Manual Test Cases

Incoming Test Cases

Adapt alertmanager to dedicated storage network
Add backup-taget connection status
Add extra disks by using raw disks
Add websocket disconnect notification
Alertmanager supports main stream receivers
All Namespace filtering in VM list
Auto provision lots of extra disks
Boot installer under Legacy BIOS and UEFI
Check can start VM after Harvester upgrade
Check conditions when stop/pause VM
Check DNS on install with Github SSH keys
Check IPAM configuration with IPAM
Check IPv4 static method in ISO installer
Check logs on Harvester
Check Network interface link status can match the available NICs in Harvester vlanconfig
Check rancher-monitoring-grafana volume size
Check support bundle for SLE Micro OS
Check the OS types in Advanced Options
Check the VM is available when Harvester upgrade failed
Check version compatibility during an upgrade
Check volume status after upgrade
Clone image (e2e_fe)
collect Fleet logs and YAMLs in support bundles
Collect system logs
Config logging in Harvester Dashboard
Configure VLAN interface on ISO installer UI
Create a harvester-specific StorageClass for Longhorn
Create multiple VM instances using VM template with EFI mode selected
Dashboard Storage usage display when node disk have warning
Dedicated storage network
Delete VM template default version (e2e_fe)
Deny the vlanconfigs overlap with the other
Deploy guest cluster to specific node with Node selector label
Download backing images
enable/disable alertmanager on demand
Enabling and Tuning KSM
enhance double check of VM’s resource modification
enhance node scheduling when vm selects network
Function keys on web VNC interface
Generate Install Support Config Bundle For Single Node
Harvester Cloud Provider compatibility check
Harvester pull Rancher agent image from private registry
Harvester rebase check on SLE Micro
Harvester supports event log
Harvester supports kube-audit log
Harvester uses active-backup as the default bond mode
Image filtering by labels
Image filtering by labels (e2e_fe)
Image handling consistency between terraform data resource and Harvester UI created image
Image naming with inline CSS (e2e_fe)
Image upload does not start when HTTP Proxy is configured
Improved resource reservation
Install Harvester over previous GNU/Linux install
Instance metadata variables are not expanded
ISO installation console UI Display
Ksmd support merge_across_node on/off
Limit VM of guest cluster in the same namespace
Local cluster user input topology key
Logging Output Filter
Multiple Disks Swapping Paths
Namespace pending on terminating
Negative change backup target while restoring backup
Negative Harvester installer input same NIC IP and VIP
Negative Restore a backup while VM is restoring
Networkconfigs function check
NIC ip and vip can’t be the same in Harvester installer
Node disk manager should prevent too many concurrent disk formatting occur within a short period
Node join fails with self-signed certificate
Node promotion for topology label
Polish harvester machine config in Rancher
Press the Enter key in setting field shouldn’t refresh page
Prevent normal users create harvester-public namespace
Project owner role on customized project open Harvester cluster
Project owner should not see additional alert
Promote remaining host when delete one
rancher-monitoring status when hosting NODE down
RBAC Cluster Owner
RBAC Create VM with restricted admin user
Reinstall agent node
Remove Pod Scheduling from harvester rke2 and rke1
Restart Button Web VNC window
Restart/Stop VM with in progress Backup
restored VM can not be cloned
Restored VM name does not support uppercases
Restricted admin should not see cattle-monitoring-system volumes
Setup and test local Harvester upgrade responder
Support configuring a VLAN at the management interface in installer config
Support multiple VLAN physical interfaces
Support private registry for Rancher agent image in Air-gap
Support Volume Clone
Support Volume Snapshot
Sync harvester node’s topology labels to rke2 guest-cluster’s node
Sync image display name to image labels
template with EFI (e2e_fe)
Terraform import VLAN
Terraformer import KUBECONFIG
Testing Harvester Storage Tiering
The count of volume snapshots should not include VM’s snapshots
Topology aware scheduling of guest cluster workloads
Unable to stop VM which in starting state
Upgrade guest cluster kubernetes version can also update the cloud provider chart version
Upgrade Harvester on node that has bonded NICs for management interface
Upgrade support of audit and event log
VLAN Upgrade Test
VM boot stress test
VM Import/Migration
VM IP addresses should be labeled per network interface
VM label names consistentency before and after the restore
VM Snapshot support
VM template is not working with Node scheduling
VMIs created from VM Template don’t have LiveMigrate evictionStrategy set
VMs can’t start if a node contains more than ~60 VMs
VolumeSnapshot Management
Wrong mgmt bond MTU size during initial ISO installation
Zero downtime upgrade

