linux-kernel - [PATCH v6 3/5] Implement modalias sysfs attribute for modules

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Date:   Fri,  2 Dec 2022 16:47:42 -0600
From:   Allen Webb <allenwebb@...gle.com>
To:     "linux-modules@...r.kernel.org" <linux-modules@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     Luis Chamberlain <mcgrof@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Allen Webb <allenwebb@...gle.com>
Subject: [PATCH v6 3/5] Implement modalias sysfs attribute for modules

When the modalias attribute is read, invoke a subsystem-specific
callback for each driver registered by the specific module.

The intent of the new modalias attribute is to expose the
match-id-based modaliases to userspace for builtin and loaded kernel
modules.

Signed-off-by: Allen Webb <allenwebb@...gle.com>
---
 include/linux/device/bus.h |  7 +++++
 kernel/module/sysfs.c      | 57 +++++++++++++++++++++++++++++++++++++-
 2 files changed, 63 insertions(+), 1 deletion(-)

diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
index 82a5583437099..cce0bedec63d9 100644
--- a/include/linux/device/bus.h
+++ b/include/linux/device/bus.h
@@ -61,6 +61,10 @@ struct fwnode_handle;
  *			this bus.
  * @dma_cleanup:	Called to cleanup DMA configuration on a device on
  *			this bus.
+ * @drv_to_modalias:    Called to convert the matching IDs in a
+ *                      struct device_driver to their corresponding modaliases.
+ *                      Note that the struct device_driver is expected to belong
+ *                      to this bus.
  * @pm:		Power management operations of this bus, callback the specific
  *		device driver's pm-ops.
  * @iommu_ops:  IOMMU specific operations for this bus, used to attach IOMMU
@@ -107,6 +111,9 @@ struct bus_type {
 	int (*dma_configure)(struct device *dev);
 	void (*dma_cleanup)(struct device *dev);
 
+	ssize_t (*drv_to_modalias)(struct device_driver *drv, char *buf,
+				   size_t count);
+
 	const struct dev_pm_ops *pm;
 
 	const struct iommu_ops *iommu_ops;
diff --git a/kernel/module/sysfs.c b/kernel/module/sysfs.c
index 8dafec7455fbe..651c677c4ab96 100644
--- a/kernel/module/sysfs.c
+++ b/kernel/module/sysfs.c
@@ -5,6 +5,8 @@
  * Copyright (C) 2008 Rusty Russell
  */
 
+#include <linux/device/bus.h>
+#include <linux/device/driver.h>
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/fs.h>
@@ -240,11 +242,64 @@ static inline void add_notes_attrs(struct module *mod, const struct load_info *i
 static inline void remove_notes_attrs(struct module *mod) { }
 #endif /* CONFIG_KALLSYMS */
 
+/* Track of the buffer and module identity in callbacks when walking the list of
+ * drivers for each bus.
+ */
+struct modalias_bus_print_state {
+	struct module_kobject *mk;
+	char *buf;
+	size_t count;
+	ssize_t len;
+};
+
+static int print_modalias_for_drv(struct device_driver *drv, void *p)
+{
+	struct modalias_bus_print_state *s = p;
+	struct module_kobject *mk = s->mk;
+	ssize_t len;
+	/* Skip drivers that do not match this module. */
+	if (mk->mod) {
+		if (mk->mod != drv->owner)
+			return 0;
+	} else if (!mk->kobj.name || !drv->mod_name ||
+		   strcmp(mk->kobj.name, drv->mod_name))
+		return 0;
+
+	if (drv->bus && drv->bus->drv_to_modalias) {
+		len = drv->bus->drv_to_modalias(drv, s->buf + s->len,
+						s->count - s->len);
+		if (len < 0)
+			return len;
+		s->len += len;
+	}
+	return 0;
+}
+
+static int print_modalias_for_bus(struct bus_type *type, void *p)
+{
+	return bus_for_each_drv(type, NULL, p, print_modalias_for_drv);
+}
+
 static ssize_t module_modalias_read(struct file *filp, struct kobject *kobj,
 				    struct bin_attribute *bin_attr,
 				    char *buf, loff_t pos, size_t count)
 {
-	return 0;
+	struct module_kobject *mk = container_of(kobj, struct module_kobject,
+						 kobj);
+	struct modalias_bus_print_state state = {mk, buf, count, 0};
+	int error = 0;
+
+	if (pos != 0)
+		return -EINVAL;
+
+	error = bus_for_each(&state, print_modalias_for_bus);
+	if (error)
+		return error;
+
+	/*
+	 * The caller checked the pos and count against our size.
+	 */
+	return state.len;
 }
 
 /* Used in kernel/params.c for builtin modules.
-- 
2.37.3