netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 2460 insertions, 0 deletions

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
new file mode 100644
index 000000000..4fec31fc0
--- /dev/null
+++ b/fs/fuse/dev.c
@@ -0,0 +1,2460 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+  FUSE: Filesystem in Userspace
+  Copyright (C) 2001-2008  Miklos Szeredi <miklos@szeredi.hu>
+*/
+
+#include "dev.h"
+#include "args.h"
+#include "dev_uring_i.h"
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/poll.h>
+#include <linux/sched/signal.h>
+#include <linux/uio.h>
+#include <linux/miscdevice.h>
+#include <linux/pagemap.h>
+#include <linux/file.h>
+#include <linux/slab.h>
+#include <linux/pipe_fs_i.h>
+#include <linux/swap.h>
+#include <linux/splice.h>
+#include <linux/sched.h>
+#include <linux/seq_file.h>
+
+#include "fuse_trace.h"
+
+MODULE_ALIAS_MISCDEV(FUSE_MINOR);
+MODULE_ALIAS("devname:fuse");
+
+static DECLARE_WAIT_QUEUE_HEAD(fuse_dev_waitq);
+
+static struct kmem_cache *fuse_req_cachep;
+
+static void fuse_request_init(struct fuse_chan *fch, struct fuse_req *req)
+{
+	INIT_LIST_HEAD(&req->list);
+	INIT_LIST_HEAD(&req->intr_entry);
+	init_waitqueue_head(&req->waitq);
+	refcount_set(&req->count, 1);
+	__set_bit(FR_PENDING, &req->flags);
+	req->chan = fch;
+	req->create_time = jiffies;
+}
+
+static struct fuse_req *fuse_request_alloc(struct fuse_chan *fch, gfp_t flags)
+{
+	struct fuse_req *req = kmem_cache_zalloc(fuse_req_cachep, flags);
+	if (req)
+		fuse_request_init(fch, req);
+
+	return req;
+}
+
+static void fuse_request_free(struct fuse_req *req)
+{
+	WARN_ON(!list_empty(&req->intr_entry));
+	kmem_cache_free(fuse_req_cachep, req);
+}
+
+static void __fuse_get_request(struct fuse_req *req)
+{
+	refcount_inc(&req->count);
+}
+
+/* Must be called with > 1 refcount */
+static void __fuse_put_request(struct fuse_req *req)
+{
+	refcount_dec(&req->count);
+}
+
+void fuse_chan_set_initialized(struct fuse_chan *fch, struct fuse_chan_param *param)
+{
+	if (param) {
+		fch->minor = param->minor;
+		fch->max_write = param->max_write;
+		fch->max_pages = param->max_pages;
+
+		if (param->io_uring_enabled)
+			fuse_uring_conn_init(fch);
+	}
+
+	/* Pairs with smp_load_acquire() readers of fch->initialized */
+	smp_store_release(&fch->initialized, 1);
+	wake_up_all(&fch->blocked_waitq);
+}
+
+static bool fuse_block_alloc(struct fuse_chan *fch, bool for_background)
+{
+	/* Pairs with smp_store_release() in fuse_chan_set_initialized() */
+	if (!smp_load_acquire(&fch->initialized))
+		return true;
+
+	return (for_background && fch->blocked) ||
+	       (fch->io_uring && fch->connected && !fuse_uring_ready(fch));
+}
+
+static void fuse_drop_waiting(struct fuse_chan *fch)
+{
+	/*
+	 * lockess check of fch->connected is okay, because atomic_dec_and_test()
+	 * provides a memory barrier matched with the one in fuse_chan_wait_aborted()
+	 * to ensure no wake-up is missed.
+	 */
+	if (atomic_dec_and_test(&fch->num_waiting) &&
+	    !READ_ONCE(fch->connected)) {
+		/* wake up aborters */
+		wake_up_all(&fch->blocked_waitq);
+	}
+}
+
+static void fuse_put_request(struct fuse_req *req);
+
+static struct fuse_req *fuse_get_req(struct fuse_chan *fch, bool for_background)
+{
+	struct fuse_req *req;
+	int err;
+
+	atomic_inc(&fch->num_waiting);
+
+	if (fuse_block_alloc(fch, for_background)) {
+		err = -EINTR;
+		if (wait_event_state_exclusive(fch->blocked_waitq,
+				!fuse_block_alloc(fch, for_background),
+				(TASK_KILLABLE | TASK_FREEZABLE)))
+			goto out;
+	}
+
+	err = -ENOTCONN;
+	if (!fch->connected)
+		goto out;
+
+	req = fuse_request_alloc(fch, GFP_KERNEL);
+	err = -ENOMEM;
+	if (!req) {
+		if (for_background)
+			wake_up(&fch->blocked_waitq);
+		goto out;
+	}
+
+	__set_bit(FR_WAITING, &req->flags);
+	if (for_background)
+		__set_bit(FR_BACKGROUND, &req->flags);
+
+	return req;
+
+ out:
+	fuse_drop_waiting(fch);
+	return ERR_PTR(err);
+}
+
+static void fuse_put_request(struct fuse_req *req)
+{
+	struct fuse_chan *fch = req->chan;
+
+	if (refcount_dec_and_test(&req->count)) {
+		if (test_bit(FR_BACKGROUND, &req->flags)) {
+			/*
+			 * We get here in the unlikely case that a background
+			 * request was allocated but not sent
+			 */
+			spin_lock(&fch->bg_lock);
+			if (!fch->blocked)
+				wake_up(&fch->blocked_waitq);
+			spin_unlock(&fch->bg_lock);
+		}
+
+		if (test_bit(FR_WAITING, &req->flags)) {
+			__clear_bit(FR_WAITING, &req->flags);
+			fuse_drop_waiting(fch);
+		}
+
+		fuse_request_free(req);
+	}
+}
+
+unsigned int fuse_len_args(unsigned int numargs, struct fuse_arg *args)
+{
+	unsigned nbytes = 0;
+	unsigned i;
+
+	for (i = 0; i < numargs; i++)
+		nbytes += args[i].size;
+
+	return nbytes;
+}
+EXPORT_SYMBOL_GPL(fuse_len_args);
+
+static u64 fuse_get_unique_locked(struct fuse_iqueue *fiq)
+{
+	fiq->reqctr += FUSE_REQ_ID_STEP;
+	return fiq->reqctr;
+}
+
+u64 fuse_get_unique(struct fuse_iqueue *fiq)
+{
+	u64 ret;
+
+	spin_lock(&fiq->lock);
+	ret = fuse_get_unique_locked(fiq);
+	spin_unlock(&fiq->lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(fuse_get_unique);
+
+unsigned int fuse_req_hash(u64 unique)
+{
+	return hash_long(unique & ~FUSE_INT_REQ_BIT, FUSE_PQ_HASH_BITS);
+}
+EXPORT_SYMBOL_GPL(fuse_req_hash);
+
+/*
+ * A new request is available, wake fiq->waitq
+ */
+static void fuse_dev_wake_and_unlock(struct fuse_iqueue *fiq, bool sync)
+__releases(fiq->lock)
+{
+	if (sync)
+		wake_up_sync(&fiq->waitq);
+	else
+		wake_up(&fiq->waitq);
+	kill_fasync(&fiq->fasync, SIGIO, POLL_IN);
+	spin_unlock(&fiq->lock);
+}
+
+struct fuse_forget_link *fuse_alloc_forget(void)
+{
+	return kzalloc_obj(struct fuse_forget_link, GFP_KERNEL_ACCOUNT);
+}
+
+void fuse_dev_queue_forget(struct fuse_iqueue *fiq,
+			   struct fuse_forget_link *forget)
+{
+	spin_lock(&fiq->lock);
+	if (fiq->connected) {
+		fiq->forget_list_tail->next = forget;
+		fiq->forget_list_tail = forget;
+		fuse_dev_wake_and_unlock(fiq, false);
+	} else {
+		kfree(forget);
+		spin_unlock(&fiq->lock);
+	}
+}
+
+void fuse_dev_queue_interrupt(struct fuse_iqueue *fiq, struct fuse_req *req)
+{
+	spin_lock(&fiq->lock);
+	/* Repeat FR_SENT test after obtaining the lock to prevent race with fuse_resend() */
+	if (list_empty(&req->intr_entry) && test_bit(FR_SENT, &req->flags)) {
+		list_add_tail(&req->intr_entry, &fiq->interrupts);
+		/*
+		 * Pairs with smp_mb() implied by test_and_set_bit()
+		 * from fuse_request_end().
