[ISSUE] Package `xen' creates service that spams dmesg when no hypervisor is running

[ISSUE] Package `xen' creates service that spams dmesg when no hypervisor is running

[voidlinux-github]

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New issue by xelxebar on void-packages repository

https://github.com/void-linux/void-packages/issues/18676

Description:
### Symptom

With the `xen` package installed, and booting *without* the hypervisor, dmesg gets spammed with the following message once every second:

    [000000.000000] xen_evtchn: unknown parameter 'xen-gnttalloc' ignored

### Cause

The problem can be traced back to the `xenstored` service installed by the `xen` package:

    $ grep xen-gnttalloc /etc/sv/xenstored/run
    modprobe -q xen-evtchn xen-gnttalloc || exit 1

This modprobe fails (logging our error) causing the service to fail. Thus `runit` (futually) tries to restart the service *ad infinitum*, leading to the dmesg spam.

### Potential Solution

The `xenstored` service should gracefully degrade to a noop in the case when xen isn't running. One way we can do this is by checking `xl list`. The following patch to shows a workaround that functions on my machine:

    --- /etc/sv/xenstored/run	2020-01-31 15:03:46.619346755 +0900
    +++ /etc/sv/xenstored/run	2020-01-31 15:03:35.912144255 +0900
    @@ -1,4 +1,5 @@
     #!/bin/sh
    +xl list >/dev/null 2>&1 || exit
     [ ! -d /run/xen ] && mkdir -p /run/xen
     modprobe -q xen-evtchn xen-gnttalloc || exit 1
     mountpoint -q /proc/xen || mount -t xenfs xenfs /proc/xen

Re: Package `xen' creates service that spams dmesg when no hypervisor is running

[ashpooljh]

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New comment by ashpooljh on void-packages repository

https://github.com/void-linux/void-packages/issues/18676#issuecomment-670920400

Comment:
Sorry, linked to the wrong issue initially.

Re: Package `xen' creates service that spams dmesg when no hypervisor is running

[ericonr]

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New comment by ericonr on void-packages repository

https://github.com/void-linux/void-packages/issues/18676#issuecomment-778970187

Comment:
@CMB what do you think about this suggestion?

Re: Package `xen' creates service that spams dmesg when no hypervisor is running

[CMB]

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New comment by CMB on void-packages repository

https://github.com/void-linux/void-packages/issues/18676#issuecomment-780135145

Comment:
Looks reasonable on the face of it, but a couple points:

* In the no-op softfail condition, I'd do something like an `exec pause` or `exec chpst ... pause`.  Otherwise runsv will just keep looping trying to start it.
* The command `xl list` pulls data from xenstored.  I'm not sure that it will return 0 before xenstored is up, so it's a chicken and egg problem.  I need to test that.  If `xl list` doesn't work, I know of other ways to test whether something is running in a Xen dom0.

Another thing I want to do with the xenstored service is have a configurable executable name.  There are two xenstored implementations shipped by Xen: the original C implementation (xenstored) and the newer ocaml implementation (oxenstored).  oxenstored is recommended by upstream and -- in my experience -- less buggy.  So xenstored/run should allow overriding the executable name in ./conf.

I'll send a well-tested PR for all of this.  It may be a day or two; I'm recovering from a 3-day power outage.

Re: Package `xen' creates service that spams dmesg when no hypervisor is running

[ericonr]

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New comment by ericonr on void-packages repository

https://github.com/void-linux/void-packages/issues/18676#issuecomment-780140960

Comment:
No rush, the issue has been open for a while, so I don't think a fix is urgent.

Thank you very much for looking into this, and good luck :)

Re: Package `xen' creates service that spams dmesg when no hypervisor is running

[github-actions]

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New comment by github-actions[bot] on void-packages repository

https://github.com/void-linux/void-packages/issues/18676#issuecomment-1099786957

Comment:
Issues become stale 90 days after last activity and are closed 14 days after that.  If this issue is still relevant bump it or assign it.

Re: [ISSUE] [CLOSED] Package `xen' creates service that spams dmesg when no hypervisor is running

[github-actions]

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Closed issue by xelxebar on void-packages repository

https://github.com/void-linux/void-packages/issues/18676

Description:
### Symptom

With the `xen` package installed, and booting *without* the hypervisor, dmesg gets spammed with the following message once every second:

    [000000.000000] xen_evtchn: unknown parameter 'xen-gnttalloc' ignored

### Cause

The problem can be traced back to the `xenstored` service installed by the `xen` package:

    $ grep xen-gnttalloc /etc/sv/xenstored/run
    modprobe -q xen-evtchn xen-gnttalloc || exit 1

This modprobe fails (logging our error) causing the service to fail. Thus `runit` (futually) tries to restart the service *ad infinitum*, leading to the dmesg spam.

### Potential Solution

The `xenstored` service should gracefully degrade to a noop in the case when xen isn't running. One way we can do this is by checking `xl list`. The following patch to shows a workaround that functions on my machine:

    --- /etc/sv/xenstored/run	2020-01-31 15:03:46.619346755 +0900
    +++ /etc/sv/xenstored/run	2020-01-31 15:03:35.912144255 +0900
    @@ -1,4 +1,5 @@
     #!/bin/sh
    +xl list >/dev/null 2>&1 || exit
     [ ! -d /run/xen ] && mkdir -p /run/xen
     modprobe -q xen-evtchn xen-gnttalloc || exit 1
     mountpoint -q /proc/xen || mount -t xenfs xenfs /proc/xen