ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

6 files changed, 1147 insertions, 0 deletions

diff --git a/tools/usb/ffs-aio-example/multibuff/device_app/aio_multibuff.c b/tools/usb/ffs-aio-example/multibuff/device_app/aio_multibuff.c
new file mode 100644
index 000000000..aaca1f44e
--- /dev/null
+++ b/tools/usb/ffs-aio-example/multibuff/device_app/aio_multibuff.c
@@ -0,0 +1,380 @@
+/*
+ * This is free and unencumbered software released into the public domain.
+ *
+ * Anyone is free to copy, modify, publish, use, compile, sell, or
+ * distribute this software, either in source code form or as a compiled
+ * binary, for any purpose, commercial or non-commercial, and by any
+ * means.
+ *
+ * In jurisdictions that recognize copyright laws, the author or authors
+ * of this software dedicate any and all copyright interest in the
+ * software to the public domain. We make this dedication for the benefit
+ * of the public at large and to the detriment of our heirs and
+ * successors. We intend this dedication to be an overt act of
+ * relinquishment in perpetuity of all present and future rights to this
+ * software under copyright law.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ *
+ * For more information, please refer to <http://unlicense.org/>
+ */
+
+#define _BSD_SOURCE /* for endian.h */
+
+#include <endian.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/poll.h>
+#include <unistd.h>
+#include <stdbool.h>
+#include <sys/eventfd.h>
+
+#include "libaio.h"
+#define IOCB_FLAG_RESFD         (1 << 0)
+
+#include <linux/usb/functionfs.h>
+
+#define BUF_LEN		8192
+#define BUFS_MAX	128
+#define AIO_MAX		(BUFS_MAX*2)
+
+/******************** Descriptors and Strings *******************************/
+
+static const struct {
+	struct usb_functionfs_descs_head_v2 header;
+	__le32 fs_count;
+	__le32 hs_count;
+	struct {
+		struct usb_interface_descriptor intf;
+		struct usb_endpoint_descriptor_no_audio bulk_sink;
+		struct usb_endpoint_descriptor_no_audio bulk_source;
+	} __attribute__ ((__packed__)) fs_descs, hs_descs;
+} __attribute__ ((__packed__)) descriptors = {
+	.header = {
+		.magic = htole32(FUNCTIONFS_DESCRIPTORS_MAGIC_V2),
+		.flags = htole32(FUNCTIONFS_HAS_FS_DESC |
+				     FUNCTIONFS_HAS_HS_DESC),
+		.length = htole32(sizeof(descriptors)),
+	},
+	.fs_count = htole32(3),
+	.fs_descs = {
+		.intf = {
+			.bLength = sizeof(descriptors.fs_descs.intf),
+			.bDescriptorType = USB_DT_INTERFACE,
+			.bNumEndpoints = 2,
+			.bInterfaceClass = USB_CLASS_VENDOR_SPEC,
+			.iInterface = 1,
+		},
+		.bulk_sink = {
+			.bLength = sizeof(descriptors.fs_descs.bulk_sink),
+			.bDescriptorType = USB_DT_ENDPOINT,
+			.bEndpointAddress = 1 | USB_DIR_IN,
+			.bmAttributes = USB_ENDPOINT_XFER_BULK,
+		},
+		.bulk_source = {
+			.bLength = sizeof(descriptors.fs_descs.bulk_source),
+			.bDescriptorType = USB_DT_ENDPOINT,
+			.bEndpointAddress = 2 | USB_DIR_OUT,
+			.bmAttributes = USB_ENDPOINT_XFER_BULK,
+		},
+	},
+	.hs_count = htole32(3),
+	.hs_descs = {
+		.intf = {
+			.bLength = sizeof(descriptors.hs_descs.intf),
+			.bDescriptorType = USB_DT_INTERFACE,
+			.bNumEndpoints = 2,
+			.bInterfaceClass = USB_CLASS_VENDOR_SPEC,
+			.iInterface = 1,
+		},
+		.bulk_sink = {
+			.bLength = sizeof(descriptors.hs_descs.bulk_sink),
+			.bDescriptorType = USB_DT_ENDPOINT,
+			.bEndpointAddress = 1 | USB_DIR_IN,
+			.bmAttributes = USB_ENDPOINT_XFER_BULK,
+			.wMaxPacketSize = htole16(512),
+		},
+		.bulk_source = {
+			.bLength = sizeof(descriptors.hs_descs.bulk_source),
+			.bDescriptorType = USB_DT_ENDPOINT,
