
+The ``specs-json/`` files carry the complete specification: for each
+parameter the type class, flags and the constraint (type, range, valid
+mask, enumerated values, alignment, size and the index of the parameter
+holding a buffer's size), the return check, errors, locks, signals,
+signal masks, side effects, state transitions, capabilities, additional
+constraints and structure specifications. Masks and flag words are
+hex strings, enumerations are lower-case tokens such as
+``"constraint_type": "buffer"``, and ``size_param_idx`` is a 0-based
+index into ``parameters`` (``null`` when unused). The ``kapi`` tool
+reads these files with ``--debugfs`` and reports the same data as
+``--vmlinux``.
+
 Performance Considerations
 ==========================
 
@@ -620,20 +683,5 @@ Submitting Specifications
 1. Add specifications to the same file as the API implementation
 2. Follow existing patterns and naming conventions
 3. Test with CONFIG_KAPI_RUNTIME_CHECKS enabled
-4. Run scripts/checkpatch.pl on your changes
-
-Review Criteria
----------------
-
-Specifications will be reviewed for:
-
-1. **Completeness**: All parameters and errors documented
-2. **Accuracy**: Specification matches implementation
-3. **Clarity**: Descriptions are clear and helpful
-4. **Consistency**: Follows framework conventions
-5. **Performance**: No unnecessary runtime overhead
-
-Contact
--------
-
-- Maintainer: Sasha Levin <[email protected]>
+4. Verify debugfs output is correct
+5. Run scripts/checkpatch.pl on your changes
diff --git a/kernel/api/Kconfig b/kernel/api/Kconfig
index 1cd55b252f0d5..6075ab82bd231 100644
--- a/kernel/api/Kconfig
+++ b/kernel/api/Kconfig
@@ -41,6 +41,26 @@ config KAPI_RUNTIME_CHECKS
 
          If unsure, say N.
 
+config KAPI_SPEC_DEBUGFS
+       bool "Export kernel API specifications via debugfs"
+       depends on KAPI_SPEC
+       depends on DEBUG_FS
+       help
+         This option enables exporting kernel API specifications through
+         the debugfs filesystem. When enabled, specifications can be
+         accessed at /sys/kernel/debug/kapi/.
+
+         The debugfs interface provides:
+         - A list of all available API specifications
+         - Detailed information for each API including parameters,
+           return values, errors, locking requirements, and constraints
+         - Complete machine-readable representation of the specs
+
+         This is useful for documentation tools, static analyzers, and
+         runtime introspection of kernel APIs.
+
+         If unsure, say N.
+
 config KAPI_KUNIT_TEST
        tristate "KUnit tests for KAPI framework" if !KUNIT_ALL_TESTS
        depends on KAPI_SPEC
diff --git a/kernel/api/Makefile b/kernel/api/Makefile
index 6e14ca243980c..2e1c3555d5aa5 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
diff --git a/kernel/api/kapi_debugfs.c b/kernel/api/kapi_debugfs.c
new file mode 100644
index 0000000000000..5d9c2649a0dc6
--- /dev/null
+++ b/kernel/api/kapi_debugfs.c
@@ -0,0 +1,553 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2026 Sasha Levin <[email protected]>
+ *
+ * Kernel API specification debugfs interface
+ *
+ * This provides a debugfs interface to expose kernel API specifications
+ * at runtime, allowing tools and users to query the complete API specs.
