lib: Introduce virDomainFDAssociate API

The API can be used to associate one or more (e.g. a RO and RW fd for a
disk backend image) FDs to a VM. They can be then used per definition.

The primary use case for now is for complex deployment where
libvirtd/virtqemud may be run inside a container and getting the image
into the container is complicated.

In the future it will also allow passing e.g. vhost FDs and other
resources to a VM without the need to have a filesystem representation
for it.

Passing raw FDs has few intricacies and thus libvirt will by default not
restore security labels.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>

include/libvirt/libvirt-domain.h

@@ -6458,4 +6458,24 @@ int virDomainStartDirtyRateCalc(virDomainPtr domain,
                                 int seconds,
                                 unsigned int flags);
 
+
+/**
+ * virDomainFDAssociateFlags:
+ *
+ * Since: 9.0.0
+ */
+typedef enum {
+    /* Attempt a best-effort restore of security labels after use (Since: 9.0.0) */
+    VIR_DOMAIN_FD_ASSOCIATE_SECLABEL_RESTORE = (1 << 0),
+    /* Use a seclabel allowing writes for the FD even if usage implies read-only mode (Since: 9.0.0) */
+    VIR_DOMAIN_FD_ASSOCIATE_SECLABEL_WRITABLE = (1 << 1),
+} virDomainFDAssociateFlags;
+
+
+int virDomainFDAssociate(virDomainPtr domain,
+                         const char *name,
+                         unsigned int nfds,
+                         int *fds,
+                         unsigned int flags);
+
 #endif /* LIBVIRT_DOMAIN_H */