Re: [PATCH] vmcoreinfo: export SECTION_HAS_MEM_MAP

[David Hildenbrand (Arm)]

On 9/28/26 11:11, Baoquan He wrote:
> On 09/28/26 at 10:48am, David Hildenbrand (Arm) wrote:
>> The crash tool currently hardcodes SECTION_HAS_MEM_MAP, and makedumpfile
>> needs similar information (although still relying on
>> SECTION_MARKED_PRESENT, it should switch to SECTION_HAS_MEM_MAP).
>>
>> Let's just export the value instead, so tools that work on vmcoreinfo
>> will not have to guess.
>>
>> Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
>> ---
>> Result of the discussion in reply to "[PATCH v2 00/13] mm/sparse: remove
>> SECTION_MARKED_PRESENT and further cleanups" [1]
>>
>> This patch can go in independently. It would be preferable if both
>> go into the same kernel release ;)
>>
>> [1] https://lore.kernel.org/r/20260921-b4-sparsemem_cleanups-v2-0-54d81d65e125@xxxxxxxxxx 
>> ---
>>  kernel/vmcore_info.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/kernel/vmcore_info.c b/kernel/vmcore_info.c
>> index 5a417f8a922a..7833a36064a8 100644
>> --- a/kernel/vmcore_info.c
>> +++ b/kernel/vmcore_info.c
>> @@ -182,6 +182,7 @@ static int __init crash_save_vmcoreinfo_init(void)
>>  	VMCOREINFO_STRUCT_SIZE(mem_section);
>>  	VMCOREINFO_OFFSET(mem_section, section_mem_map);
>>  	VMCOREINFO_NUMBER(SECTION_SIZE_BITS);
>> +	VMCOREINFO_NUMBER(SECTION_HAS_MEM_MAP);
>>  	VMCOREINFO_NUMBER(MAX_PHYSMEM_BITS);
>>  #endif
>>  	VMCOREINFO_STRUCT_SIZE(page);
> 
> It would be good to add one section in
> Documentation/admin-guide/kdump/vmcoreinfo.rst, e.g
> 
> SECTION_HAS_MEM_MAP
> -------------------
> 
> Indicates a memory section has struct page array (mem_map). User-space
> tools should read this value but not hardcode it since the bit position
> could change between kernel versions.

I'm not particularly happy about having core-kernel defines documented in
kdump/vmcoreinfo.rst, though?

If it would be something vmcoreinfo special, sure. But not for basic defines.

"See the kernel source code" is really what anybody using this should be doing?

-- 
Cheers,

David