Elasticity: Dracut

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Friday, June 9, 2017

Rapido: Quick Kernel Testing From Source (Video)

I presented a short talk at the 2017 openSUSE Conference on Linux kernel testing using Rapido.

There were many other interesting talks during the conference, all of which can be viewed on the oSC 2017 media site.
A video of my presentation is embedded below.

Many thanks to the organisers and sponsors for putting on a great event.

Tuesday, December 13, 2016

Rapido: A Glorified Wrapper for Dracut and QEMU

Introduction

I've blogged a few of times about how Dracut and QEMU can be combined to greatly improve Linux kernel dev/test turnaround.

My first post covered the basics of building the kernel, running dracut, and booting the resultant image with qemu-kvm.
A later post took a closer look at network configuration, and focused on bridging VMs with the hypervisor.
Finally, my third post looked at how this technique could be combined with Ceph, to provide a similarly efficient workflow for Ceph development.

In bringing this series to a conclusion, I'd like to introduce the newly released Rapido project. Rapido combines all of the procedures and techniques described in the articles above into a handful of scripts, which can be used to test specific Linux kernel functionality, standalone or alongside other technologies such as Ceph.

Usage - Standalone Linux VM

The following procedure was tested on openSUSE Leap 42.3 and SLES 12SP3, but should work fine on many other Linux distributions.

Step 1: Checkout and Build

Checkout the Linux kernel and Rapido source repositories:

~/> cd ~
~/> git clone https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
~/> git clone https://github.com/rapido-linux/rapido.git

Build the kernel (using a config provided with the Rapido source):

~/> cp rapido/kernel/vanilla_config linux/.config
~/> cd linux
~/linux/> make -j6
~/linux/> make modules
~/linux/> INSTALL_MOD_PATH=./mods make modules_install

Step 2: Configuration

Install Rapido dependencies: dracut and qemu.

Create a master rapido.conf configuration file using the example template:

~/linux/> cd ~/rapido
~/rapido/> cp rapido.conf.example rapido.conf
~/rapido/> vi rapido.conf

set KERNEL_SRC="/home/<user>/linux"
set KERNEL_INSTALL_MOD_PATH="${KERNEL_SRC}/mods"
the remaining options can be left as is for now

Step 3: Image Generation

Generate a minimal Linux VM image which includes binaries, libraries and kernel modules for filesystem testing:

~/rapido/> ./cut_fstests_local.sh
...
 dracut: *** Creating initramfs image file 'initrds/myinitrd' done ***
~/rapido/> ls -lah initrds/myinitrd
-rw-r--r-- 1 ddiss users 30M Dec 13 18:17 initrds/myinitrd

Step 4 - Boot!

 ~/rapido/> ./vm.sh
+ mount -t btrfs /dev/zram1 /mnt/scratch
[    3.542927] BTRFS info (device zram1): disk space caching is enabled
...
btrfs filesystem mounted at /mnt/test and /mnt/scratch
rapido1:/#

In a whopping four seconds, or thereabouts, the VM should have booted to a rapido:/# bash prompt. Leaving you with two zram backed Btrfs filesystems mounted at /mnt/test and /mnt/scratch.

Everything, including the VM's root filesystem, is in memory, so any changes will not persist across reboot. Use the rapido.conf QEMU_EXTRA_ARGS parameter if you wish to add persistent storage to a VM.

Once you're done playing around, you can shutdown:

rapido1:/# shutdown
[  267.304313] sysrq: SysRq : sysrq: Power Off
rapido1:/# [  268.168447] ACPI: Preparing to enter system sleep state S5
[  268.169493] reboot: Power down
+ exit 0

Step 5: Network Configuration

The fstests_local VM above is networkless, so doesn't require bridge network configuration. For VMs that do (e.g. CephFS client below) edit rapido.conf:

set TAP_USER="<user>"
set MAC_ADDR1 to a valid MAC address, e.g. "b8:ac:24:45:c5:01"
set MAC_ADDR2 to a valid MAC address, e.g. "b8:ac:24:45:c5:02"

Configure the isolated bridge and tap network devices. This must be done as root:

~/rapido/> sudo tools/br_setup.sh
~/rapido/> ip addr show br0
4: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    ...
    inet 192.168.155.1/24 scope global br0

Usage - Ceph vstart.sh cluster and CephFS client VM

This usage guide builds on the previous standalone Linux VM procedure, but this time adds Ceph to the mix. If you're not interested in Ceph (how could you not be!) then feel free to skip to the next section.

