This sample demonstrates how to use blk_interposer.
It show how to properly connect the interposer module to kernel,
and perform the simplest monitoring of the number of bio.

Signed-off-by: Sergei Shtepa <redacted>
---
 samples/blk_interposer/Makefile         |   2 +
 samples/blk_interposer/blk-interposer.c | 276 ++++++++++++++++++++++++
 2 files changed, 278 insertions(+)
 create mode 100644 samples/blk_interposer/Makefile
 create mode 100644 samples/blk_interposer/blk-interposer.c

diff --git a/samples/blk_interposer/Makefile b/samples/blk_interposer/Makefile
new file mode 100644
index 000000000000..b11aefde2b1c
--- /dev/null
+++ b/samples/blk_interposer/Makefile

@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0
+obj-$(CONFIG_SAMPLE_BLK_INTERPOSER) += blk-interposer.o

diff --git a/samples/blk_interposer/blk-interposer.c b/samples/blk_interposer/blk-interposer.c
new file mode 100644
index 000000000000..92b4c1fcf8f7
--- /dev/null
+++ b/samples/blk_interposer/blk-interposer.c

@@ -0,0 +1,276 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Block layer interposer allow to interpose bio requests from kernel module.
+ * This allows you to monitor requests, modify requests, add new request,
+ * or even redirect requests to another devices.
+ *
+ * This sample demonstrates how to use blk_interposer.
+ * It show how to properly connect the interposer module to kernel,
+ * and perform the simplest monitoring of the number of bio.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/blkdev.h>
+#include <linux/genhd.h>
+#include <linux/blk-mq.h>
+
+int device_major = 8;
+int device_minor;
+int fmode = FMODE_READ | FMODE_WRITE;
+
+/*
+ * Each interposer must have a common part in the form of the blk_interposer structure,
+ * as well as its own unique data.
+ */
+struct my_interposer {
+	/*
+	 * Common part of block device interposer.
+	 */
+	struct blk_interposer interposer;
+	/*
+	 * Specific part for our interposer data.
+	 */
+	atomic_t counter;
+};
+
+struct my_interposer my_ip;
+
+/**
+ * blk_interposer_attach - Attach interposer to disk
+ * @disk: target disk
+ * @interposer: block device interposer
+ */
+static int blk_interposer_attach(struct gendisk *disk, struct blk_interposer *interposer)
+{
+	int ret = 0;
+
+	/*
+	 * Stop disks queue processing.
+	 */
+	blk_mq_freeze_queue(disk->queue);
+	blk_mq_quiesce_queue(disk->queue);
+
+	/*
+	 * Check if the interposer is already busy.
+	 * The interposer will only connect if it is not busy.
+	 */
+	if (blk_has_interposer(disk)) {
+		pr_info("The interposer is already busy.\n");
+		ret = -EBUSY;
+		goto out;
+	}
+
+	/*
+	 * Attach the interposer.
+	 */
+	disk->interposer = interposer;
+	/*
+	 * And while the queue is stopped, we can do something specific for our module.
+	 */
+	pr_info("Block device interposer attached successfully.\n");
+
+out:
+	/*
+	 * Resume disks queue processing
+	 */
+	blk_mq_unquiesce_queue(disk->queue);
+	blk_mq_unfreeze_queue(disk->queue);
+
+	return ret;
+}
+
+/**
+ * blk_interposer_detach - Detach interposer from disk
+ * @disk: target disk
+ * @interposer: block device interposer
+ */
+static int blk_interposer_detach(struct gendisk *disk, struct blk_interposer *interposer)
+{
+	int ret = 0;
+
+	if (WARN_ON(!disk))
+		return -EINVAL;
+
+	/*
+	 * Stop disks queue processing.
+	 */
+	blk_mq_freeze_queue(disk->queue);
+	blk_mq_quiesce_queue(disk->queue);
+
+	/*
+	 * Check if the interposer is still available.
+	 */
+	if (!disk->interposer) {
+		pr_info("The interposer is not available.\n");
+		return -ENOENT;
+		goto out;
+	}
+	/*
+	 * Check if it is really our interposer.
+	 */
+	if (disk->interposer->ip_submit_bio != interposer->ip_submit_bio) {
+		pr_info("The interposer found is not ours.\n");
+		return -EPERM;
+		goto out;
+	}
+
+	/*
+	 * Detach interposer.
+	 */
+	disk->interposer = NULL;
+	/*
+	 * And while the queue is stopped, we can do something specific for our module.
+	 */
+	pr_info("Block device interposer detached successfully.\n");
+
+out:
+	/*
+	 * Resume disks queue processing.
+	 */
+	blk_mq_unquiesce_queue(disk->queue);
+	blk_mq_unfreeze_queue(disk->queue);
+
+	return ret;
+}