package/kmod: enable dlopen() for compression libraries (if any)

With dlopen() enabled, kmod will load compression libraries only if
actually needed (loading compressed modules into the kernel does not
if the kernel can handle decompression, depending on its
configuration), and only the needed one.

Use compressed modules in the kmod test without enabling in-kernel
decompression to verify decompression in kmod works.

Signed-off-by: Fiona Klute <fiona.klute@gmx.de>
Signed-off-by: Marcus Hoffmann <buildroot@bubu1.eu>

package/kmod/kmod.mk

@@ -28,6 +28,10 @@ endif
 
 KMOD_CONF_OPTS += -Dfishcompletiondir=no -Dzshcompletiondir=no
 
+# load compression libraries (if any are enabled below) as needed
+# using dlopen()
+KMOD_CONF_OPTS += -Ddlopen=all
+
 ifeq ($(BR2_PACKAGE_ZLIB),y)
 KMOD_DEPENDENCIES += zlib
 KMOD_CONF_OPTS += -Dzlib=enabled

support/testing/tests/package/test_kmod.py

@@ -4,10 +4,13 @@ import infra.basetest
 
 
 class TestKmod(infra.basetest.BRTest):
-    # This test uses the "virtio_net" driver compiled as a module. We
-    # need to recompile a Kernel for that.
-    kernel_fragment = \
-        infra.filepath("tests/package/test_kmod/linux-virtio-net.fragment")
+    # This test uses the "virtio_net" driver compiled as a module, and
+    # compressed modules to test that kmod can handle them. We need to
+    # compile a kernel for that.
+    kernel_fragments = (
+        infra.filepath("tests/package/test_kmod/compressed-modules.fragment"),
+        infra.filepath("tests/package/test_kmod/linux-virtio-net.fragment"),
+    )
     config = \
         f"""
         BR2_aarch64=y
@@ -18,10 +21,13 @@ class TestKmod(infra.basetest.BRTest):
         BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="6.6.135"
         BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
         BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="board/qemu/aarch64-virt/linux.config"
-        BR2_LINUX_KERNEL_CONFIG_FRAGMENT_FILES="{kernel_fragment}"
+        BR2_LINUX_KERNEL_CONFIG_FRAGMENT_FILES="{" ".join(kernel_fragments)}"
         BR2_PACKAGE_BUSYBOX_SHOW_OTHERS=y
         BR2_PACKAGE_KMOD=y
         BR2_PACKAGE_KMOD_TOOLS=y
+        BR2_PACKAGE_ZSTD=y
+        BR2_PACKAGE_HOST_KMOD=y
+        BR2_PACKAGE_HOST_KMOD_ZSTD=y
         BR2_TARGET_ROOTFS_EXT2=y
         BR2_TARGET_ROOTFS_EXT2_4=y
         # BR2_TARGET_ROOTFS_TAR is not set
@@ -48,6 +54,7 @@ class TestKmod(infra.basetest.BRTest):
         out, ret = self.emulator.run("modprobe --version")
         self.assertEqual(ret, 0)
         self.assertTrue(out[0].startswith("kmod version"))
+        self.assertIn("+ZSTD", out[1])
 
         # List modules with "kmod list", the virtio-net module should
         # NOT be loaded yet.
@@ -61,6 +68,7 @@ class TestKmod(infra.basetest.BRTest):
         lsmod_out = "\n".join(out)
         self.assertRegex(lsmod_out, r'name: *virtio_net')
         self.assertRegex(lsmod_out, r'description: *Virtio network driver')
+        self.assertRegex(lsmod_out, r'filename:\s+/.*/virtio_net.ko.zst')
 
         # With this test configuration, we are not supposed to have an
         # eth0 Ethernet interface yet. Attempting to show info on this

support/testing/tests/package/test_kmod/compressed-modules.fragment

@@ -0,0 +1,3 @@
+CONFIG_MODULE_COMPRESS=y
+CONFIG_MODULE_COMPRESS_ZSTD=y
+CONFIG_MODULE_COMPRESS_ALL=y