Re: [PATCH v9 1/9] kho: make debugfs interface optional

[Yanjun.Zhu]

On 11/12/25 5:41 PM, Yanjun.Zhu wrote:
> On 11/11/25 7:26 AM, Pasha Tatashin wrote:
> > On Mon, Nov 10, 2025 at 11:11 PM Zhu Yanjun <yanjun.zhu@xxxxxxxxx> 
> > wrote:
> > > In FC42, when I run "./luo_multi_session"
> > >
> > > # ./luo_multi_session
> > > # [STAGE 1] Starting pre-kexec setup for multi-session test...
> > > # [STAGE 1] Creating state file for next stage (2)...
> > > # [STAGE 1] Creating empty sessions 'multi-test-empty-1' and
> > > 'multi-test-empty-2'...
> > > # [STAGE 1] Creating session 'multi-test-files-1' with one memfd...
> > > # [STAGE 1] Creating session 'multi-test-files-2' with two memfds...
> > > # [STAGE 1] Executing kexec...
> > >
> > > Then the system hang. And via virt-viewer, a calltrace will appear.
> > Looks like mountroot fails, are you passing the same kernel parameters
> > as the during cold boot?
> > i.e. kexec -l -s --reuse-cmdline --initrd=[initramfs] [kernel]
>
>
> Thanks a lot. It can work now.  The logs are as below:
>
> "
>
> # [STAGE 2] Starting post-kexec verification...
> # [STAGE 2] Retrieving all sessions...
> # [STAGE 2] Verifying contents of session 'multi-test-files-1'...
> # [STAGE 2] Verifying contents of session 'multi-test-files-2'...
> # [STAGE 2] Test data verified successfully.
> # [STAGE 2] Finalizing all test sessions...
> # [STAGE 2] Finalizing state session...
> #
> --- MULTI-SESSION KEXEC TEST PASSED ---
> "
>
> Yanjun.Zhu


Hi, Pasha

In my tests, I found that luo_kexec_simple and luo_multi_session 
currently depend on the glibc-static library.
If this library is not installed, build errors occur.
By making the following changes, luo_kexec_simple and luo_multi_session 
would no longer depend on glibc-static, reducing external library 
dependencies.
I am not sure whether you agree with these proposed changes.

diff --git a/tools/testing/selftests/liveupdate/Makefile 
b/tools/testing/selftests/liveupdate/Makefile
index 6ee6efeec62d..b226b9976150 100644
--- a/tools/testing/selftests/liveupdate/Makefile
+++ b/tools/testing/selftests/liveupdate/Makefile
@@ -3,7 +3,6 @@
 KHDR_INCLUDES ?= -I../../../../usr/include
 CFLAGS += -Wall -O2 -Wno-unused-function
 CFLAGS += $(KHDR_INCLUDES)
-LDFLAGS += -static
 OUTPUT ?= .