+ */
+
+#include <linux/debugfs.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/seq_file.h>
+#include <linux/kernel_api_spec.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+
+#include "internal.h"
+
+/* Helper to print parameter flags */
+static void print_param_flags(struct seq_file *m, u32 flags)
+{
+       seq_puts(m, "    flags: ");
+       if ((flags & KAPI_PARAM_INOUT) == KAPI_PARAM_INOUT)
+               seq_puts(m, "INOUT ");
+       else if (flags & KAPI_PARAM_IN)
+               seq_puts(m, "IN ");
+       else if (flags & KAPI_PARAM_OUT)
+               seq_puts(m, "OUT ");
+       if (flags & KAPI_PARAM_OPTIONAL)
+               seq_puts(m, "OPTIONAL ");
+       if (flags & KAPI_PARAM_CONST)
+               seq_puts(m, "CONST ");
+       if (flags & KAPI_PARAM_USER)
+               seq_puts(m, "USER ");
+       if (flags & KAPI_PARAM_VOLATILE)
+               seq_puts(m, "VOLATILE ");
+       if (flags & KAPI_PARAM_DMA)
+               seq_puts(m, "DMA ");
+       if (flags & KAPI_PARAM_ALIGNED)
+               seq_puts(m, "ALIGNED ");
+       seq_puts(m, "\n");
+}
+
+/* Helper to print context flags */
+static void print_context_flags(struct seq_file *m, u32 flags)
+{
+       seq_puts(m, "Context flags: ");
+       if (flags & KAPI_CTX_PROCESS)
+               seq_puts(m, "PROCESS ");
+       if (flags & KAPI_CTX_HARDIRQ)
+               seq_puts(m, "HARDIRQ ");
+       if (flags & KAPI_CTX_SOFTIRQ)
+               seq_puts(m, "SOFTIRQ ");
+       if (flags & KAPI_CTX_NMI)
+               seq_puts(m, "NMI ");
+       if (flags & KAPI_CTX_SLEEPABLE)
+               seq_puts(m, "SLEEPABLE ");
+       if (flags & KAPI_CTX_ATOMIC)
+               seq_puts(m, "ATOMIC ");
+       if (flags & KAPI_CTX_PREEMPT_DISABLED)
+               seq_puts(m, "PREEMPT_DISABLED ");
+       if (flags & KAPI_CTX_IRQ_DISABLED)
+               seq_puts(m, "IRQ_DISABLED ");
+       seq_puts(m, "\n");
+}
+
+/*
+ * Print a multi-line value with every line indented, so that no line of it
+ * can be mistaken for a field of its own.
+ */
+static void print_block(struct seq_file *m, const char *text)
+{
+       while (*text) {
+               size_t len = strcspn(text, "\n");
+
+               if (len)
+                       seq_printf(m, "  %.*s", (int)len, text);
+               seq_putc(m, '\n');
+               text += len;
+               if (*text == '\n')
+                       text++;
+       }
+}
+
+/* Helper to print a list of signed values */
+static void print_s64_list(struct seq_file *m, const char *label,
+                          const s64 *vals, u32 count)
+{
+       u32 i;
+
+       if (!vals || !count)
+               return;
+
+       seq_printf(m, "%s:", label);
+       for (i = 0; i < count; i++)
+               seq_printf(m, " %lld", vals[i]);
+       seq_puts(m, "\n");
+}
+
+/* Helper to print which parameter carries a buffer's element count */
+static void print_size_param(struct seq_file *m,
+                            const struct kernel_api_spec *spec,
+                            const struct kapi_param_spec *param)
+{
+       int idx = param->size_param_idx - 1;
+
+       if (idx < 0)
+               return;
+
+       seq_printf(m, "      size_param: %s (index %d)\n",
+                  idx < spec->param_count && idx < KAPI_MAX_PARAMS ?