Step I - Checkout and Build

We already have a clone of the Rapido and Linux kernel repositories. All that's needed for CephFS testing is a Ceph build:

~/> git clone https://github.com/ceph/ceph
~/> cd ceph
<install Ceph build dependencies>
~/ceph/> ./do_cmake.sh -DWITH_MANPAGE=0 -DWITH_OPENLDAP=0 -DWITH_FUSE=0 -DWITH_NSS=0 -DWITH_LTTNG=0
~/ceph/> cd build
~/ceph/build/> make -j4

Step II - Start a vstart.sh Ceph "cluster"

Once Ceph has finished compiling, vstart.sh can be run with the following parameters to configure and locally start three OSDs, one monitor process, and one MDS.

~/ceph/build/> OSD=3 MON=1 RGW=0 MDS=1 ../src/vstart.sh -i 192.168.155.1 -n
...
~/ceph/build/> bin/ceph -c status
...
     health HEALTH_OK
     monmap e2: 1 mons at {a=192.168.155.1:40160/0}
            election epoch 4, quorum 0 a
      fsmap e5: 1/1/1 up {0=a=up:active}
        mgr no daemons active 
     osdmap e10: 3 osds: 3 up, 3 in

Step III - Rapido configuration

Edit rapido.conf, the master Rapido configuration file:

~/ceph/build/> cd ~/rapido
~/rapido/> vi rapido.conf

set CEPH_SRC="/home/<user>/ceph/src"
KERNEL_SRC and network parameters were configured earlier

Step IV - Image Generation

The cut_cephfs.sh script generates a VM image with the Ceph configuration and keyring from the vstart.sh cluster, as well as the CephFS kernel module.

~/rapido/> ./cut_cephfs.sh

...
 dracut: *** Creating initramfs image file 'initrds/myinitrd' done ***

Step V - Boot!

Booting the newly generated image should bring you to a shell prompt, with the vstart.sh provisioned CephFS filesystem mounted under /mnt/cephfs:

~/rapido/> ./vm.sh

...

+ mount -t ceph 192.168.155.1:40160:/ /mnt/cephfs -o name=admin,secret=...
[    3.492742] libceph: mon0 192.168.155.1:40160 session established
...
rapido1:/# df -h /mnt/cephfs
Filesystem             Size  Used Avail Use% Mounted on
192.168.155.1:40160:/  1.3T  611G  699G  47% /mnt/cephfs

CephFS is a clustered filesystem, in which case testing from multiple clients is also of interest. From another window, boot a second VM:

~/rapido/> ./vm.sh

Further Use Cases

Rapido ships with a bunch of scripts for testing different kernel components:

cut_cephfs.sh (shown above)

Image: includes Ceph config, credentials and CephFS kernel module
Boot: mounts CephFS filesystem

cut_cifs.sh

Image: includes CIFS (SMB client) kernel module
Boot: mounts share using details and credentials specified in rapido.conf

cut_dropbear.sh

Image: includes dropbear SSH server
Boot: starts an SSH server with SSH_AUTHORIZED_KEY

cut_fstests_cephfs.sh

Image: includes xfstests and CephFS kernel client
Boot: mounts CephFS filesystem and runs FSTESTS_AUTORUN_CMD

cut_fstests_local.sh (shown above)

Image: includes xfstests and local Btrfs and XFS dependencies
Boot: provisions local xfstest zram devices. Runs FSTESTS_AUTORUN_CMD

cut_lio_local.sh

Image: includes LIO, loopback dev and dm-delay kernel modules
Boot: provisions an iSCSI target, with three LUs exposed

cut_lio_rbd.sh

Image: includes LIO and Ceph RBD kernel modules
Boot: provisions an iSCSI target backed by CEPH_RBD_IMAGE, using target_core_rbd

cut_qemu_rbd.sh

Image: CEPH_RBD_IMAGE is attached to the VM using qemu-block-rbd
Boot: runs shell only

cut_rbd.sh

Image: includes Ceph config, credentials and Ceph RBD kernel module
Boot: maps CEPH_RBD_IMAGE using the RBD kernel clien

cut_samba_cephfs.sh

Image: includes Ceph vstart config, credentials and libcephfs from CEPH_SRC, and additionally pulls in Samba from a (pre compiled) SAMBA_SRC
Boot: configures smb.conf with a CephFS backed share and starts Samba

cut_samba_local.sh

Image: includes local kernel filesystem utils, and pulls in Samba from SAMBA_SRC
Boot: configures smb.conf with a zram backed share and starts Samba

cut_tcmu_rbd_loop.sh

Image: includes Ceph config, librados, librbd, and pulls in tcmu-runner from TCMU_RUNNER_SRC
Boot: starts tcmu-runner and configures a tcmu+rbd backstore exposing CEPH_RBD_IMAGE via the LIO loopback fabric

cut_usb_rbd.sh (see https://github.com/ddiss/rbd-usb)