 # --- Test Configuration (Edit this section when adding new tests) ---

Yanjun.Zhu

> > Pasha
> >
> > > The call trace is in the attachment.
> > >
> > > Yanjun.Zhu
> > >
> > > 在 2025/11/10 7:26, Pasha Tatashin 写道:
> > > > On Mon, Nov 10, 2025 at 8:16 AM Pratyush Yadav 
> > > > <pratyush@xxxxxxxxxx> wrote:
> > > > > On Sun, Nov 09 2025, Zhu Yanjun wrote:
> > > > >
> > > > > > 在 2025/11/8 10:13, Pasha Tatashin 写道:
> > > > > > > On Fri, Nov 7, 2025 at 6:36 PM Yanjun.Zhu <yanjun.zhu@xxxxxxxxx> 
> > > > > > > wrote:
> > > > > > > > On 11/7/25 4:02 AM, Pasha Tatashin wrote:
> > > > > > > > > On Fri, Nov 7, 2025 at 7:00 AM Pasha Tatashin 
> > > > > > > > > <pasha.tatashin@xxxxxxxxxx> wrote:
> > > > > > > > > > > Hi, Pasha
> > > > > > > > > > >
> > > > > > > > > > > In our previous discussion, we talked about counting the 
> > > > > > > > > > > number of times
> > > > > > > > > > > the kernel is rebooted via kexec. At that time, you 
> > > > > > > > > > > suggested adding a
> > > > > > > > > > > variable in debugfs to keep track of this count.
> > > > > > > > > > > However, since debugfs is now optional, where would be an 
> > > > > > > > > > > appropriate
> > > > > > > > > > > place to store this variable?
> > > > > > > > > > It is an optional config and can still be enabled if the live 
> > > > > > > > > > update
> > > > > > > > > > reboot number value needs to be accessed through debugfs. 
> > > > > > > > > > However,
> > > > > > > > > > given that debugfs does not guarantee a stable interface, 
> > > > > > > > > > tooling
> > > > > > > > > > should not be built to require these interfaces.
> > > > > > > > > >
> > > > > > > > > > In the WIP LUO [1] I have, I pr_info() the live update number 
> > > > > > > > > > during
> > > > > > > > > > boot and also store it in the incoming LUO FDT tree, which 
> > > > > > > > > > can also be
> > > > > > > > > > accessed through this optional debugfs interface.
> > > > > > > > > >
> > > > > > > > > > The pr_info message appears like this during boot:
> > > > > > > > > > [    0.000000] luo: Retrieved live update data, liveupdate 
> > > > > > > > > > number: 17
> > > > > > > > > >
> > > > > > > > > > Pasha
> > > > > > > > > Forgot to add link to WIP LUOv5:
> > > > > > > > > [1] https://github.com/soleen/linux/tree/luo/v5rc04
> > > > > > > > Thanks a lot. I’ve carefully read this commit:
> > > > > > > > https://github.com/soleen/linux/commit/60205b9a95c319dc9965f119303a1d83f0ff08fa. 
> > > > > > > >
> > > > > > > >
> > > > > > > > To be honest, I’d like to run some tests with who/luo, 
> > > > > > > > including the
> > > > > > > > selftest for kho/luo. Could you please share the steps with me?
> > > > > > > >
> > > > > > > > If the testing steps have already been documented somewhere, 
> > > > > > > > could you
> > > > > > > > please share the link?
> > > > > > > Currently the test performs in-kernel tests for FLB data, it 
> > > > > > > creates a
> > > > > > > number of FLB for every registered LUO file-handler, which at the
> > > > > > > moment is only memfd.
> > > > > > >
> > > > > > > It works together with any of the kexec based live update tests. In
> > > > > > > v5, I introduce two tests:
> > > > > > > luo_kexec_simple
> > > > > > > luo_multi_session
> > > > > > >
> > > > > > > For example, with luo_multi_session:
> > > > > > Hi, Pasha
> > > > > >
> > > > > > I enabled "CONFIG_LIVEUPDATE=y"
> > > > > >
> > > > > > # ./luo_multi_session
> > > > > > 1..0 # SKIP Failed to open /dev/liveupdate. Is the luo module 
> > > > > > loaded?
> > > > > >
> > > > > > # ls /dev/liveupdate
> > > > > > ls: cannot access '/dev/liveupdate': No such file or directory
> > > > > >
> > > > > > # grep "LIVEUPDATE" -inrHI /boot/config-`uname -r`
> > > > > > /boot/config-next-20251107-luo+:349:CONFIG_LIVEUPDATE=y
> > > > > > /boot/config-next-20251107-luo+:11985:CONFIG_LIVEUPDATE_TEST=y
> > > > > >
> > > > > > I made tests on FC42. But /dev/liveupdate is missing.
> > > > > You need to add liveupdate=1 to your kernel cmdline to enable LUO and
> > > > > get /dev/liveupdate.
> > > > +1, kernel parameters require: kho=1 liveupdate=1
> > > >
> > > > > Pasha, your LUO series doesn't add the liveupdate parameter to
> > > > > kernel-parameters.txt. I think it should be done in the next 
> > > > > version to
> > > > > this parameter is discoverable.
> > > > Yeah, that is missing, I will update that in a standalone patch, or in
> > > > a next version.
> > > >
> > > > Thanks,
> > > > Pasha
> > > --
> > > Best Regards,
> > > Yanjun.Zhu