+		 */
+		smp_mb();
+		if (test_bit(FR_FINISHED, &req->flags)) {
+			list_del_init(&req->intr_entry);
+			spin_unlock(&fiq->lock);
+		} else  {
+			fuse_dev_wake_and_unlock(fiq, false);
+		}
+	} else {
+		spin_unlock(&fiq->lock);
+	}
+}
+
+static inline void fuse_request_assign_unique_locked(struct fuse_iqueue *fiq,
+						     struct fuse_req *req)
+{
+	if (req->in.h.opcode != FUSE_NOTIFY_REPLY)
+		req->in.h.unique = fuse_get_unique_locked(fiq);
+
+	/* tracepoint captures in.h.unique and in.h.len */
+	trace_fuse_request_send(req);
+}
+
+inline void fuse_request_assign_unique(struct fuse_iqueue *fiq,
+				       struct fuse_req *req)
+{
+	if (req->in.h.opcode != FUSE_NOTIFY_REPLY)
+		req->in.h.unique = fuse_get_unique(fiq);
+
+	/* tracepoint captures in.h.unique and in.h.len */
+	trace_fuse_request_send(req);
+}
+EXPORT_SYMBOL_GPL(fuse_request_assign_unique);
+
+static void fuse_dev_queue_req(struct fuse_iqueue *fiq, struct fuse_req *req)
+{
+	bool sync = test_and_clear_bit(FR_SYNC_WAKEUP, &req->flags);
+
+	spin_lock(&fiq->lock);
+	if (fiq->connected) {
+		fuse_request_assign_unique_locked(fiq, req);
+		list_add_tail(&req->list, &fiq->pending);
+		fuse_dev_wake_and_unlock(fiq, sync);
+	} else {
+		spin_unlock(&fiq->lock);
+		req->out.h.error = -ENOTCONN;
+		clear_bit(FR_PENDING, &req->flags);
+		fuse_request_end(req);
+	}
+}
+
+static const struct fuse_iqueue_ops fuse_dev_fiq_ops = {
+	.send_forget	= fuse_dev_queue_forget,
+	.send_interrupt	= fuse_dev_queue_interrupt,
+	.send_req	= fuse_dev_queue_req,
+};
+
+void fuse_iqueue_init(struct fuse_iqueue *fiq, const struct fuse_iqueue_ops *ops, void *priv)
+{
+	spin_lock_init(&fiq->lock);
+	init_waitqueue_head(&fiq->waitq);
+	INIT_LIST_HEAD(&fiq->pending);
+	INIT_LIST_HEAD(&fiq->interrupts);
+	fiq->forget_list_tail = &fiq->forget_list_head;
+	fiq->connected = 1;
+	fiq->ops = ops;
+	fiq->priv = priv;
+}
+EXPORT_SYMBOL_GPL(fuse_iqueue_init);
+
+void fuse_chan_release(struct fuse_chan *fch)
+{
+	struct fuse_iqueue *fiq = &fch->iq;
+
+	if (fiq->ops->release)
+		fiq->ops->release(fiq);
+
+	if (fch->timeout.req_timeout)
+		cancel_delayed_work_sync(&fch->timeout.work);
+}
+
+void fuse_chan_free(struct fuse_chan *fch)
+{
+	WARN_ON(!list_empty(&fch->devices));
+	kfree(fch->pq_prealloc);
+	kfree(fch);
+}
+EXPORT_SYMBOL_GPL(fuse_chan_free);
+
+struct fuse_chan *fuse_chan_new(void)
+{
+	struct fuse_chan *fch = kzalloc_obj(struct fuse_chan);
+	if (!fch)
+		return NULL;
+
+	spin_lock_init(&fch->lock);
+	INIT_LIST_HEAD(&fch->devices);
+	spin_lock_init(&fch->bg_lock);
+	INIT_LIST_HEAD(&fch->bg_queue);
+	init_waitqueue_head(&fch->blocked_waitq);
+	atomic_set(&fch->num_waiting, 0);
+	fch->max_background = FUSE_DEFAULT_MAX_BACKGROUND;
+	fch->initialized = 0;
+	fch->blocked = 0;
+	fch->connected = 1;
+	fch->timeout.req_timeout = 0;
+
+	return fch;
+}
+EXPORT_SYMBOL_GPL(fuse_chan_new);
+
+struct list_head *fuse_pqueue_alloc(void)
+{
+	struct list_head *pq = kzalloc_objs(struct list_head, FUSE_PQ_HASH_SIZE);
+
+	if (pq) {
+		for (int i = 0; i < FUSE_PQ_HASH_SIZE; i++)
+			INIT_LIST_HEAD(&pq[i]);
+	}
+	return pq;
+}
+
+struct fuse_chan *fuse_dev_chan_new(void)
+{
+	struct fuse_chan *fch __free(kfree) = fuse_chan_new();
+	if (!fch)
+		return NULL;
+
+	fch->pq_prealloc = fuse_pqueue_alloc();
+	if (!fch->pq_prealloc)
+		return NULL;
+
+	fuse_iqueue_init(&fch->iq, &fuse_dev_fiq_ops, NULL);
+
+	return no_free_ptr(fch);
+}
+EXPORT_SYMBOL_GPL(fuse_dev_chan_new);
+
+unsigned int fuse_chan_num_background(struct fuse_chan *fch)
+{
+	return READ_ONCE(fch->num_background);
+}
+
+unsigned int fuse_chan_max_background(struct fuse_chan *fch)
+{
+	return READ_ONCE(fch->max_background);
+}
+
+void fuse_chan_max_background_set(struct fuse_chan *fch, unsigned int val)
+{
+	spin_lock(&fch->bg_lock);
+	fch->max_background = val;
+	fch->blocked = fch->num_background >= fch->max_background;
+	if (!fch->blocked)
+		wake_up_nr(&fch->blocked_waitq,
+			   fch->max_background - fch->num_background);
+	spin_unlock(&fch->bg_lock);
+}
+
+unsigned int fuse_chan_num_waiting(struct fuse_chan *fch)
+{
+	return atomic_read(&fch->num_waiting);
+}
+
+void fuse_chan_set_fc(struct fuse_chan *fch, struct fuse_conn *fc)
+{
+	fch->conn = fc;
+}
+
+void fuse_pqueue_init(struct fuse_pqueue *fpq)
+{
+	spin_lock_init(&fpq->lock);
+	INIT_LIST_HEAD(&fpq->io);
+	fpq->connected = 1;
+	fpq->processing = NULL;
+}
+
+static struct fuse_dev *fuse_dev_alloc_no_pq(void)
+{
+	struct fuse_dev *fud;
+
+	fud = kzalloc_obj(struct fuse_dev);
+	if (!fud)
+		return NULL;
+
+	refcount_set(&fud->ref, 1);
+	fuse_pqueue_init(&fud->pq);
+
+	return fud;
+}
+
+struct fuse_dev *fuse_dev_alloc(void)
+{
+	struct fuse_dev *fud __free(kfree) = fuse_dev_alloc_no_pq();
+	if (!fud)
+		return NULL;
+
+	fud->pq.processing = fuse_pqueue_alloc();
+	if (!fud->pq.processing)
+		return NULL;
+
+	return no_free_ptr(fud);
+}
+EXPORT_SYMBOL_GPL(fuse_dev_alloc);
+
+/*
+ * Installs @fch into @fud, return true on success.  "Consumes" @pq in either case.
