Re: [PATCH] kernel-doc: add support for handling global variables

[Randy Dunlap <rdunlap@infradead.org>]

On 9/9/25 9:18 AM, Mauro Carvalho Chehab wrote:
> On Tue, Sep 09, 2025 at 08:57:07AM -0700, Randy Dunlap wrote:
>> Hi Mauro,
>>
>> On 9/9/25 12:27 AM, Randy Dunlap wrote:
>>> Hi Mauro,
>>>
>>> I have a few patch nits below, then some testing info.
>>>
>>>
>>> On 9/7/25 9:22 AM, Mauro Carvalho Chehab wrote:
>>>> Specially on kAPI, sometimes it is desirable to be able to
>>>> describe global variables that are part of kAPI.
>>>>
>>>> Documenting vars with Sphinx is simple, as we don't need
>>>> to parse a data struct. All we need is the variable
>>>> declaration and use natice C domain ::c:var: to format it
>>>> for us.
>>>>
>>>> Add support for it.
>>>>
>>>> Link: https://lore.kernel.org/linux-doc/491c3022-cef8-4860-a945-c9c4a3b63c09@infradead.org/T/#m947c25d95cb1d96a394410ab1131dc8e9e5013f1
>>>> Suggested-by: Randy Dunlap <rdunlap@infradead.org>
>>>> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
>>>> ---
>>>>  scripts/lib/kdoc/kdoc_output.py | 31 +++++++++++++++++++++++++++++++
>>>>  scripts/lib/kdoc/kdoc_parser.py | 25 ++++++++++++++++++++++++-
>>>>  2 files changed, 55 insertions(+), 1 deletion(-)
>>>>
>>
>>
>>> So, I grabbed some global data from 6-8 places in the kernel and put them intoinit/kdoc-globals-test.c. Then I modified Documentation/core-api/kernel-api.rst
>>> like this at the end of that file:
>>>
>>> +
>>> +Kernel Globals
>>> +==========================
>>> +
>>> +.. kernel-doc:: init/kdoc-globals-test.c
>>> +   :identifiers:
>>>
>>> The html output says
>>> "Kernel Globals"
>>> but nothing else.
>>>
>>> My test files are attached. I dumbed down (simplified) a few
>>> of the globals from fancy types to just unsigned long, but that
>>> didn't help the output results any.
>>>
>>> What's happening?
>>> Thanks.
>>>
>>
>> My problems here could be from a patch mis-merge.
>> Maybe your patch was against a tree or previous patches that I don't have.
>>
>> You could supply an updated patch or I can just wait until all
>> the patches are synchronized for further testing.
>> Or you could just take my sample and keep testing it.
> 
> I applied it after my sphinx-build-wrapper patch series,
> but it doesn't touch kernel-doc. I did a rebase just to make
> sure, on the top of docs-next branch from Jon's tree, e.g. 
> on the top of:
> 
>     git://git.lwn.net/linux.git docs-next
> 
> e.g. applying it after:
> 
>     7e5a0fe4e8ae ("doc: filesystems: proc: remove stale information from intro")
> 
> Patch applied cleanly.
> 
> Notice that it probably depends on some changes that Jon
> applied for kernel-doc after -rc1.
> 
> If you prefer, the patch is here at global_vars branch:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-docs.git/log/?h=global_vars

Yes, this is much better.

For the simplified global data, it's very good. It produces
2 complaints but the html output is still good:

linux-next-20250909/Documentation/core-api/kernel-api:435: ../init/kdoc-globals-test.c:10: WARNING: Invalid C declaration: Expected end of definition. [error at 32]
  enum system_states system_state __read_mostly;
  --------------------------------^
linux-next-20250909/Documentation/core-api/kernel-api:435: ../init/kdoc-globals-test.c:20: WARNING: Invalid C declaration: Expected end of definition. [error at 25]
  char *saved_command_line __ro_after_init;
  -------------------------^

I suspect that this is not a surprise to you.

For the non-simplified global data, a few of the global items are
completely omitted from the html output. This is the html production:

Kernel Globals
dev_t ROOT_DEV;
system root device

enum system_states system_state __read_mostly;
system state used during boot or suspend/hibernate/resume

char *saved_command_line __ro_after_init;
kernel’s command line, saved from use at any later time in the kernel.

unsigned long preset_lpj;
lpj (loops per jiffy) value set from kernel command line using “lpj=VALUE”

static atomic64_t diskseq;
unique sequence number for block device instances


so these are completely missing/dropped: (they have
initializers or use DEFINE_MUTEX())

/**
 * global loop_per_jiffy - calculated loop count needed to consume one jiffy
 * of time
 */
unsigned long loops_per_jiffy = (1<<12);

// from init/version.c:
/**
 * global linux_proc_banner - text used from /proc/version file
 *
 * * first %s is sysname (e.g., "Linux")
 * * second %s is release
 * * third %s is version
 */
const char linux_proc_banner[] =
	"%s version %s"
	" (" LINUX_COMPILE_BY "@" LINUX_COMPILE_HOST ")"
	" (" LINUX_COMPILER ") %s\n";
//char linux_proc_banner[];

// from init/version-timestamp.c:
/**
 * global linux_banner - Linux boot banner, usually printed at boot time
 */
const char linux_banner[] =
	"Linux version " UTS_RELEASE " (" LINUX_COMPILE_BY "@"
	LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION "\n";
//const char linux_banner[];

// from net/core/rtnetlink.c:
/**
 * global rtnl_mutex - historical global lock for networking control operations.
 *
 * @rtnl_mutex is used to serialize rtnetlink requests
 * and protect all kernel internal data structures related to networking.
 *
 * See Documentation/networking/netdevices.rst for details.
 * Often known as the rtnl_lock, although rtnl_lock is a kernel function.
 */
static DEFINE_MUTEX(rtnl_mutex);


It's looking good. Thanks.

-- 
~Randy