+                  spec->params[idx].name : "?", idx);
+       if (param->size_multiplier)
+               seq_printf(m, "      size_multiplier: %zu\n",
+                          param->size_multiplier);
+}
+
+/* Show function for individual API spec */
+static int kapi_spec_show(struct seq_file *m, void *v)
+{
+       struct kernel_api_spec *spec = m->private;
+       int i;
+
+       seq_puts(m, "Kernel API Specification\n");
+       seq_puts(m, "========================\n\n");
+
+       /* Basic info */
+       seq_printf(m, "Name: %s\n", spec->name);
+       seq_printf(m, "Version: %u\n", spec->version);
+       seq_printf(m, "Description: %s\n", spec->description);
+       if (spec->long_description && *spec->long_description) {
+               seq_puts(m, "Long description:\n");
+               print_block(m, spec->long_description);
+       }
+
+       /* Context */
+       print_context_flags(m, spec->context_flags);
+       seq_puts(m, "\n");
+
+       /* Parameters */
+       if (spec->param_count > 0) {
+               seq_printf(m, "Parameters (%u):\n", spec->param_count);
+               for (i = 0; i < spec->param_count && i < KAPI_MAX_PARAMS; i++) {
+                       struct kapi_param_spec *param = &spec->params[i];
+
+                       seq_printf(m, "  [%d] %s:\n", i, param->name);
+                       seq_printf(m, "    type: %s (%s)\n",
+                                  kapi_param_type_to_string(param->type), 
param->type_name);
+                       print_param_flags(m, param->flags);
+                       if (param->description && *param->description)
+                               seq_printf(m, "    description: %s\n", 
param->description);
+                       if (param->size > 0)
+                               seq_printf(m, "    size: %zu\n", param->size);
+                       if (param->alignment > 0)
+                               seq_printf(m, "    alignment: %zu\n", 
param->alignment);
+
+                       /* Print constraints if any */
+                       if (param->constraint_type != KAPI_CONSTRAINT_NONE ||
+                           (param->constraints && *param->constraints)) {
+                               seq_puts(m, "    constraints:\n");
+                               switch (param->constraint_type) {
+                               case KAPI_CONSTRAINT_NONE:
+                                       break;
+                               case KAPI_CONSTRAINT_RANGE:
+                                       seq_puts(m, "      type: range\n");
+                                       seq_printf(m, "      min: %lld\n", 
param->min_value);
+                                       seq_printf(m, "      max: %lld\n", 
param->max_value);
+                                       break;
+                               case KAPI_CONSTRAINT_MASK:
+                                       seq_puts(m, "      type: mask\n");
+                                       seq_printf(m, "      valid_bits: 
0x%llx\n",
+                                                  param->valid_mask);
+                                       break;
+                               case KAPI_CONSTRAINT_ENUM:
+                                       seq_puts(m, "      type: enum\n");
+                                       seq_printf(m, "      count: %u\n", 
param->enum_count);
+                                       print_s64_list(m, "      values",
+                                                      param->enum_values,
+                                                      param->enum_count);
+                                       break;
+                               case KAPI_CONSTRAINT_USER_STRING:
+                                       seq_puts(m, "      type: 
user_string\n");
+                                       seq_printf(m, "      min_len: %lld\n", 
param->min_value);
+                                       seq_printf(m, "      max_len: %lld\n", 
param->max_value);
+                                       break;
+                               case KAPI_CONSTRAINT_USER_PATH:
+                                       seq_puts(m, "      type: user_path\n");
+                                       seq_puts(m, "      max_len: PATH_MAX 
(4096)\n");
+                                       break;
+                               case KAPI_CONSTRAINT_USER_PTR:
+                                       seq_puts(m, "      type: user_ptr\n");
+                                       seq_printf(m, "      size: %zu 
bytes\n", param->size);
+                                       print_size_param(m, spec, param);
+                                       break;
+                               case KAPI_CONSTRAINT_BUFFER:
+                                       seq_puts(m, "      type: buffer\n");
+                                       print_size_param(m, spec, param);
+                                       break;
+                               case KAPI_CONSTRAINT_ALIGNMENT:
+                                       seq_puts(m, "      type: alignment\n");
+                                       seq_printf(m, "      alignment: %zu\n", 
param->alignment);
+                                       break;
+                               case KAPI_CONSTRAINT_POWER_OF_TWO:
+                                       seq_puts(m, "      type: 
power_of_two\n");
+                                       break;
+                               case KAPI_CONSTRAINT_PAGE_ALIGNED:
+                                       seq_puts(m, "      type: 
page_aligned\n");