Advanced

Addons

Enable Harvester addons and check deployment state
PCI Devices Controller
vGPU/SR-IOV GPU

Change api-ui-source bundled (e2e_fe)
Change api-ui-source external (e2e_fe)
Change log level debug
Change log level Info (e2e_fe)
Change log level Trace (e2e_fe)
Cluster TLS customization
Fleet support with Harvester
Set backup target S3 (e2e_fe)
Set backup-target NFS (e2e_fe)
Set backup-target NFS invalid target
Set backup-target S3 invalid target
SSL Certificate
Timeout option for support bundle
Verify that vm-force-reset-policy works

Authentication

Authentication Validation
Change user password (e2e_fe)
Create SSH key from templates page
First Time Login (e2e_fe)
Login after password reset (e2e_fe)
Logout from the UI and login again
Multi-browser login
UI enables option to display password on login page
Verify SSH key was added from Github during install

Backup and Restore

Backup S3 reduce permissions
Backup Single VM (e2e_be)
Backup Single VM that has been live migrated before (e2e_be)
Backup single VM with node off
Backup Target error message
Create Backup Target (e2e_be)
Delete backup from backups list (e2e_be)
Delete first backup in chained backup (e2e_be)
Delete last backup in chained backup (e2e_be)
Delete middle backup in chained backup (e2e_be)
Delete multiple backups
Edit backup read YAML from file
Edit backup via YAML (e2e_be)
Filter backups
Negative create backup on store that is full (NFS)
Negative Create Backup Target
Negative delete backup while restore is in progress
Negative delete multiple backups
Negative delete single backup
Negative disrupt backup server while restore is in progress
Negative edit backup read from file YAML
Negative edit backup YAML
Negative initiate a backup while system is taking another backup
Negative Power down the node where the VM is getting replaced by the restore
Negative power down the node where the VM is getting restored
Negative restore backup replace existing VM
Negative restore backup replace existing VM with backup from same VM that is turned on
Negative restore backup replace existing VM with backup from same VM that is turned on (e2e_be)
Restore backup create new vm (e2e_be)
Restore backup create new vm in another namespace
Restore Backup for VM that was live migrated (e2e_be)
Restore backup replace existing VM with backup from same VM (e2e_be)
Restore First backup in chained backup
Restore last backup in chained backup
Restore middle backup in chained backup
VM Backup with metadata

Deployment Tests for Harvester

Add a node to existing cluster (e2e_be)
Additional trusted CA configure-ability
Automatically get VIP during PXE installation
Change DNS servers while installing
Http proxy setting on harvester
Install 2 node Harvester with a Harvester token with multiple words
Install Harvester from USB disk
Install Harvester on a bare Metal node using ISO image
Install Harvester on a bare Metal node using ISO image
Install Harvester on a bare Metal node using PXE boot (e2e_be)
Install Harvester on NVMe SSD
Install Option HwAddr for Network Interface
Install Option install.device support symbolic link
Manual upgrade from 0.3.0 to 1.0.0
Power down a node out of three nodes available for the Cluster
Power down the management node.
PXE instll without iso_url field
Reboot the management node/added node.
Remove a node from the existing cluster
Verify and Configure Networking Connection (e2e_be)
Verify Configuring SSH keys
Verify Configuring via HTTP URL
Verify the installation confirmation screen
Verify the Installer Options
Verify the Proxy configuration
VIP Load balancer verification (e2e_be)