+ */
+static bool fuse_dev_install_with_pq(struct fuse_dev *fud, struct fuse_chan *fch,
+				     struct list_head *pq)
+{
+	struct fuse_chan *old_fch;
+
+	guard(spinlock)(&fch->lock);
+	/*
+	 * Pairs with:
+	 *  - xchg() in fuse_dev_release()
+	 *  - smp_load_acquire() in fuse_dev_fc_get()
+	 */
+	old_fch = cmpxchg(&fud->chan, NULL, fch);
+	if (old_fch) {
+		/*
+		 * failed to set fud->chan because
+		 *  - it was already set to a different fc
+		 *  - it was set to disconneted
+		 */
+		kfree(pq);
+		return false;
+	}
+	if (pq) {
+		WARN_ON(fud->pq.processing);
+		fud->pq.processing = pq;
+	}
+	list_add_tail(&fud->entry, &fch->devices);
+	fuse_conn_get(fch->conn);
+	wake_up_all(&fuse_dev_waitq);
+	return true;
+}
+
+void fuse_dev_install(struct fuse_dev *fud, struct fuse_chan *fch)
+{
+	struct list_head *pq = fch->pq_prealloc;
+
+	fch->pq_prealloc = NULL;
+	if (!fuse_dev_install_with_pq(fud, fch, pq)) {
+		/* Channel is not usable without a dev */
+		fuse_chan_abort(fch, false);
+	}
+}
+EXPORT_SYMBOL_GPL(fuse_dev_install);
+
+struct fuse_dev *fuse_dev_alloc_install(struct fuse_chan *fch)
+{
+	struct fuse_dev *fud;
+
+	fud = fuse_dev_alloc_no_pq();
+	if (!fud)
+		return NULL;
+
+	fuse_dev_install(fud, fch);
+	return fud;
+}
+EXPORT_SYMBOL_GPL(fuse_dev_alloc_install);
+
+void fuse_dev_put(struct fuse_dev *fud)
+{
+	struct fuse_chan *fch;
+
+	if (!refcount_dec_and_test(&fud->ref))
+		return;
+
+	fch = fuse_dev_chan_get(fud);
+	if (fch && fch != FUSE_DEV_CHAN_DISCONNECTED) {
+		/* This is the virtiofs case (fuse_dev_release() not called) */
+		spin_lock(&fch->lock);
+		list_del(&fud->entry);
+		spin_unlock(&fch->lock);
+
+		fuse_conn_put(fch->conn);
+	}
+	kfree(fud->pq.processing);
+	kfree(fud);
+}
+EXPORT_SYMBOL_GPL(fuse_dev_put);
+
+bool fuse_dev_is_installed(struct fuse_dev *fud)
+{
+	struct fuse_chan *fch = fuse_dev_chan_get(fud);
+
+	return fch != NULL && fch != FUSE_DEV_CHAN_DISCONNECTED;
+}
+
+/*
+ * Checks if @fc matches the one installed in @fud
+ */
+bool fuse_dev_verify(struct fuse_dev *fud, struct fuse_chan *fch)
+{
+	return fuse_dev_chan_get(fud) == fch;
+}
+
+bool fuse_dev_is_sync_init(struct fuse_dev *fud)
+{
+	return fud->sync_init;
+}
+
+struct fuse_dev *fuse_dev_grab(struct file *file)
+{
+	struct fuse_dev *fud = fuse_file_to_fud(file);
+
+	refcount_inc(&fud->ref);
+	return fud;
+}
+
+static void fuse_send_one(struct fuse_iqueue *fiq, struct fuse_req *req)
+{
+	req->in.h.len = sizeof(struct fuse_in_header) +
+		fuse_len_args(req->args->in_numargs,
+			      (struct fuse_arg *) req->args->in_args);
+	fiq->ops->send_req(fiq, req);
+}
+
+void fuse_chan_queue_forget(struct fuse_chan *fch, struct fuse_forget_link *forget,
+			    u64 nodeid, u64 nlookup)
+{
+	struct fuse_iqueue *fiq = &fch->iq;
+
+	forget->forget_one.nodeid = nodeid;
+	forget->forget_one.nlookup = nlookup;
+
+	fiq->ops->send_forget(fiq, forget);
+}
+
+static void flush_bg_queue(struct fuse_chan *fch)
+{
+	struct fuse_iqueue *fiq = &fch->iq;
+
+	while (fch->active_background < fch->max_background &&
+	       !list_empty(&fch->bg_queue)) {
+		struct fuse_req *req;
+
+		req = list_first_entry(&fch->bg_queue, struct fuse_req, list);
+		list_del(&req->list);
+		fch->active_background++;
+		fuse_send_one(fiq, req);
+	}
+}
+
+void fuse_request_bg_finish(struct fuse_chan *fch, struct fuse_req *req)
+{
+	lockdep_assert_held(&fch->bg_lock);
+
+	clear_bit(FR_BACKGROUND, &req->flags);
+	if (fch->num_background == fch->max_background) {
+		fch->blocked = 0;
+		wake_up(&fch->blocked_waitq);
+	} else if (!fch->blocked) {
+		/*
+		 * Wake up next waiter, if any.  It's okay to use
+		 * waitqueue_active(), as we've already synced up
+		 * fch->blocked with waiters with the wake_up() call
+		 * above.
+		 */
+		if (waitqueue_active(&fch->blocked_waitq))
+			wake_up(&fch->blocked_waitq);
+	}
+
+	fch->num_background--;
+	fch->active_background--;
+}
+
+/*
+ * This function is called when a request is finished.  Either a reply
+ * has arrived or it was aborted (and not yet sent) or some error
+ * occurred during communication with userspace, or the device file
+ * was closed.  The requester thread is woken up (if still waiting),
+ * the 'end' callback is called if given, else the reference to the
+ * request is released
+ */
+void fuse_request_end(struct fuse_req *req)
+{
+	struct fuse_chan *fch = req->chan;
+	struct fuse_iqueue *fiq = &fch->iq;
+
+	if (test_and_set_bit(FR_FINISHED, &req->flags))
+		goto put_request;
+
+	trace_fuse_request_end(req);
+	/*
+	 * test_and_set_bit() implies smp_mb() between bit
+	 * changing and below FR_INTERRUPTED check. Pairs with
+	 * smp_mb() from queue_interrupt().