+                                       break;
+                               case KAPI_CONSTRAINT_NONZERO:
+                                       seq_puts(m, "      type: nonzero\n");
+                                       break;
+                               case KAPI_CONSTRAINT_CUSTOM:
+                                       seq_puts(m, "      type: custom\n");
+                                       break;
+                               default:
+                                       seq_printf(m, "      type: unknown 
(%d)\n",
+                                                  param->constraint_type);
+                                       break;
+                               }
+                               if (param->constraints && *param->constraints)
+                                       seq_printf(m, "      description: %s\n",
+                                                  param->constraints);
+                       }
+                       seq_puts(m, "\n");
+               }
+       }
+
+       /* Return value */
+       seq_puts(m, "Return value:\n");
+       seq_printf(m, "  type: %s\n", spec->return_spec.type_name);
+       if (spec->return_spec.description && *spec->return_spec.description)
+               seq_printf(m, "  description: %s\n", 
spec->return_spec.description);
+
+       switch (spec->return_spec.check_type) {
+       case KAPI_RETURN_EXACT:
+               seq_printf(m, "  success: == %lld\n", 
spec->return_spec.success_value);
+               break;
+       case KAPI_RETURN_RANGE:
+               seq_printf(m, "  success: [%lld, %lld]\n",
+                          spec->return_spec.success_min,
+                          spec->return_spec.success_max);
+               break;
+       case KAPI_RETURN_FD:
+               seq_puts(m, "  success: valid file descriptor (>= 0)\n");
+               break;
+       case KAPI_RETURN_ERROR_CHECK:
+               seq_puts(m, "  success: error check\n");
+               print_s64_list(m, "  error values",
+                              spec->return_spec.error_values,
+                              spec->return_spec.error_count);
+               break;
+       case KAPI_RETURN_CUSTOM:
+               seq_puts(m, "  success: custom check\n");
+               break;
+       case KAPI_RETURN_NO_RETURN:
+               seq_puts(m, "  success: does not return\n");
+               break;
+       default:
+               break;
+       }
+       seq_puts(m, "\n");
+
+       /* Errors */
+       if (spec->error_count > 0) {
+               seq_printf(m, "Errors (%u):\n", spec->error_count);
+               for (i = 0; i < spec->error_count && i < KAPI_MAX_ERRORS; i++) {
+                       struct kapi_error_spec *err = &spec->errors[i];
+
+                       seq_printf(m, "  %s (%d): %s\n",
+                                  err->name, err->error_code, 
err->description);
+                       if (err->condition && *err->condition)
+                               seq_printf(m, "    condition: %s\n", 
err->condition);
+               }
+               seq_puts(m, "\n");
+       }
+
+       /* Locks */
+       if (spec->lock_count > 0) {
+               seq_printf(m, "Locks (%u):\n", spec->lock_count);
+               for (i = 0; i < spec->lock_count && i < KAPI_MAX_LOCKS; i++) {
+                       struct kapi_lock_spec *lock = &spec->locks[i];
+
+                       seq_printf(m, "  %s (%s): %s\n", lock->lock_name,
+                                  kapi_lock_type_to_string(lock->lock_type),
+                                  lock->description);
+                       seq_printf(m, "    scope: %s\n",
+                                  kapi_lock_scope_to_string(lock->scope));
+               }
+               seq_puts(m, "\n");
+       }
+
+       /* Constraints */
+       if (spec->constraint_count > 0) {
+               seq_printf(m, "Additional constraints (%u):\n", 
spec->constraint_count);
+               for (i = 0; i < spec->constraint_count && i < 
KAPI_MAX_CONSTRAINTS; i++) {
+                       struct kapi_constraint_spec *cons = 
&spec->constraints[i];
+
+                       seq_printf(m, "  - %s", cons->name);
+                       if (cons->description && *cons->description)
+                               seq_printf(m, ": %s", cons->description);
+                       seq_puts(m, "\n");
+                       if (cons->expression && *cons->expression)
+                               seq_printf(m, "    expression: %s\n", 
cons->expression);
+               }
+               seq_puts(m, "\n");
+       }
+
+       /* Signals */
+       if (spec->signal_count > 0) {
+               seq_printf(m, "Signal handling (%u):\n", spec->signal_count);
+               for (i = 0; i < spec->signal_count && i < KAPI_MAX_SIGNALS; 
i++) {
+                       struct kapi_signal_spec *sig = &spec->signals[i];
+
+                       seq_printf(m, "  %s (%d):\n", sig->signal_name, 
sig->signal_num);
+                       seq_puts(m, "    direction: ");
+                       if (sig->direction & KAPI_SIGNAL_SEND)
+                               seq_puts(m, "send ");
+                       if (sig->direction & KAPI_SIGNAL_RECEIVE)
+                               seq_puts(m, "receive ");
+                       if (sig->direction & KAPI_SIGNAL_HANDLE)
+                               seq_puts(m, "handle ");
+                       if (sig->direction & KAPI_SIGNAL_BLOCK)
+                               seq_puts(m, "block ");
+                       if (sig->direction & KAPI_SIGNAL_IGNORE)