+			.bEndpointAddress = 2 | USB_DIR_OUT,
+			.bmAttributes = USB_ENDPOINT_XFER_BULK,
+			.wMaxPacketSize = htole16(512),
+		},
+	},
+};
+
+#define STR_INTERFACE "AIO Test"
+
+static const struct {
+	struct usb_functionfs_strings_head header;
+	struct {
+		__le16 code;
+		const char str1[sizeof(STR_INTERFACE)];
+	} __attribute__ ((__packed__)) lang0;
+} __attribute__ ((__packed__)) strings = {
+	.header = {
+		.magic = htole32(FUNCTIONFS_STRINGS_MAGIC),
+		.length = htole32(sizeof(strings)),
+		.str_count = htole32(1),
+		.lang_count = htole32(1),
+	},
+	.lang0 = {
+		htole16(0x0409), /* en-us */
+		STR_INTERFACE,
+	},
+};
+
+/********************** Buffer structure *******************************/
+
+struct io_buffer {
+	struct iocb **iocb;
+	unsigned char **buf;
+	unsigned cnt;
+	unsigned len;
+	unsigned requested;
+};
+
+/******************** Endpoints handling *******************************/
+
+static void display_event(struct usb_functionfs_event *event)
+{
+	static const char *const names[] = {
+		[FUNCTIONFS_BIND] = "BIND",
+		[FUNCTIONFS_UNBIND] = "UNBIND",
+		[FUNCTIONFS_ENABLE] = "ENABLE",
+		[FUNCTIONFS_DISABLE] = "DISABLE",
+		[FUNCTIONFS_SETUP] = "SETUP",
+		[FUNCTIONFS_SUSPEND] = "SUSPEND",
+		[FUNCTIONFS_RESUME] = "RESUME",
+	};
+	switch (event->type) {
+	case FUNCTIONFS_BIND:
+	case FUNCTIONFS_UNBIND:
+	case FUNCTIONFS_ENABLE:
+	case FUNCTIONFS_DISABLE:
+	case FUNCTIONFS_SETUP:
+	case FUNCTIONFS_SUSPEND:
+	case FUNCTIONFS_RESUME:
+		printf("Event %s\n", names[event->type]);
+	}
+}
+
+static void handle_ep0(int ep0, bool *ready)
+{
+	int ret;
+	struct usb_functionfs_event event;
+
+	ret = read(ep0, &event, sizeof(event));
+	if (!ret) {
+		perror("unable to read event from ep0");
+		return;
+	}
+	display_event(&event);
+	switch (event.type) {
+	case FUNCTIONFS_SETUP:
+		if (event.u.setup.bRequestType & USB_DIR_IN)
+			write(ep0, NULL, 0);
+		else
+			read(ep0, NULL, 0);
+		break;
+
+	case FUNCTIONFS_ENABLE:
+		*ready = true;
+		break;
+
+	case FUNCTIONFS_DISABLE:
+		*ready = false;
+		break;
+
+	default:
+		break;
+	}
+}
+
+void init_bufs(struct io_buffer *iobuf, unsigned n, unsigned len)
+{
+	unsigned i;
+	iobuf->buf = malloc(n*sizeof(*iobuf->buf));
+	iobuf->iocb = malloc(n*sizeof(*iobuf->iocb));
+	iobuf->cnt = n;
+	iobuf->len = len;
+	iobuf->requested = 0;
+	for (i = 0; i < n; ++i) {
+		iobuf->buf[i] = malloc(len*sizeof(**iobuf->buf));
+		iobuf->iocb[i] = malloc(sizeof(**iobuf->iocb));
+	}
+	iobuf->cnt = n;
+}
+
+void delete_bufs(struct io_buffer *iobuf)
+{
+	unsigned i;
+	for (i = 0; i < iobuf->cnt; ++i) {
+		free(iobuf->buf[i]);
+		free(iobuf->iocb[i]);
+	}
+	free(iobuf->buf);
+	free(iobuf->iocb);
+}
+
+int main(int argc, char *argv[])
+{
+	int ret;
+	unsigned i, j;
+	char *ep_path;
+
+	int ep0, ep1;
+
+	io_context_t ctx;
+
+	int evfd;
+	fd_set rfds;
+
+	struct io_buffer iobuf[2];
+	int actual = 0;
+	bool ready;
+
+	if (argc != 2) {
+		printf("ffs directory not specified!\n");
+		return 1;
+	}
+
+	ep_path = malloc(strlen(argv[1]) + 4 /* "/ep#" */ + 1 /* '\0' */);
+	if (!ep_path) {
+		perror("malloc");
+		return 1;
+	}
+
+	/* open endpoint files */
+	sprintf(ep_path, "%s/ep0", argv[1]);
+	ep0 = open(ep_path, O_RDWR);
+	if (ep0 < 0) {
+		perror("unable to open ep0");
+		return 1;
+	}
+	if (write(ep0, &descriptors, sizeof(descriptors)) < 0) {
+		perror("unable do write descriptors");
+		return 1;
+	}
+	if (write(ep0, &strings, sizeof(strings)) < 0) {
+		perror("unable to write strings");
+		return 1;
+	}
+	sprintf(ep_path, "%s/ep1", argv[1]);