+	 */
+	if (test_bit(FR_INTERRUPTED, &req->flags)) {
+		spin_lock(&fiq->lock);
+		list_del_init(&req->intr_entry);
+		spin_unlock(&fiq->lock);
+	}
+	WARN_ON(test_bit(FR_PENDING, &req->flags));
+	WARN_ON(test_bit(FR_SENT, &req->flags));
+	if (test_bit(FR_BACKGROUND, &req->flags)) {
+		spin_lock(&fch->bg_lock);
+		fuse_request_bg_finish(fch, req);
+		flush_bg_queue(fch);
+		spin_unlock(&fch->bg_lock);
+	} else {
+		/* Wake up waiter sleeping in request_wait_answer() */
+		wake_up(&req->waitq);
+	}
+
+	if (test_bit(FR_ASYNC, &req->flags))
+		req->args->end(req->args, req->out.h.error);
+put_request:
+	fuse_put_request(req);
+}
+EXPORT_SYMBOL_GPL(fuse_request_end);
+
+static int queue_interrupt(struct fuse_req *req)
+{
+	struct fuse_iqueue *fiq = &req->chan->iq;
+
+	/* Check for we've sent request to interrupt this req */
+	if (unlikely(!test_bit(FR_INTERRUPTED, &req->flags)))
+		return -EINVAL;
+
+	fiq->ops->send_interrupt(fiq, req);
+
+	return 0;
+}
+
+bool fuse_remove_pending_req(struct fuse_req *req, spinlock_t *lock)
+{
+	spin_lock(lock);
+	if (test_bit(FR_PENDING, &req->flags)) {
+		/*
+		 * FR_PENDING does not get cleared as the request will end
+		 * up in destruction anyway.
+		 */
+		list_del(&req->list);
+		spin_unlock(lock);
+		__fuse_put_request(req);
+		req->out.h.error = -EINTR;
+		return true;
+	}
+	spin_unlock(lock);
+	return false;
+}
+
+static void request_wait_answer(struct fuse_req *req)
+{
+	struct fuse_chan *fch = req->chan;
+	struct fuse_iqueue *fiq = &fch->iq;
+	int err;
+
+	if (!fch->no_interrupt) {
+		/* Any signal may interrupt this */
+		err = wait_event_interruptible(req->waitq,
+					test_bit(FR_FINISHED, &req->flags));
+		if (!err)
+			return;
+
+		set_bit(FR_INTERRUPTED, &req->flags);
+		/* matches barrier in fuse_dev_do_read() */
+		smp_mb__after_atomic();
+		if (test_bit(FR_SENT, &req->flags))
+			queue_interrupt(req);
+	}
+
+	if (!test_bit(FR_FORCE, &req->flags)) {
+		bool removed;
+
+		/* Only fatal signals may interrupt this */
+		err = wait_event_killable(req->waitq,
+					test_bit(FR_FINISHED, &req->flags));
+		if (!err)
+			return;
+
+		if (req->args->abort_on_kill) {
+			fuse_chan_abort(fch, false);
+			goto wait_for_finish;
+		}
+
+		if (test_bit(FR_URING, &req->flags))
+			removed = fuse_uring_remove_pending_req(req);
+		else
+			removed = fuse_remove_pending_req(req, &fiq->lock);
+		if (removed)
+			return;
+	}
+
+wait_for_finish:
+	/*
+	 * Either request is already in userspace, or it was forced.
+	 * Wait it out.
+	 */
+	wait_event(req->waitq, test_bit(FR_FINISHED, &req->flags));
+}
+
+static void __fuse_request_send(struct fuse_req *req)
+{
+	struct fuse_iqueue *fiq = &req->chan->iq;
+
+	BUG_ON(test_bit(FR_BACKGROUND, &req->flags));
+
+	/* acquire extra reference, since request is still needed after
+	   fuse_request_end() */
+	__fuse_get_request(req);
+	/*
+	 * This is a synchronous request: the caller will block waiting for
+	 * the answer. Hint the scheduler via wake_up_sync().
+	 */
+	set_bit(FR_SYNC_WAKEUP, &req->flags);
+	fuse_send_one(fiq, req);
+
+	request_wait_answer(req);
+	/* Pairs with smp_wmb() in fuse_request_end() */
+	smp_rmb();
+}
+
+static void fuse_adjust_compat(struct fuse_chan *fch, struct fuse_args *args)
+{
+	if (fch->minor < 4 && args->opcode == FUSE_STATFS)
+		args->out_args[0].size = FUSE_COMPAT_STATFS_SIZE;
+
+	if (fch->minor < 9) {
+		switch (args->opcode) {
+		case FUSE_LOOKUP:
+		case FUSE_CREATE:
+		case FUSE_MKNOD:
+		case FUSE_MKDIR:
+		case FUSE_SYMLINK:
+		case FUSE_LINK:
+			args->out_args[0].size = FUSE_COMPAT_ENTRY_OUT_SIZE;
+			break;
+		case FUSE_GETATTR:
+		case FUSE_SETATTR:
+			args->out_args[0].size = FUSE_COMPAT_ATTR_OUT_SIZE;
+			break;
+		}
+	}
+	if (fch->minor < 12) {
+		switch (args->opcode) {
+		case FUSE_CREATE:
+			args->in_args[0].size = sizeof(struct fuse_open_in);
+			break;
+		case FUSE_MKNOD:
+			args->in_args[0].size = FUSE_COMPAT_MKNOD_IN_SIZE;
+			break;
+		}
+	}
+}
+
+static void fuse_args_to_req(struct fuse_req *req, struct fuse_args *args)
+{
+	req->in.h.opcode = args->opcode;
+	req->in.h.nodeid = args->nodeid;
+	req->in.h.uid = args->uid;
+	req->in.h.gid = args->gid;
+	req->in.h.pid = args->pid;
+	req->args = args;
+	if (args->is_ext)
+		req->in.h.total_extlen = args->in_args[args->ext_idx].size / 8;
+	if (args->end)
+		__set_bit(FR_ASYNC, &req->flags);
+}
+
+ssize_t fuse_chan_send(struct fuse_chan *fch, struct fuse_args *args)
+{
+	struct fuse_req *req;
+	ssize_t ret;
+
+	if (args->force) {
+		atomic_inc(&fch->num_waiting);
+		req = fuse_request_alloc(fch, GFP_KERNEL | __GFP_NOFAIL);
+
+		__set_bit(FR_WAITING, &req->flags);
+		if (!args->abort_on_kill)
+			__set_bit(FR_FORCE, &req->flags);
+	} else {
+		req = fuse_get_req(fch, false);
+		if (IS_ERR(req))
+			return PTR_ERR(req);
+	}
+
+	/* Needs to be done after fuse_get_req() so that fch->minor is valid */
+	fuse_adjust_compat(fch, args);
+	fuse_args_to_req(req, args);
+
+	if (!args->noreply)
+		__set_bit(FR_ISREPLY, &req->flags);
+	__fuse_request_send(req);
+	ret = req->out.h.error;
+	if (!ret && args->out_argvar) {
+		BUG_ON(args->out_numargs == 0);
+		ret = args->out_args[args->out_numargs - 1].size;
+	}
+	fuse_put_request(req);
+
+	return ret;
+}
+
+#ifdef CONFIG_FUSE_IO_URING
+static bool fuse_request_queue_background_uring(struct fuse_req *req)
+{
+	struct fuse_iqueue *fiq = &req->chan->iq;
+
+	req->in.h.len = sizeof(struct fuse_in_header) +
+		fuse_len_args(req->args->in_numargs,
+			      (struct fuse_arg *) req->args->in_args);
+	fuse_request_assign_unique(fiq, req);
+
+	return fuse_uring_queue_bq_req(req);
+}
+#endif
+
+/*
+ * @return true if queued
+ */
+static int fuse_request_queue_background(struct fuse_req *req)
+{
+	struct fuse_chan *fch = req->chan;
+	bool queued = false;
+
+	WARN_ON(!test_bit(FR_BACKGROUND, &req->flags));
+	if (!test_bit(FR_WAITING, &req->flags)) {
+		__set_bit(FR_WAITING, &req->flags);
+		atomic_inc(&fch->num_waiting);
+	}
+	__set_bit(FR_ISREPLY, &req->flags);
+
+#ifdef CONFIG_FUSE_IO_URING
+	if (fuse_uring_ready(fch))
+		return fuse_request_queue_background_uring(req);
+#endif
+
+	spin_lock(&fch->bg_lock);
+	if (likely(fch->connected)) {
+		fch->num_background++;
+		if (fch->num_background == fch->max_background)
+			fch->blocked = 1;
+		list_add_tail(&req->list, &fch->bg_queue);
+		flush_bg_queue(fch);
+		queued = true;
+	}
+	spin_unlock(&fch->bg_lock);
+
+	return queued;
+}
+
+int fuse_chan_send_bg(struct fuse_chan *fch, struct fuse_args *args, gfp_t gfp_flags)
+{
+	struct fuse_req *req;
+
+	if (args->force) {
+		req = fuse_request_alloc(fch, gfp_flags);
+		if (!req)
+			return -ENOMEM;
+		__set_bit(FR_BACKGROUND, &req->flags);
+	} else {
+		req = fuse_get_req(fch, true);
+		if (IS_ERR(req))
+			return PTR_ERR(req);
+	}
+
+	fuse_args_to_req(req, args);
+
+	if (!fuse_request_queue_background(req)) {
+		fuse_put_request(req);
+		return -ENOTCONN;
+	}
+
+	return 0;
+}
+
+int fuse_chan_send_notify_reply(struct fuse_chan *fch, struct fuse_args *args, u64 unique)
+{
+	struct fuse_req *req;
+	struct fuse_iqueue *fiq = &fch->iq;
+
+	req = fuse_get_req(fch, false);
+	if (IS_ERR(req))
+		return PTR_ERR(req);
+
+	__clear_bit(FR_ISREPLY, &req->flags);
+	req->in.h.unique = unique;
+
+	fuse_args_to_req(req, args);
+
+	fuse_send_one(fiq, req);
+
+	return 0;
+}
+
+/*
+ * Lock the request.  Up to the next unlock_request() there mustn't be
+ * anything that could cause a page-fault.  If the request was already
+ * aborted bail out.
