Tue, Feb 03, 2026 at 04:49:46AM +0100, kuba@kernel.org wrote:

On Wed, 28 Jan 2026 13:25:32 +0200 Tariq Toukan wrote:

quoted

From: Jiri Pirko <redacted>

Multiple PFs may reside on the same physical chip, running a single
firmware. Some of the resources and configurations may be shared among
these PFs. Currently, there is no good object to pin the configuration
knobs on.

Introduce a shared devlink instance, instantiated upon probe of the
first PF and removed during remove of the last PF. The shared devlink
instance is backed by a faux device, as there is no PCI device related
to it. The implementation uses reference counting to manage the
lifecycle: each PF that probes calls devlink_shd_get() to get or create
the shared instance, and calls devlink_shd_put() when it removes. The
shared instance is automatically destroyed when the last PF removes.

quoted

diff --git a/include/net/devlink.h b/include/net/devlink.h
index cb839e0435a1..c453faec8ebf 100644
--- a/include/net/devlink.h
+++ b/include/net/devlink.h

@@ -1644,6 +1644,12 @@ void devlink_register(struct devlink *devlink);
 void devlink_unregister(struct devlink *devlink);
 void devlink_free(struct devlink *devlink);
 
+struct devlink *devlink_shd_get(const char *id,
+				const struct devlink_ops *ops,
+				size_t priv_size);
+void devlink_shd_put(struct devlink *devlink);
+void *devlink_shd_get_priv(struct devlink *devlink);

Would Cosmin or someone else be willing to take on co-maintainership 
of this API (including reviews of other drivers using it)?
We could add a maintainers entry with:

K:	devlink_shd_

So y'all get CCed.

quoted

+#include <linux/device/faux.h>
+#include <net/devlink.h>

quoted

+/* This structure represents a shared devlink instance,
+ * there is one created per identifier (e.g., serial number).
+ */
+struct devlink_shd {
+	struct list_head list; /* Node in shd list */
+	const char *id; /* Identifier string (e.g., serial number) */

Why does this have to be a string? The identifier should be irrelevant,
and if something like serial number exists it can be reported in dev
info for the shared instance?

String gives drivers flexibility to use anything. Perhaps I'm missing
your point. Are you againts free-form or just string and buf+buf_len
would be fine?

quoted

+	struct faux_device *faux_dev; /* Related faux device */
+	refcount_t refcount; /* Reference count */
+	char priv[] __aligned(NETDEV_ALIGN); /* Driver private data */

size member annotated with __counted_by() is missing here

Will add.

quoted

+};

quoted

+static struct devlink_shd *devlink_shd_create(const char *id,
+					      const struct devlink_ops *ops,
+					      size_t priv_size)
+{
+	struct faux_device *faux_dev;
+	struct devlink_shd *shd;
+	struct devlink *devlink;
+
+	/* Create faux device - probe will be called synchronously */
+	faux_dev = faux_device_create(id, NULL, NULL);
+	if (!faux_dev)
+		return NULL;
+
+	devlink = devlink_alloc(ops, sizeof(struct devlink_shd) + priv_size,
+				&faux_dev->dev);
+	if (!devlink)
+		goto err_devlink_alloc;

error labels should be named after the target not the source in new code

Okay. Tried to be consistent with the rest of the code. But as you wish.

quoted

+	shd = devlink_priv(devlink);
+
+	shd->id = kstrdup(id, GFP_KERNEL);
+	if (!shd->id)
+		goto err_kstrdup_id;
+	shd->faux_dev = faux_dev;
+	refcount_set(&shd->refcount, 1);
+
+	devl_lock(devlink);
+	devl_register(devlink);
+	devl_unlock(devlink);
+
+	list_add_tail(&shd->list, &shd_list);
+
+	return shd;
+
+err_kstrdup_id:
+	devlink_free(devlink);
+
+err_devlink_alloc:
+	faux_device_destroy(faux_dev);
+	return NULL;
+}

quoted

+struct devlink *devlink_shd_get(const char *id,
+				const struct devlink_ops *ops,
+				size_t priv_size)
+{
+	struct devlink_shd *shd;
+
+	if (WARN_ON(!id || !ops))
+		return NULL;

Seems a little too defensive to check input attrs against NULL.
Let the kernel crash if someone is foolish enough..

Okay.

quoted

+	mutex_lock(&shd_mutex);
+
+	shd = devlink_shd_lookup(id);
+	if (!shd)
+		shd = devlink_shd_create(id, ops, priv_size);
+	else
+		refcount_inc(&shd->refcount);
+
+	mutex_unlock(&shd_mutex);
+	return shd ? priv_to_devlink(shd) : NULL;
+}
+EXPORT_SYMBOL_GPL(devlink_shd_get);
+
+/**
+ * devlink_shd_put - Release a reference on a shared devlink instance
+ * @devlink: Shared devlink instance
+ *
+ * Release a reference on a shared devlink instance obtained via
+ * devlink_shd_get().
+ */
+void devlink_shd_put(struct devlink *devlink)
+{
+	struct devlink_shd *shd;
+
+	if (WARN_ON(!devlink))
+		return;

ditto

Okay.

quoted

+	mutex_lock(&shd_mutex);
+	shd = devlink_priv(devlink);
+	if (refcount_dec_and_test(&shd->refcount))
+		devlink_shd_destroy(shd);
+	mutex_unlock(&shd_mutex);
+}
+EXPORT_SYMBOL_GPL(devlink_shd_put);