From 9f0051263884783fa0f81a4800cbe0f30e856455 Mon Sep 17 00:00:00 2001
From: Hari Bathini <hbathini@linux.ibm.com>
Date: Thu, 17 Sep 2020 19:42:48 +0530
Subject: [PATCH 1/3] Add steps to compile a custom kernel and boot into it on
 coreos

---
 boot_custom_kernel.md | 57 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)
 create mode 100644 boot_custom_kernel.md

diff --git a/boot_custom_kernel.md b/boot_custom_kernel.md
new file mode 100644
index 0000000..289a548
--- /dev/null
+++ b/boot_custom_kernel.md
@@ -0,0 +1,57 @@
+# Steps/Commands to compile and boot into a custom kernel on RHCOS node:
+  
+  # cd /var/home/core
+  
+  # cat dockfile
+  FROM fedora:latest
+  
+  RUN dnf install -y kexec-tools make gcc git openssl-devel bison flex autoconf automake bc
+  # 
+  
+  *** Setup container image to build the kernel ***
+  # podman build -t fedora:build -f dockfile
+  
+  # cp /lib/modules/`uname -r`/config .
+  
+  # podman run -it -v /var/home/core:/root --privileged=true -- fedora:build bash
+  
+  *** Build the kernel in container ***
+  # cd /root
+  
+  # git clone --depth=1 git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
+  
+  # cp config linux/.config
+  
+  # cd linux
+  
+  # make oldconfig
+  
+  # make vmlinux; make modules
+  
+  # make INSTALL_MOD_STRIP=1 INSTALL_MOD_PATH=/root modules_install
+  
+  # cp vmlinux /root/vmlinux-<kver>
+  
+  # cp /sbin/kexec /root
+  
+  # exit
+  
+  *** Back to RHCOS host ***
+  
+  *** To build initrd image, pick dracut options from existing RHCOS initrd in /boot/ostree and use the same options,
+  *** plus "--kmoddir '/var/home/core/lib/modules/5.9.0-rc5'" to find the modules since we could not install kernel modules
+  *** at the usual place as /lib/modules directory is read-only.  ***
+  # mkdir /tmp/dracut
+  # dracut --reproducible --gzip -v --add 'ostree' --tmpdir '/tmp/dracut' -f --add 'ignition' --no-hostonly --add-drivers 'mptspi vmw_pvscsi' --omit-drivers 'nouveau' --omit 'nfs' --add 'iscsi' --add 'ifcfg' --add 'fips' --kmoddir '/var/home/core/lib/modules/<kver>' initramfs-<kver>.img <kver>
+  
+  ** Ready to load and kexec into the just built kernel ***
+  # ./kexec -l --append="`cat /proc/cmdline`" --initrd=initramfs-<kver>.img vmlinux-<kver>
+  
+  # ./kexec -e
+  
+  Note: After booting past initrd, 'modprobe' would fail to find modules as the modules for the custom kernel could not be placed in
+        /lib/modules directory (read-only) where they are looks for. Three options to workaround it:
+             a. Use alias "modprobe -d /var/home/core" for "modprobe"
+             b. Build the missing kernel modules into the initrd with add-drivers option
+             c. Compile the modules into the kernel (=y instead of =m)
+

From b4bcc7282478281a97add01ea8f73987747c11d9 Mon Sep 17 00:00:00 2001
From: Hari Bathini <hbathini@linux.ibm.com>
Date: Thu, 17 Sep 2020 19:52:30 +0530
Subject: [PATCH 2/3] Format the file that talks about steps to boot a custom
 kernel

---
 boot_custom_kernel.md | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/boot_custom_kernel.md b/boot_custom_kernel.md
index 289a548..a187e50 100644
--- a/boot_custom_kernel.md
+++ b/boot_custom_kernel.md
@@ -1,5 +1,6 @@
 # Steps/Commands to compile and boot into a custom kernel on RHCOS node:
-  
+
+```
   # cd /var/home/core
   
   # cat dockfile
@@ -54,4 +55,5 @@
              a. Use alias "modprobe -d /var/home/core" for "modprobe"
              b. Build the missing kernel modules into the initrd with add-drivers option
              c. Compile the modules into the kernel (=y instead of =m)
+```
 

From 2606b3a13b0fc7300e28593219e2a2d4566696ec Mon Sep 17 00:00:00 2001
From: Hari Bathini <hbathini@linux.ibm.com>
Date: Mon, 28 Sep 2020 11:57:33 +0530
Subject: [PATCH 3/3] Use the conventional filename for Containerfile

---
 boot_custom_kernel.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/boot_custom_kernel.md b/boot_custom_kernel.md
index a187e50..34c14e0 100644
--- a/boot_custom_kernel.md
+++ b/boot_custom_kernel.md
@@ -3,14 +3,14 @@
 ```
   # cd /var/home/core
   
-  # cat dockfile
+  # cat Dockerfile
   FROM fedora:latest
   
   RUN dnf install -y kexec-tools make gcc git openssl-devel bison flex autoconf automake bc
   # 
   
   *** Setup container image to build the kernel ***
-  # podman build -t fedora:build -f dockfile
+  # podman build -t fedora:build -f Dockerfile
   
   # cp /lib/modules/`uname -r`/config .