Home Home > 2017 > 07
Sign up | Login

Archive for July, 2017

Highlights of YaST development sprint 38

July 14th, 2017 by

Here we go again with a new report from the YaST trenches. This time with the storage reimplementation as the clear star of the show.

Storage reimplementation: the proposal adapts, you succeed

As we have announced in our previous sprints and as you probably already know, the YaST team is working hard to rewrite the whole storage stack on time for SLE15 and openSUSE Leap 15. As part of this reimplementation we have designed a brand new storage proposal that automagically offers the user the best combination of partitions and LVM volumes based on the current configuration of the system and the user preferences.

The storage proposal in action

When we are working with very small disks or with special technologies like DASD (which doesn’t accept more than three partitions by device), the storage proposal might not be able to generate a valid initial proposal honoring the initial requirements of the product (e.g. creating a separate home partition and enabling btrfs snapshots for the root partition in the openSUSE Leap case). Now the proposal is not limited to fail when it is not possible to satisfy the default product requirements. Before giving up, the new system looks for alternatives, like discarding the separate home partition or disabling snapshots. Moreover, now the proposal is able to automatically adjust the size requirements not only for root, but also for swap and home. And, of course, the guided setup continues there for fine tuning the proposal settings.

Desktop selection improvements

As our usual readers also know, we recently introduced a more fair desktop selection screen for openSUSE, both Leap 42.3 and Tumbleweed. We used part of the latest sprint to implement some feedback we gathered about the wording and behavior of that dialog.

Revamped desktop selection screen

That feedback gathering included some discussions on how to make user experience nicer after selecting one of the user interfaces available through the “custom” option. As a result, the awesome openSUSE crew created a new mechanism for selecting the default window manager on each graphical login, so YaST can delegate the details to the maintainers of those alternative interfaces.

How everything works now? Glad you asked. 🙂

If the user select KDE or GNOME in the YaST dialog, /etc/sysconfig/windowmanager is configured to point to that desktop by default. If the “custom” option is selected, then YaST does not enforce any interface in that file and the new mechanism comes into play. It relies in the default.desktop file, which defines the default window manager and can be managed by the common update-alternatives workflow. Meaning it can be easily tweaked by the package maintainers and by the users, specially since YaST includes a nice module for managing alternatives.

Storage reimplementation: improvements in the expert partitioner

Although, as explained above, we keep improving the storage automatic proposal to support more and more situations, we cannot ignore that flexibility and adaptability have always been two of the flagships of (open)SUSE. And one of the most prominent examples is the YaST Expert Partitioner.

As detailed in our report of the sprint 36, we have been rewriting that powerful Swiss Army knife using the new storage stack but keeping the same user interface and functionality. So far, the new implementation was only able to display information about the existing partitions, LVM systems and MD RAIDs. But now we added many options to create, edit and delete partitions.

Using the expert partitioner during installation

It is still a work in progress because the number of possibilities offered by the YaST Partitioner is sometimes overwhelming and implementing them all takes time, but it’s progressing nicely.

Beside the improvements in the Partitioner itself, we also worked on its integration in the installation workflow. Now the Expert Partitioner can be used to refine the schema automatically proposed by the installer. As a bonus, the behavior of the “abort” and “finish” buttons has been improved in relation to the Expert Partitioner currently available in (open)SUSE, which historically shows a usability inconsistency there compared to the rest of the installation process.

Fixed Automatic Patch Installation

In both SLE and openSUSE Leap, the online updates can be installed either manually or automatically at some regular intervals. For the automatic installation we provide the yast2-online-update-configuration package which provides a cron job script and an YaST module for configuring it (hint: it is not installed by default, you might give it a try, maybe it is something “new” for you).

Configuring online updates via YaST

You can configure how often the patches should be installed or filter the patch categories in the YaST module, but we got a bug report saying that when multiple patch categories are selected only one is actually used.

It turned out to be a trivial mistake in the cron job and we fixed it for SLE12-SP2 and Leap 42.2, as well as for the upcoming SLE12-SP3 and Leap 42.3. So if you use this module and want to use the category filter then it’s recommended to upgrade the package.

Storage reimplementation: many steps forward in the AutoYaST integration

And going back to our new storage stack, we keep working to integrate it better with other parts of YaST, specially AutoYaST. During this sprint we polished some rough edges and we added support for MD RAID. With all that, now is possible to automatically setup a system based on an AutoYaST profile containing any combination of partitions, LVM systems and MD arrays, including encryption at any of the levels.

AutoYaST summary of actions on partitions, MD RAID and  LVM

But the relation of AutoYaST with the system works in both directions. Apart from being able to install a system based on an AutoYaST profile, it also offers the interface to export the current system configuration, including the storage layout, to a profile in order to reproduce the system later. During this sprint we also ported that logic to rely on the new storage layer.

