From: Corentin LABBE <clabbe@baylibre.com>

Checking if some firmware is missing need to check dmesg for error message,
and on some machine this information could be lost since dmesg uses a ring buffer.
Having the list of all firmware requests is useful in many situations,
like selecting the minimal list when doing some buildroot config
or reducing the size of linux-firmware on gentoo via saveconfig.

So for letting thoses tasks to be automated easily, it is better to have all
loaded firmware in one place.
This patch adds a debugfs with all firmware that was tried to be loaded and the
result of those actions.

Signed-off-by: Corentin LABBE <clabbe@baylibre.com>
---

Hello

I believe the list could setup more appropriate elsewhere in /sys, but
without idea, I used debugfs.
If you have better idea, let me know it.

Regards
 drivers/base/firmware_loader/main.c | 100 ++++++++++++++++++++++++++++
 1 file changed, 100 insertions(+)

diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c
index 24213a0ea831..786d9b2b096e 100644
--- a/drivers/base/firmware_loader/main.c
+++ b/drivers/base/firmware_loader/main.c
@@ -11,7 +11,9 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/capability.h>
+#include <linux/debugfs.h>
 #include <linux/device.h>
+#include <linux/errname.h>
 #include <linux/kernel_read_file.h>
 #include <linux/module.h>
 #include <linux/init.h>
@@ -35,6 +37,7 @@
 #include <linux/syscore_ops.h>
 #include <linux/reboot.h>
 #include <linux/security.h>
+#include <linux/seq_file.h>
 #include <linux/zstd.h>
 #include <linux/xz.h>
 
@@ -48,6 +51,95 @@ MODULE_AUTHOR("Manuel Estrada Sainz");
 MODULE_DESCRIPTION("Multi purpose firmware loading support");
 MODULE_LICENSE("GPL");
 
+struct fw_loaded_entry {
+	struct list_head node;
+	const char *driver;
+	const char *fw_name;
+	int result;
+};
+
+static LIST_HEAD(fw_loaded_list);
+static DEFINE_MUTEX(fw_loaded_lock);
+static struct dentry *fw_debugfs_dir;
+
+static void fw_record_request(struct device *device, const char *name, int ret)
+{
+	const char *driver = device ? dev_driver_string(device) : "(none)";
+	struct fw_loaded_entry *entry;
+
+	if (!name || name[0] == '\0')
+		return;
+
+	guard(mutex)(&fw_loaded_lock);
+
+	/* Update in place if we have already seen this request. */
+	list_for_each_entry(entry, &fw_loaded_list, node) {
+		if (!strcmp(entry->driver, driver) &&
+		    !strcmp(entry->fw_name, name)) {
+			entry->result = ret;
+			return;
+		}
+	}
+
+	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
+	if (!entry)
+		return;
+
+	entry->driver = kstrdup(driver, GFP_KERNEL);
+	entry->fw_name = kstrdup(name, GFP_KERNEL);
+	if (!entry->driver || !entry->fw_name) {
+		kfree(entry->driver);
+		kfree(entry->fw_name);
+		kfree(entry);
+		return;
+	}
+
+	entry->result = ret;
+	list_add_tail(&entry->node, &fw_loaded_list);
+}
+
+static int fw_list_show(struct seq_file *m, void *v)
+{
+	struct fw_loaded_entry *entry;
+
+	guard(mutex)(&fw_loaded_lock);
+
+	list_for_each_entry(entry, &fw_loaded_list, node) {
+		const char *name;
+
+		if (entry->result >= 0) {
+			seq_printf(m, "%s %s OK\n",
+				   entry->driver, entry->fw_name);
+			continue;
+		}
+
+		name = errname(-entry->result);
+		if (name)
+			seq_printf(m, "%s %s %s\n",
+				   entry->driver, entry->fw_name, name);
+		else
+			seq_printf(m, "%s %s %d\n",
+				   entry->driver, entry->fw_name, entry->result);
+	}
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(fw_list);
+
+static void fw_loaded_list_free(void)
+{
+	struct fw_loaded_entry *entry, *tmp;
+
+	guard(mutex)(&fw_loaded_lock);
+
+	list_for_each_entry_safe(entry, tmp, &fw_loaded_list, node) {
+		list_del(&entry->node);
+		kfree(entry->driver);
+		kfree(entry->fw_name);
+		kfree(entry);
+	}
+}
+
 struct firmware_cache {
 	/* firmware_buf instance will be added into the below list */
 	spinlock_t lock;
@@ -911,6 +1003,8 @@ _request_firmware(const struct firmware **firmware_p, const char *name,
 		fw_log_firmware_info(fw, name, device);
 	}
 
+	fw_record_request(device, name, ret);
+
 	*firmware_p = fw;
 	return ret;
 }
@@ -1727,6 +1821,10 @@ static int __init firmware_class_init(void)
 	if (ret)
 		goto out;
 