+                               seq_puts(m, "ignore ");
+                       seq_puts(m, "\n");
+                       seq_puts(m, "    action: ");
+                       switch (sig->action) {
+                       case KAPI_SIGNAL_ACTION_DEFAULT:
+                               seq_puts(m, "default");
+                               break;
+                       case KAPI_SIGNAL_ACTION_TERMINATE:
+                               seq_puts(m, "terminate");
+                               break;
+                       case KAPI_SIGNAL_ACTION_COREDUMP:
+                               seq_puts(m, "coredump");
+                               break;
+                       case KAPI_SIGNAL_ACTION_STOP:
+                               seq_puts(m, "stop");
+                               break;
+                       case KAPI_SIGNAL_ACTION_CONTINUE:
+                               seq_puts(m, "continue");
+                               break;
+                       case KAPI_SIGNAL_ACTION_CUSTOM:
+                               seq_puts(m, "custom");
+                               break;
+                       case KAPI_SIGNAL_ACTION_RETURN:
+                               seq_puts(m, "return");
+                               break;
+                       case KAPI_SIGNAL_ACTION_RESTART:
+                               seq_puts(m, "restart");
+                               break;
+                       case KAPI_SIGNAL_ACTION_QUEUE:
+                               seq_puts(m, "queue");
+                               break;
+                       case KAPI_SIGNAL_ACTION_DISCARD:
+                               seq_puts(m, "discard");
+                               break;
+                       case KAPI_SIGNAL_ACTION_TRANSFORM:
+                               seq_puts(m, "transform");
+                               break;
+                       default:
+                               seq_puts(m, "unknown");
+                               break;
+                       }
+                       seq_puts(m, "\n");
+                       if (sig->description && *sig->description)
+                               seq_printf(m, "    description: %s\n", 
sig->description);
+               }
+               seq_puts(m, "\n");
+       }
+
+       /* Side effects */
+       if (spec->side_effect_count > 0) {
+               seq_printf(m, "Side effects (%u):\n", spec->side_effect_count);
+               for (i = 0; i < spec->side_effect_count && i < 
KAPI_MAX_SIDE_EFFECTS; i++) {
+                       const struct kapi_side_effect *eff = 
&spec->side_effects[i];
+
+                       seq_printf(m, "  - %s", eff->target);
+                       if (eff->description && *eff->description)
+                               seq_printf(m, ": %s", eff->description);
+                       if (eff->reversible)
+                               seq_puts(m, " (reversible)");
+                       seq_puts(m, "\n");
+               }
+               seq_puts(m, "\n");
+       }
+
+       /* State transitions */
+       if (spec->state_trans_count > 0) {
+               seq_printf(m, "State transitions (%u):\n", 
spec->state_trans_count);
+               for (i = 0; i < spec->state_trans_count && i < 
KAPI_MAX_STATE_TRANS; i++) {
+                       const struct kapi_state_transition *trans = 
&spec->state_transitions[i];
+
+                       seq_printf(m, "  %s: %s -> %s\n", trans->object,
+                                  trans->from_state, trans->to_state);
+                       if (trans->description && *trans->description)
+                               seq_printf(m, "    %s\n", trans->description);
+               }
+               seq_puts(m, "\n");
+       }
+
+       /* Capabilities */
+       if (spec->capability_count > 0) {
+               seq_printf(m, "Capabilities (%u):\n", spec->capability_count);
+               for (i = 0; i < spec->capability_count && i < 
KAPI_MAX_CAPABILITIES; i++) {
+                       const struct kapi_capability_spec *cap = 
&spec->capabilities[i];
+
+                       seq_printf(m, "  %s (%d):\n", cap->cap_name,
+                                  cap->capability);
+                       if (cap->allows && *cap->allows)
+                               seq_printf(m, "    allows: %s\n", cap->allows);
+                       if (cap->without_cap && *cap->without_cap)
+                               seq_printf(m, "    without: %s\n", 
cap->without_cap);
+               }
+               seq_puts(m, "\n");
+       }
+
+       /* Additional info */
+       if (spec->examples && *spec->examples) {
+               seq_puts(m, "Examples:\n");
+               print_block(m, spec->examples);
+               seq_putc(m, '\n');
+       }
+       if (spec->notes && *spec->notes) {
+               seq_puts(m, "Notes:\n");
+               print_block(m, spec->notes);
+               seq_putc(m, '\n');
+       }
+
+       return 0;
+}
+
+static int kapi_spec_open(struct inode *inode, struct file *file)
+{
+       return single_open(file, kapi_spec_show, inode->i_private);
+}
+
+static const struct file_operations kapi_spec_fops = {
+       .open = kapi_spec_open,
+       .read = seq_read,
+       .llseek = seq_lseek,
+       .release = single_release,
+};
+
+/*
+ * JSON view of a single spec.  kapi_export_json() writes straight into the
+ * seq_file buffer; when the output does not fit, flagging an overflow makes
+ * seq_file retry with a larger buffer, so no fixed size limit applies.
