[PATCH v2 9/9] remote: Don't attempt remote connection from libvirtd

[Peter Krempa]

When a hypervisor driver is not compiled in and a user enables the
monolithic libvirtd, they get the following misleading error:

  $ virsh -c qemu:///system
  error: failed to connect to the hypervisor
  error: Failed to connect socket to '/var/run/libvirt/virtqemud-sock': No such file or directory

The issue is that the daemon side of the remote driver can't find the
appropriate driver, but the remote driver always accepts everything and
thus attempts to delegate further, which in case of libvirtd makes no
sense.

Refuse opening a connection for local URIS even when the requested
driver is not registered in case when we are inside 'libvirtd' as
libvirtd doesn't have anything to delegate to.

  $ virsh -c qemu:///system
  error: failed to connect to the hypervisor
  error: no connection driver available for qemu:///system

Discovered when investigating https://gitlab.com/libvirt/libvirt/-/issues/370

Signed-off-by: Peter Krempa <pkrempa at redhat.com>
---
 src/remote/remote_driver.c | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/src/remote/remote_driver.c b/src/remote/remote_driver.c
index 33cc6b1fce..a4efe101a3 100644
--- a/src/remote/remote_driver.c
+++ b/src/remote/remote_driver.c
@@ -73,6 +73,7 @@ VIR_LOG_INIT("remote.remote_driver");
 #endif

 static bool inside_daemon;
+static bool monolithic_daemon;

 struct private_data {
     virMutex lock;
@@ -168,7 +169,7 @@ static void make_nonnull_domain_snapshot(remote_nonnull_domain_snapshot *snapsho
 static int
 remoteStateInitialize(bool privileged G_GNUC_UNUSED,
                       const char *root G_GNUC_UNUSED,
-                      bool monolithic G_GNUC_UNUSED,
+                      bool monolithic,
                       virStateInhibitCallback callback G_GNUC_UNUSED,
                       void *opaque G_GNUC_UNUSED)
 {
@@ -176,6 +177,7 @@ remoteStateInitialize(bool privileged G_GNUC_UNUSED,
      * re-entering ourselves
      */
     inside_daemon = true;
+    monolithic_daemon = monolithic;
     return VIR_DRV_STATE_INIT_COMPLETE;
 }

@@ -1244,16 +1246,22 @@ remoteConnectOpen(virConnectPtr conn,
         if (!conn->uri)
             return VIR_DRV_OPEN_DECLINED;

-        /* If there's a driver registered we must defer to that.
-         * If there isn't a driver, we must connect in "direct"
-         * mode - see doRemoteOpen.
-         * One exception is if we are trying to connect to an
-         * unknown socket path as that might be proxied to remote
-         * host */
-        if (!conn->uri->server &&
-            virHasDriverForURIScheme(driver) &&
-            !virURICheckUnixSocket(conn->uri))
-            return VIR_DRV_OPEN_DECLINED;
+        /* Handle deferring to local drivers if we are dealing with a default
+         * local URI. (Unknown local socket paths may be proxied to a remote
+         * host so they are treated as remote too).
+         *
+         * Deferring to a local driver is needed if:
+         * - the driver is registered in the current daemon
+         * - if we are running monolithic libvirtd, in which case we consider
+         *   even un-registered drivers as local
+         */
+        if (!conn->uri->server && !virURICheckUnixSocket(conn->uri)) {
+            if (virHasDriverForURIScheme(driver))
+                return VIR_DRV_OPEN_DECLINED;
+
+            if (monolithic_daemon)
+                return VIR_DRV_OPEN_DECLINED;
+        }
     }

     if (!(priv = remoteAllocPrivateData()))
-- 
2.37.1