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Qemu

1. Host System

Prepare host system for virtual machines, this includes create new user, loading necessary modules and configure network. Load kvm module, in this example intel module is loaded but depends on host cpu;

        # modprobe -a kvm-intel tun virtio

Add users to kvm group;

        # usermod -a -G kvm c9admin
        # usermod -a -G kvm username

2. Disk images

Qemu supports multiple disk images types.

img: Raw disk image, allows dd to a physical device.
raw: Raw disk image, allows dd to a physical device.
qcow2: Qcow disk image file used by qemu.

Create hard disk image, there is different types, this describes how to create a qcow2 type;

        $ qemu-img create -f qcow2 crux-img.qcow2 15G

2.1. Mount images

Qemu disk images can be treated as regular disks using qemu disk network block device server;

        $ sudo modprobe nbd
        $ sudo qemu-nbd -c /dev/nbd0 crux-img.qcow2

Information about preparing partitions and storage administration. You can use image as a normal disk, example how to use parted to create a gpt system table;

	parted --script ${DEV} \
	     mklabel gpt \
	     unit mib \
	     mkpart primary 2 4 \
	     name 1 grub \
	     mkpart ESP fat32 4 128 \
	     name 2 efi \
	     mkpart primary ext4 128 1128 \
	     name 3 boot \
	     mkpart primary ext4 1128 12128 \
	     name 4 root \
	     mkpart primary ext4 12128 14128 \
	     name 5 var \
	     mkpart primary ext4 14128 100% \
	     name 6 lvm \
	     set 1 bios_grub on \
	     set 2 boot on \
	     set 6 lvm on

        # kpartx -a -s -l -u /dev/nbd0

Use /dev/mapper/$(name_of_device) to assign correct blocks;

	mkfs.fat -F 32  /dev/mapper/${DEV_NAME}p2
	mkfs.ext4       /dev/mapper/${DEV_NAME}p3
	mkfs.ext4       /dev/mapper/${DEV_NAME}p4
	mkfs.ext4       /dev/mapper/${DEV_NAME}p5
	pvcreate        /dev/mapper/${DEV_NAME}p6

Read lvm documentation on how to setup virtual group and logic volumes.

Mount partition;

	mount /dev/mapper/${DEV_NAME}p4 $CHROOT
	mkdir -p $CHROOT/proc
	mkdir -p $CHROOT/sys
	mkdir -p $CHROOT/dev
	mkdir -p $CHROOT/media

	mkdir -p $CHROOT/boot
	mount /dev/mapper/${DEV_NAME}p3 $CHROOT/boot
	mkdir -p $CHROOT/boot/efi
	mount /dev/mapper/${DEV_NAME}p2 $CHROOT/boot/efi
	mkdir -p $CHROOT/var
	mount /dev/mapper/${DEV_NAME}p5 $CHROOT/var

Before disconnecting image, clean dev mappings;

        $ sudo kpartx -d /dev/nbd0
        $ sudo qemu-nbd -d /dev/nbd0

2.2. Resize images

Verify disk image information;

        $ qemu-img info c1-storage.qcow2

	image: c1-storage.qcow2
	file format: qcow2
	virtual size: 10G (10737418240 bytes)
	disk size: 7.6G
	cluster_size: 65536
	Format specific information:
	    compat: 1.1
	    lazy refcounts: false
	    refcount bits: 16
	    corrupt: false
	$

In this example is added 25G to the image;

	$ qemu-img resize c1-storage.qcow2 +25G

Read lvm resize if image is using lvm, or use resize2fs. If size is not provided to resize2fs, by default it will grow file system to all partition;

        $ sudo qemu-nbd -c /dev/nbd0 /srv/qemu/img/c1-server.qcow2

        # kpartx -a -s -l -u /dev/nbd0
        GPT:Primary header thinks Alt. header is not at the end of the disk.
        GPT:Alternate GPT header not at the end of the disk.
        GPT: Use GNU Parted to correct# 2-arg version of allocate-array.

allocate-array2:  # ad: (addr allocation-descriptor), elem-size: int, array-len: int, out: (addr handle array _)
    # . prologue
    55/push-ebp
    89/<- %ebp 4/r32/esp
    # . save registers
    50/push-eax
    #
    8b/-> *(ebp+0xc) 0/r32/eax
    f7 4/subop/multiply-into 0/r32/eax *(ebp+0x10)
    (allocate-array *(ebp+8) %eax *(ebp+0x14))
$allocate-array2:end:
    # . restore registers
    58/pop-to-eax
    # . epilogue
    89/<- %esp 5/r32/ebp
    5d/pop-to-ebp
    c3/return

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