+ */
+static int kapi_spec_json_show(struct seq_file *m, void *v)
+{
+       const struct kernel_api_spec *spec = m->private;
+       size_t size;
+       char *buf;
+       int ret;
+
+       if (!spec)
+               return -EINVAL;
+
+       size = seq_get_buf(m, &buf);
+       ret = size ? kapi_export_json(spec, buf, size) : -E2BIG;
+       if (ret == -E2BIG) {
+               seq_commit(m, -1);
+               return 0;
+       }
+       if (ret < 0)
+               return ret;
+
+       seq_commit(m, ret);
+       return 0;
+}
+
+static int kapi_spec_json_open(struct inode *inode, struct file *file)
+{
+       return single_open(file, kapi_spec_json_show, inode->i_private);
+}
+
+static const struct file_operations kapi_spec_json_fops = {
+       .open = kapi_spec_json_open,
+       .read = seq_read,
+       .llseek = seq_lseek,
+       .release = single_release,
+};
+
+/*
+ * Show all available API specs.
+ *
+ * Note: This only iterates the static .kapi_specs section. Specs registered
+ * dynamically via kapi_register_spec() are not included in this listing
+ * or in the per-spec debugfs files.
+ */
+static int kapi_list_show(struct seq_file *m, void *v)
+{
+       const struct kernel_api_spec * const *pp;
+       int count = 0;
+
+       seq_puts(m, "Available Kernel API Specifications\n");
+       seq_puts(m, "===================================\n\n");
+
+       for (pp = __start_kapi_specs; pp < __stop_kapi_specs; pp++) {
+               const struct kernel_api_spec *spec = *pp;
+
+               if (!spec)
+                       continue;
+               seq_printf(m, "%s - %s\n", spec->name, spec->description);
+               count++;
+       }
+
+       seq_printf(m, "\nTotal: %d specifications\n", count);
+       return 0;
+}
+
+static int kapi_list_open(struct inode *inode, struct file *file)
+{
+       return single_open(file, kapi_list_show, NULL);
+}
+
+static const struct file_operations kapi_list_fops = {
+       .open = kapi_list_open,
+       .read = seq_read,
+       .llseek = seq_lseek,
+       .release = single_release,
+};
+
+static int __init kapi_debugfs_init(void)
+{
+       const struct kernel_api_spec * const *pp;
+       struct dentry *root, *spec_dir, *json_dir;
+
+       root = debugfs_create_dir("kapi", NULL);
+       debugfs_create_file("list", 0444, root, NULL, &kapi_list_fops);
+       spec_dir = debugfs_create_dir("specs", root);
+       json_dir = debugfs_create_dir("specs-json", root);
+
+       for (pp = __start_kapi_specs; pp < __stop_kapi_specs; pp++) {
+               const struct kernel_api_spec *spec = *pp;
+
+               if (!spec || !spec->name)
+                       continue;
+               debugfs_create_file(spec->name, 0444, spec_dir,
+                                   (void *)spec, &kapi_spec_fops);
+               debugfs_create_file(spec->name, 0444, json_dir,
+                                   (void *)spec, &kapi_spec_json_fops);
+       }
+
+       return 0;
+}
+
+/* Initialize as part of kernel, not as a module */
+fs_initcall(kapi_debugfs_init);
-- 
2.53.0


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