Re: [RFC PATCH 00/39] sysctl: replace overloaded extra pointers with typed bounds and context

[Wen Yang <wen.yang@linux.dev>]

On 11/11/26 19:55, Joel Granados wrote:
> On Wed, Nov 11, 2026 at 01:45:15AM +0800, Wen Yang wrote:
>>
>>
>> On 11/9/26 18:07, Joel Granados wrote:
>>> On Sat, Nov 07, 2026 at 05:05:07PM +0000, David Laight wrote:
>>>> On Sat, 7 Nov 2026 16:27:39 +0100
>>>> Joel Granados <joel.granados@kernel.org> wrote:
>>>>
>>>>> On Mon, Nov 02, 2026 at 11:40:40PM +0800, Wen Yang wrote:
>>>>>>
>>>>>>
>>>>>> On 10/29/26 18:58, David Laight wrote:
>>>>>>> On Thu, 29 Oct 2026 00:34:39 +0800
>>>>>>> wen.yang@linux.dev wrote:
>>>>>>>> From: Wen Yang <wen.yang@linux.dev>
>>>>>>>>
>>>>>>>> struct ctl_table describes an entry with data, maxlen and, until this
>>>>>>>> series, two untyped misc pointers in extra1 and extra2. Those two pointers
>>>>>>>> have accumulated at least seven unrelated jobs: a fixed bound, a bound read
>>>>>>>> through a pointer on every call, an object or namespace pointer, a small
>>>>>>>> integer cookie encoded into the pointer, a lock signal, NULL standing for
>>>>>>>> "no bound", and a value the core itself casts to unsigned int while
>>>>>>>> validating a u8 range. Nothing in the entry says which job applies, so
>>>>>>>> readers infer it from the handler, and the core gets it wrong where it
>>>>>>>> treats extra1 as an unsigned int.
>>>>> <--- snip --->
> <--- snip --->
>>    for (i = 0; i < head->ctl_table_size; i++) {
>>            entry = sysctl_entry_at(head, i);
>>            node = &head->node[i];
>>            ...
>>    }
>>
>> Insertion/deletion would take the node directly. Readdir would retain
>> its RB-tree node cursor, recovering each entry through that node's header:
>>
>>      entry = sysctl_entry_at(node->header, node - node->header->node);
>>
>> No entry - head->ctl_table, caller slot constants or per-slot wrappers.
>> RB-tree order remains unchanged. Old APIs and generated directory/link
>> tables use sizeof(struct ctl_table).
>>
>> The two mechanisms have existing precedents:
>>
>>    /* include/linux/bsearch.h: explicit element size */
>>    pivot = base + (num >> 1) * size;
>>    result = cmp(key, pivot);
>>
>>    /* include/linux/hwmon-sysfs.h: extended descriptor */
>>    struct sensor_device_attribute {
>>            struct device_attribute dev_attr;
>>            int index;
>>    };
>>
>>    /* drivers/hwmon/adcxx.c: ordinary device_attribute callback */
>>    const struct sensor_device_attribute *attr = to_sensor_dev_attr(devattr);
>>
>> hwmon registers &ad_input[i].dev_attr via device_create_file(); the core
>> passes that same base descriptor to the callback. These are precedents
>> for explicit-size traversal and embedded callback context separately,
>> not an existing strided sysctl registration API.
>>
>> I agree that my fixed-slot solution adds maintenance overhead. Would
>> it make sense to explore this in three small steps?
>>
>>    1. Entry-access helpers, unchanged packed layout.
>>    2. Header stride and compatible registration wrappers.
>>    3. nf_log conversion and code/memory comparison.
>>
>> I would appreciate your thoughts on whether this is worth pursuing.
> 
> Hey Wen
> 
> Without a series, it is hard to see how everything fits. Maybe you can
> send out an RFC with just the changes to the sysctl core and one or two
> examples of how it would be used in the more involved users.
> 
> The rest of the users can be "vibe coded" (so it compiles) and put into
> one big commit that we will ignore for the first RFC. Just so we get a
> clear idea of what you mean.
> 
> Tell me what you think
> 

Thanks.

That makes total sense. I will prepare a focused RFC series based on
the next-20261111 structured as follows:

Patch 1: sysctl: add numeric bounds and core stride infrastructure
(ctl_table_stride in header, sysctl_entry_at(), register_*_stride())

Patch 2: sysctl: cover numeric bounds and table containers in KUnit

Patch 3: netfilter: embed logger sysctl context using stride
(demonstrates the use of container_of(), and also eliminating some 
wrapper functions)

Patch 4: net/ipv4: embed device sysctl context using stride
(demonstrates the use of container_of(), and also eliminating some 
wrapper functions)

Patch 5: scripts/coccinelle: add script to detect and convert sysctl bounds
(provides automatic conversion and proves that no extra1/extra2 fields 
remain)


The ctl_table_stride and type are packed as u16 in struct 
ctl_table_header, yielding zero size increas.

I will send out this v2 RFC shortly for review.



--
Best wishes,
Wen