+ */
+static int lock_request(struct fuse_req *req)
+{
+	int err = 0;
+	if (req) {
+		spin_lock(&req->waitq.lock);
+		if (test_bit(FR_ABORTED, &req->flags))
+			err = -ENOENT;
+		else
+			set_bit(FR_LOCKED, &req->flags);
+		spin_unlock(&req->waitq.lock);
+	}
+	return err;
+}
+
+/*
+ * Unlock request.  If it was aborted while locked, caller is responsible
+ * for unlocking and ending the request.
+ */
+static int unlock_request(struct fuse_req *req)
+{
+	int err = 0;
+	if (req) {
+		spin_lock(&req->waitq.lock);
+		if (test_bit(FR_ABORTED, &req->flags))
+			err = -ENOENT;
+		else
+			clear_bit(FR_LOCKED, &req->flags);
+		spin_unlock(&req->waitq.lock);
+	}
+	return err;
+}
+
+void fuse_copy_init(struct fuse_copy_state *cs, bool write,
+		    struct iov_iter *iter)
+{
+	memset(cs, 0, sizeof(*cs));
+	cs->write = write;
+	cs->iter = iter;
+}
+
+/* Unmap and put previous page of userspace buffer */
+void fuse_copy_finish(struct fuse_copy_state *cs)
+{
+	if (cs->currbuf) {
+		struct pipe_buffer *buf = cs->currbuf;
+
+		if (cs->write)
+			buf->len = PAGE_SIZE - cs->len;
+		cs->currbuf = NULL;
+	} else if (cs->pg) {
+		if (cs->write) {
+			flush_dcache_page(cs->pg);
+			set_page_dirty_lock(cs->pg);
+		}
+		put_page(cs->pg);
+	}
+	cs->pg = NULL;
+}
+
+/*
+ * Get another pagefull of userspace buffer, and map it to kernel
+ * address space, and lock request
+ */
+static int fuse_copy_fill(struct fuse_copy_state *cs)
+{
+	struct page *page;
+	int err;
+
+	err = unlock_request(cs->req);
+	if (err)
+		return err;
+
+	fuse_copy_finish(cs);
+	if (cs->pipebufs) {
+		struct pipe_buffer *buf = cs->pipebufs;
+
+		if (!cs->write) {
+			err = pipe_buf_confirm(cs->pipe, buf);
+			if (err)
+				return err;
+
+			BUG_ON(!cs->nr_segs);
+			cs->currbuf = buf;
+			cs->pg = buf->page;
+			cs->offset = buf->offset;
+			cs->len = buf->len;
+			cs->pipebufs++;
+			cs->nr_segs--;
+		} else {
+			if (cs->nr_segs >= cs->pipe->max_usage)
+				return -EIO;
+
+			page = alloc_page(GFP_HIGHUSER);
+			if (!page)
+				return -ENOMEM;
+
+			buf->page = page;
+			buf->offset = 0;
+			buf->len = 0;
+
+			cs->currbuf = buf;
+			cs->pg = page;
+			cs->offset = 0;
+			cs->len = PAGE_SIZE;
+			cs->pipebufs++;
+			cs->nr_segs++;
+		}
+	} else {
+		size_t off;
+		err = iov_iter_get_pages2(cs->iter, &page, PAGE_SIZE, 1, &off);
+		if (err < 0)
+			return err;
+		BUG_ON(!err);
+		cs->len = err;
+		cs->offset = off;
+		cs->pg = page;
+	}
+
+	return lock_request(cs->req);
+}
+
+/* Do as much copy to/from userspace buffer as we can */
+static int fuse_copy_do(struct fuse_copy_state *cs, void **val, unsigned *size)
+{
+	unsigned ncpy = min(*size, cs->len);
+	if (val) {
+		void *pgaddr = kmap_local_page(cs->pg);
+		void *buf = pgaddr + cs->offset;
+
+		if (cs->write)
+			memcpy(buf, *val, ncpy);
+		else
+			memcpy(*val, buf, ncpy);
+
+		kunmap_local(pgaddr);
+		*val += ncpy;
+	}
+	*size -= ncpy;
+	cs->len -= ncpy;
+	cs->offset += ncpy;
+	if (cs->is_uring)
+		cs->ring.copied_sz += ncpy;
+
+	return ncpy;
+}
+
+static int fuse_check_folio(struct folio *folio)
+{
+	if (folio_mapped(folio) ||
+	    folio->mapping != NULL ||
+	    (folio->flags.f & PAGE_FLAGS_CHECK_AT_PREP &
+	     ~(1 << PG_locked |
+	       1 << PG_referenced |
+	       1 << PG_lru |
+	       1 << PG_active |
+	       1 << PG_workingset |
+	       1 << PG_reclaim |
+	       1 << PG_waiters |
+	       LRU_GEN_MASK | LRU_REFS_MASK))) {
+		dump_page(&folio->page, "fuse: trying to steal weird page");
+		return 1;
+	}
+	return 0;
+}
+
+/*
+ * Attempt to steal a page from the splice() pipe and move it into the
+ * pagecache. If successful, the pointer in @pagep will be updated. The
+ * folio that was originally in @pagep will lose a reference and the new
+ * folio returned in @pagep will carry a reference.