Image: usb_f_mass_storage, zram, dm-crypt, and RBD_USB_SRC
Boot: starts the conf-fs.sh script from RBD_USB_SRC

Conclusion

Dracut and QEMU can be combined for super-fast Linux kernel testing and development.
Rapido is mostly just a glorified wrapper around these utilities, but does provide some useful tools for automated testing of specific Linux kernel functionality.

If you run into any problems, or wish to provide any kind of feedback (always appreciated), please feel free to leave a message below, or raise a ticket in the Rapido issue tracker.

Update 20170106:

Add cut_tcmu_rbd_loop.sh details and fix the example CEPH_SRC path.

Update 20180312:

Use KERNEL_INSTALL_MOD_PATH instead of an ugly symlink
Update Github links to refer to new project URL
Remove old brctl and tunctl dependencies
Split network setup into a separate section, as fstests_local VMs are now networkless
Add cut_samba_cephfs.sh and cut_samba_local.sh details

Tuesday, May 10, 2016

Rapid Ceph Kernel Module Testing with vstart.sh

Introduction

Ceph's vstart.sh utility is very useful for deploying and testing a mock cluster directly from the Ceph source repository. It can:

Generate a cluster configuration file and authentication keys
Provision and deploy a number of OSDs

Backed by local disk, or memory using the --memstore parameter

Deploy an arbitrary number of monitor, MDS or rados-gateway nodes

All services are deployed as the running user. I.e. root access is not needed.

Once deployed, the mock cluster can be used with any of the existing Ceph client utilities, or exercised with the unit tests in the Ceph src/test directory.

When developing or testing Linux kernel changes for CephFS or RBD, it's useful to also be able to use these kernel clients against a vstart.sh deployed Ceph cluster.

Test Environment Overview - image based on content by Sage Weil

The instructions below walk through configuration and deployment of all components needed to test Linux kernel RBD and CephFS modules against a mock Ceph cluster. The procedure was performed on openSUSE Leap 42.1, but should also be applicable for other Linux distributions.

Network Setup

First off, configure a bridge interface to connect the Ceph cluster with a kernel client VM network:

> sudo /sbin/brctl addbr br0
> sudo ip addr add 192.168.155.1/24 dev br0
> sudo ip link set dev br0 up

br0 will not be bridged with any physical adapters, just the kernel VM via a TAP interface which is configured with:

> sudo /sbin/tunctl -u $(whoami) -t tap0
> sudo /sbin/brctl addif br0 tap0
> sudo ip link set tap0 up

For more information on the bridge setup, see:
http://blog.elastocloud.org/2015/07/qemukvm-bridged-network-with-tap.html

Ceph Cluster Deployment

The Ceph cluster can now be deployed, with all nodes accepting traffic on the bridge network:

> cd $ceph_source_dir
<build Ceph>
> cd src
> OSD=3 MON=1 RGW=0 MDS=1 ./vstart.sh -i 192.168.155.1 -n --memstore

$ceph_source_dir should be replaced with the actual path. Be sure to specify the same IP address with -i as was assigned to the br0 interface.

More information about vstart.sh usage can be found at:
http://docs.ceph.com/docs/hammer/dev/dev_cluster_deployement/

Kernel VM Deployment

Build a kernel:

> cd $kernel_source_dir
> make menuconfig

$kernel_source_dir should be replaced with the actual path. Ensure CONFIG_BLK_DEV_RBD=m, CONFIG_CEPH_FS=y, CONFIG_CEPH_LIB=y, CONFIG_E1000=y and CONFIG_IP_PNP=y are set in the kernel config. A sample can be found here.

> make
> INSTALL_MOD_PATH=./mods make modules_install

Create a link to the modules directory ./mods, so that Dracut can find them:

> sudo ln -s $PWD/mods/lib/modules/$(make kernelrelease) \
                /lib/modules/$(make kernelrelease)

Generate an initramfs with Dracut. This image will be used as the test VM.

