On 02/01/2026 18:24, Breno Leitao wrote:
> Hello Usama,
>
> On Fri, Jan 02, 2026 at 06:09:57PM +0300, Usama Arif wrote:
>>
>> On 02/01/2026 17:53, Breno Leitao wrote:
>>> Track and display the number of kexec boots since the last cold reboot
>>> when CONFIG_KEXEC_HISTORY is enabled.
>>>
>>> This extends the previous kernel release tracking feature by adding
>>> a counter that increments with each kexec boot. The counter provides
>>> visibility into the kexec chain depth, which is useful for understanding
>>> boot history in production environments.
>>>
>>> Add a new property, "kexec-count" in KHO FDT alongside the existing
>>> "previous-release" property. The counter is:
>>>
>>> - Initialized to 0 when kho_in is instantiated.
>>> - Incremented by 1 on each subsequent kexec.
>>> - Printed alongside the previous kernel release version.
>>>
>>> The counter is stored as a 32-bit unsigned integer in FDT format and is
>>> only active when CONFIG_KEXEC_HISTORY is enabled.
>>>
>>> Signed-off-by: Breno Leitao <[email protected]>
>>> Suggested-by: Pasha Tatashin <[email protected]>
>>> ---
>>> kernel/liveupdate/kexec_handover.c | 25 +++++++++++++++++++++++--
>>> 1 file changed, 23 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/kernel/liveupdate/kexec_handover.c
>>> b/kernel/liveupdate/kexec_handover.c
>>> index 06d99627bb3c..fe5a2c5c4c86 100644
>>> --- a/kernel/liveupdate/kexec_handover.c
>>> +++ b/kernel/liveupdate/kexec_handover.c
>>> @@ -38,6 +38,7 @@
>>> #define PROP_PRESERVED_MEMORY_MAP "preserved-memory-map"
>>> #define PROP_SUB_FDT "fdt"
>>> #define PROP_PREVIOUS_RELEASE "previous-release"
>>> +#define PROP_KEXEC_COUNT "kexec-count"
>>>
>>> #define KHO_PAGE_MAGIC 0x4b484f50U /* ASCII for 'KHOP' */
>>>
>>> @@ -1257,6 +1258,7 @@ struct kho_in {
>>> phys_addr_t scratch_phys;
>>> #ifdef CONFIG_KEXEC_HISTORY
>>> char previous_release[__NEW_UTS_LEN + 1];
>>> + u32 kexec_count;
>>> #endif
>>> struct kho_debugfs dbg;
>>> };
>>> @@ -1330,6 +1332,9 @@ static __init int kho_out_fdt_setup(void)
>>> void *root = kho_out.fdt;
>>> u64 empty_mem_map = 0;
>>> int err;
>>> +#ifdef CONFIG_KEXEC_HISTORY
>>> + u32 kexec_count;
>>> +#endif
>>>
>>> err = fdt_create(root, PAGE_SIZE);
>>> err |= fdt_finish_reservemap(root);
>>> @@ -1340,6 +1345,10 @@ static __init int kho_out_fdt_setup(void)
>>> #ifdef CONFIG_KEXEC_HISTORY
>>> err |= fdt_property_string(root, PROP_PREVIOUS_RELEASE,
>>> init_uts_ns.name.release);
>>> + /* kho_in.kexec_count is set to 0 on cold boot */
>>> + kexec_count = cpu_to_fdt32(kho_in.kexec_count + 1);
>>
>> Should this be kexec_count = cpu_to_fdt32(kho_in.kexec_count) + 1; ?
>
> I don't think so. Basically we want to increment the counter in native
> endianess and then convert to the Big Endian (FDT/DT are big endian
> AFAIK) and then store (line below) to the DT.
>
> If we convert to big endian and then sum 1, it will mess with the
> result.
ack, Thanks for explaining, I didnt think of endianess!
>
>> + err |= fdt_property(root, PROP_KEXEC_COUNT, &kexec_count,
>>> + sizeof(kexec_count));
>
> Thanks for the review,
> --breno
