tpm: lookup cancel path under tpm device class

Since Linux commit 313d21eeab9282e, tpm devices have their own device
class "tpm" and the cancel path must be looked up under
/sys/class/tpm/ instead of /sys/class/misc/.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>

hw/tpm/tpm_passthrough.c

@@ -214,7 +214,8 @@ static size_t tpm_passthrough_get_buffer_size(TPMBackend *tb)
  * Unless path or file descriptor set has been provided by user,
  * determine the sysfs cancel file following kernel documentation
  * in Documentation/ABI/stable/sysfs-class-tpm.
- * From /dev/tpm0 create /sys/class/misc/tpm0/device/cancel
+ * From /dev/tpm0 create /sys/class/tpm/tpm0/device/cancel
+ * before 4.0: /sys/class/misc/tpm0/device/cancel
  */
 static int tpm_passthrough_open_sysfs_cancel(TPMPassthruState *tpm_pt)
 {
@@ -225,26 +226,35 @@ static int tpm_passthrough_open_sysfs_cancel(TPMPassthruState *tpm_pt)
     if (tpm_pt->options->cancel_path) {
         fd = qemu_open(tpm_pt->options->cancel_path, O_WRONLY);
         if (fd < 0) {
-            error_report("Could not open TPM cancel path : %s",
+            error_report("tpm_passthrough: Could not open TPM cancel path: %s",
                          strerror(errno));
         }
         return fd;
     }
 
     dev = strrchr(tpm_pt->tpm_dev, '/');
-    if (dev) {
-        dev++;
-        if (snprintf(path, sizeof(path), "/sys/class/misc/%s/device/cancel",
-                     dev) < sizeof(path)) {
-            fd = qemu_open(path, O_WRONLY);
-            if (fd < 0) {
-                error_report("tpm_passthrough: Could not open TPM cancel "
-                             "path %s : %s", path, strerror(errno));
+    if (!dev) {
+        error_report("tpm_passthrough: Bad TPM device path %s",
+                     tpm_pt->tpm_dev);
+        return -1;
+    }
+
+    dev++;
+    if (snprintf(path, sizeof(path), "/sys/class/tpm/%s/device/cancel",
+                 dev) < sizeof(path)) {
+        fd = qemu_open(path, O_WRONLY);
+        if (fd < 0) {
+            if (snprintf(path, sizeof(path), "/sys/class/misc/%s/device/cancel",
+                         dev) < sizeof(path)) {
+                fd = qemu_open(path, O_WRONLY);
             }
         }
+    }
+
+    if (fd < 0) {
+        error_report("tpm_passthrough: Could not guess TPM cancel path");
     } else {
-       error_report("tpm_passthrough: Bad TPM device path %s",
-                    tpm_pt->tpm_dev);
+        tpm_pt->options->cancel_path = g_strdup(path);
     }
 
     return fd;