[libvirt] [RFC PATCHv2 0/2] Implement tiered driver loading

This patchset implements a tiered driver loading system. I split the hypervisor drivers out into their own tier, which is loaded after the other drivers. This has the net effect of ensuring that things like secrets, networks, etc., are initialized and auto-started before any hypervisors, such as QEMU, LXC, etc. This resolves the race condition currently present when starting libvirtd while domains are running, which happens when restarting libvirtd after having started at least one domain. This patch will work without my config driver patchset, which is about to be submitted, as well. Without the config driver patchset, however, RBD storage pools using CephX authentication can not be auto-started due to a circular dependency between the QEMU and storage drivers. This may also affect other storage backends, but I currently only have the capacity to test with RBD and file backed storage pools. The reason this interferes with RBD storage pools is that currently, the storage driver has a hard-coded connection to QEMU in order to look up secrets. After this patchset, the QEMU driver will not be loaded until after the storage driver has completed its initialization and auto-start routines, which causes issues looking up secrets. Any pool type that does not use or need data from outside of the base storage pool definition should continue to auto-start along with no longer being affected by the current race condition. I have verified that file-based storage pools definitely auto-start fine after this patchset, and no longer have any issue with the current race condition. For anyone who is not familiar with the race condition I mention above, the basic description is that upon restarting libvirtd, any running QEMU domains using storage volumes are killed randomly due to their associated storage pool not yet being online. This is due to storage pool auto-start not having completed prior to QEMU initialization. In my prior testing, I found that this race condition affected at least one domain approximately 40% of the time. I sent this information to the mailing list back on 06DEC2013, if anyone is interested in going back and re-reading my description. I would appreciate any comments and suggestions about this patchset. It works for me on 4 machines running three different distros of Linux (Archlinux, Gentoo, and CentOS), so I would imagine that it should work most anywhere. Adam Walters (2): driver: Implement new state driver field libvirt: Implement tiered driver loading src/check-driverimpls.pl | 1 + src/driver.h | 7 +++++ src/interface/interface_backend_netcf.c | 1 + src/libvirt.c | 45 ++++++++++++++++++++------------- src/libxl/libxl_driver.c | 1 + src/lxc/lxc_driver.c | 1 + src/network/bridge_driver.c | 1 + src/node_device/node_device_hal.c | 1 + src/node_device/node_device_udev.c | 1 + src/nwfilter/nwfilter_driver.c | 1 + src/qemu/qemu_driver.c | 1 + src/remote/remote_driver.c | 1 + src/secret/secret_driver.c | 1 + src/storage/storage_driver.c | 1 + src/uml/uml_driver.c | 1 + src/xen/xen_driver.c | 1 + 16 files changed, 48 insertions(+), 18 deletions(-) -- 1.8.5.2