Add supported image formats in sm-list

Introduction

At XCP-ng, we are enhancing support for QCOW2 images in SMAPI. The primary motivation for this change is to overcome the 2TB size limitation imposed by the VHD format. By adding support for QCOW2, a Storage Repository (SR) will be able to host disks in VHD and/or QCOW2 formats, depending on the SR type. In the future, additional formats—such as VHDx—could also be supported.

We need a mechanism to expose to end users which image formats are supported by a given SR. The proposal is to extend the SM API object with a new field that clients (such as XenCenter, XenOrchestra, etc.) can use to determine the available formats.

Design Proposal

To expose the available image formats to clients (e.g., XenCenter, XenOrchestra, etc.), we propose adding a new field called supported-image-formats to the Storage Manager (SM) module. This field will be included in the output of the SM.get_all_records call.

The supported-image-formats field will be populated by retrieving information from the SMAPI drivers. Specifically, each driver will update its DRIVER_INFO dictionary with a new key, supported_image_formats, which will contain a list of strings representing the supported image formats (for example: ["vhd", "raw", "qcow2"]).

The list designates the driver’s preferred VDI format as its first entry. That means that when migrating a VDI, the destination storage repository will attempt to create a VDI in this preferred format. If the default format cannot be used (e.g., due to size limitations), an error will be generated.

If a driver does not provide this information (as is currently the case with existing drivers), the default value will be an empty array. This signifies that it is the driver that decides which format it will use. This ensures that the modification remains compatible with both current and future drivers.

With this new information, listing all parameters of the SM object will return:

# xe sm-list params=all

will output something like:

uuid ( RO)                         : c6ae9a43-fff6-e482-42a9-8c3f8c533e36
name-label ( RO)                   : Local EXT3 VHD
name-description ( RO)             : SR plugin representing disks as VHD files stored on a local EXT3 filesystem, created inside an LVM volume
type ( RO)                         : ext
vendor ( RO)                       : Citrix Systems Inc
copyright ( RO)                    : (C) 2008 Citrix Systems Inc
required-api-version ( RO)         : 1.0
capabilities ( RO) [DEPRECATED]     : SR_PROBE; SR_SUPPORTS_LOCAL_CACHING; SR_UPDATE; THIN_PROVISIONING; VDI_ACTIVATE; VDI_ATTACH; VDI_CLONE; VDI_CONFIG_CBT; VDI_CREATE; VDI_DEACTIVATE; VDI_DELETE; VDI_DETACH; VDI_GENERATE_CONFIG; VDI_MIRROR; VDI_READ_CACHING; VDI_RESET_ON_BOOT; VDI_RESIZE; VDI_SNAPSHOT; VDI_UPDATE
features (MRO)                    : SR_PROBE: 1; SR_SUPPORTS_LOCAL_CACHING: 1; SR_UPDATE: 1; THIN_PROVISIONING: 1; VDI_ACTIVATE: 1; VDI_ATTACH: 1; VDI_CLONE: 1; VDI_CONFIG_CBT: 1; VDI_CREATE: 1; VDI_DEACTIVATE: 1; VDI_DELETE: 1; VDI_DETACH: 1; VDI_GENERATE_CONFIG: 1; VDI_MIRROR: 1; VDI_READ_CACHING: 1; VDI_RESET_ON_BOOT: 2; VDI_RESIZE: 1; VDI_SNAPSHOT: 1; VDI_UPDATE: 1
configuration ( RO)               : device: local device path (required) (e.g. /dev/sda3)
driver-filename ( RO)              : /opt/xensource/sm/EXTSR
required-cluster-stack ( RO)       :
supported-image-formats ( RO)       : vhd, raw, qcow2

This change impacts the SM data model, and as such, the XAPI database version will be incremented.

Impact

• Data Model: A new field (supported-image-formats) is added to the SM records.
• Client Awareness: Clients like the xe CLI will now be able to query and display the supported image formats for a given SR.
• Database Versioning: The XAPI database version will be updated to reflect this change.