Notes for building KVM-based virtualization components from upstream git

I frequently need to have latest KVM, QEMU, libvirt and libguestfs while testing with OpenStack RDO. I either build from upstream git master branch or from Fedora Rawhide (mostly this suffices). Below I describe the exact sequence I try to build from git. These instructions are available in some form in the README files of the said packages, just noting them here explicitly for convenience. My primary development/test environment is Fedora, but it should be similar on other distributions. (Maybe I should just script it all.)

Build KVM from git

I think it’s worth noting the distinction (from traditional master branch) of these KVM git branches: remotes/origin/queue and remotes/origin/next. queue and next branches are same most of the time with the distinction that KVM queue is the branch where patches are usually tested before moving them to the KVM next branch. And, commits from next branch are submitted (as a PULL request) to Linus during the next Kernel merge window. (I recall this from an old conversation with Gleb Natapov (thank you), one of the previous KVM maintainers on IRC).

# Clone the repo
$ git clone \
  git://git.kernel.org/pub/scm/virt/kvm/kvm.git

# To test out of tree patches,
# it's cleaner to do in a new branch
$ git checkout -b test_branch

# Make a config file
$ make defconfig

# Compile
$ make -j4 && make bzImage && make modules

# Install
$ sudo -i
$ make modules_install && make install

Build QEMU from git

To build QEMU (only x86_64 target) from its git:

# Install buid dependencies of QEMU
$ yum-builddep qemu

# Clone the repo
$ git clone git://git.qemu.org/qemu.git

# Create a build directory to isolate source directory 
# from build directory
$ mkdir -p ~/build/qemu && cd ~/build/qemu

# Run the configure script
$ ~/src/qemu/./configure --target-list=x86_64-softmmu \
  --disable-werror --enable-debug 

# Compile
$ make -j4

I previously discussed about QEMU building here.

Build libvirt from git

To build libvirt from its upstream git:

# Install build dependencies of libvirt
$ yum-builddep libvirt

# Clone the libvirt repo
$ git clone git://libvirt.org/libvirt.git && cd libvirt

# Create a build directory to isolate source directory
# from build directory
$ mkdir -p ~/build/libvirt && cd ~/build/libvirt

# Run the autogen script
$ ../src/libvirt/autogen.sh

# Compile
$ make -j4

# Run tests
$ make check

# Invoke libvirt programs without having to install them
$ ./run tools/virsh [. . .]

[Or, prepare RPMs and install them]

# Make RPMs (assumes Fedora `rpmbuild` setup
# is properly configured)
$ make rpm

# Install/update
$ yum update *.rpm

Build libguestfs from git
To build libguestfs from its upstream git:

# Install build dependencies of libvirt
$ yum-builddep libguestfs

# Clone the libguestfs repo
$ git clone git://github.com/libguestfs/libguestfs.git \
   && cd libguestfs

# Run the autogen script
$ ./autogen.sh

# Compile
$ make -j4

# Run tests
$ make check

# Invoke libguestfs programs without having to install them
$ ./run guestfish [. . .]

If you’d rather prefer libguestfs to use the custom QEMU built from git (as noted above), QEMU wrappers are useful in this case.

Alternate to building from upstream git, if you’d prefer to build the above components locally from Fedora master here are some instructions .

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Resize a fedora 19 guest with libguestfs tools

The inimitable Rich Jones writes some incredibly useful software. I can’t count how many times they helped me debugging disk images, or gave great insights into different aspects of linux virtualization. One of those instances again — I had to resize my OpenStack Fedora guest as its root file system merely had 5.4 GB to start with. So, I wanted to add atleast 15 GB more. After a bit of trial & error, here’s how I got it working. I’m using Fedora-19 in this case, but any other distro which supports libguestfs should be just fine.

Firstly, let’s check disk space inside the guest:

$ df -hT
    Filesystem              Type      Size  Used Avail Use% Mounted on
    /dev/mapper/fedora-root ext4      5.4G  5.4G     0 100% /
    devtmpfs                devtmpfs  4.7G     0  4.7G   0% /dev
    tmpfs                   tmpfs     4.7G     0  4.7G   0% /dev/shm
    tmpfs                   tmpfs     4.7G  392K  4.7G   1% /run
    tmpfs                   tmpfs     4.7G     0  4.7G   0% /sys/fs/cgroup
    tmpfs                   tmpfs     4.7G  472K  4.7G   1% /tmp
    /dev/vda1               ext4      477M   87M  365M  20% /boot
    /dev/loop0              ext4      4.6G   10M  4.4G   1% /srv/node/device1
    /dev/loop1              ext4      4.6G   10M  4.4G   1% /srv/node/device2
    /dev/loop2              ext4      4.6G   10M  4.4G   1% /srv/node/device3
    /dev/loop3              ext4      4.6G   10M  4.4G   1% /srv/node/device4
    /dev/vdb                ext4       17G   44M   16G   1% /mnt/newdisk

