Re: [libvirt] [PATCH 2/3] maxmem: implement virDomainSetMaxMemory API of the qemu driver

On 04/07/2011 11:08 PM, Taku Izumi wrote: > > This patch implements the code to support virDomainSetMaxMemory API, > and to support VIR_DOMAIN_MEM_MAXIMUM flag in qemudDomainSetMemoryFlags function. > As a result, we can change the maximum memory size of inactive QEMU guests. >

> +static int qemudDomainSetMaxMemory(virDomainPtr dom, unsigned long memory) { > + return qemudDomainSetMemoryFlags(dom, memory, > + VIR_DOMAIN_MEM_MAXIMUM | VIR_DOMAIN_MEM_LIVE); Hmm. Given the above implementation, this will _always_ fail. Then again, the failure message will be nicer (the function used to fail with "not implemented", now it fails with "cannot resize memory on an active domain"), so I guess it's okay to provide this stub. And given the documentation in libvirt.c, this is accurate (that documentation explicitly stated that it only works on live domains). But the real clincher is how xen behaves. I just tested, and my RHEL 5 machine with xen:/// was able to change persistent max memory of an inactive domain, so the documentation in libvirt.c is wrong. I then

tried an active domain, which (surprisingly) changed the max cap, then promptly forgot the change when the domain went inactive again proving that it behaved like _LIVE and not _LIVE|_CONFIG. Qemu can't change max mem on a live domain (it's capped at qemu startup time) even if xen can,

so if we tweak the libvirt.c wording to accommodate both xen and qemu behaviors (since it was already inaccurate for xen), then we can make this function succeed some of the time by defaulting to _CURRENT|_MAXIMUM instead of _LIVE|_MAXIMUM.