[libvirt] [PATCH 1/5] qemuDomainBuildNamespace: Move /dev/* mountpoints later

[Michal Privoznik]

When setting up mount namespace for a qemu domain the following
steps are executed:

1) get list of mountpoints under /dev/
2) move them to /var/run/libvirt/qemu/$domName.ext
3) start constructing new device tree under /var/run/libvirt/qemu/$domName.dev
4) move the mountpoint of the new device tree to /dev
5) restore original mountpoints from step 2)

Not the problem with this approach is that if some device in step
3) requires access to a mountpoint from step 2) it will fail as
the mountpoint is not there anymore. For instance consider the
following domain disk configuration:

    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/dev/shm/vhostmd0'/>
      <target dev='vdb' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/>
    </disk>

In this case operation fails as we are unable to create vhostmd0
in the new device tree because after step 2) there is no /dev/shm
anymore. Leave aside fact that we shouldn't try to create devices
living in other mountpoints. That's a separate bug that will be
addressed later.

Currently, the order described above is rearranged to:

1) get list of mountpoints under /dev/
2) start constructing new device tree under /var/run/libvirt/qemu/$domName.dev
3) move them to /var/run/libvirt/qemu/$domName.ext
4) move the mountpoint of the new device tree to /dev
5) restore original mountpoints from step 3)

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/qemu/qemu_domain.c | 54 +++++++++++++++++++++++++-------------------------
 1 file changed, 27 insertions(+), 27 deletions(-)

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 00b0b4a..be02d54 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -7950,33 +7950,6 @@ qemuDomainBuildNamespace(virQEMUDriverConfigPtr cfg,
     if (qemuDomainSetupDev(cfg, mgr, vm, devPath) < 0)
         goto cleanup;
 
-    /* Save some mount points because we want to share them with the host */
-    for (i = 0; i < ndevMountsPath; i++) {
-        struct stat sb;
-
-        if (devMountsSavePath[i] == devPath)
-            continue;
-
-        if (stat(devMountsPath[i], &sb) < 0) {
-            virReportSystemError(errno,
-                                 _("Unable to stat: %s"),
-                                 devMountsPath[i]);
-            goto cleanup;
-        }
-
-        /* At this point, devMountsPath is either a regular file or a directory. */
-        if ((S_ISDIR(sb.st_mode) && virFileMakePath(devMountsSavePath[i]) < 0) ||
-            (S_ISREG(sb.st_mode) && virFileTouch(devMountsSavePath[i], sb.st_mode) < 0)) {
-            virReportSystemError(errno,
-                                 _("Failed to create %s"),
-                                 devMountsSavePath[i]);
-            goto cleanup;
-        }
-
-        if (virFileMoveMount(devMountsPath[i], devMountsSavePath[i]) < 0)
-            goto cleanup;
-    }
-
     if (qemuDomainSetupAllDisks(cfg, vm, devPath) < 0)
         goto cleanup;
 
@@ -8001,6 +7974,33 @@ qemuDomainBuildNamespace(virQEMUDriverConfigPtr cfg,
     if (qemuDomainSetupAllRNGs(cfg, vm, devPath) < 0)
         goto cleanup;
 
+    /* Save some mount points because we want to share them with the host */
+    for (i = 0; i < ndevMountsPath; i++) {
+        struct stat sb;
+
+        if (devMountsSavePath[i] == devPath)
+            continue;
+
+        if (stat(devMountsPath[i], &sb) < 0) {
+            virReportSystemError(errno,
+                                 _("Unable to stat: %s"),
+                                 devMountsPath[i]);
+            goto cleanup;
+        }
+
+        /* At this point, devMountsPath is either a regular file or a directory. */
+        if ((S_ISDIR(sb.st_mode) && virFileMakePath(devMountsSavePath[i]) < 0) ||
+            (S_ISREG(sb.st_mode) && virFileTouch(devMountsSavePath[i], sb.st_mode) < 0)) {
+            virReportSystemError(errno,
+                                 _("Failed to create %s"),
+                                 devMountsSavePath[i]);
+            goto cleanup;
+        }
+
+        if (virFileMoveMount(devMountsPath[i], devMountsSavePath[i]) < 0)
+            goto cleanup;
+    }
+
     if (virFileMoveMount(devPath, "/dev") < 0)
         goto cleanup;
 
-- 
2.10.2