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AutoYaST Support in storage-ng

About this document

This document describes which components are involved and how they cooperate to create a partitioning proposal for AutoYaST.

Use Cases Levels

When it comes to partitioning, we can categorize AutoYaST use cases into three different levels:

  1. Automatic partitioning. The user does not care about the partitioning and trusts in AutoYaST to do the right thing.
  2. Semi-automatic partitioning. The user would like to set some basic settings. E.g., a user would like to use LVM but has no idea about how to configure devices and partitions.
  3. Expert partitioning. The user specifies how the layout should look. However, a complete definition is not required, and AutoYaST should propose reasonable defaults for missing parts.

Profile Content

An AutoYaST profile can define two different kinds of storage settings:

  • General settings, which allows altering the partitioning section of the product features and enabling/disabling multipath.
  • Partitioning layout settings, which defines how the partitioning should look like (partitions, volume groups, RAIDs devices, etc.).

Translating these groups of settings to use cases levels:

  • Level 1: no settings at all.
  • Level 2: just general settings.
  • Level 3: partitioning layout settings and, optionally, general settings.

Process Overview

The AutoYaST partitioning process starts in the storage_auto client, which lives in the autoyast2-installation package. This client relies heavily on the AutoinstStorage module, which is responsible, among other things, of importing the AutoYaST profile (via the #Import method) and performing the partitioning (#Write).

This document focuses on the #Import method, which creates a partitioning proposal and provides libstorage-ng with the desired devicegraph. The following is just a sketch of the steps of the partitioning process (the rest of the sections contain the details for all of them):

  1. The general settings are imported. It happens before the AutoinstStorage#Import method is called.
  2. The settings are preprocessed. Currently, the only preprocessing which takes place is replacing device=ask with a real device name after asking the user. Any preprocessing which implies interacting with the user should be done at this point.
  3. Build the proposed devicegraph. It is the complicated part, and it involves a lot of stuff that is described later.
  4. If any issue is found during step 3, present it to the user.

The third step is quite generic, and it is completely different depending on the use case. The Y2Autoinstall::StorageProposal class decides which approach to follow:

  • If there is no <partitioning> section, AutoYaST relies in the {Y2Storage::GuidedProposal} class (levels 1 and 2).
  • If a <partitioning> section exists, AutoYaST applies an specific process (level 3).

Level 1 Procedure

In this case, the user does not specify any partitioning setting, and AutoYaST is responsible for proposing a sensible layout. Under the hood, AutoYaST basically relies on the {Y2Storage::GuidedProposal} using the default configuration for the installation product.

Level 2 Procedure

With this approach, the user can define some high-level settings and let AutoYaST build the proposal.

<general>
  <storage>
    <proposal>
      <lvm config:type="boolean">true</lvm>
    </proposal>
    <start_multipath config:type="boolean">true</start_multipath>
  </storage>
</general>

The elements in the proposal section are merged with those in the product's control file. It is like adjusting the guided proposal parameters in the regular installer. However, only a few of them are supported.

Level 3 procedure

When the profile contains a partitioning section, AutoYaST does not use the guided proposal, but it follows these steps (see {Y2Storage::AutoinstProposal}):

  1. Convert the AutoYaST profile --a hash containing nested hashes and arrays-- into something better to work with.
  2. Associate each drive section included in the profile with a real device.
  3. Plan for new stuff by creating a set of planned devices.
  4. Delete unwanted stuff from the devicegraph.
  5. Modify the devicegraph according to the list of planned devices.
  6. Add devices required to boot if needed.

Phase one: converting the profile data into proper objects

As you may know, an AutoYaST profile is basically an XML file which is converted into a complex hash, including nested hashes and arrays. Working with such a data structure is not convenient at all. For that reason, as a first step, the partitioning section of the profile is turned into a {Y2Storage::AutoinstProfile::PartitioningSection} object, which offers a better API for this use case.

This class does not work in isolation, as each section of the profile is represented by different classes ({Y2Storage::AutoinstProfile::DriveSection}, {Y2Storage::AutoinstProfile::PartitionSection}, etc.).

As a side note, the {Y2Storage::AutoinstProfile::PartitioningSection} class is used when cloning a system too. Check the {Y2Storage::AutoinstProfile::PartitioningSection.new_from_storage} method for further details.

Phase two: assigning the drives

The partitioning section of the AutoYaST profile is organized into drives containing a list of partitions each. The result must honor that organization. E.g., two partitions that are listed in the same drive will always end up in the same disk and two partitions in different drives cannot end up sharing the disk.

