af2405e118
Because of the libvirt issue[1], there is a bug[2] that if we set cache mode
whose write semantic is not O_DIRECT (.i.e unsafe, writeback or writethrough),
there will be a problem with the volume drivers
(.i.e nova.virt.libvirt.volume.LibvirtISCSIVolumeDriver,
nova.virt.libvirt.volume.LibvirtNFSVolumeDriver and so on), which designate
native io explicitly.
That problem will generate a libvirt xml for the instance,
whose content contains
```
...
<disk ... >
<driver ... cache='unsafe/writeback/writethrough' io='native' />
</disk>
...
```
In turn, it will fail to start the instance or attach the disk.
> When qemu is configured with a block device that has aio=native set, but
> the cache mode doesn't use O_DIRECT (i.e. isn't cache=none/directsync or any
> unnamed mode with explicit cache.direct=on), then the raw-posix block driver
> for local files and block devices will silently fall back to aio=threads.
> The blockdev-add interface rejects such combinations, but qemu can't
> change the existing legacy interfaces that libvirt uses today.
[1]: 058384003d
[2]: https://bugzilla.redhat.com/show_bug.cgi?id=1086704
Closes-Bug: #1841363
Change-Id: If9acc054100a6733f3659a15dd9fc2d462e84d64
15 lines
674 B
YAML
15 lines
674 B
YAML
---
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fixes:
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- |
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Since Libvirt v.1.12.0 and the introduction of the `libvirt issue`_ ,
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there is a fact that if we set cache mode whose write semantic is not
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O_DIRECT (i.e. "unsafe", "writeback" or "writethrough"), there will
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be a problem with the volume drivers (i.e. LibvirtISCSIVolumeDriver,
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LibvirtNFSVolumeDriver and so on), which designate native io explicitly.
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When the driver_cache (default is none) has been configured as neither
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"none" nor "directsync", the libvirt driver will ensure the driver_io
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to be "threads" to avoid an instance spawning failure.
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.. _`libvirt issue`: https://bugzilla.redhat.com/show_bug.cgi?id=1086704
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