Harvester Rancher Integration

01-Import existing Harvester clusters in Rancher
02-Integrate to Rancher from Harvester settings (e2e_be)
03-Manage VM in Downstream Harvester
04-Manage Node in Downstream Harvester
05-Manage Image in Downstream Harvester
06-Manage Network in Downstream Harvester
07-Add and grant project-owner user to harvester (e2e_be)
08-Add and grant project-readonly user to harvester
09-Add and grant project-member user to harvester
10-Add and grant project-custom user to harvester
11-Create New Project in Harvester
12-Create New Namespace in Harvester
13-Add and grant project-owner user to custom project
14-Add and grant project-readonly user to custom project
15-Add and grant project-member user to custom project
16-Add and grant project-custom user to custom project
17-Delete Imported Harvester Cluster (e2e_be)
18-Delete Failed Imported Harvester Cluster
19-Enable Harvester Node Driver
20-Create RKE1 Kubernetes Cluster
21-Delete RKE1 Kubernetes Cluster
22-Create RKE2 Kubernetes Cluster (e2e_be)
23-Delete RKE2 Kubernetes Cluster (e2e_be)
24-Delete RKE1 Kubernetes Cluster in Provisioning
25-Delete RKE1 Kubernetes Cluster in Failure
26-Delete RKE2 Kubernetes Cluster in Provisioning
27-Delete RKE2 Kubernetes Cluster in Failure
28-Deploy Harvester cloud provider to RKE1 Cluster
29-Deploy Harvester cloud provider to RKE2 Cluster
30-Configure Harvester LoadBalancer service
31-Specify “pool” IPAM mode in LoadBalancer service
32-Deploy Harvester CSI provider to RKE 1 Cluster
33-Deploy Harvester CSI provider to RKE 2 Cluster
34-Hot plug and unplug volumes in RKE1 cluster
35-Hot plug and unplug volumes in RKE2 cluster
36-Remove Harvester LoadBalancer service
37-Import Online Harvester From the Airgapped Rancher
37-Import Online Harvester From the Airgapped Rancher
38-Import Airgapped Harvester From the Airgapped Rancher
39-Standard user no Harvester Access
40-RBAC Add restricted admin User Harvester
41-Import Harvester into nested Rancher
42-Add cloud credential KUBECONFIG
43-Scale up node driver RKE1
44-Scale up node driver RKE2
45-Scale down node driver RKE1
46-Scale down node driver RKE2
47-Verify Backup and restore on same server
48-Verify Backup and restore on server migration
49-Overprovision Harvester
50-Use fleet when a harvester cluster is imported to rancher
51-Use harvester cloud provider to provision an LB - rke1
52-Use harvester cloud provider to provision an LB - rke2
53-Disable Harvester flag with Harvester cluster added
54-Import Airgapped Harvester From the Online Rancher
55-Import Harvester to Rancher in airgapped different subnet
56-Import Harvester to Rancher in airgapped different subnet
57-Import airgapped harvester from airgapped rancher with Proxy
58-Negative-Fully power cycle harvester node machine should recover RKE2 cluster
59-Create K3s Kubernetes Cluster
60-Delete K3s Kubernetes Cluster
61-Deploy Harvester cloud provider to k3s Cluster
62-Configure the K3s “DHCP” LoadBalancer service
62-Configure the K3s “DHCP” LoadBalancer service
63-Configure the K3s “Pool” LoadBalancer service
65-Configure the K3s “Pool” LoadBalancer health check
66-Deploy Harvester csi driver to k3s Cluster
67-Harvester persistent volume on k3s Cluster
68-Fully airgapped rancher integrate with harvester with no proxy
69-DHCP Harvester LoadBalancer service no health check
70-Pool LoadBalancer service no health check
71-Manually Deploy Harvester csi driver to RKE2 Cluster
72-Use ipxe example to test fully airgapped rancher integration
Better Load Balancer Config of Harvester cloud provider
Check can apply the resource quota limit to project and namespace
Check default and customized project and namespace details page
Create a VM through the Rancher dashboard
Create RKE2 cluster with no cloud provider
Delete 3 node RKE2 cluster
Mark some features as experimental
Provision RKE2 cluster with resource quota configured
Rancher import harvester enhancement
Rancher Resource quota management
Reboot a cluster and check VIP
toggle harvester node driver with the harvester global flag
Use template to create cluster through virtualization management

