dibs: Define dibs loopback

The first stage of loopback-ism was implemented as part of the
SMC module [1]. Now that we have the dibs layer, provide access to a
dibs_loopback device to all dibs clients.

This is the first step of moving loopback-ism from net/smc/smc_loopback.*
to drivers/dibs/dibs_loopback.*. One global structure lo_dev is allocated
and added to the dibs devices. Follow-on patches will move functionality.

Same as smc_loopback, dibs_loopback is provided by a config option.
Note that there is no way to dynamically add or remove the loopback
device. That could be a future improvement.

When moving code to drivers/dibs, replace ism_ prefix with dibs_ prefix.
As this is mostly a move of existing code, copyright and authors are
unchanged.

Link: https://lore.kernel.org/lkml/20240428060738.60843-1-guwen@linux.alibaba.com/ [1]
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Link: https://patch.msgid.link/20250918110500.1731261-7-wintera@linux.ibm.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 78 insertions, 0 deletions

diff --git a/drivers/dibs/dibs_loopback.c b/drivers/dibs/dibs_loopback.c
new file mode 100644
index 000000000000..225514a452a8
--- /dev/null
+++ b/drivers/dibs/dibs_loopback.c
@@ -0,0 +1,78 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  Functions for dibs loopback/loopback-ism device.
+ *
+ *  Copyright (c) 2024, Alibaba Inc.
+ *
+ *  Author: Wen Gu <guwen@linux.alibaba.com>
+ *          Tony Lu <tonylu@linux.alibaba.com>
+ *
+ */
+
+#include <linux/dibs.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+
+#include "dibs_loopback.h"
+
+/* global loopback device */
+static struct dibs_lo_dev *lo_dev;
+
+static void dibs_lo_dev_exit(struct dibs_lo_dev *ldev)
+{
+	dibs_dev_del(ldev->dibs);
+}
+
+static int dibs_lo_dev_probe(void)
+{
+	struct dibs_lo_dev *ldev;
+	struct dibs_dev *dibs;
+	int ret;
+
+	ldev = kzalloc(sizeof(*ldev), GFP_KERNEL);
+	if (!ldev)
+		return -ENOMEM;
+
+	dibs = dibs_dev_alloc();
+	if (!dibs) {
+		kfree(ldev);
+		return -ENOMEM;
+	}
+
+	ldev->dibs = dibs;
+
+	ret = dibs_dev_add(dibs);
+	if (ret)
+		goto err_reg;
+	lo_dev = ldev;
+	return 0;
+
+err_reg:
+	/* pairs with dibs_dev_alloc() */
+	kfree(dibs);
+	kfree(ldev);
+
+	return ret;
+}
+
+static void dibs_lo_dev_remove(void)
+{
+	if (!lo_dev)
+		return;
+
+	dibs_lo_dev_exit(lo_dev);
+	/* pairs with dibs_dev_alloc() */
+	kfree(lo_dev->dibs);
+	kfree(lo_dev);
+	lo_dev = NULL;
+}
+
+int dibs_loopback_init(void)
+{
+	return dibs_lo_dev_probe();
+}
+
+void dibs_loopback_exit(void)
+{
+	dibs_lo_dev_remove();
+}