+ */
+static int fuse_try_move_folio(struct fuse_copy_state *cs, struct folio **foliop)
+{
+	int err;
+	struct folio *oldfolio = *foliop;
+	struct folio *newfolio;
+	struct pipe_buffer *buf = cs->pipebufs;
+
+	folio_get(oldfolio);
+	err = unlock_request(cs->req);
+	if (err)
+		goto out_put_old;
+
+	fuse_copy_finish(cs);
+
+	err = pipe_buf_confirm(cs->pipe, buf);
+	if (err)
+		goto out_put_old;
+
+	BUG_ON(!cs->nr_segs);
+	cs->currbuf = buf;
+	cs->len = buf->len;
+	cs->pipebufs++;
+	cs->nr_segs--;
+
+	if (cs->len != folio_size(oldfolio))
+		goto out_fallback;
+
+	if (!pipe_buf_try_steal(cs->pipe, buf))
+		goto out_fallback;
+
+	newfolio = page_folio(buf->page);
+
+	folio_clear_uptodate(newfolio);
+	folio_clear_mappedtodisk(newfolio);
+
+	if (folio_test_large(newfolio))
+		goto out_fallback_unlock;
+
+	if (fuse_check_folio(newfolio) != 0)
+		goto out_fallback_unlock;
+
+	/*
+	 * This is a new and locked page, it shouldn't be mapped or
+	 * have any special flags on it
+	 */
+	if (WARN_ON(folio_mapped(oldfolio)))
+		goto out_fallback_unlock;
+	if (WARN_ON(folio_has_private(oldfolio)))
+		goto out_fallback_unlock;
+	if (WARN_ON(folio_test_dirty(oldfolio) ||
+				folio_test_writeback(oldfolio)))
+		goto out_fallback_unlock;
+	if (WARN_ON(folio_test_mlocked(oldfolio)))
+		goto out_fallback_unlock;
+
+	err = lock_request(cs->req);
+	if (err)
+		goto out_fallback_unlock;
+
+	replace_page_cache_folio(oldfolio, newfolio);
+
+	folio_get(newfolio);
+
+	if (!(buf->flags & PIPE_BUF_FLAG_LRU))
+		folio_add_lru(newfolio);
+
+	/*
+	 * Release while we have extra ref on stolen page.  Otherwise
+	 * anon_pipe_buf_release() might think the page can be reused.
+	 */
+	pipe_buf_release(cs->pipe, buf);
+
+	*foliop = newfolio;
+	folio_unlock(oldfolio);
+	/* Drop ref for ap->pages[] array */
+	folio_put(oldfolio);
+	cs->len = 0;
+
+	err = 0;
+out_put_old:
+	/* Drop ref obtained in this function */
+	folio_put(oldfolio);
+	return err;
+
+out_fallback_unlock:
+	folio_unlock(newfolio);
+out_fallback:
+	cs->pg = buf->page;
+	cs->offset = buf->offset;
+
+	err = lock_request(cs->req);
+	if (!err)
+		err = 1;
+
+	goto out_put_old;
+}
+
+static int fuse_ref_folio(struct fuse_copy_state *cs, struct folio *folio,
+			  unsigned offset, unsigned count)
+{
+	struct pipe_buffer *buf;
+	int err;
+
+	if (cs->nr_segs >= cs->pipe->max_usage)
+		return -EIO;
+
+	folio_get(folio);
+	err = unlock_request(cs->req);
+	if (err) {
+		folio_put(folio);
+		return err;
+	}
+
+	fuse_copy_finish(cs);
+
+	buf = cs->pipebufs;
+	buf->page = &folio->page;
+	buf->offset = offset;
+	buf->len = count;
+
+	cs->pipebufs++;
+	cs->nr_segs++;
+	cs->len = 0;
+
+	return lock_request(cs->req);
+}
+
+/*
+ * Copy a folio in the request to/from the userspace buffer.  Must be
+ * done atomically
+ */
+int fuse_copy_folio(struct fuse_copy_state *cs, struct folio **foliop,
+		    unsigned offset, unsigned count, int zeroing)
+{
+	int err;
+	struct folio *folio = *foliop;
+	size_t size;
+
+	if (folio) {
+		size = folio_size(folio);
+		if (zeroing && count < size) {
+			/*
+			 * When the copy is skipped the folio already holds the
+			 * payload, so only the bytes outside [offset, offset +
+			 * count) may be zeroed.
+			 *
+			 * Otherwise, the whole folio is cleared first so that a
+			 * failed copy leaves zeros rather than stale folio
+			 * contents.
+			 */
+			if (cs->skip_folio_copy)
+				folio_zero_segments(folio, 0, offset,
+						    offset + count, size);
+			else
+				folio_zero_range(folio, 0, size);
+		}
+	}
+
+	while (!cs->skip_folio_copy && count) {
+		if (cs->write && cs->pipebufs && folio) {
+			/*
+			 * Can't control lifetime of pipe buffers, so always
+			 * copy user pages.
+			 */
+			if (cs->req->args->user_pages) {
+				err = fuse_copy_fill(cs);
+				if (err)
+					return err;
+			} else {
+				return fuse_ref_folio(cs, folio, offset, count);
+			}
+		} else if (!cs->len) {
+			if (cs->move_folios && folio &&
+			    offset == 0 && count == size) {
+				err = fuse_try_move_folio(cs, foliop);
+				if (err <= 0)
+					return err;
+			} else {
+				err = fuse_copy_fill(cs);
+				if (err)
+					return err;
+			}
+		}
+		if (folio) {
+			void *mapaddr = kmap_local_folio(folio, offset);
+			void *buf = mapaddr;
+			unsigned int copy = count;
+			unsigned int bytes_copied;
+
+			if (folio_test_highmem(folio) && count > PAGE_SIZE - offset_in_page(offset))
+				copy = PAGE_SIZE - offset_in_page(offset);
+
+			bytes_copied = fuse_copy_do(cs, &buf, &copy);
+			kunmap_local(mapaddr);
+			offset += bytes_copied;
+			count -= bytes_copied;
+		} else
+			offset += fuse_copy_do(cs, NULL, &count);
+	}
+	if (folio && !cs->write)
+		flush_dcache_folio(folio);
+	return 0;
+}
+
+/* Copy folios in the request to/from userspace buffer */
+static int fuse_copy_folios(struct fuse_copy_state *cs, unsigned nbytes,
+			    int zeroing)
+{
+	unsigned i;
+	struct fuse_req *req = cs->req;
+	struct fuse_args_pages *ap = container_of(req->args, typeof(*ap), args);
+
+	for (i = 0; i < ap->num_folios && (nbytes || zeroing); i++) {
+		int err;
+		unsigned int offset = ap->descs[i].offset;
+		unsigned int count = min(nbytes, ap->descs[i].length);
+
+		err = fuse_copy_folio(cs, &ap->folios[i], offset, count, zeroing);
+		if (err)
+			return err;
+
+		nbytes -= count;
+	}
+	return 0;
+}
+
+/* Copy a single argument in the request to/from userspace buffer */
+int fuse_copy_one(struct fuse_copy_state *cs, void *val, unsigned size)
+{
+	while (size) {
+		if (!cs->len) {
+			int err = fuse_copy_fill(cs);
+			if (err)
+				return err;
+		}
+		fuse_copy_do(cs, &val, &size);
+	}
+	return 0;
+}
+
+/* Copy request arguments to/from userspace buffer */
+int fuse_copy_args(struct fuse_copy_state *cs, unsigned numargs,
+		   unsigned argpages, struct fuse_arg *args,
+		   int zeroing)
+{
+	int err = 0;
+	unsigned i;
+
+	for (i = 0; !err && i < numargs; i++)  {
+		struct fuse_arg *arg = &args[i];
+		if (i == numargs - 1 && argpages)
+			/*
+			 * if cs->skip_folio_copy is set, this just does any
+			 * needed zeroing. No copying is involved.