+	ep1 = open(ep_path, O_RDWR);
+	if (ep1 < 0) {
+		perror("unable to open ep1");
+		return 1;
+	}
+
+	free(ep_path);
+
+	memset(&ctx, 0, sizeof(ctx));
+	/* setup aio context to handle up to AIO_MAX requests */
+	if (io_setup(AIO_MAX, &ctx) < 0) {
+		perror("unable to setup aio");
+		return 1;
+	}
+
+	evfd = eventfd(0, 0);
+	if (evfd < 0) {
+		perror("unable to open eventfd");
+		return 1;
+	}
+
+	for (i = 0; i < sizeof(iobuf)/sizeof(*iobuf); ++i)
+		init_bufs(&iobuf[i], BUFS_MAX, BUF_LEN);
+
+	while (1) {
+		FD_ZERO(&rfds);
+		FD_SET(ep0, &rfds);
+		FD_SET(evfd, &rfds);
+
+		ret = select(((ep0 > evfd) ? ep0 : evfd)+1,
+			     &rfds, NULL, NULL, NULL);
+		if (ret < 0) {
+			if (errno == EINTR)
+				continue;
+			perror("select");
+			break;
+		}
+
+		if (FD_ISSET(ep0, &rfds))
+			handle_ep0(ep0, &ready);
+
+		/* we are waiting for function ENABLE */
+		if (!ready)
+			continue;
+
+		/*
+		 * when we're preparing new data to submit,
+		 * second buffer being transmitted
+		 */
+		for (i = 0; i < sizeof(iobuf)/sizeof(*iobuf); ++i) {
+			if (iobuf[i].requested)
+				continue;
+			/* prepare requests */
+			for (j = 0; j < iobuf[i].cnt; ++j) {
+				io_prep_pwrite(iobuf[i].iocb[j], ep1,
+					       iobuf[i].buf[j],
+					       iobuf[i].len, 0);
+				/* enable eventfd notification */
+				iobuf[i].iocb[j]->u.c.flags |= IOCB_FLAG_RESFD;
+				iobuf[i].iocb[j]->u.c.resfd = evfd;
+			}
+			/* submit table of requests */
+			ret = io_submit(ctx, iobuf[i].cnt, iobuf[i].iocb);
+			if (ret >= 0) {
+				iobuf[i].requested = ret;
+				printf("submit: %d requests buf: %d\n", ret, i);
+			} else
+				perror("unable to submit requests");
+		}
+
+		/* if event is ready to read */
+		if (!FD_ISSET(evfd, &rfds))
+			continue;
+
+		uint64_t ev_cnt;
+		ret = read(evfd, &ev_cnt, sizeof(ev_cnt));
+		if (ret < 0) {
+			perror("unable to read eventfd");
+			break;
+		}
+
+		struct io_event e[BUFS_MAX];
+		/* we read aio events */
+		ret = io_getevents(ctx, 1, BUFS_MAX, e, NULL);
+		if (ret > 0) /* if we got events */
+			iobuf[actual].requested -= ret;
+
+		/* if all req's from iocb completed */
+		if (!iobuf[actual].requested)
+			actual = (actual + 1)%(sizeof(iobuf)/sizeof(*iobuf));
+	}
+
+	/* free resources */
+
+	for (i = 0; i < sizeof(iobuf)/sizeof(*iobuf); ++i)
+		delete_bufs(&iobuf[i]);
+	io_destroy(ctx);
+
+	close(ep1);
+	close(ep0);
+
+	return 0;
+}
diff --git a/tools/usb/ffs-aio-example/multibuff/host_app/Makefile b/tools/usb/ffs-aio-example/multibuff/host_app/Makefile
new file mode 100644
index 000000000..df36e4c28
--- /dev/null
+++ b/tools/usb/ffs-aio-example/multibuff/host_app/Makefile
@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: GPL-2.0
+CC = gcc
+LIBUSB_CFLAGS = $(shell pkg-config --cflags libusb-1.0)
+LIBUSB_LIBS = $(shell pkg-config --libs libusb-1.0)
+WARNINGS = -Wall -Wextra
+CFLAGS = $(LIBUSB_CFLAGS) $(WARNINGS)
+LDFLAGS = $(LIBUSB_LIBS)
+
+all: test
+%: %.c
+	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+clean:
+	$(RM) test
diff --git a/tools/usb/ffs-aio-example/multibuff/host_app/test.c b/tools/usb/ffs-aio-example/multibuff/host_app/test.c
new file mode 100644
index 000000000..2cbcce6e8
--- /dev/null
+++ b/tools/usb/ffs-aio-example/multibuff/host_app/test.c
@@ -0,0 +1,175 @@
+/*
+ * This is free and unencumbered software released into the public domain.
+ *
+ * Anyone is free to copy, modify, publish, use, compile, sell, or
+ * distribute this software, either in source code form or as a compiled
+ * binary, for any purpose, commercial or non-commercial, and by any
+ * means.
