Re: [libvirt] [RFC PATCH 0/7] Adding 'config' driver
On 01/20/14 17:27, Daniel P. Berrange wrote:
On Fri, Dec 20, 2013 at 11:03:53PM -0500, Adam Walters wrote:
> This patchset adds a driver named 'config' that allows access to
configuration
> data, such as secret and storage definitions. This is a pre-requisite for my
> next patchset which resolves the race condition on libvirtd startup and the
> circular dependencies between QEMU and the storage driver.
I vaguely recall something being mentioned in the past, but not the
details. Can you explain the details of the circular dependancy
problem that you're currently facing ?
The problem is that when we are re-starting with running VMs that have
storage placed on RBD volumes with secrets stored in the secret driver
we encounter the following dependancy:
1) the qemu driver depends on the storage driver to be started so that
disk type="volume" can be resolved to the actual volumes
2) the storage driver depends on requesting credentials from the secret
driver and thus needs a connection to do so. For some strange reason the
storage driver opens "qemu:///system" for this purpose:
static void
storageDriverAutostart(virStorageDriverStatePtr driver) {
size_t i;
virConnectPtr conn = NULL;
/* XXX Remove hardcoding of QEMU URI */
if (driverState->privileged)
conn = virConnectOpen("qemu:///system");
else
conn = virConnectOpen("qemu:///session");
/* Ignoring NULL conn - let backends decide */
This works if the drivers are initialized, but breaks in the case we use
RBD volumes with secrets that and <disk type=volume, where we need to
initialize the storage driver before the qemu driver.
Peter
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