Hosts

Add/remove disk to Host config
Agent Node should not rely on specific master Node
Attach unpartitioned NVMe disks to host
Automatically get VIP during PXE installation
Check crash dump when there’s a kernel panic
check detailed network status in host page
Check Longhorn volume mount point
Check redirect for editing server URL setting
Cluster with Witness Node
Delete Host (e2e_be)
Delete host that has VMs on it
Disk can only be added once on UI
Disk devices used for VM storage should be globally configurable
Download host YAML
Edit Config (e2e_be)
Edit Config YAML (e2e_be)
Host list should display the disk error message on failure
Maintenance mode for host with multiple VMs
Maintenance mode for host with one VM (e2e_be)
Maintenance mode on node with no vms (e2e_be)
Migrate back VMs that were on host after taking host out of maintenance mode
Move Longhorn storage to another partition
Node Labeling for VM scheduling
Nodes with cordoned status should not be in VM migration list
Power down and power up the node
Power down the node
Power node triggers VM reschedule
PXE instll without iso_url field
Reboot a cluster and check VIP
Reboot host that is in maintenance mode (e2e_be)
Reboot host trigger VM migration
Reboot node
Recover cordon and maintenace node after harvester node machine reboot
Remove a management node from a 3 nodes cluster and add it back to the cluster by reinstalling it
Remove unavailable node with VMs on it
Set maintenance mode on the last available node shouldn’t be allowed
Shut down host in maintenance mode and verify label change
Shut down host then delete hosted VM
Start Host in maintenance mode (e2e_be)
Take host out of maintenance mode that has been rebooted (e2e_be)
Take host out of maintenance mode that has not been rebooted (e2e_be)
Temporary network disruption
Test NTP server timesync
Turn off host that is in maintenance mode (e2e_be)
Verify Enabling maintenance mode
Verify the Filter on the Host page
Verify the info of the node
Verify the state for Powered down node

Images

Add Labels (e2e_be_fe)
Create Images with valid image URL (e2e_be_fe)
Create with invalid image (e2e_be_fe)
Delete the image (e2e_be_fe)
Delete VM with exported image(e2e_fe)
Edit images (e2e_be_fe)
Update image labels after deleting source VM(e2e_fe)
Upload Cloud Image (e2e_be)
Upload image that is invalid
Upload ISO Image(e2e_fe)
Verify the options available for image

Live Migration

Initiate multiple migrations at one time
Migrate a turned on VM from one host to another
Migrate a VM created with cloud init config data
Migrate a VM created with user data config
Migrate a VM that has multiple volumes
Migrate a VM that was created from a template
Migrate a VM that was created using a restore backup to new VM
Migrate a VM with 1 backup
Migrate a VM with a saved SSH Key
Migrate a VM with multiple backups
Migrate a VM with multiple networks
Migrate to Node without replicaset
Migrate VM from Restored backup
Negative migrate a turned on VM from one host to another
Negative network disconnection for a longer time while migration is in progress
Negative network disconnection for a short time while migration is in progress
Negative node down while migration is in progress
Negative node un-schedulable during live migration
Support volume hot plug live migrate
Test aborting live migration
Test zero downtime for live migration download test
Test zero downtime for live migration ping test

Misc

Button of Download KubeConfig (e2e_fe)
Check favicon and title on pages
Check Harvester CloudInit CRDs within Harvester, Terraform & Rancher
Create support bundle in multi-node Harvester cluster with one node off
Download kubeconfig after shutting down harvester cluster
Test NTP server timesync
Verify network data template

Network

Add multiple Networks via form
Add multiple Networks via YAML (e2e_be)
Add network reachability detection from host for the VLAN network
Add VLAN network (e2e_be)
Create new network (e2e_be_fe)
Delete external VLAN network via form
Delete external VLAN network via YAML (e2e_be)
Delete management network via form
Delete management network via YAML (e2e_be)
Disable and enable vlan cluster network
Edit network via form change external VLAN to management network
Edit network via form change management network to external VLAN
Edit network via YAML change external VLAN to management network (e2e_be)
Edit network via YAML change management network to external VLAN (e2e_be)
Enabling vlan on a bonded NIC on vagrant install
Negative network comes back up after reboot external VLAN (e2e_be)
Negative network comes back up after reboot management network (e2e_be)
Switch the vlan interface of harvester node
Try to add a network with no name (e2e_be)
Validate network connectivity external VLAN (e2e_be)
Validate network connectivity invalid external VLAN (e2e_be)
Validate network connectivity management network (e2e_be)
VIP configured in a VLAN network should be reached
VIP is accessibility with VLAN enabled on management port