+ *
+ * In jurisdictions that recognize copyright laws, the author or authors
+ * of this software dedicate any and all copyright interest in the
+ * software to the public domain. We make this dedication for the benefit
+ * of the public at large and to the detriment of our heirs and
+ * successors. We intend this dedication to be an overt act of
+ * relinquishment in perpetuity of all present and future rights to this
+ * software under copyright law.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ *
+ * For more information, please refer to <http://unlicense.org/>
+ */
+
+#include <libusb.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#define VENDOR	0x1d6b
+#define PRODUCT	0x0105
+
+#define BUF_LEN		8192
+
+/*
+ * struct test_state - describes test program state
+ * @list: list of devices returned by libusb_get_device_list function
+ * @found: pointer to struct describing tested device
+ * @ctx: context, set to NULL
+ * @handle: handle of tested device
+ * @attached: indicates that device was attached to kernel, and has to be
+ *            reattached at the end of test program
+ */
+
+struct test_state {
+	libusb_device *found;
+	libusb_context *ctx;
+	libusb_device_handle *handle;
+	int attached;
+};
+
+/*
+ * test_init - initialize test program
+ */
+
+int test_init(struct test_state *state)
+{
+	int i, ret;
+	ssize_t cnt;
+	libusb_device **list;
+
+	state->found = NULL;
+	state->ctx = NULL;
+	state->handle = NULL;
+	state->attached = 0;
+
+	ret = libusb_init(&state->ctx);
+	if (ret) {
+		printf("cannot init libusb: %s\n", libusb_error_name(ret));
+		return 1;
+	}
+
+	cnt = libusb_get_device_list(state->ctx, &list);
+	if (cnt <= 0) {
+		printf("no devices found\n");
+		goto error1;
+	}
+
+	for (i = 0; i < cnt; ++i) {
+		libusb_device *dev = list[i];
+		struct libusb_device_descriptor desc;
+		ret = libusb_get_device_descriptor(dev, &desc);
+		if (ret) {
+			printf("unable to get device descriptor: %s\n",
+			       libusb_error_name(ret));
+			goto error2;
+		}
+		if (desc.idVendor == VENDOR && desc.idProduct == PRODUCT) {
+			state->found = dev;
+			break;
+		}
+	}
+
+	if (!state->found) {
+		printf("no devices found\n");
+		goto error2;
+	}
+
+	ret = libusb_open(state->found, &state->handle);
+	if (ret) {
+		printf("cannot open device: %s\n", libusb_error_name(ret));
+		goto error2;
+	}
+
+	if (libusb_claim_interface(state->handle, 0)) {
+		ret = libusb_detach_kernel_driver(state->handle, 0);
+		if (ret) {
+			printf("unable to detach kernel driver: %s\n",
+			       libusb_error_name(ret));
+			goto error3;
+		}
+		state->attached = 1;
+		ret = libusb_claim_interface(state->handle, 0);
+		if (ret) {
+			printf("cannot claim interface: %s\n",
+			       libusb_error_name(ret));
+			goto error4;
+		}
+	}
+
+	return 0;
+
+error4:
+	if (state->attached == 1)
+		libusb_attach_kernel_driver(state->handle, 0);
+
+error3:
+	libusb_close(state->handle);
+
+error2:
+	libusb_free_device_list(list, 1);
+
+error1:
+	libusb_exit(state->ctx);
+	return 1;
+}
+
+/*
+ * test_exit - cleanup test program
+ */
+
+void test_exit(struct test_state *state)
+{
+	libusb_release_interface(state->handle, 0);
+	if (state->attached == 1)
+		libusb_attach_kernel_driver(state->handle, 0);
+	libusb_close(state->handle);
+	libusb_exit(state->ctx);
+}
+
+int main(void)
+{
+	struct test_state state;
+	struct libusb_config_descriptor *conf;
+	struct libusb_interface_descriptor const *iface;
+	unsigned char addr;
+
+	if (test_init(&state))
+		return 1;
+
+	libusb_get_config_descriptor(state.found, 0, &conf);
+	iface = &conf->interface[0].altsetting[0];
+	addr = iface->endpoint[0].bEndpointAddress;
+
+	while (1) {
+		static unsigned char buffer[BUF_LEN];
+		int bytes;
+		libusb_bulk_transfer(state.handle, addr, buffer, BUF_LEN,
+				     &bytes, 500);
+	}
+	test_exit(&state);
+}
diff --git a/tools/usb/ffs-aio-example/simple/device_app/aio_simple.c b/tools/usb/ffs-aio-example/simple/device_app/aio_simple.c
new file mode 100644
index 000000000..96616eb46
--- /dev/null
+++ b/tools/usb/ffs-aio-example/simple/device_app/aio_simple.c
@@ -0,0 +1,386 @@
+/*
+ * This is free and unencumbered software released into the public domain.
