criu: improve prepareCriuRestoreMounts

1. Replace the big "if !" block with the if block and continue,
   simplifying the code flow.

2. Move comments closer to the code, improving readability.

This commit is best reviewed with --ignore-all-space or similar.

Signed-off-by: Kir Kolyshkin <[email protected]>

Author: kolyshkin

libcontainer/criu_linux.go

@@ -572,9 +572,6 @@ func (c *Container) prepareCriuRestoreMounts(mounts []*configs.Mount) error {
 			tmpfs = append(tmpfs, m.Destination)
 		}
 	}
-	// Now go through all mounts and create the mountpoints
-	// if the mountpoints are not on a tmpfs, as CRIU will
-	// restore the complete tmpfs content from its checkpoint.
 	umounts := []string{}
 	defer func() {
 		for _, u := range umounts {
@@ -590,28 +587,32 @@ func (c *Container) prepareCriuRestoreMounts(mounts []*configs.Mount) error {
 			})
 		}
 	}()
+	// Now go through all mounts and create the required mountpoints.
 	for _, m := range mounts {
-		if !isPathInPrefixList(m.Destination, tmpfs) {
-			if err := c.makeCriuRestoreMountpoints(m); err != nil {
+		// If the mountpoint is on a tmpfs, skip it as CRIU will
+		// restore the complete tmpfs content from its checkpoint.
+		if isPathInPrefixList(m.Destination, tmpfs) {
+			continue
+		}
+		if err := c.makeCriuRestoreMountpoints(m); err != nil {
+			return err
+		}
+		// If the mount point is a bind mount, we need to mount
+		// it now so that runc can create the necessary mount
+		// points for mounts in bind mounts.
+		// This also happens during initial container creation.
+		// Without this CRIU restore will fail
+		// See: https://github.com/opencontainers/runc/issues/2748
+		// It is also not necessary to order the mount points
+		// because during initial container creation mounts are
+		// set up in the order they are configured.
+		if m.Device == "bind" {
+			if err := utils.WithProcfd(c.config.Rootfs, m.Destination, func(dstFd string) error {
+				return mountViaFds(m.Source, nil, m.Destination, dstFd, "", unix.MS_BIND|unix.MS_REC, "")
+			}); err != nil {
 				return err
 			}
-			// If the mount point is a bind mount, we need to mount
-			// it now so that runc can create the necessary mount
-			// points for mounts in bind mounts.
-			// This also happens during initial container creation.
-			// Without this CRIU restore will fail
-			// See: https://github.com/opencontainers/runc/issues/2748
-			// It is also not necessary to order the mount points
-			// because during initial container creation mounts are
-			// set up in the order they are configured.
-			if m.Device == "bind" {
-				if err := utils.WithProcfd(c.config.Rootfs, m.Destination, func(dstFd string) error {
-					return mountViaFds(m.Source, nil, m.Destination, dstFd, "", unix.MS_BIND|unix.MS_REC, "")
-				}); err != nil {
-					return err
-				}
-				umounts = append(umounts, m.Destination)
-			}
+			umounts = append(umounts, m.Destination)
 		}
 	}
 	return nil