+			 */
+			err = fuse_copy_folios(cs, arg->size, zeroing);
+		else
+			err = fuse_copy_one(cs, arg->value, arg->size);
+	}
+	return err;
+}
+
+static int forget_pending(struct fuse_iqueue *fiq)
+{
+	return fiq->forget_list_head.next != NULL;
+}
+
+static int request_pending(struct fuse_iqueue *fiq)
+{
+	return !list_empty(&fiq->pending) || !list_empty(&fiq->interrupts) ||
+		forget_pending(fiq);
+}
+
+/*
+ * Transfer an interrupt request to userspace
+ *
+ * Unlike other requests this is assembled on demand, without a need
+ * to allocate a separate fuse_req structure.
+ *
+ * Called with fiq->lock held, releases it
+ */
+static int fuse_read_interrupt(struct fuse_iqueue *fiq, struct fuse_copy_state *cs)
+__releases(fiq->lock)
+{
+	struct fuse_req *req = list_first_entry(&fiq->interrupts, struct fuse_req, intr_entry);
+	struct fuse_interrupt_in arg = {
+		.unique = req->in.h.unique,
+	};
+	struct fuse_in_header ih = {
+		.opcode = FUSE_INTERRUPT,
+		.unique = (req->in.h.unique | FUSE_INT_REQ_BIT),
+		.len = sizeof(ih) + sizeof(arg),
+	};
+	int err;
+
+	list_del_init(&req->intr_entry);
+	spin_unlock(&fiq->lock);
+
+	err = fuse_copy_one(cs, &ih, sizeof(ih));
+	if (!err)
+		err = fuse_copy_one(cs, &arg, sizeof(arg));
+	fuse_copy_finish(cs);
+
+	return err ? err : ih.len;
+}
+
+static struct fuse_forget_link *fuse_dequeue_forget(struct fuse_iqueue *fiq,
+						    unsigned int max,
+						    unsigned int *countp)
+{
+	struct fuse_forget_link *head = fiq->forget_list_head.next;
+	struct fuse_forget_link **newhead = &head;
+	unsigned count;
+
+	for (count = 0; *newhead != NULL && count < max; count++)
+		newhead = &(*newhead)->next;
+
+	fiq->forget_list_head.next = *newhead;
+	*newhead = NULL;
+	if (fiq->forget_list_head.next == NULL)
+		fiq->forget_list_tail = &fiq->forget_list_head;
+
+	if (countp != NULL)
+		*countp = count;
+
+	return head;
+}
+
+static int fuse_read_single_forget(struct fuse_iqueue *fiq,
+				   struct fuse_copy_state *cs)
+__releases(fiq->lock)
+{
+	int err;
+	struct fuse_forget_link *forget = fuse_dequeue_forget(fiq, 1, NULL);
+	struct fuse_forget_in arg = {
+		.nlookup = forget->forget_one.nlookup,
+	};
+	struct fuse_in_header ih = {
+		.opcode = FUSE_FORGET,
+		.nodeid = forget->forget_one.nodeid,
+		.unique = fuse_get_unique_locked(fiq),
+		.len = sizeof(ih) + sizeof(arg),
+	};
+
+	spin_unlock(&fiq->lock);
+	kfree(forget);
+
+	err = fuse_copy_one(cs, &ih, sizeof(ih));
+	if (!err)
+		err = fuse_copy_one(cs, &arg, sizeof(arg));
+	fuse_copy_finish(cs);
+
+	if (err)
+		return err;
+
+	return ih.len;
+}
+
+static int fuse_read_batch_forget(struct fuse_iqueue *fiq,
+				   struct fuse_copy_state *cs, size_t nbytes)
+__releases(fiq->lock)
+{
+	int err;
+	unsigned max_forgets;
+	unsigned count;
+	struct fuse_forget_link *head;
+	struct fuse_batch_forget_in arg = { .count = 0 };
+	struct fuse_in_header ih = {
+		.opcode = FUSE_BATCH_FORGET,
+		.unique = fuse_get_unique_locked(fiq),
+		.len = sizeof(ih) + sizeof(arg),
+	};
+
+	max_forgets = (nbytes - ih.len) / sizeof(struct fuse_forget_one);
+	head = fuse_dequeue_forget(fiq, max_forgets, &count);
+	spin_unlock(&fiq->lock);
+
+	arg.count = count;
+	ih.len += count * sizeof(struct fuse_forget_one);
+	err = fuse_copy_one(cs, &ih, sizeof(ih));
+	if (!err)
+		err = fuse_copy_one(cs, &arg, sizeof(arg));
+
+	while (head) {
+		struct fuse_forget_link *forget = head;
+
+		if (!err) {
+			err = fuse_copy_one(cs, &forget->forget_one,
+					    sizeof(forget->forget_one));
+		}
+		head = forget->next;
+		kfree(forget);
+	}
+
+	fuse_copy_finish(cs);
+
+	if (err)
+		return err;
+
+	return ih.len;
+}
+
+static int fuse_read_forget(struct fuse_chan *fch, struct fuse_iqueue *fiq,
+			    struct fuse_copy_state *cs,
+			    size_t nbytes)
+__releases(fiq->lock)
+{
+	if (fch->minor < 16 || fiq->forget_list_head.next->next == NULL)
+		return fuse_read_single_forget(fiq, cs);
+	else
+		return fuse_read_batch_forget(fiq, cs, nbytes);
+}
+
+/*
+ * Read a single request into the userspace filesystem's buffer.  This
+ * function waits until a request is available, then removes it from
+ * the pending list and copies request data to userspace buffer.  If
+ * no reply is needed (FORGET) or request has been aborted or there
+ * was an error during the copying then it's finished by calling
+ * fuse_request_end().  Otherwise add it to the processing list, and set
+ * the 'sent' flag.
+ */
+static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
+				struct fuse_copy_state *cs, size_t nbytes)
+{
+	ssize_t err;
+	struct fuse_chan *fch = fud->chan;
+	struct fuse_iqueue *fiq = &fch->iq;
+	struct fuse_pqueue *fpq = &fud->pq;
+	struct fuse_req *req;
+	struct fuse_args *args;
+	unsigned reqsize;
+	unsigned int hash;
+
+	/*
+	 * Require sane minimum read buffer - that has capacity for fixed part
+	 * of any request header + negotiated max_write room for data.
+	 *
+	 * Historically libfuse reserves 4K for fixed header room, but e.g.
+	 * GlusterFS reserves only 80 bytes
+	 *
+	 *	= `sizeof(fuse_in_header) + sizeof(fuse_write_in)`
+	 *
+	 * which is the absolute minimum any sane filesystem should be using
+	 * for header room.