+ *
+ * Anyone is free to copy, modify, publish, use, compile, sell, or
+ * distribute this software, either in source code form or as a compiled
+ * binary, for any purpose, commercial or non-commercial, and by any
+ * means.
+ *
+ * In jurisdictions that recognize copyright laws, the author or authors
+ * of this software dedicate any and all copyright interest in the
+ * software to the public domain. We make this dedication for the benefit
+ * of the public at large and to the detriment of our heirs and
+ * successors. We intend this dedication to be an overt act of
+ * relinquishment in perpetuity of all present and future rights to this
+ * software under copyright law.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ *
+ * For more information, please refer to <http://unlicense.org/>
+ */
+
+/* $(CROSS_COMPILE)cc -g -o aio_simple aio_simple.c -laio */
+
+#define _DEFAULT_SOURCE /* for endian.h */
+
+#include <endian.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/poll.h>
+#include <unistd.h>
+#include <stdbool.h>
+#include <sys/eventfd.h>
+
+#include "libaio.h"
+#define IOCB_FLAG_RESFD         (1 << 0)
+
+#include <linux/usb/functionfs.h>
+
+#define BUF_LEN		8192
+
+/*
+ * cpu_to_le16/32 are used when initializing structures, a context where a
+ * function call is not allowed. To solve this, we code cpu_to_le16/32 in a way
+ * that allows them to be used when initializing structures.
+ */
+
+#if BYTE_ORDER == __LITTLE_ENDIAN
+#define cpu_to_le16(x)  (x)
+#define cpu_to_le32(x)  (x)
+#else
+#define cpu_to_le16(x)  ((((x) >> 8) & 0xffu) | (((x) & 0xffu) << 8))
+#define cpu_to_le32(x)  \
+	((((x) & 0xff000000u) >> 24) | (((x) & 0x00ff0000u) >>  8) | \
+	(((x) & 0x0000ff00u) <<  8) | (((x) & 0x000000ffu) << 24))
+#endif
+
+/******************** Descriptors and Strings *******************************/
+
+static const struct {
+	struct usb_functionfs_descs_head_v2 header;
+	__le32 fs_count;
+	__le32 hs_count;
+	struct {
+		struct usb_interface_descriptor intf;
+		struct usb_endpoint_descriptor_no_audio bulk_sink;
+		struct usb_endpoint_descriptor_no_audio bulk_source;
+	} __attribute__ ((__packed__)) fs_descs, hs_descs;
+} __attribute__ ((__packed__)) descriptors = {
+	.header = {
+		.magic = cpu_to_le32(FUNCTIONFS_DESCRIPTORS_MAGIC_V2),
+		.flags = cpu_to_le32(FUNCTIONFS_HAS_FS_DESC |
+				     FUNCTIONFS_HAS_HS_DESC),
+		.length = cpu_to_le32(sizeof(descriptors)),
+	},
+	.fs_count = cpu_to_le32(3),
+	.fs_descs = {
+		.intf = {
+			.bLength = sizeof(descriptors.fs_descs.intf),
+			.bDescriptorType = USB_DT_INTERFACE,
+			.bNumEndpoints = 2,
+			.bInterfaceClass = USB_CLASS_VENDOR_SPEC,
+			.iInterface = 1,
+		},
+		.bulk_sink = {
+			.bLength = sizeof(descriptors.fs_descs.bulk_sink),
+			.bDescriptorType = USB_DT_ENDPOINT,
+			.bEndpointAddress = 1 | USB_DIR_IN,
+			.bmAttributes = USB_ENDPOINT_XFER_BULK,
+		},
+		.bulk_source = {
+			.bLength = sizeof(descriptors.fs_descs.bulk_source),
+			.bDescriptorType = USB_DT_ENDPOINT,
+			.bEndpointAddress = 2 | USB_DIR_OUT,
+			.bmAttributes = USB_ENDPOINT_XFER_BULK,
+		},
+	},
+	.hs_count = cpu_to_le32(3),
+	.hs_descs = {
+		.intf = {
+			.bLength = sizeof(descriptors.hs_descs.intf),
+			.bDescriptorType = USB_DT_INTERFACE,
+			.bNumEndpoints = 2,
+			.bInterfaceClass = USB_CLASS_VENDOR_SPEC,
+			.iInterface = 1,
+		},
+		.bulk_sink = {
+			.bLength = sizeof(descriptors.hs_descs.bulk_sink),
+			.bDescriptorType = USB_DT_ENDPOINT,
+			.bEndpointAddress = 1 | USB_DIR_IN,
