The driver URI scheme:
"$drivername:///embed?root=/some/path"
enables a new way to use the drivers by embedding them directly in the
calling process. To use this the process must have a thread running the
libvirt event loop. This URI will then cause libvirt to dynamically load
the driver module and call its global initialization function. This
syntax is applicable to any driver, but only those will have been
modified to support a custom root directory and embed URI path will
successfully open.
The application can now make normal libvirt API calls which are all
serviced in-process with no RPC layer involved.
It is required to specify an explicit root directory, and locks will be
acquired on this directory to avoid conflicting with another app that
might accidentally pick the same directory.
Use of '/' is not explicitly forbidden, but note that the file layout
used underneath the embedded driver root does not match the file
layout used by system/session mode drivers. So this cannot be used as
a backdoor to interact with, or fake, the system/session mode drivers.
Libvirt will create arbitrary files underneath this root directory. The
root directory can be kept untouched across connection open attempts if
the application needs persistence. The application is responsible for
purging everything underneath this root directory when finally no longer
required.
Even when a virt driver is used in embedded mode, it is still possible
for it to in turn use functionality that calls out to other secondary
drivers in libvirtd. For example an embedded instance of QEMU can open
the network, secret or storage drivers in the system libvirtd.
That said, the application would typically want to at least open an
embedded secret driver ("secret:///embed?root=/some/path"). Note that
multiple different embedded drivers can use the same root prefix and
co-operate just as they would inside a normal libvirtd daemon.
A key thing to note is that for this to work, the application that links
to libvirt *MUST* be built with -Wl,--export-dynamic to ensure that
symbols from libvirt.so are exported & thus available to the dynamically
loaded driver module. If libvirt.so itself was dynamically loaded then
RTLD_GLOBAL must be passed to dlopen().
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
The intent here is to allow the virt drivers to be run directly embedded
in an arbitrary process without interfering with libvirtd. To achieve
this they need to store all their configuration & state in a separate
directory tree from the main system or session libvirtd instances.
This can be useful for doing testing of the virt drivers in "make check"
without interfering with the user's own libvirtd instances.
It can also be used for applications using KVM/QEMU as a piece of
infrastructure to build an service, rather than for general purpose
OS hosting. A long standing example is libguestfs, which would prefer
if its temporary VMs did show up in the main libvirtd VM list, because
this confuses apps such as OpenStack Nova. A more recent example would
be Kata which is using KVM as a technology to build containers.
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
When running in libvirtd, we are happy for any of the drivers to simply
skip their initialization in virStateInitialize, as other drivers are
still potentially useful.
When running in per-driver daemons though, we want the daemon to abort
startup if the driver cannot initialize itself, as the daemon will be
useless without it.
Reviewed-by: Andrea Bolognani <abologna@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
https://bugzilla.redhat.com/show_bug.cgi?id=1685151
This reverts commit e4a969092b.
Now that drivers may call virConnectOpen() on secondary drivers, it
doesn't make much sense to have autostart separated from driver
initialization callback. In fact, it creates a problem because one
driver during its initialization might try to fetch an object from
another driver but since the object is yet to be autostarted the fetch
fails. This has been observed in reality: qemu driver performs
qemuProcessReconnect() during qemu's stateInitialize phase which may
call virDomainDiskTranslateSourcePool() which connects to the storage
driver to look up the volume. But the storage driver did not autostart
its pools yet therefore volume lookup fails and the domain is killed.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Require that all headers are guarded by a symbol named
LIBVIRT_$FILENAME
where $FILENAME is the uppercased filename, with all characters
outside a-z changed into '_'.
Note we do not use a leading __ because that is technically a
namespace reserved for the toolchain.
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
With the large number of APIs in libvirt the driver.h file,
it is easy to get lost looking for things. Split each driver
into a separate header file based on the functional driver
groups.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
