libxl: fix cleanup of tap devices in libxl__device_destroy

We pass be_path to tapdisk_destroy but we've already deleted it so it
fails to read tapdisk-params. However it appears that we need to
destroy the tap device after tearing down xenstore, to avoid the leak
reported by Greg Wettstein in
<201207312141.q6VLfJje012656@wind.enjellic.com>.

So read the tapdisk-params in the cleanup transaction, before the
remove, and pass that down to destroy_tapdisk instead. tapdisk-params
may of course be NULL if the device isn't a tap device.

There is no need to tear down the tap device from
libxl__initiate_device_remove since this ultimately calls
libxl__device_destroy.

Propagate and log errors from libxl__device_destroy_tapdisk.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
index 6d8e562e9e..8e8410e214 100644
--- a/tools/libxl/libxl_device.c
+++ b/tools/libxl/libxl_device.c
@@ -522,8 +522,10 @@ DEFINE_DEVICES_ADD(nic)
 
 int libxl__device_destroy(libxl__gc *gc, libxl__device *dev)
 {
-    char *be_path = libxl__device_backend_path(gc, dev);
+    const char *be_path = libxl__device_backend_path(gc, dev);
     const char *fe_path = libxl__device_frontend_path(gc, dev);
+    const char *tapdisk_path = GCSPRINTF("%s/%s", be_path, "tapdisk-params");
+    const char *tapdisk_params;
     xs_transaction_t t = 0;
     int rc;
 
@@ -531,6 +533,10 @@ int libxl__device_destroy(libxl__gc *gc, libxl__device *dev)
         rc = libxl__xs_transaction_start(gc, &t);
         if (rc) goto out;
 
+        /* May not exist if this is not a tap device */
+        rc = libxl__xs_read_checked(gc, t, tapdisk_path, &tapdisk_params);
+        if (rc) goto out;
+
         libxl__xs_path_cleanup(gc, t, fe_path);
         libxl__xs_path_cleanup(gc, t, be_path);
 
@@ -539,7 +545,8 @@ int libxl__device_destroy(libxl__gc *gc, libxl__device *dev)
         if (rc < 0) goto out;
     }
 
-    libxl__device_destroy_tapdisk(gc, be_path);
+    if (tapdisk_params)
+        rc = libxl__device_destroy_tapdisk(gc, tapdisk_params);
 
 out:
     libxl__xs_transaction_abort(gc, &t);
@@ -790,8 +797,6 @@ void libxl__initiate_device_remove(libxl__egc *egc,
         if (rc < 0) goto out;
     }
 
-    libxl__device_destroy_tapdisk(gc, be_path);
-
     rc = libxl__ev_devstate_wait(gc, &aodev->backend_ds,
                                  device_backend_callback,
                                  state_path, XenbusStateClosed,