of_overlay_apply_kunit(9)

💅 of_overlay_apply_kunit(9) 💅

okay so bestie, welcome to the Kernel API Manual ✨ — this one's a lil macro called of_overlay_apply_kunit, and it's genuinely iconic once you get what it's doing. let's get into it 🫶

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🌸 NAME 🌸

of_overlay_apply_kunit — it tests the managed of_overlay_fdt_apply() for built-in overlays 💖 no cap, that's the whole job.

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🦋 SYNOPSIS 🦋

of_overlay_apply_kunit (test , overlay_name );

yep, that's it. two args, one macro, zero drama ✨

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🎀 ARGUMENTS 🎀

• test — the test context, obvi. it's your KUnit test struct, the main character of the function 🐸
• overlay_name — the name of the overlay you wanna apply. literally just the name, we'll get to the whole dtbo thing in a sec 🧚

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⭐ DESCRIPTION ⭐

so this macro applies a device tree overlay. the overlay has to be built with the cmd_dt_S_dtbo rule in scripts/Makefile.lib, and it has to be compiled into the kernel image or into the KUnit test module. then — and this is the slay part — the overlay gets automatically removed when the test is finished 💅 the cleanup is handled for you, you don't have to think about it.

if your unit test needs device tree nodes, here's the vibe: compile an overlay file as overlay_name.dtbo.o in your Makefile right alongside your unit test, then load that overlay during the test. the overlay_name matches the filename of the overlay, minus the dtbo filename extension. easy ✨

💀 important vibe check: if CONFIG_OF_OVERLAY is not enabled, the test will be skipped. like, it just won't run. so don't come crying to me when nothing happens, check your config first bestie 😭

in the Makefile 🎀

obj-$(CONFIG_OF_OVERLAY_KUNIT_TEST) += overlay_test.o kunit_overlay_test.dtbo.o

in the test 🌈

static void of_overlay_kunit_of_overlay_apply(struct kunit *test)
{
        struct device_node *np;

        KUNIT_ASSERT_EQ(test, 0,
                        of_overlay_apply_kunit(test, kunit_overlay_test));

        np = of_find_node_by_name(NULL, "test-kunit");
        KUNIT_EXPECT_NOT_ERR_OR_NULL(test, np);
        of_node_put(np);
}

see how kunit_overlay_test is the overlay name and it lines up with kunit_overlay_test.dtbo.o in the Makefile? that's the whole bit 🔥 also peep the of_node_put(np) at the end — put your nodes back, don't leak, that's just manners 🫶

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👑 RETURN 👑

• 0 on success — we love a clean win 💖
• negative errno on failure — not the vibe, but at least you know 😭

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🦄 SEE ALSO 🦄

• Kernel file ./include/kunit/of.h
• __of_overlay_apply_kunit(9) — the lowercase-undercover version of this whole thing, go read it iykyk 👀

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and that's the page babes ✨ this lil gem lives under ./include/kunit and the manual's dated October 2026 📅 — so if you're reading this in the future, hi, hope the overlay applied cleanly 💜🎀🦋