The matching between a drive and the real disk can be done explicitly in the profile (using the device tag) or can be left for AutoYaST to decide. In the latter case, the algorithm used by AutoYaST is dead simple: it just tries to use the first available device that is not explicitly skipped (there is also a syntax for skipping devices). The documentation states it tries to find a device that "looks reasonable" but, in reality, it just uses whatever is not skipped, with no optimization in place or even without checking if the device is big enough.

The relationship between profile and real drives is kept in an instance of {Y2Storage::Proposal::AutoinstDrivesMap}.

Phase three: planning new stuff

With the drives map in-place, the profile information can already be used to create {Y2Storage::Planned::Device} objects. Those objects are meant to contain information about the devices that will be created or reused. There are especialized classes for each device: {Y2Storage::Planned::Partition}, {Y2Storage::Planned::LvmLv}, {Y2Storage::Planned::LvmVg}, {Y2Storage::Planned::Md}, {Y2Storage::Planned::Bcache}, {Y2Storage::Planned::StrayBlkDevice}, {Y2Storage::Planned::Nfs} and {Y2Storage::Planned::Btrfs} for multi-device Btrfs filesystems.

The class responsible for driving this phase is {Y2Storage::Proposal::AutoinstDevicesPlanner}. Basically, it goes through the list of drives contained in the profile creating the corresponding planned devices according to the type (:CT_DISK, :CT_LVM, etc.).

However, each type of drive is processed by a different planner class:

  • {Y2Storage::Proposal::AutoinstDiskDevicePlanner} for :CT_DISK and CT_DMMULTIPATH (the latter is deprecated).
  • {Y2Storage::Proposal::AutoinstVgPlanner} for :CT_LVM.
  • {Y2Storage::Proposal::AutoinstMdPlanner} for :CT_MD.
  • {Y2Storage::Proposal::AutoinstBcachePlanner} for :CT_BCACHE.
  • {Y2Storage::Proposal::AutoinstNfsPlanner} for :CT_NFS.
  • {Y2Storage::Proposal::AutoinstBtrfsPlanner} for :CT_BTRFS.

Phase four: deleting old stuff

All delete operations are postponed until the list of planned devices is ready. The reason is that AutoYaST needs to know which devices are going to be reused to avoid removing them.

{Y2Storage::Proposal::AutoinstSpaceMaker} is the class responsible for cleaning up the devicegraph according to the use and initialize attributes of each drive section.

Phase five: adding the planned stuff to the devicegraph

This phase consists on updating the devicegraph to contain the planned devices. For that purpose, and similarly to the {Y2Storage::Proposal::AutoinstDevicesPlanner} case, a {Y2Storage::Proposal::AutoinstDevicesCreator} class exists. It receives the devicegraph and the list of planned devices.

The logic to create each plan device, however, is splitted into several classes:

  • {Y2Storage::Proposal::LvmCreator} for {Y2Storage::Planned::LvmVg}.
  • {Y2Storage::Proposal::AutoinstMdCreator} for {Y2Storage::Planned::Md}.
  • {Y2Storage::Proposal::AutoinstBcacheCreator} for {Y2Storage::Planned::Bcache}.
  • {Y2Storage::Proposal::NfsCreator} for {Y2Storage::Planned::Nfs}.
  • {Y2Storage::Proposal::BtrfsCreator} for {Y2Storage::Planned::Btrfs}.

Note that there are no separate classes for {Y2Storage::Planned::Disk} and {Y2Storage::Planned::StrayBlkDevice}. The logic for that kind of devices lives in the {Y2Storage::Proposal::AutoinstDevicesCreator} for historical reasons and, ideally, it should be extracted.

It is worth to mention that, if not enough space is found, AutoYaST will try to reduce the size of the planned devices to make them fit. Check the {Y2Storage::Proposal::AutoinstPartitionSize} for further details.

Phase six: adding boot devices (if needed)

After adjusting the devicegraph to include the list of planned devices, AutoYaST checks whether the resulting system is bootable. If that's not the case, AutoYaST will try to add the needed devices to the devicegraph.

{Y2Storage::BootRequirementsChecker} is the class responsible for finding out whether the system is bootable and determining the missing partitions (if any).

Issues reporting

It is possible that, given a profile, AutoYaST finds issues when trying to figure out the partitioning layout. Some of those issues might be severe enough to stop the installation; in other cases, it just displays a warning.

The {Y2Storage::AutoinstIssues} module uses Installation::AutoinstIssues::List (defined in yast2 package). {Y2Storage::AutoinstIssues} contains a set of possible issues -- all of them are classes which inherit from Installation::AutoinstIssues::Issue --.