+			.bmAttributes = USB_ENDPOINT_XFER_BULK,
+			.wMaxPacketSize = cpu_to_le16(512),
+		},
+		.bulk_source = {
+			.bLength = sizeof(descriptors.hs_descs.bulk_source),
+			.bDescriptorType = USB_DT_ENDPOINT,
+			.bEndpointAddress = 2 | USB_DIR_OUT,
+			.bmAttributes = USB_ENDPOINT_XFER_BULK,
+			.wMaxPacketSize = cpu_to_le16(512),
+		},
+	},
+};
+
+#define STR_INTERFACE "AIO Test"
+
+static const struct {
+	struct usb_functionfs_strings_head header;
+	struct {
+		__le16 code;
+		const char str1[sizeof(STR_INTERFACE)];
+	} __attribute__ ((__packed__)) lang0;
+} __attribute__ ((__packed__)) strings = {
+	.header = {
+		.magic = cpu_to_le32(FUNCTIONFS_STRINGS_MAGIC),
+		.length = cpu_to_le32(sizeof(strings)),
+		.str_count = cpu_to_le32(1),
+		.lang_count = cpu_to_le32(1),
+	},
+	.lang0 = {
+		cpu_to_le16(0x0409), /* en-us */
+		STR_INTERFACE,
+	},
+};
+
+/******************** Endpoints handling *******************************/
+
+static void display_event(struct usb_functionfs_event *event)
+{
+	static const char *const names[] = {
+		[FUNCTIONFS_BIND] = "BIND",
+		[FUNCTIONFS_UNBIND] = "UNBIND",
+		[FUNCTIONFS_ENABLE] = "ENABLE",
+		[FUNCTIONFS_DISABLE] = "DISABLE",
+		[FUNCTIONFS_SETUP] = "SETUP",
+		[FUNCTIONFS_SUSPEND] = "SUSPEND",
+		[FUNCTIONFS_RESUME] = "RESUME",
+	};
+	switch (event->type) {
+	case FUNCTIONFS_BIND:
+	case FUNCTIONFS_UNBIND:
+	case FUNCTIONFS_ENABLE:
+	case FUNCTIONFS_DISABLE:
+	case FUNCTIONFS_SETUP:
+	case FUNCTIONFS_SUSPEND:
+	case FUNCTIONFS_RESUME:
+		printf("Event %s\n", names[event->type]);
+	}
+}
+
+static void handle_ep0(int ep0, bool *ready)
+{
+	struct usb_functionfs_event event;
+	int ret;
+
+	struct pollfd pfds[1];
+	pfds[0].fd = ep0;
+	pfds[0].events = POLLIN;
+
+	ret = poll(pfds, 1, 0);
+
+	if (ret && (pfds[0].revents & POLLIN)) {
+		ret = read(ep0, &event, sizeof(event));
+		if (!ret) {
+			perror("unable to read event from ep0");
+			return;
+		}
+		display_event(&event);
+		switch (event.type) {
+		case FUNCTIONFS_SETUP:
+			if (event.u.setup.bRequestType & USB_DIR_IN)
+				write(ep0, NULL, 0);
+			else
+				read(ep0, NULL, 0);
+			break;
+
+		case FUNCTIONFS_ENABLE:
+			*ready = true;
+			break;
+
+		case FUNCTIONFS_DISABLE:
+			*ready = false;
+			break;
+
+		default:
+			break;
+		}
+	}
+}
+
+int main(int argc, char *argv[])
+{
+	int i, ret;
+	char *ep_path;
+
+	int ep0;
+	int ep[2];
+
+	io_context_t ctx;
+
+	int evfd;
+	fd_set rfds;
+
+	char *buf_in, *buf_out;
+	struct iocb *iocb_in, *iocb_out;
+	int req_in = 0, req_out = 0;
+	bool ready;
+
+	if (argc != 2) {
+		printf("ffs directory not specified!\n");
+		return 1;
+	}
+
+	ep_path = malloc(strlen(argv[1]) + 4 /* "/ep#" */ + 1 /* '\0' */);
+	if (!ep_path) {
+		perror("malloc");
+		return 1;
+	}
+
+	/* open endpoint files */
+	sprintf(ep_path, "%s/ep0", argv[1]);
+	ep0 = open(ep_path, O_RDWR);
+	if (ep0 < 0) {
+		perror("unable to open ep0");
+		return 1;
+	}
+	if (write(ep0, &descriptors, sizeof(descriptors)) < 0) {
+		perror("unable do write descriptors");
+		return 1;
+	}
+	if (write(ep0, &strings, sizeof(strings)) < 0) {
+		perror("unable to write strings");
+		return 1;
+	}
+	for (i = 0; i < 2; ++i) {
+		sprintf(ep_path, "%s/ep%d", argv[1], i+1);
+		ep[i] = open(ep_path, O_RDWR);
+		if (ep[i] < 0) {
+			printf("unable to open ep%d: %s\n", i+1,
+			       strerror(errno));
+			return 1;
+		}
+	}
+
+	free(ep_path);
+
+	memset(&ctx, 0, sizeof(ctx));
+	/* setup aio context to handle up to 2 requests */