> export CEPH_SRC=$ceph_source_dir/src
> dracut --no-compress  --kver "$(cat include/config/kernel.release)" \
        --install "tail blockdev ps rmdir resize dd vim grep find df sha256sum \
                   strace mkfs.xfs /lib64/libkeyutils.so.1" \
        --include "$CEPH_SRC/mount.ceph" "/sbin/mount.ceph" \
        --include "$CEPH_SRC/ceph.conf" "/etc/ceph/ceph.conf" \
        --add-drivers "rbd" \
        --no-hostonly --no-hostonly-cmdline \
        --modules "bash base network ifcfg" \
        --force myinitrd

Boot the kernel and initramfs directly using QEMU/KVM:

> qemu-kvm -smp cpus=2 -m 512 \
        -kernel arch/x86/boot/bzImage -initrd myinitrd \
        -device e1000,netdev=network1,mac=b8:ac:6f:31:45:70 \
        -netdev tap,id=network1,script=no,downscript=no,ifname=tap0 \
        -append "ip=192.168.155.2:::255.255.255.0:myhostname \
                rd.shell=1 console=ttyS0 rd.lvm=0 rd.luks=0" \
        -nographic

This should bring up a Dracut debug shell in the VM, with a network configuration matching the values parsed in via the ip= kernel parameter.

dracut:/# ip a
...
2: eth0: ... mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether b8:ac:6f:31:45:70 brd ff:ff:ff:ff:ff:ff
    inet 192.168.155.2/24 brd 192.168.155.255 scope global eth0

For more information on kernel setup, see:
http://blog.elastocloud.org/2015/06/rapid-linux-kernel-devtest-with-qemu.html

RBD Image Provisioning

An RBD volume can be provisioned using the regular Ceph utilities in the Ceph source directory:

> cd $ceph_source_dir/src
> ./rados lspools
rbd
...

By default, an rbd pool is created by vstart.sh, which can be used for RBD images:

> ./rbd create --image-format 1 --size 1024 1g_vstart_img
> ./rbd ls -l
NAME           SIZE PARENT FMT PROT LOCK
1g_vstart_img 1024M          1

Note: "--image-format 1" is specified to ensure that the kernel supports all features of the provisioned RBD image.

Kernel RBD Usage

From the Dracut shell, the newly provisioned 1g_vstart_img image can be mapped locally using the sysfs filesystem:

dracut:/# modprobe rbd
[    9.031056] rbd: loaded
dracut:/# echo -n "192.168.155.1:6789 name=admin,secret=AQBPiuhd9389dh28djASE32Ceiojc234AF345w== rbd 1g_vstart_img -" > /sys/bus/rbd/add
[  347.743272] libceph: mon0 192.168.155.1:6789 session established
[  347.744284] libceph: client4121 fsid 234b432f-a895-43d2-23fd-9127a1837b32
[  347.749516] rbd: rbd0: added with size 0x40000000

Note: The monitor address and admin credentials can be retrieved from the ceph.conf and keyring files respectively, located in the Ceph source directory.

The /dev/rbd0 mapped image can now be used like any other block device:

dracut:/# mkfs.xfs /dev/rbd0 
...
dracut:/# mkdir -p /mnt/rbdfs
dracut:/# mount /dev/rbd0 /mnt/rbdfs
[  415.841757] XFS (rbd0): Mounting V4 Filesystem
[  415.917595] XFS (rbd0): Ending clean mount
dracut:/# df -h /mnt/rbdfs
Filesystem      Size  Used Avail Use% Mounted on
/dev/rbd0      1014M   33M  982M   4% /mnt/rbdfs

Kernel CephFS Usage

vstart.sh already goes to the effort of deploying a filesystem:

> cd $ceph_source_dir/src
> ./ceph fs ls
> name: cephfs_a, metadata pool: cephfs_metadata_a, data pools: [cephfs_data_a ]

All that's left is to mount it from the kernel VM using the mount.ceph binary that was copied into the initramfs:

dracut:/# mkdir -p /mnt/mycephfs
dracut:/# mount.ceph 192.168.155.1:6789:/ /mnt/mycephfs \
                -o name=admin,secret=AQBPiuhd9389dh28djASE32Ceiojc234AF345w==
[  723.103153] libceph: mon0 192.168.155.1:6789 session established
[  723.184978] libceph: client4122 fsid 234b432f-a895-43d2-23fd-9127a1837b32

dracut:/# df -h /mnt/mycephfs/
Filesystem            Size  Used Avail Use% Mounted on
192.168.155.1:6789:/  3.0G  4.0M  3.0G   1% /mnt/mycephfs

Note: The monitor address and admin credentials can be retrieved from the ceph.conf and keyring files respectively, located in the Ceph source directory.

