Re: [libvirt] [RFC PATCH 2/2] lib: Add note that bulk stats API queries may overrun RPC buffers

On Mon, May 22, 2017 at 06:00:13PM +0200, Peter Krempa wrote: > Hint that the users should limit the number of VMs queried in the bulk > stats API. > --- > src/libvirt-domain.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/src/libvirt-domain.c b/src/libvirt-domain.c > index 310b91b37..b01f2705c 100644 > --- a/src/libvirt-domain.c > +++ b/src/libvirt-domain.c > @@ -11315,6 +11315,10 @@ virConnectGetDomainCapabilities(virConnectPtr conn, > * VIR_CONNECT_GET_ALL_DOMAINS_STATS_SHUTOFF and/or > * VIR_CONNECT_GET_ALL_DOMAINS_STATS_OTHER for all other states. > * > + * Note that this API is prone to exceeding maximum RPC message size on hosts > + * with lots of VMs so it's suggested to use virDomainListGetStats with a > + * reasonable list of VMs as the argument. > + * > * Returns the count of returned statistics structures on success, -1 on error. > * The requested data are returned in the @retStats parameter. The returned > * array should be freed by the caller. See virDomainStatsRecordListFree. > @@ -11386,6 +11390,9 @@ virConnectGetAllDomainStats(virConnectPtr conn, > * Note that any of the domain list filtering flags in @flags may be rejected > * by this function. > * > + * Note that this API is prone to exceeding maximum RPC message size on hosts > + * with lots of VMs so it's suggested to limit the number of VMs queried. With the way this is worded, applications have no guidance on what is a sensible max number of VMs they can safely use, so I don't think it is particularly useful, except as a way to say "we told you so" when apps report a bug. I'd be inclined to explicitly put a limit of 100 VMs[1] in the API, and document that hard limit, so apps immediately know to write their code to chunk in 100 VM blocks.

Regards, Daniel [1] 100 is entirely arbitrary for this email - we'd actually pick a number based on what we reasonably expect to fit in the RPC message size. -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| -- libvir-list mailing list libvir-list(a)redhat.com https://www.redhat.com/mailman/listinfo/libvir-list