Re: Design for kexec/kexec-load system service

[RuiRui Yang]

Fix the list address.
On 05/12/20 at 12:10pm, Dave Young wrote:
>  Hi Bhupesh,
>  
>  Thanks for raising up the topic.
>  On 05/12/20 at 12:21am, Bhupesh Sharma wrote:
>  > Hi All,
>  > 
>  > Dave and I talked a bit last week about having a service for
>  > kexec/kexec-load similar to what we have for kdump right now in
>  > RHEL/Fedora (/usr/lib/systemd/system/kdump.service).
>  > My plan is to enable it first in Fedora and then in RHEL-8.
>  > 
>  > Now, similar two services 'kexec-load.service' and 'kexec.service'
>  > also exist in other distribution(s) like Suse (see:
>  >
> <https://documentation.suse.com/sles/15-SP1/html/SLES-all/cha-tuning-kexec...
>  > for example). I talked to a Suse guy privately today on IRC and he
>  > mentioned the following steps they use on Suse to run kexec:
>  > 
>  > To use Kexec, ensure the respective service is enabled and running:
>  > > sudo systemctl enable kexec-load.service
>  > > sudo systemctl start kexec-load.service
>  > 
>  > > systemctl kexec (try rebooting into a new Kernel with Kexec)
>  > 
>  > On our RHEL kexec-tools, we also seem to have a left-over 'kexec'
>  > service, but it seems broken currently. See some logs from my arm64
>  > board below:
>  > [root@cav-sabre-cn99xx-01 ~]# systemctl kexec
>  > Failed to open "/boot/efi/loader/loader.conf": No such file or directory
>  > Failed to read boot config from "/boot/efi/loader/loader.conf": No
>  > such file or directory
>  > Failed to load bootspec config from "/boot/efi/loader": No such file
>  > or directory
>  
>  It seems work fine on my x86 legacy vm.
>  
>  Actually we do not need to use systemctl kexec, just run "reboot" it
>  will go to kexec path automatically.
>  
>  > 
>  > So, I am thinking to having two services (similar to Suse) for Fedora
>  > and RHEL as well:
>  > - One for kexec-load (i.e. kexec -l or kexec -l -s),
>  > - Second for kexec'ing into 2nd kernel (i.e. kexec -e).
>  
>  The second one is up to systemd and installed by default so if we have
>  any bugs just open to systemd then.
>  
>  > 
>  > I wanted to get more opinions from the team about this (having 2
>  > services or 1, naming etc), before I send the first Fedora patch for
>  > review
>  > Here is some RFC code I have added so far:
>  > 
>  > For the 1st RFC, I am thinking of having a simple service like (it
>  > actually executes a new executable '/usr/sbin/kexecctl') :
>  > 
>  > /usr/lib/systemd/system/kexec-load.service
>  > ------------------------------------------------------------
>  > [Unit]
>  > Description=loads the kernel
>  > Documentation=man:kexec(8)
>  > DefaultDependencies=no
>  > Before=shutdown.target umount.target final.target
>  > 
>  > [Service]
>  > Type=oneshot
>  > ExecStart=/usr/sbin/kexecctl
>  
>  "kexectl"?  and maybe also need some "start" "stop"
> "restart" "reload" etc
>  
>  > 
>  > [Install]
>  > WantedBy=kexec.target
>  
>  The default behavior of systemctl kexec is 
>  
>  * run kexec reboot in case kexec kernel loaded
>  * otherwise just go to physical reboot
>  
>  So it is not strictly blocked by us:
>  https://lists.freedesktop.org/archives/systemd-devel/2012-March/004764.html
>  
>  But there are above discussion we can refer to.
>  
>  > 
>  > A simple implementation of ''/usr/sbin/kexecctl' looks like this (we
>  > can add further details as we go further):
>  > 
>  > /usr/sbin/kexecctl:
>  > -------------------------
>  > 
>  > standard_kexec_args="-l"
>  
>  It would be good to use a sysconfig like kdump so that people can tune
>  the args easily, eg.
>  
>  /etc/sysconfig/kexec
>  
>  > load_kexec()
>  > {
>  >     KEXEC_ARGS=$(prepare_kexec_args "${KEXEC_ARGS}")
>  > 
>  >    if [ "$KEXEC_FILE_LOAD" == "on" ]; then
>  >         echo "Using kexec file based syscall."
>  >         KEXEC_ARGS="$KEXEC_ARGS -s"
>  >     fi
>  > 
>  >     $KEXEC $KEXEC_ARGS $standard_kexec_args \
>  >          --initrd=$TARGET_INITRD $kdump_kernel
>  >     if [ $? == 0 ]; then
>  >         echo "kexec: loaded kexec kernel"
>  >         return 0
>  >     else
>  >         echo "kexec: failed to load kexec kernel" >&2
>  >         if [ "$KEXEC_FILE_LOAD" == "on" ]; then
>  >             echo "kexec_file_load() failed, please try kexec_load()"
> >&2
>  >         fi
>  >         return 1
>  >     fi
>  > }
>  > 
>  > Please help me by sharing your comments.
>  > 
>  > Thanks,
>  > Bhupesh
>  > 
>  
>  Thanks
>  Dave