Node Driver

Add a custom “Docker Install URL”
Add a custom “Insecure Registries”
Add a custom “Registry Mirrors”
Add a custom “Storage Driver”
Add cluster driver
Add the different roles to the cluster
Add/remove a node in the created harvester cluster
Backup and restore of harvester cluster
Basic functional verification of Harvester cluster after creation
Cluster add labs
Cluster add Taints
Create a 3 nodes harvester cluster with RKE1 (only with mandatory info, other values stays with default)
Create a 3 nodes harvester cluster with RKE2 (only with mandatory info, other values stays with default)
Create a harvester cluster and add Taint to a node
Create a harvester cluster with 3 master nodes
Create a harvester cluster with a non-default version of k8s
Create a harvester cluster with different images
Create a harvester cluster, template drop-down list validation
Create harvester cluster using non-default CPUs, Memory, Disk
Create harvester clusters with different Bus
Create harvester clusters with different Networks
Deactivate/activate/delete Harvester Node Driver
Delete Cluster
Guest CSI Driver
Import External Harvester
Import internal harvester
Use a non-admin user
Verify “Add Node Pool”

Rancher2 Terraform Provider Integration

Terraform Rancher2 Provider Testing

Templates

allow users to create cloud-config template on the VM creating page
Chain VM templates and images
Create SSH key from templates page
Verify network data template
Volume size should be editable on derived template

Terraform Provider

Installation of the Harvester terraform provider (e2e_be)
Target Harvester by setting the variable kubeconfig with your kubeconfig file in the provider.tf file (e2e_be)
Target Harvester with the default kubeconfig located in $HOME/.kube/config (e2e_be)
Test a deployment with ALL resources at the same time (e2e_be)
Test the harvester_clusternetwork resource (e2e_be)
Test the harvester_image resource (e2e_be)
Test the harvester_network resource (e2e_be)
Test the harvester_ssh_key resource (e2e_be)
Test the harvester_virtualmachine resource (e2e_be)
Test the harvester_volume resource (e2e_be)

Terraformer

Check that you can communicate with the Harvester cluster
Import and make changes to clusternetwork resource
Import and make changes to image resource
Import and make changes to network resource
Import and make changes to ssh_key resource
Import and make changes to virtual machine resource
Import and make changes to volume resource

UI

Verify the external link at the bottom of the page
Verify the Harvester UI URL (e2e_fe)
Verify the left side menu (e2e_fe)
Verify the links which navigate to the internal pages

Upgrade Harvester

Rejoin node machine after Harvester upgrade
Upgrade Harvester from new cluster network design (after v1.1.0)
Upgrade Harvester from traditonal cluster network design (before v1.1.0)
Upgrade Harvester in Fully Airgapped Environment
Upgrade Harvester with bonded NICs on network
Upgrade Harvester with HDD Disks
Upgrade Harvester with IPv6 DHCP

