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

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.

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.

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

+/* 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?

+	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

+};

+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

+	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;
+}

+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..

+	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

+	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);