Print the libvirt XML to get the source of the disk

$ virsh dumpxml f19-test | grep -i source
      <source file='/var/lib/libvirt/images/f19-test.qcow2'/>

Above, I’m using a qcow2 disk image, I converted it to raw:

$ qemu-img convert -f qcow2 -O raw \
  /var/lib/libvirt/images/f19-test.qcow2 \
  /var/lib/libvirt/images/f19-test.raw

List the filesystems, partitions, block devices inside the raw disk image:

$ virt-filesystems --long --all -h -a \ 
  /var/lib/libvirt/images/f19-test.raw
Name              Type        VFS   Label  MBR  Size  Parent
/dev/sda1         filesystem  ext4  -      -    500M  -
/dev/fedora/root  filesystem  ext4  -      -    5.6G  -
/dev/fedora/swap  filesystem  swap  -      -    3.9G  -
/dev/fedora/root  lv          -     -      -    5.6G  /dev/fedora
/dev/fedora/swap  lv          -     -      -    3.9G  /dev/fedora
/dev/fedora       vg          -     -      -    9.5G  /dev/sda2
/dev/sda2         pv          -     -      -    9.5G  -
/dev/sda1         partition   -     -      83   500M  /dev/sda
/dev/sda2         partition   -     -      8e   9.5G  /dev/sda
/dev/sda          device      -     -      -    10G   -

Now, extend the file size of the raw disk image, using truncate:

# Create a new file based on original
$ truncate -r f19-test.raw f19-test.raw.new
# Adjust the new file size to 15G
$ truncate -s +15G f19-test.raw.new

List the file system partition info to find out the block device name:

$ virt-filesystems --partitions \
  --long -h -a f19-test.raw
Name       Type       MBR  Size  Parent
/dev/sda1  partition  83   500M  /dev/sda
/dev/sda2  partition  8e   9.5G  /dev/sda

Now, resize the new disk image using virt-resize. Note that, the --lv-expand option expands the root file system (thx Rich!):

$ virt-resize --expand /dev/sda2 --lv-expand \
  /dev/fedora/root f19-test.raw f19-test.raw.new
    Examining f19-test.raw ...
    **********
    
    Summary of changes:
    
    /dev/sda1: This partition will be left alone.
    
    /dev/sda2: This partition will be resized from 9.5G to 24.5G.  The LVM 
        PV on /dev/sda2 will be expanded using the 'pvresize' method.
    
    /dev/fedora/root: This logical volume will be expanded to maximum size. 
         The filesystem ext4 on /dev/fedora/root will be expanded using the 
        'resize2fs' method.
    
    **********
    Setting up initial partition table on f19-test.raw.new ...
    Copying /dev/sda1 ...
     100% ⟦▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒⟧ 00:00
    Copying /dev/sda2 ...
     100% ⟦▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒⟧ 00:00
    Expanding /dev/sda2 using the 'pvresize' method ...
    Expanding /dev/fedora/root using the 'resize2fs' method ...
    
    Resize operation completed with no errors.  Before deleting the old 
    disk, carefully check that the resized disk boots and works correctly.

Now, the size of the both new guests

$ ls -lash f19-test.raw f19-test.raw.new
2.7G -rw-r--r--. 1 qemu qemu 10G Apr 10 11:12 f19-test.raw
11G -rw-r--r--. 1 root root 25G Apr 10 12:13 f19-test.raw.new

Replace the old one w/ new one (you might want to take backup of the old one here, just in case):

$ mv f19-test.raw.new f19-test.raw

Also, update the libvirt XML file of the guest to reflect the raw disk image:

# Update source file path
$ virsh edit f19-test 
# grep the xml file to ensure.
$ grep source /etc/libvirt/qemu/f19-test.xml 
	
	

List file systems inside the newly created guest:

$ virt-filesystems --partitions --long -h -a f19-test.raw
Name       Type       MBR  Size  Parent
/dev/sda1  partition  83   500M  /dev/sda
/dev/sda2  partition  8e   25G   /dev/sda

Start the guest & ensure if everything looks sane:

$ virsh start f19-test --console