Virtual Machines

Add a network to an existing VM with only 1 network (e2e_be_fe)
Add a network to an existing VM with two networks
Chain VM templates and images
Check VM creation required-fields
Clone VM and don’t select start after creation
Clone VM that is turned off
Clone VM that is turned on
Clone VM that was created from existing volume
Clone VM that was created from image
Clone VM that was created from template
Clone VM that was not created from image
CPU overcommit on VM (e2e_fe)
Create a new VM and add Enable USB tablet option (e2e_be_fe)
Create a new VM and add Install guest agent option (e2e_be_fe)
Create a new VM with Network Data from the form (e2e_fe)
Create a new VM with Network Data from YAML (e2e_be)
Create a new VM with User Data from the form
Create a VM on a VLAN with an existing machine and then change the existing machine’s VLAN
Create a VM with 2 networks (e2e_be)
Create a vm with all the default values (e2e_be_fe)
Create a VM with Start VM on Creation checked (e2e_be)
Create a VM with start VM on creation unchecked (e2e_be)
Create multiple instances of the vm with ISO image (e2e_be)
Create multiple instances of the vm with raw image (e2e_be_fe)
Create multiple instances of the vm with Windows Image (e2e_be)
Create new VM with a machine type of PC (e2e_be)
Create new VM with a machine type of q35 (e2e_be)
Create one VM on a VLAN and then move another VM to that VLAN
Create one VM on a VLAN that has other VMs then change it to a different VLAN
Create Single instances of the vm with ISO image
Create Single instances of the vm with ISO image (e2e_be)
Create Single instances of the vm with ISO image with machine type pc
Create Single instances of the vm with raw image (e2e_be)
Create Single instances of the vm with Windows Image (e2e_be)
Create two VMs in the same VLAN (e2e_be)
Create two VMs on separate VLANs
Create two VMs on the same VLAN and change one
Create VM and add SSH key (e2e_be)
Create vm using a template of default version
Create vm using a template of default version with machine type pc
Create vm using a template of default version with machine type q35
Create vm using a template of non-default version (e2e_fe)
Create vm with both CPU and Memory not in cluster (e2e_be)
Create vm with CPU not in cluster. (e2e_be)
Create VM with existing Volume (e2e_be_fe)
Create vm with Memory not in cluster. (e2e_be)
Create VM with resources that are only on one node in cluster CPU
Create VM with resources that are only on one node in cluster CPU (e2e_be)
Create VM with resources that are only on one node in cluster CPU and Memory (e2e_be)
Create VM with resources that are only on one node in cluster Memory
Create VM with resources that are only on one node in cluster Memory (e2e_be)
Create VM with saved SSH key (e2e_be)
Create VM with the default network (e2e_be)
Create VM with two disk volumes (e2e_be)
Create VM without memory provided (e2e_fe)
Create Windows VM
Delete multiple VMs with disks (e2e_be)
Delete multiple VMs without disks (e2e_be)
Delete single vm all disks (e2e_be)
Delete VM Negative (e2e_be)
Delete VM with exported image (e2e_fe)
Edit a VM and add install Enable usb tablet option (e2e_be)
Edit a VM and add install guest agent option (e2e_be)
Edit a VM from the form to add Network Data
Edit a VM from the form to add user data (e2e_fe)
Edit a VM from the YAML to add Network Data (e2e_be)
Edit a VM from the YAML to add user data (e2e_be)
Edit an existing VM to another machine type (e2e_be)
Edit vm and insert ssh and check the ssh key is accepted for the login (e2e_be_fe)
Edit vm config after Eject CDROM and delete volume
Edit VM Form Negative
Edit vm network and verify the network is working as per configuration (e2e_be)
Edit VM via form with CPU
Edit VM via form with CPU and Memory
Edit VM via form with Memory
Edit VM via YAML with CPU (e2e_be)
Edit VM via YAML with CPU and Memory (e2e_be)
Edit VM via YAML with Memory (e2e_be)
Edit VM with resources that are only on one node in cluster CPU and Memory
Edit VM YAML Negative
Memory overcommit on VM
Negative vm clone tests
Run multiple instances of the console
Start VM and stop node Negative
Start VM Negative (e2e_be)
Stop VM Negative (e2e_fe)
Update image labels after deleting source VM
Validate QEMU agent installation
Verify operations like Stop, restart, pause, download YAML, generate template (e2e_be)
Verify that vm-force-reset-policy works
View log function on virtual machine
VM on error state
VM scheduling on Specific node (e2e_fe)
VM’s CPU maximum limitation

Volumes

Add/remove disk to Host config
Check Longhorn volume mount point
Create image from Volume(e2e_fe)
Create Volume root disk blank Form with label
Create volume root disk VM Image Form with label (e2e_be)
Create volume root disk VM Image Form(e2e_fe)
Delete volume that is not attached to a VM (e2e_be_fe)
Delete volume that was attached to VM but now is not (e2e_be_fe)
Detach volume from virtual machine (e2e_fe)
Edit volume decrease size via YAML
Edit volume decrease size via YAML
Edit Volume Form add label
Edit volume increase size via form (e2e_fe)
Edit volume increase size via YAML (e2e_be)
Edit Volume YAML add label (e2e_be)
Negative delete Volume that is in use (e2e_be)
Support Volume Hot Unplug (e2e_fe)
Validate volume shows as in use when attached (e2e_be)
Verify that vm-force-reset-policy works
Verify that VMs stay up when disks are evicted

Webhooks

datavolumes.cdi.kubevirt.io
keypairs.harvesterhci.io
network-attachment-definitions.k8s.cni.cncf.io
virtualmachineimages.harvesterhci.io
virtualmachinerestores.harvesterhci.io
virtualmachinetemplateversions.harvesterhci.io

Start VM and stop node Negative

Start the VM
In a multi-node setup disconnect/shutdown the node where the VM is running

Expected Results

You should not be able to start the VM