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>

4 files changed, 34 insertions, 18 deletions

diff --git a/tools/libxl/libxl_blktap2.c b/tools/libxl/libxl_blktap2.c
index 2c40182057..2053403a5b 100644
--- a/tools/libxl/libxl_blktap2.c
+++ b/tools/libxl/libxl_blktap2.c
@@ -51,28 +51,37 @@ char *libxl__blktap_devpath(libxl__gc *gc,
 }
 
 
-void libxl__device_destroy_tapdisk(libxl__gc *gc, char *be_path)
+int libxl__device_destroy_tapdisk(libxl__gc *gc, const char *params)
 {
-    char *path, *params, *type, *disk;
+    char *type, *disk;
     int err;
     tap_list_t tap;
 
-    path = libxl__sprintf(gc, "%s/tapdisk-params", be_path);
-    if (!path) return;
+    type = libxl__strdup(gc, params);
 
-    params = libxl__xs_read(gc, XBT_NULL, path);
-    if (!params) return;
-
-    type = params;
-    disk = strchr(params, ':');
-    if (!disk) return;
+    disk = strchr(type, ':');
+    if (!disk) {
+        LOG(ERROR, "Unable to parse params %s", params);
+        return ERROR_INVAL;
+    }
 
     *disk++ = '\0';
 
     err = tap_ctl_find(type, disk, &tap);
-    if (err < 0) return;
+    if (err < 0) {
+        /* returns -errno */
+        LOGEV(ERROR, -err, "Unable to find type %s disk %s", type, disk);
+        return ERROR_FAIL;
+    }
+
+    err = tap_ctl_destroy(tap.id, tap.minor);
+    if (err < 0) {
+        LOGEV(ERROR, -err, "Failed to destroy tap device id %d minor %d",
+              tap.id, tap.minor);
+        return ERROR_FAIL;
+    }
 
-    tap_ctl_destroy(tap.id, tap.minor);
+    return 0;
 }
 
 /*
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,
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 674c88172a..cf5d9e92df 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -1344,8 +1344,9 @@ _hidden char *libxl__blktap_devpath(libxl__gc *gc,
 /* libxl__device_destroy_tapdisk:
  *   Destroys any tapdisk process associated with the backend represented
  *   by be_path.
+ *   Always logs on failure.
  */
-_hidden void libxl__device_destroy_tapdisk(libxl__gc *gc, char *be_path);
+_hidden int libxl__device_destroy_tapdisk(libxl__gc *gc, const char *params);
 
 _hidden int libxl__device_from_disk(libxl__gc *gc, uint32_t domid,
                                    libxl_device_disk *disk,
diff --git a/tools/libxl/libxl_noblktap2.c b/tools/libxl/libxl_noblktap2.c
index 246b0de63b..5a86ed1b6a 100644
--- a/tools/libxl/libxl_noblktap2.c
+++ b/tools/libxl/libxl_noblktap2.c
@@ -28,8 +28,9 @@ char *libxl__blktap_devpath(libxl__gc *gc,
     return NULL;
 }
 
-void libxl__device_destroy_tapdisk(libxl__gc *gc, char *be_path)
+int libxl__device_destroy_tapdisk(libxl__gc *gc, const char *params)
 {
+    return 0;
 }
 
 /*