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Kernel: Virtualizing the Clock and Linux 4.21/5.0 Merges

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Linux
  • Virtualizing the Clock

    Dmitry Safonov wanted to implement a namespace for time information. The twisted and bizarre thing about virtual machines is that they get more virtual all the time. There's always some new element of the host system that can be given its own namespace and enter the realm of the virtual machine. But as that process rolls forward, virtual systems have to share aspects of themselves with other virtual systems and the host system itself—for example, the date and time.

    Dmitry's idea is that users should be able to set the day and time on their virtual systems, without worrying about other systems being given the same day and time. This is actually useful, beyond the desire to live in the past or future. Being able to set the time in a container is apparently one of the crucial elements of being able to migrate containers from one physical host to another, as Dmitry pointed out in his post.

    [...]

    So, there clearly are many nuances to consider. The discussion ended there, but this is a good example of the trouble with extending Linux to create virtual machines. It's almost never the case that a whole feature can be fully virtualized and isolated from the host system. Security concerns, speed concerns, and even code complexity and maintainability come into the picture. Even really elegant solutions can be shot down by, for example, the possibility of hostile users creating files with unnaturally old timestamps.

  • A Big Batch Of DRM Feature Updates Line Up Ahead Of Linux 4.21

    With the Linux 4.20 merge window having ended this past weekend, the first big batch of new feature material to DRM-Next from the "DRM-Misc" area has been submitted for the follow-on Linux 4.21 cycle.

    The DRM-Misc-Next pull request sent in this morning is on the large side as it's the first big feature pull for this area of the Direct Rendering Manager subsystem that touches the core DRM interfaces and smaller drivers.

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