Cleanup

Unmount CephFS:

dracut:/# umount /mnt/mycephfs

Unmount the RBD image:

dracut:/# umount /dev/rbd0
[ 1592.592510] XFS (rbd0): Unmounting Filesystem

Unmap the RBD image (0 is derived from /dev/rbdX):

dracut:/# echo -n 0 > /sys/bus/rbd/remove

Power-off the VM:

dracut:/# echo 1 > /proc/sys/kernel/sysrq && echo o > /proc/sysrq-trigger
[ 1766.387417] sysrq: SysRq : Power Off
dracut:/# [ 1766.811686] ACPI: Preparing to enter system sleep state S5
[ 1766.812217] reboot: Power down

Shutdown the Ceph cluster:

> cd $ceph_source_dir/src
> ./stop.sh

Conclusion

A mock Ceph cluster can be deployed from source in a matter of seconds using the vstart.sh utility.
Likewise, a kernel can be booted directly from source alongside a throwaway VM and connected to the mock Ceph cluster in a couple of minutes with Dracut and QEMU/KVM.

This environment is ideal for rapid development and integration testing of Ceph user-space and kernel components, including RBD and CephFS.

Sunday, July 12, 2015

QEMU/KVM Bridged Network with TAP interfaces

In my previous post, Rapid Linux Kernel Dev/Test with QEMU, KVM and Dracut, I described how build and boot a Linux kernel quickly, making use of port forwarding between hypervisor and guest VM for virtual network traffic.

This post describes how to plumb the Linux VM directly into a hypervisor network, through the use of a bridge.

Start by creating a bridge on the hypervisor system:

> sudo ip link add br0 type bridge

Clear the IP address on the network interface that you'll be bridging (e.g. eth0).
Note: This will disable network traffic on eth0!

> sudo ip addr flush dev eth0

Add the interface to the bridge:

> sudo ip link set eth0 master br0

Next up, create a TAP interface:

> sudo ip tuntap add dev tap0 mode tap user $(whoami)

The user parameter ensures that the current user will be able to connect to the TAP interface.

Add the TAP interface to the bridge:

> sudo ip link set tap0 master br0

Make sure everything is up:

> sudo ip link set dev br0 up
> sudo ip link set dev tap0 up

The TAP interface is now ready for use. Assuming that a DHCP server is available on the bridged network, the VM can now obtain an IP address during boot via:

> qemu-kvm -kernel arch/x86/boot/bzImage \
           -initrd initramfs \
           -device e1000,netdev=network0,mac=52:55:00:d1:55:01 \
           -netdev tap,id=network0,ifname=tap0,script=no,downscript=no \
           -append "ip=dhcp rd.shell=1 console=ttyS0" -nographic

The MAC address is explicitly specified, so care should be taken to ensure its uniqueness.

The DHCP server response details are printed alongside network interface configuration. E.g.

[    3.792570] e1000: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX
[    3.796085] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
[    3.812083] Sending DHCP requests ., OK
[    4.824174] IP-Config: Got DHCP answer from 10.155.0.42, my address is 10.155.0.1
[    4.825119] IP-Config: Complete:
[    4.825476]      device=eth0, hwaddr=52:55:00:d1:55:01, ipaddr=10.155.0.1, mask=255.255.0.0, gw=10.155.0.254
[    4.826546]      host=rocksolid-sles, domain=suse.de, nis-domain=suse.de
...

Didn't get an IP address? There are a few things to check:

Confirm that the kernel is built with boot-time DHCP client (CONFIG_IP_PNP_DHCP=y) and E1000 network driver (CONFIG_E1000=y) support.
Check the -device and -netdev arguments specify a valid e1000 TAP interface.
Ensure that ip=dhcp is provided as a kernel boot parameter, and that the DHCP server is up and running.

Happy hacking

Update 20161223:

Use 'ip' instead of 'brctl' to manipulate the bridge device - thanks Yagamy Light!

Update 20171220:

Use 'ip tuntap' instead of 'tunctl' to create the TAP interface - thanks Johannes!

Update 20200930:

For performance reasons, I strongly recommend using virtio network adapters instead of e1000.