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Subject[PATCH v10 04/11] module.h: MODULE_DEVICE_TABLE for built-in modules
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Implement MODULE_DEVICE_TABLE for build-in modules to make it possible
to generate a builtin.alias file to complement modules.alias.

Signed-off-by: Allen Webb <allenwebb@google.com>
---
include/linux/module.h | 36 +++++++++++++++++++++++++++++-------
1 file changed, 29 insertions(+), 7 deletions(-)

diff --git a/include/linux/module.h b/include/linux/module.h
index 4435ad9439ab..b1cb12e06996 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -237,14 +237,36 @@ extern void cleanup_module(void);
/* What your module does. */
#define MODULE_DESCRIPTION(_description) MODULE_INFO(description, _description)

-#ifdef MODULE
-/* Creates an alias so file2alias.c can find device table. */
+/*
+ * Creates an alias so file2alias.c can find device table.
+ *
+ * Use this in cases where a device table is used to match devices because it
+ * surfaces match-id based module aliases to userspace for:
+ * - Automatic module loading through modules.alias.
+ * - Tools like USBGuard which block devices based on policy such as which
+ * modules match a device.
+ *
+ * The only use-case for built-in drivers today is to enable userspace to
+ * prevent / allow probe for devices on certain subsystems even if the driver is
+ * already loaded. An example is the USB subsystem with its authorized_default
+ * sysfs attribute. For more details refer to the kernel's Documentation for USB
+ * about authorized_default.
+ *
+ * The module name is included in the alias for two reasons:
+ * - It avoids creating two aliases with the same name for built-in modules.
+ * Historically MODULE_DEVICE_TABLE was a no-op for built-in modules, so
+ * there was nothing to stop different modules from having the same device
+ * table name and consequently the same alias when building as a module.
+ * - The module name is needed by files2alias.c to associate a particular
+ * device table with its associated module for built-in modules since
+ * files2alias would otherwise see the module name as `vmlinuz.o`.
+ */
#define MODULE_DEVICE_TABLE(type, name) \
-extern typeof(name) __mod_##type##__##name##_device_table \
- __attribute__ ((unused, alias(__stringify(name))))
-#else /* !MODULE */
-#define MODULE_DEVICE_TABLE(type, name)
-#endif
+extern void *CONCATENATE( \
+ CONCATENATE(__mod_##type##__##name##__, \
+ __KBUILD_MODNAME), \
+ _device_table) \
+ __attribute__ ((unused, alias(__stringify(name))))

/* Version of form [<epoch>:]<version>[-<extra-version>].
* Or for CVS/RCS ID version, everything but the number is stripped.
--
2.39.2
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