[PATCH v3 6/7] block: add secondary DPS root partition type UUID

[Vincent Mailhol <mailhol@kernel.org>]

Some 64-bit architectures can run 32-bit user space. For those
configurations, also allow DPS root discovery to use the compatible
32-bit root partition type UUID as a fallback.

Add a secondary root partition type UUID Kconfig symbol and include it
in the DPS root lookup when it is defined.

Try the secondary UUID only when the native lookup returns -ENODEV.

The fallback reflects compatibility support built into the kernel. If
32-bit execution is disabled, for example with ia32_emulation=0, the
selected root's 32-bit init will fail to execute. Do not check
ia32_enabled(): rejecting the fallback would instead leave no
discoverable root partition, resulting in a kernel panic either way.

Suggested-by: Dave Hansen <dave.hansen@intel.com>
Link: https://lore.kernel.org/r/03be57ae-0e41-4b8a-adc5-bdd85ccce951@intel.com
Signed-off-by: Vincent Mailhol <mailhol@kernel.org>
---
 block/Kconfig        | 7 +++++++
 block/early-lookup.c | 3 +++
 2 files changed, 10 insertions(+)

diff --git a/block/Kconfig b/block/Kconfig
index 3b5d3ad42dde..f3a0730ffcde 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -222,6 +222,13 @@ config DPS_ROOT_PARTITION_TYPE_UUID
 	default "4f68bce3-e8cd-4db1-96e7-fbcaf984b709" if X86_64
 	default "44479540-f297-41b2-9af7-d131d5f0458a" if X86
 
+config DPS_ROOT_PARTITION_TYPE_UUID_SECONDARY
+	depends on DPS_ROOT_PARTITION_TYPE_UUID != "" && COMPAT
+	string
+	default "69dad710-2ce4-4e3c-b16c-21a1d49abed3" if ARM64
+	default "60d5a7fe-8e7d-435c-b714-3dd8162144e1" if RISCV
+	default "44479540-f297-41b2-9af7-d131d5f0458a" if X86_64 && IA32_EMULATION
+
 config DPS_ROOT_AUTO_DISCOVERY
 	def_bool DPS_ROOT_PARTITION_TYPE_UUID != ""
 
diff --git a/block/early-lookup.c b/block/early-lookup.c
index c59d14889fee..2e7dace5efa3 100644
--- a/block/early-lookup.c
+++ b/block/early-lookup.c
@@ -340,6 +340,9 @@ int __init early_lookup_dps_root(dev_t *dev)
 {
 	static const char root_type_uuids[][UUID_STRING_LEN + 1] __initconst = {
 		CONFIG_DPS_ROOT_PARTITION_TYPE_UUID,
+#ifdef CONFIG_DPS_ROOT_PARTITION_TYPE_UUID_SECONDARY
+		CONFIG_DPS_ROOT_PARTITION_TYPE_UUID_SECONDARY,
+#endif
 	};
 	static char esp_partuuid[UUID_STRING_LEN + 1] __initdata;
 	int err;

-- 
2.56.0