pci: fail FLR when reset callback is missing

include/libvfio-user.h

@@ -120,6 +120,10 @@ vfu_create_ctx(vfu_trans_t trans, const char *path,
  * mandatory to be called before vfu_attach_ctx().
  * @vfu_ctx: the libvfio-user context
  *
+ * Devices advertising PCIe Function Level Reset capability must
+ * register a reset callback via vfu_setup_device_reset_cb()
+ * before realization, otherwise realization fails with EINVAL.
+ *
  * @returns: 0 on success, -1 on error. Sets errno.
  */
 int

lib/libvfio-user.c

@@ -1798,7 +1798,18 @@ vfu_realize_ctx(vfu_ctx_t *vfu_ctx)
     if (vfu_ctx->pci.nr_caps != 0) {
         vfu_ctx->pci.config_space->hdr.sts.cl = 0x1;
     }
+    if (vfu_ctx->pci_cap_exp_off >= 0) {
+        struct pxcap *px;
 
+        px = (struct pxcap *)pci_config_space_ptr(vfu_ctx,
+		vfu_ctx->pci_cap_exp_off);
+
+        if (px->pxdcap.flrc && vfu_ctx->reset == NULL) {
+            vfu_log(vfu_ctx, LOG_ERR,
+                    "FLR capability requires a reset callback");
+            return ERROR_INT(EINVAL);
+        }
+    }
     vfu_ctx->realized = true;
 
     return 0;

test/py/test_pci_caps.py

@@ -342,6 +342,29 @@ def test_pci_cap_write_px(mock_quiesce, mock_reset):
                          expect=errno.EINVAL)
 
 
+@patch('libvfio_user.quiesce_cb')
+def test_pci_cap_write_px_no_reset_cb(mock_quiesce):
+    """
+    FLR must fail if no reset callback exists.
+    """
+
+    global ctx
+
+    # recreate context without reset callback
+    vfu_destroy_ctx(ctx)
+
+    ctx = vfu_create_ctx(flags=LIBVFIO_USER_FLAG_ATTACH_NB)
+    assert ctx is not None
+
+    vfu_setup_device_quiesce_cb(ctx)
+
+    setup_pci_dev(realize=False)
+    setup_flrc(ctx)
+    ret = vfu_realize_ctx(ctx)
+    assert ret == -1
+    assert c.get_errno() == errno.EINVAL
+
+
 def test_pci_cap_write_msi():
     setup_pci_dev(realize=True)
     client = connect_client(ctx)