It was harder than it sounds, due to the need of keeping the backwards-compatibility with several behaviors that have been introduced along the AutoYaST history to adapt to several specific situations. On the bright side, the new code is easier to follow, includes behavior-driven automated tests (RSpec) and contains information about the rationale of each decision… which in some cases required some archaeology.

Storage reimplementation: fixed bootloader proposal in S/390 and PowerPC

Another part of YaST we are constantly working to integrate better with the new storage stack is yast2-bootloader. Although the new storage system was already able to correctly setup a valid disk layout for most situations and architectures (each one with it’s own requirements for booting), our bootloader module is still not fully compatible with the new system in all those scenarios.

During this sprint, we adapted it to ensure all the combinations suggested by the new storage stack (partitions, LVM, encryption and so on) are correctly covered by YaST2-Bootloader. As a result, we can already say that our testing ISO images are fully installable in any x86_64, PowerPC and S/390 system by just clicking “next” a few times. And we have automated integration tests (a separate openQA instance) to ensure the resulting system boots just fine.

UDEV device id on PowerPC

We know some of our readers enjoy our more technical posts and like to lurk into the kitchen to see how we deal with all kind of surprises maintaining a complex tool like YaST. Today’s chapter in that regard started with a bug report about the bootloader being installed in the wrong device name (/dev/vda instead of /dev/vdb) in an emulated PowerPC machine in openQA.

After a lot of investigation and with help from our PowerPC expert, we found the culprit, that turned out to be an emulator quirk. The next couple of paragraphs may be interesting or daunting, depending how much virtualization and PowerPC jargon you know. Be warned.

On POWER, the PReP partition containing the bootloader has no unique identifier other than the serial number of the disk on which it created. QEMU virtualization does not provide any disk serial number when the user does not explicitly specify one. This means that the PReP partition in QEMU installation does not have any unique identification and the partition name may change when a disk is added or removed from the virtual machine or the storage configuration otherwise changes. This may lead to system errors related to bootloader installation and updates.

It is recommended to assign a unique serial number to each disk in a QEMU virtual machine on POWER when it is expected the storage configuration of the virtual machine may change. Otherwise, there is nothing YaST or any other tool running within the virtual machine can do to avoid the problems. So this time we only did the investigation part, with the fix coming from the openQA side, which was improved to explicitly set serial numbers when needed.

Storage reimplementation: better support for advanced scenarios

As exposed above, our StorageNG testing image already works in all the supported architectures and in scenarios combining plain partitions, LVM, RAID and encryption in any way. But there are even more situations and technologies currently supported by YaST that we need to incorporate into the new stack.

First of all, we used this sprint to add Multipath I/O support to the new libstorage. Now it can also be combined with all the other mentioned technologies (like having an LVM system on top of an encrypted multipath device), although the storage proposal still needs to be adapted to play nicely with preexisting multipath setups.

As usual with the library stuff, the best “screenshot” we have to offer is one of its geeky autogenerated graphs.

A multipath layout in libstorage-ng

Another scenario that goes beyond the most regular use cases is installing the system into a network storage device, instead of a local hard disk. Now, the new storage system can report whether a root filesystem via a network is used. When that happens, YaST sets the network interfaces with the start mode nfsroot, which is used to avoid interface shutdown and, therefore, the unavailability of the system.

That’s all, folks!

Once again, we omitted the boring parts about bugfixing (with yast2-ntp-client being the star in that regard) and similar stuff. We hope you enjoyed the report and we hope to reach you again in two weeks. Meanwhile…

Have a lot of fun testing the Leap 42.3 pre-releases and reporting bugs!

Highlights of YaST development sprint 37

July 3rd, 2017 by

Since we announced in the latest report, we decided to shorten our development sprints from three to only two weeks. As a natural consequence, this is the first report of a series of shorter ones. But shorter doesn’t have to mean less juicy! Keep reading and enjoy.

Displaying very long changelog

We got a bug report about YaST not responding when a very long package changelog was displaying in the package manager. It turned out that some packages have a huge change log history with several thousands entries (almost 5000 for the kernel-default package). That produces a very long table which takes long time to parse and display in the UI.

The solution is to limit the maximum number of displayed items in the UI. You cannot easily read that very long text anyway, for such a long text you would need some search functionality which the YaST UI does not provide.

Finding the limit, that magic number, was not easy as we want to be backward compatible and display as much as possible but still avoid that pathological cases with a huge list.

In the end we decided to go for a limit of 512 change entries. The vast majority of packages have way fewer entries, so you should not notice this clipping functionality. When the limit is reached a command to display the full log is displayed at the end so you can easily see the missing part when needed. (Hint: the widget supports the usual copy&paste functionality, you can copy (with Ctrl+C) the displayed command and paste it into a terminal window directly.)

