[libvirt PATCH 1/2] conf: add killpriv v2 attribute for virtiofs

Ján Tomko jtomko at redhat.com
Thu Jan 6 15:27:01 UTC 2022

On a Wednesday in 2022, Daniel P. Berrangé wrote:
>On Wed, Jan 05, 2022 at 04:06:49PM +0100, Ján Tomko wrote:
>> Add a new attribute to control the killpriv feature:
>>   <filesystem>
>>     ...
>>     <binary>
>>       <killpriv v2='off'/>
>>     </binary>
>>   </filesystem>
>Ewww, ewww, ewww.
>This is a horrible element & attribute name. Even with the docs I have
>little clue as to why we would ever need this or what its real effects
>are. Having now read the libvirt and related QEMU bugzilla, I now see
>that   killpriv v2 is enabled by default in virtiofs because it is
>faster and more reliable. A limitation in NFS, however, means that
>some specific syscalls don't work correctly with it, so QEMU folks
>are saying killpriv v2 should not be used with NFS.

Thank you for the short summary of the bug, I did not realize it was
private :(


>At this point I ask why doesn't virtiofsd just do the right thing.
>It can statfs() the root of the export it is configured with and see
>that it is NFS.  I'm not convinced by a need to expose this knob in
>libvirt, especially with such an unintelligible name & difficult to
>understand behavioural impact.
>> https://bugzilla.redhat.com/show_bug.cgi?id=1972571
>> Signed-off-by: Ján Tomko <jtomko at redhat.com>
>> ---
>>  docs/formatdomain.rst                             |  4 ++++
>>  docs/schemas/domaincommon.rng                     |  7 +++++++
>>  src/conf/domain_conf.c                            | 15 +++++++++++++++
>>  src/conf/domain_conf.h                            |  1 +
>>  .../qemuxml2argvdata/vhost-user-fs-fd-memory.xml  |  1 +
>>  5 files changed, 28 insertions(+)
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