Re: [PATCH v3 2/9] kernel/api: enable kerneldoc-based API specifications

[Nicolas Schier <nsc@kernel.org>]

On Fri, Apr 24, 2026 at 12:51:22PM -0400, Sasha Levin wrote:
> This patch adds support for extracting API specifications from
> kernel-doc comments and generating C macro invocations for the
> kernel API specification framework.
> 
> Changes include:
> - New kdoc_apispec.py module for generating API spec macros
> - Updates to kernel-doc.py to support -apispec output format
> - Build system integration in Makefile.build
> - Generator script for collecting all API specifications
> - Support for API-specific sections in kernel-doc comments
> 
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  Documentation/dev-tools/kernel-api-spec.rst |   11 +
>  scripts/Makefile.build                      |   31 +
>  scripts/Makefile.clean                      |    3 +
>  tools/docs/kernel-doc                       |    5 +
>  tools/lib/python/kdoc/kdoc_apispec.py       | 1249 +++++++++++++++++++
>  tools/lib/python/kdoc/kdoc_output.py        |    9 +-
>  tools/lib/python/kdoc/kdoc_parser.py        |   86 +-
>  7 files changed, 1389 insertions(+), 5 deletions(-)
>  create mode 100644 tools/lib/python/kdoc/kdoc_apispec.py
> 
> diff --git a/Documentation/dev-tools/kernel-api-spec.rst b/Documentation/dev-tools/kernel-api-spec.rst
> index 395c2294d5209..479bc78797ba8 100644
> --- a/Documentation/dev-tools/kernel-api-spec.rst
> +++ b/Documentation/dev-tools/kernel-api-spec.rst
> @@ -239,6 +239,17 @@ execution context, and return values. Parameter violations are reported via
>  ``pr_warn_ratelimited`` and return value violations via ``WARN_ONCE`` to avoid
>  flooding the kernel log.
>  
> +.. warning::
> +
> +   Userspace errno is affected when this option is on. For syscalls that
> +   violate their parameter specification, KAPI short-circuits the call and
> +   returns ``-EINVAL`` from the validator **before** the real handler runs.
> +   That errno can differ from what the real handler would have produced for
> +   the same condition (for example, ``-ENOMEM`` from an allocation path or
> +   ``-EFAULT`` from a deeper copy-in). ``CONFIG_KAPI_RUNTIME_CHECKS`` is a
> +   debug-only option; do not enable it on production kernels or in
> +   userspace-visible test environments where error-code fidelity matters.
> +
>  Custom Validators
>  -----------------
>  
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 3652b85be5459..ef203e490c797 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -174,6 +174,37 @@ ifneq ($(KBUILD_EXTRA_WARN),)
>  endif
>  endif
>  
> +# Generate API spec headers from kernel-doc comments
> +ifeq ($(CONFIG_KAPI_SPEC),y)
> +# Function to check if a file has API specifications
> +has-apispec = $(shell grep -qE '^\s*\*\s*context-flags:' $(src)/$(1) 2>/dev/null && echo $(1))
> +
> +# Get base names without directory prefix
> +c-objs-base := $(notdir $(real-obj-y) $(real-obj-m))
> +# Filter to only .o files with corresponding .c source files
> +c-files := $(foreach o,$(c-objs-base),$(if $(wildcard $(src)/$(o:.o=.c)),$(o:.o=.c)))

Looks to me as if the two lines above are redundant, since 'find'
(below) will find all files gathered in $(c-files).


> +# Also check for any additional .c files that contain API specs but are included
> +extra-c-files := $(shell find $(src) -maxdepth 1 -name "*.c" -exec grep -l '^\s*\*\s*\(long-desc\|context-flags\|state-trans\):' {} \; 2>/dev/null | xargs -r basename -a)
> +# Combine both lists and remove duplicates
> +all-c-files := $(sort $(c-files) $(extra-c-files))
> +# Only include files that actually have API specifications
> +apispec-files := $(foreach f,$(all-c-files),$(call has-apispec,$(f)))
> +# Generate apispec targets with proper directory prefix
> +apispec-y := $(addprefix $(obj)/,$(apispec-files:.c=.apispec.h))

To goal is to find any relevant C file in $(src)/ (but not deeper below)
that holds KAPI documentation, right?

I do not like the find call, as it picks up anything.  Might it make
sense to evaluate $(obj-) along with $(obj-y) and $(obj-m) to pick up
all C files that are references in kbuild?



# in top definition block -- before 'include $(kbuild-file)' et al.
obj- :=

# below the definitions of real-obj-{y,m}
real-obj-any := $(call real-search, $(obj-y) $(obj-m) $(obj-), .o, -objs -y -m -)

has-apispec = $(shell grep -lE '^\s*\*\s*context-flags:' $(1) 2>/dev/null)
apispec-y := $(patsubst $(src)/%.c, $(obj)/%.apispec.h, $(call has-apispec,
		    $(patsubst $(obj)/%.o, $(src)/%.c, $(real-obj-any))))

#...

# Source files that include their own apispec.h need to depend on it
$(apispec-y:.apispec.h=.o): $(obj)/%.o: $(obj)/%.apispec.h

(untested)

> +always-y += $(apispec-y)
> +targets += $(apispec-y)
> +
> +quiet_cmd_apispec = APISPEC $@
> +      cmd_apispec = PYTHONDONTWRITEBYTECODE=1 $(KERNELDOC) -apispec \
> +                    $(KDOCFLAGS) $< > $@ || rm -f $@
> +
> +$(obj)/%.apispec.h: $(src)/%.c $(KERNELDOC) FORCE
> +	$(call if_changed,apispec)
> +
> +# Source files that include their own apispec.h need to depend on it
> +$(foreach f,$(apispec-files),$(eval $(obj)/$(f:.c=.o): $(obj)/$(f:.c=.apispec.h)))
> +endif
> +
>  # Compile C sources (.c)
>  # ---------------------------------------------------------------------------
>  
> diff --git a/scripts/Makefile.clean b/scripts/Makefile.clean
> index 6ead00ec7313b..f78dbbe637f27 100644
> --- a/scripts/Makefile.clean
> +++ b/scripts/Makefile.clean
> @@ -35,6 +35,9 @@ __clean-files   := $(filter-out $(no-clean-files), $(__clean-files))
>  
>  __clean-files   := $(wildcard $(addprefix $(obj)/, $(__clean-files)))
>  
> +# Also clean generated apispec headers (computed dynamically in Makefile.build)
> +__clean-files   += $(wildcard $(obj)/*.apispec.h)

We have a list of wildcard clean patterns in top-level Makefile
(line 2114 ff.); please add '*.apispec.h' there instead.



When I apply the series on top of v7.1, compilation fails with

../fs/open.c:2148:10: fatal error: open.apispec.h: No such file or directory
../fs/read_write.c:2519:10: fatal error: read_write.apispec.h: No such file or directory

Kind regards,
Nicolas