Clipping the kernel changelog

Storage reimplementation: MD RAID support in the rewritten partitioner

In the previous report we told you we are rewriting the YaST partitioner to use the new storage stack and modern reusable CWM widgets under the hood while retaining exactly the same behavior and look&feel on the surface. We are reimplementing one feature at a time, and this sprint it was the MD RAID’s turn.

Now the partitioner displays current RAIDs, with details about them and the devices used to construct each RAID. If a picture is worth a thousand words, here you have 3,000 words:

RAID list in the rewritten partitioner

Devices in a given RAID in the rewritten partitioner

RAID details in the rewritten partitioner

No, you can’t have a separate partition for /var/lib/docker for CaaSP – so here you have it

Our brand new containers-oriented solutions, SUSE CaaSP and its openSUSE counterpart Kubic, need to have /var/lib/docker as a separate partition for several reasons. It was a separate Btrfs subvolume already, but that wasn't quite separate enough. 🙂

The problem was just that the automated storage proposal in the old YaST storage subsystem is not prepared for anything like this; it can deal with root, swap and optionally a separate home partition (or volume if using LVM). That's it. Extending the current syntax of the control.xml file to be able to specify arbitrary partitions and adapting the code of the old proposal to understand and handle this new specification was unfortunately almost impossible. Sadly, we have to admit the old code is hardly maintainable these days and not flexible enough to accommodate this kind of changes in a safe way.

This is one (out of many) reasons why we are currently in the process of rewriting that entire YaST storage subsystem, as you already know from many previous posts in this blog. But, as you also know, the new system will debut in SLES15 and openSUSE Leap 15.0, too late for the current SUSE CaaSP and openSUSE Kubic.

We decided we'd introduce a hack based in the old proposal, well knowing that hacks accumulated in code can develop their own life just like Dust Puppy. But we plan to kill that hack immediately once StorageNG arrives.

So the hack was to simply use the logic for the separate home partition and repurpose it, keeping all the respective parameters in control.xml and introducing yet another one called home_path where the actual mount point for that partition can be specified — in this case /var/lib/docker. The tradeoff is that there can be no separate /home anymore in parallel to that.

That "feature" should not be used outside of that very specific use case in CaaSP and we even considered the possibility of not documenting it too publicly to avoid misuse. But we are living the open source spirit and whatever we do, we do in public. Even if it's the (quite embarrassing) fact that we consider changes to certain parts of our own code too risky. But again, that's why we are pushing the storage layer reimplementation (Storage-NG) so hard: we want to regain control over that part.

Storage reimplementation: custom partitioning with AutoYaST

And talking about the new storage layer and our previous posts, you already know we are working hard to integrate it with AutoYaST. For the time being, custom partitioning layouts are supported, but only using plain partitions and LVM. Other features, like RAID or Btrfs subvolumes support, are still missing.

A nice thing about the new code is that it relies as much as possible on the new storage layer. On older versions, AutoYaST implemented some logic on its own and that caused some unexpected troubles. Fortunately, that is not the case anymore, and the new code looks way easier to extend and maintain.

YaST does not write directly in /etc/vconsole.conf anymore

When configuring the system keyboard, YaST used to write the keyboard map configuration directly in the /etc/vconsole.conf file. However, this approach is no longer appropriated since it may cause undesired effects to other tools. Now YaST uses the Systemd tool localectl to set the keyboard map in /etc/vconsole.conf, instead of writing in it directly. Another step to make YaST a good citizen of the Systemd world.

Storage reimplementation: named RAID arrays

If you use MD RAID arrays you probably know there are two ways of identifying them – by number or assigning a meaningful name to them. Named arrays use device names like /dev/md/<name> instead of /dev/md<number>.

During this sprint, we taught the new libstorage how to create and manage named RAID array, in addition to the already supported numbered ones. If the user decides so, the MD RAID name is used in fstab instead of the UUID (which was the only option with the old libstorage). We also made sure to improve the behavior in several scenarios, so we consider some bugs of the old storage to be fixed (or obsoleted, if you prefer) with storage-ng.

Linux also supports names of the form /dev/md_<name>. The new library is also able to handle this format, but the feature is intentionally disabled and documented to be unsupported because other parts of the system could not be 100% verified to work in that scenario. And we take quality assurance very seriously before labeling a feature as “supported”.

If you are not happy enough with the screenshots showing the RAID support in the partitioner, here you have more pictures. But, as usual with stuff implemented in the library, here “pictures” doesn’t mean screenshots, but fancy automatically generated graphs.

Stay tuned

Of course there are a lot of other things we did during the last two weeks, although some of them were considered not interesting enough for this report or were not finished on time. We are already working in finishing the unfinished stuff and implementing new exciting improvements. And the bright side is that you only have to wait two weeks to know more… so stay tuned.