[libvirt] [PATCH 1/7] Implement public API for virDomainIOThreadsSet

[Ján Tomko]

On Thu, Mar 19, 2015 at 01:08:22PM -0400, John Ferlan wrote:
> Add virDomainIOThreadsSet to allow setting the number of IOThreads for
> a domain.
> 
> The API supports updating both the --live domain and the --config data.
> 
> Signed-off-by: John Ferlan <jferlan at redhat.com>
> ---
>  include/libvirt/libvirt-domain.h |  3 ++
>  src/driver-hypervisor.h          |  6 ++++
>  src/libvirt-domain.c             | 60 ++++++++++++++++++++++++++++++++++++++++
>  src/libvirt_public.syms          |  1 +
>  4 files changed, 70 insertions(+)
> 

This one has been siting there for a while, I'll think out loud just to
get a discussion going.

> --- a/src/libvirt-domain.c
> +++ b/src/libvirt-domain.c
> @@ -8042,6 +8042,66 @@ virDomainPinIOThread(virDomainPtr domain,
>  
>  
>  /**
> + * virDomainSetIOThreads:
> + * @domain: pointer to domain object
> + * @niothreads: the new number of IOThreads for this domain
> + * @flags: bitwise-OR of virDomainModificationImpact
> + *
> + * Dynamically change the number of IOThreads used by the domain.
> + * Note that this call faiy fail if the underlying virtualization hypervisor
> + * does not support it or if growing the number is arbitrarily limited.
> + * This function may require privileged access to the hypervisor.
> + *
> + * @flags may include VIR_DOMAIN_AFFECT_LIVE to affect a running
> + * domain (which may fail if domain is not active), or
> + * VIR_DOMAIN_AFFECT_CONFIG to affect the next boot via the XML
> + * description of the domain.  Both flags may be set.
> + * If neither flag is specified (that is, @flags is VIR_DOMAIN_AFFECT_CURRENT),
> + * then an inactive domain modifies persistent setup, while an active domain
> + * is hypervisor-dependent on whether just live or both live and persistent
> + * state is changed.
> + *
> + * Not all hypervisors can support all flag combinations.
> + *
> + * Returns 0 in case of success, -1 in case of failure.
> + */
> +int
> +virDomainSetIOThreads(virDomainPtr domain,
> +                      unsigned int niothreads,
> +                      unsigned int flags)
> +{

This seems ok for the use case where we just give a domain a few
iothreads and all the disks will share them.

But if you go for one iothread per disk, creating holes in iothread
indexes could make sense - we allow unplugging disks from the middle.

I can't think of a case where hotplugging a thread with id=6 would be
useful if there are only 3 threads.

Maybe there should be separate APIs for adding and deleting threads?

Jan
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