+	if (io_setup(2, &ctx) < 0) {
+		perror("unable to setup aio");
+		return 1;
+	}
+
+	evfd = eventfd(0, 0);
+	if (evfd < 0) {
+		perror("unable to open eventfd");
+		return 1;
+	}
+
+	/* alloc buffers and requests */
+	buf_in = malloc(BUF_LEN);
+	buf_out = malloc(BUF_LEN);
+	iocb_in = malloc(sizeof(*iocb_in));
+	iocb_out = malloc(sizeof(*iocb_out));
+
+	while (1) {
+		FD_ZERO(&rfds);
+		FD_SET(ep0, &rfds);
+		FD_SET(evfd, &rfds);
+
+		ret = select(((ep0 > evfd) ? ep0 : evfd)+1,
+			     &rfds, NULL, NULL, NULL);
+		if (ret < 0) {
+			if (errno == EINTR)
+				continue;
+			perror("select");
+			break;
+		}
+
+		if (FD_ISSET(ep0, &rfds))
+			handle_ep0(ep0, &ready);
+
+		/* we are waiting for function ENABLE */
+		if (!ready)
+			continue;
+
+		/* if something was submitted we wait for event */
+		if (FD_ISSET(evfd, &rfds)) {
+			uint64_t ev_cnt;
+			ret = read(evfd, &ev_cnt, sizeof(ev_cnt));
+			if (ret < 0) {
+				perror("unable to read eventfd");
+				break;
+			}
+
+			struct io_event e[2];
+			/* we wait for one event */
+			ret = io_getevents(ctx, 1, 2, e, NULL);
+			/* if we got event */
+			for (i = 0; i < ret; ++i) {
+				if (e[i].obj->aio_fildes == ep[0]) {
+					printf("ev=in; ret=%lu\n", e[i].res);
+					req_in = 0;
+				} else if (e[i].obj->aio_fildes == ep[1]) {
+					printf("ev=out; ret=%lu\n", e[i].res);
+					req_out = 0;
+				}
+			}
+		}
+
+		if (!req_in) { /* if IN transfer not requested*/
+			/* prepare write request */
+			io_prep_pwrite(iocb_in, ep[0], buf_in, BUF_LEN, 0);
+			/* enable eventfd notification */
+			iocb_in->u.c.flags |= IOCB_FLAG_RESFD;
+			iocb_in->u.c.resfd = evfd;
+			/* submit table of requests */
+			ret = io_submit(ctx, 1, &iocb_in);
+			if (ret >= 0) { /* if ret > 0 request is queued */
+				req_in = 1;
+				printf("submit: in\n");
+			} else
+				perror("unable to submit request");
+		}
+		if (!req_out) { /* if OUT transfer not requested */
+			/* prepare read request */
+			io_prep_pread(iocb_out, ep[1], buf_out, BUF_LEN, 0);
+			/* enable eventfs notification */
+			iocb_out->u.c.flags |= IOCB_FLAG_RESFD;
+			iocb_out->u.c.resfd = evfd;
+			/* submit table of requests */
+			ret = io_submit(ctx, 1, &iocb_out);
+			if (ret >= 0) { /* if ret > 0 request is queued */
+				req_out = 1;
+				printf("submit: out\n");
+			} else
+				perror("unable to submit request");
+		}
+	}
+
+	/* free resources */
+
+	io_destroy(ctx);
+
+	free(buf_in);
+	free(buf_out);
+	free(iocb_in);
+	free(iocb_out);
+
+	for (i = 0; i < 2; ++i)
+		close(ep[i]);
+	close(ep0);
+
+	return 0;
+}
diff --git a/tools/usb/ffs-aio-example/simple/host_app/Makefile b/tools/usb/ffs-aio-example/simple/host_app/Makefile
new file mode 100644
index 000000000..c3523837c
--- /dev/null
+++ b/tools/usb/ffs-aio-example/simple/host_app/Makefile
@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: GPL-2.0-only
+CC = gcc
+LIBUSB_CFLAGS = $(shell pkg-config --cflags libusb-1.0)
+LIBUSB_LIBS = $(shell pkg-config --libs libusb-1.0)
+WARNINGS = -Wall -Wextra
+CFLAGS = $(LIBUSB_CFLAGS) $(WARNINGS)
+LDFLAGS = $(LIBUSB_LIBS)
+
+all: test
+%: %.c
+	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+clean:
+	$(RM) test
diff --git a/tools/usb/ffs-aio-example/simple/host_app/test.c b/tools/usb/ffs-aio-example/simple/host_app/test.c
new file mode 100644
index 000000000..aed86ffff
--- /dev/null
+++ b/tools/usb/ffs-aio-example/simple/host_app/test.c
@@ -0,0 +1,178 @@
+/*
+ * This is free and unencumbered software released into the public domain.
