In part 1 we setup the build environment for yocto build. In this part we actually setup yocto and do our basic build. Before we do there is a small update. When I was trying to build yocto I was hitting an error OSError: [Errno 23] Too many open files in system after 3-5 minutes after starting the build. Aparently virtiofs daemon keeps the file descriptor open on host system even after the VM has closed it. I had a discussion about this on a gitlab issue you can checkout here. TLDR is to use --inode-file-handles=mandatory

WARNING: this flag needs to be run as sudo so the qemu command also needs to be run as sudo else you get error Failed to connect to '/tmp/vm-share.sock': Permission denied

So new virtiofsd commands would be following

# If your `uid,gid` is 1000
sudo /usr/lib/virtiofsd \
  --inode-file-handles=mandatory \
  --socket-path=/tmp/vm-share.sock \
  --shared-dir="$HOME/yocto"

# If your `uid,gid` is not 1000
sudo /usr/lib/virtiofsd \
  --inode-file-handles=mandatory \
  --socket-path=/tmp/vm-share.sock \
  --shared-dir="$HOME/yocto" \
  --sandbox namespace \
  --uid-map ":1000:<uid>:1:" \
  --gid-map ":1000:<gid>:1:"

fstab entry for automount

The part 1 we ended by mounting the virtiofs shared partition. This can get annoying as you have to type the mount command each time you start the VM. So we setup fstab entry for it to automount.

1. Start the virtiofsd /usr/lib/virtiofsd --socket-path=/t..
2. Start the VM qemu-system-x86_64 -enable-kvm...
3. SSH into the VM ssh vmUsername@localhost -p 2222
4. Open fstab file in editor: vim /etc/fstab
5. Add following at the end, make sure to replace the username

   myfs   /home/<vmUsername>/yocto   virtiofs   defaults   0   0

6. Evaluate the mounts: sudo mount -a
7. Verify mount: sudo mount | grep virtiofs

Yocto build

Now its time to do a yocto build for beaglebone black

Setup poky

All the commands are supposed to be run on HOST machine. For VM it will be specified

1. We'll get the poky sources for scarthgap.

   # cd into the yocto dir
   cd ~/yocto
   
   # clone poky
   git clone -b scarthgap https://git.yoctoproject.org/poky

2. Switch to VM and source the oe-init-build-env.

   # RUN in VM
   cd ~/yocto/poky
   
   # I like to keep the build outside the poky dir, thats why ../build
   source oe-init-build-env ../build

3. Now on host machine, we can look into the local.conf file and change the machine to beaglebone black

   # cd into the yocto conf dir
   cd ~/yocto/build/conf
   
   # open the local.conf in editor
   vim local.conf
   
   # Look for following line, it will be commented. Uncomment it
   MACHINE ?= "beaglebone-yocto"

4. We are finally good to start the build. Switch back to VM and start the build

   # RUN in VM
   
   # Invoke bitbake to build the core-image-minimal
   # The -k flag keeps the build to continue if some error occur
   bitbake -k core-image-minimal

core-image-minimal build

If you did everything right you should see following when start bitbake.

Build Configuration:
BB_VERSION           = "2.8.1"
BUILD_SYS            = "x86_64-linux"
NATIVELSBSTRING      = "universal"
TARGET_SYS           = "arm-poky-linux-gnueabi"
MACHINE              = "beaglebone-yocto"
DISTRO               = "poky"
DISTRO_VERSION       = "5.0.18"
TUNE_FEATURES        = "arm vfp cortexa8 neon callconvention-hard"
TARGET_FPU           = "hard"
meta                 
meta-poky            
meta-yocto-bsp       = "scarthgap:44dcf08572ce391d7c0df4f8c7510af5e096baca"

Make sure you have MACHINE = "beaglebone-yocto". If you do CONGRATULATIONS 🎉 you have the correct setup. Now its going to build over 4K packages so gonna take a while.

If you build fails for some reason, mostly likely it will be fine, you just need to restart the build. In some cases you get repeated error from a particular package, you just clean it and redo the build bitbake -c cleansstate <package_name>