Re: [PATCH] kunit: use scoped_with_init_fs() in tests that resolve paths

[David Disseldorp <ddiss@suse.de>]

Hi Christian,

Sorry for the late response, I missed this...

On Wed, 01 Jul 2026 16:54:23 +0200, Christian Brauner wrote:

> KUnit runs each test in a kthread (kunit_generic_run_threadfn_adapter()).
...
> The initramfs tests hit the same
> wall: they call unpack_to_rootfs() (init_mkdir()/init_mknod() under the
> hood) and then verify with relative-name init_stat()/init_unlink()/
> filp_open(), all of which resolve against the nullfs root and pwd.
> 
> Wrap the path-resolving regions of both suites in scoped_with_init_fs(),
> which borrows the userspace init fs_struct (set up by init_userspace_fs()
> before kunit_run_all_tests()) for the duration. This is the same opt-in
> the rest of the tree uses for kthread path resolution. Doing it per test
> rather than blanket-wrapping the KUnit runner keeps the nullfs isolation
> in place for the many tests that should never touch the filesystem.

Doing it per-test certainly makes sense, but for initramfs I think it'd
be a little cleaner to just use the existing per-test init() callback
instead. I.e.:

diff --git a/init/initramfs_test.c b/init/initramfs_test.c
index bc55306d226dc..9cf316c13ffa5 100644
--- a/init/initramfs_test.c
+++ b/init/initramfs_test.c
@@ -3,6 +3,7 @@
 #include <linux/fcntl.h>
 #include <linux/file.h>
 #include <linux/fs.h>
+#include <linux/fs_struct.h>
 #include <linux/init.h>
 #include <linux/init_syscalls.h>
 #include <linux/initrd.h>
@@ -562,7 +563,7 @@ static struct kunit_case __refdata initramfs_test_cases[] = {
        {},
 };
 
-static int __init initramfs_test_init(struct kunit_suite *suite)
+static int __init initramfs_suite_init(struct kunit_suite *suite)
 {
        /*
         * unpack_to_rootfs() uses module-static state (victim, byte_count,
@@ -574,9 +575,23 @@ static int __init initramfs_test_init(struct kunit_suite *suite)
        return 0;
 }
 
+/* Tests run in a nullfs kthread; always use the init fs for path resolution. */
+static int __init initramfs_test_init(struct kunit *test)
+{
+       test->priv = __override_init_fs();
+       return 0;
+}
+
+static void __init initramfs_test_exit(struct kunit *test)
+{
+       __revert_init_fs(test->priv);
+}
+
 static struct kunit_suite __refdata initramfs_test_suite = {
        .name = "initramfs",
-       .suite_init = initramfs_test_init,
+       .suite_init = initramfs_suite_init,
+       .init = initramfs_test_init,
+       .exit = initramfs_test_exit,
        .test_cases = initramfs_test_cases,
 };
 kunit_test_init_section_suites(&initramfs_test_suite);

What do you think?

Cheers, David