+ *
+ * Anyone is free to copy, modify, publish, use, compile, sell, or
+ * distribute this software, either in source code form or as a compiled
+ * binary, for any purpose, commercial or non-commercial, and by any
+ * means.
+ *
+ * In jurisdictions that recognize copyright laws, the author or authors
+ * of this software dedicate any and all copyright interest in the
+ * software to the public domain. We make this dedication for the benefit
+ * of the public at large and to the detriment of our heirs and
+ * successors. We intend this dedication to be an overt act of
+ * relinquishment in perpetuity of all present and future rights to this
+ * software under copyright law.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ *
+ * For more information, please refer to <http://unlicense.org/>
+ */
+
+#include <libusb.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#define VENDOR	0x1d6b
+#define PRODUCT	0x0105
+
+#define BUF_LEN		8192
+
+/*
+ * struct test_state - describes test program state
+ * @list: list of devices returned by libusb_get_device_list function
+ * @found: pointer to struct describing tested device
+ * @ctx: context, set to NULL
+ * @handle: handle of tested device
+ * @attached: indicates that device was attached to kernel, and has to be
+ *            reattached at the end of test program
+ */
+
+struct test_state {
+	libusb_device *found;
+	libusb_context *ctx;
+	libusb_device_handle *handle;
+	int attached;
+};
+
+/*
+ * test_init - initialize test program
+ */
+
+int test_init(struct test_state *state)
+{
+	int i, ret;
+	ssize_t cnt;
+	libusb_device **list;
+
+	state->found = NULL;
+	state->ctx = NULL;
+	state->handle = NULL;
+	state->attached = 0;
+
+	ret = libusb_init(&state->ctx);
+	if (ret) {
+		printf("cannot init libusb: %s\n", libusb_error_name(ret));
+		return 1;
+	}
+
+	cnt = libusb_get_device_list(state->ctx, &list);
+	if (cnt <= 0) {
+		printf("no devices found\n");
+		goto error1;
+	}
+
+	for (i = 0; i < cnt; ++i) {
+		libusb_device *dev = list[i];
+		struct libusb_device_descriptor desc;
+		ret = libusb_get_device_descriptor(dev, &desc);
+		if (ret) {
+			printf("unable to get device descriptor: %s\n",
+			       libusb_error_name(ret));
+			goto error2;
+		}
+		if (desc.idVendor == VENDOR && desc.idProduct == PRODUCT) {
+			state->found = dev;
+			break;
+		}
+	}
+
+	if (!state->found) {
+		printf("no devices found\n");
+		goto error2;
+	}
+
+	ret = libusb_open(state->found, &state->handle);
+	if (ret) {
+		printf("cannot open device: %s\n", libusb_error_name(ret));
+		goto error2;
+	}
+
+	if (libusb_claim_interface(state->handle, 0)) {
+		ret = libusb_detach_kernel_driver(state->handle, 0);
+		if (ret) {
+			printf("unable to detach kernel driver: %s\n",
+			       libusb_error_name(ret));
+			goto error3;
+		}
+		state->attached = 1;
+		ret = libusb_claim_interface(state->handle, 0);
+		if (ret) {
+			printf("cannot claim interface: %s\n",
+			       libusb_error_name(ret));
+			goto error4;
+		}
+	}
+
+	return 0;
+
+error4:
+	if (state->attached == 1)
+		libusb_attach_kernel_driver(state->handle, 0);
+
+error3:
+	libusb_close(state->handle);
+
+error2:
+	libusb_free_device_list(list, 1);
+
+error1:
+	libusb_exit(state->ctx);
+	return 1;
+}
+
+/*
+ * test_exit - cleanup test program
+ */
+
+void test_exit(struct test_state *state)
+{
+	libusb_release_interface(state->handle, 0);
+	if (state->attached == 1)
+		libusb_attach_kernel_driver(state->handle, 0);
+	libusb_close(state->handle);
+	libusb_exit(state->ctx);
+}
+
+int main(void)
+{
+	struct test_state state;
+	struct libusb_config_descriptor *conf;
+	struct libusb_interface_descriptor const *iface;
+	unsigned char in_addr, out_addr;
+
+	if (test_init(&state))
+		return 1;
+
+	libusb_get_config_descriptor(state.found, 0, &conf);
+	iface = &conf->interface[0].altsetting[0];
+	in_addr = iface->endpoint[0].bEndpointAddress;
+	out_addr = iface->endpoint[1].bEndpointAddress;
+
+	while (1) {
+		static unsigned char buffer[BUF_LEN];
+		int bytes;
+		libusb_bulk_transfer(state.handle, in_addr, buffer, BUF_LEN,
+				     &bytes, 500);
+		libusb_bulk_transfer(state.handle, out_addr, buffer, BUF_LEN,
+				     &bytes, 500);
+	}
+	test_exit(&state);
+}