+	fw_debugfs_dir = debugfs_create_dir("firmware_loader", NULL);
+	debugfs_create_file("firmware_list", 0444, fw_debugfs_dir, NULL,
+			    &fw_list_fops);
+
 	return register_sysfs_loader();
 
 out:
@@ -1739,6 +1837,8 @@ static void __exit firmware_class_exit(void)
 	unregister_fw_pm_ops();
 	unregister_reboot_notifier(&fw_shutdown_nb);
 	unregister_sysfs_loader();
+	debugfs_remove_recursive(fw_debugfs_dir);
+	fw_loaded_list_free();
 }
 
 fs_initcall(firmware_class_init);
-- 
2.53.0

(Cc: driver-core; please make sure to Cc all relevant mailing lists)

On Wed Jul 15, 2026 at 3:13 PM CEST, Corentin Labbe wrote:
> From: Corentin LABBE <clabbe@baylibre.com>
>
> Checking if some firmware is missing need to check dmesg for error message,
> and on some machine this information could be lost since dmesg uses a ring buffer.
> Having the list of all firmware requests is useful in many situations,
> like selecting the minimal list when doing some buildroot config
> or reducing the size of linux-firmware on gentoo via saveconfig.

The proposed implementation aside, I don't see why this needs a new kernel
interface.

  - Why can't you use 'modinfo -F firmware' for all compiled modules?

  - Don't you have a journal persisting the dmesg logs?

  - Why can't you use kprobe_event on the kernel command line if you really need
    a runtime trace?

Untested, but something like

	kprobe_event=p:fw_req,_request_firmware,name=+0(%si):string

should work I think.

Thanks,
Danilo

Le Wed, Jul 15, 2026 at 07:23:25PM +0200, Danilo Krummrich a écrit :
> (Cc: driver-core; please make sure to Cc all relevant mailing lists)
> 
> On Wed Jul 15, 2026 at 3:13 PM CEST, Corentin Labbe wrote:
> > From: Corentin LABBE <clabbe@baylibre.com>
> >
> > Checking if some firmware is missing need to check dmesg for error message,
> > and on some machine this information could be lost since dmesg uses a ring buffer.
> > Having the list of all firmware requests is useful in many situations,
> > like selecting the minimal list when doing some buildroot config
> > or reducing the size of linux-firmware on gentoo via saveconfig.
> 
> The proposed implementation aside, I don't see why this needs a new kernel
> interface.

Hello

You miss the point that I propose an easy way to know.
All your proposals imply scripting, grepping in difference place.
I propose a unique easy way to know the list, without any requirement

> 
>   - Why can't you use 'modinfo -F firmware' for all compiled modules?

Because it display all possible firmware for each module, I want only required/tried module for the host system

>   - Don't you have a journal persisting the dmesg logs?
> 

I propose something that work with embeded devices without storage and/or without syslog/journald.

>   - Why can't you use kprobe_event on the kernel command line if you really need
>     a runtime trace?
> 
> Untested, but something like
> 
> 	kprobe_event=p:fw_req,_request_firmware,name=+0(%si):string
> 
> should work I think.
This imply command line hacking, something I prefer to avoid, it is better when it just works without change.

Thanks
Regards

On Thu Jul 16, 2026 at 11:29 AM CEST, Corentin LABBE wrote:
> Le Wed, Jul 15, 2026 at 07:23:25PM +0200, Danilo Krummrich a écrit :
>> (Cc: driver-core; please make sure to Cc all relevant mailing lists)
>> 
>> On Wed Jul 15, 2026 at 3:13 PM CEST, Corentin Labbe wrote:
>> > From: Corentin LABBE <clabbe@baylibre.com>
>> >
>> > Checking if some firmware is missing need to check dmesg for error message,
>> > and on some machine this information could be lost since dmesg uses a ring buffer.
>> > Having the list of all firmware requests is useful in many situations,
>> > like selecting the minimal list when doing some buildroot config
>> > or reducing the size of linux-firmware on gentoo via saveconfig.
>> 
>> The proposed implementation aside, I don't see why this needs a new kernel
>> interface.
>
> Hello
>
> You miss the point that I propose an easy way to know.
> All your proposals imply scripting, grepping in difference place.
> I propose a unique easy way to know the list, without any requirement

No, I get that, but I think that the overhead of the proposed patch is not
justified, given that there are reasonable alternatives.

>> Untested, but something like
>> 
>> 	kprobe_event=p:fw_req,_request_firmware,name=+0(%si):string
>> 
>> should work I think.
> This imply command line hacking, something I prefer to avoid, it is better when it just works without change.

Adding a kernel command line parameter seems perfectly reasonable for your
use-case. We could maybe consider a dedicated TRACE_EVENT for firmware being
loaded if this turns out to be a thing people commonly want to have, but for now
it seems a kprobe_event works for your case.