+	 */
+	if (nbytes < max_t(size_t, FUSE_MIN_READ_BUFFER,
+			   sizeof(struct fuse_in_header) +
+			   sizeof(struct fuse_write_in) +
+			   fch->max_write))
+		return -EINVAL;
+
+ restart:
+	for (;;) {
+		spin_lock(&fiq->lock);
+		if (!fiq->connected || request_pending(fiq))
+			break;
+		spin_unlock(&fiq->lock);
+
+		if (file->f_flags & O_NONBLOCK)
+			return -EAGAIN;
+		err = wait_event_interruptible_exclusive(fiq->waitq,
+				!fiq->connected || request_pending(fiq));
+		if (err)
+			return err;
+	}
+
+	if (!fiq->connected) {
+		err = fch->abort_with_err ? -ECONNABORTED : -ENODEV;
+		goto err_unlock;
+	}
+
+	if (!list_empty(&fiq->interrupts))
+		return fuse_read_interrupt(fiq, cs);
+
+	if (forget_pending(fiq)) {
+		if (list_empty(&fiq->pending) || fiq->forget_batch-- > 0)
+			return fuse_read_forget(fch, fiq, cs, nbytes);
+
+		if (fiq->forget_batch <= -8)
+			fiq->forget_batch = 16;
+	}
+
+	req = list_entry(fiq->pending.next, struct fuse_req, list);
+	clear_bit(FR_PENDING, &req->flags);
+	list_del_init(&req->list);
+	spin_unlock(&fiq->lock);
+
+	args = req->args;
+	reqsize = req->in.h.len;
+
+	/* If request is too large, reply with an error and restart the read */
+	if (nbytes < reqsize) {
+		req->out.h.error = -EIO;
+		/* SETXATTR is special, since it may contain too large data */
+		if (args->opcode == FUSE_SETXATTR)
+			req->out.h.error = -E2BIG;
+		fuse_request_end(req);
+		goto restart;
+	}
+	spin_lock(&fpq->lock);
+	/*
+	 *  Must not put request on fpq->io queue after having been shut down by
+	 *  fuse_chan_abort()
+	 */
+	if (!fpq->connected) {
+		req->out.h.error = err = -ECONNABORTED;
+		goto out_end;
+	}
+	list_add(&req->list, &fpq->io);
+	spin_unlock(&fpq->lock);
+	cs->req = req;
+	err = fuse_copy_one(cs, &req->in.h, sizeof(req->in.h));
+	if (!err)
+		err = fuse_copy_args(cs, args->in_numargs, args->in_pages,
+				     (struct fuse_arg *) args->in_args, 0);
+	fuse_copy_finish(cs);
+	spin_lock(&fpq->lock);
+	clear_bit(FR_LOCKED, &req->flags);
+	if (!fpq->connected) {
+		err = fch->abort_with_err ? -ECONNABORTED : -ENODEV;
+		goto out_end;
+	}
+	if (err) {
+		req->out.h.error = -EIO;
+		goto out_end;
+	}
+	if (!test_bit(FR_ISREPLY, &req->flags)) {
+		err = reqsize;
+		goto out_end;
+	}
+	hash = fuse_req_hash(req->in.h.unique);
+	list_move_tail(&req->list, &fpq->processing[hash]);
+	__fuse_get_request(req);
+	set_bit(FR_SENT, &req->flags);
+	trace_fuse_request_sent(req);
+	spin_unlock(&fpq->lock);
+	/* matches barrier in request_wait_answer() */
+	smp_mb__after_atomic();
+	if (test_bit(FR_INTERRUPTED, &req->flags))
+		queue_interrupt(req);
+	fuse_put_request(req);
+
+	return reqsize;
+
+out_end:
+	if (!test_bit(FR_PRIVATE, &req->flags))
+		list_del_init(&req->list);
+	spin_unlock(&fpq->lock);
+	fuse_request_end(req);
+	return err;
+
+ err_unlock:
+	spin_unlock(&fiq->lock);
+	return err;
+}
+
+static int fuse_dev_open(struct inode *inode, struct file *file)
+{
+	struct fuse_dev *fud = fuse_dev_alloc_no_pq();
+
+	if (!fud)
+		return -ENOMEM;
+
+	file->private_data = fud;
+	return 0;
+}
+
+struct fuse_dev *fuse_get_dev(struct file *file)
+{
+	struct fuse_dev *fud = fuse_file_to_fud(file);
+	int err;
+
+	if (unlikely(!fuse_dev_chan_get(fud))) {
+		/* only block waiting for mount if sync init was requested */
+		if (!fud->sync_init)
+			return ERR_PTR(-EPERM);
+
+		err = wait_event_interruptible(fuse_dev_waitq, fuse_dev_chan_get(fud) != NULL);
+		if (err)
+			return ERR_PTR(err);
+	}
+
+	return fud;
+}
+
+static ssize_t fuse_dev_read(struct kiocb *iocb, struct iov_iter *to)
+{
+	struct fuse_copy_state cs;
+	struct file *file = iocb->ki_filp;
+	struct fuse_dev *fud = fuse_get_dev(file);
+
+	if (IS_ERR(fud))
+		return PTR_ERR(fud);
+
+	if (!user_backed_iter(to))
+		return -EINVAL;
+
+	fuse_copy_init(&cs, true, to);
+
+	return fuse_dev_do_read(fud, file, &cs, iov_iter_count(to));
+}
+
+static ssize_t fuse_dev_splice_read(struct file *in, loff_t *ppos,
+				    struct pipe_inode_info *pipe,
+				    size_t len, unsigned int flags)
+{
+	int total, ret;
+	int page_nr = 0;
+	struct pipe_buffer *bufs;
+	struct fuse_copy_state cs;
+	struct fuse_dev *fud = fuse_get_dev(in);
+
+	if (IS_ERR(fud))
+		return PTR_ERR(fud);
+
+	bufs = kvmalloc_objs(struct pipe_buffer, pipe->max_usage);
+	if (!bufs)
+		return -ENOMEM;
+
+	fuse_copy_init(&cs, true, NULL);
+	cs.pipebufs = bufs;
+	cs.pipe = pipe;
+	ret = fuse_dev_do_read(fud, in, &cs, len);
+	if (ret < 0)
+		goto out;
+
+	if (pipe_buf_usage(pipe) + cs.nr_segs > pipe->max_usage) {
+		ret = -EIO;
+		goto out;
+	}
+
+	for (ret = total = 0; page_nr < cs.nr_segs; total += ret) {
+		/*
+		 * Need to be careful about this.  Having buf->ops in module
+		 * code can Oops if the buffer persists after module unload.
+		 */
+		bufs[page_nr].ops = &nosteal_pipe_buf_ops;
+		bufs[page_nr].flags = 0;
+		ret = add_to_pipe(pipe, &bufs[page_nr++]);
+		if (unlikely(ret < 0))
+			break;
+	}
+	if (total)
+		ret = total;
+out:
+	for (; page_nr < cs.nr_segs; page_nr++)
+		put_page(bufs[page_nr].page);
+
+	kvfree(bufs);
+	return ret;
+}
+
+/*
+ * Resending all processing queue requests.
+ *
+ * During a FUSE daemon panics and failover, it is possible for some inflight
+ * requests to be lost and never returned. As a result, applications awaiting
+ * replies would become stuck forever. To address this, we can use notification
+ * to trigger resending of these pending requests to the FUSE daemon, ensuring
+ * they are properly processed again.
+ *
+ * Please note that this strategy is applicable only to idempotent requests or
+ * if the FUSE daemon takes careful measures to avoid processing duplicated
+ * non-idempotent requests.
+ */
+void fuse_chan_resend(struct fuse_chan *fch)
+{
+	struct fuse_dev *fud;
+	struct fuse_req *req;
+	struct fuse_iqueue *fiq = &fch->iq;
+	LIST_HEAD(to_queue);
+	unsigned int i;
+
+	spin_lock(&fch->lock);
+	if (!fch->connected) {
+		spin_unlock(&fch->lock);
+		return;
+	}
+
+	list_for_each_entry(fud, &fch->devices, entry) {
+		struct fuse_pqueue *fpq = &fud->pq;
+
+		spin_lock(&fpq->lock);
+		for (i = 0; i < FUSE_PQ_HASH_SIZE; i++) {
+			struct list_head *this_queue = &fpq->processing[i];
+
+			list_for_each_entry(req, this_queue, list)
+				clear_bit(FR_SENT, &req->flags);
+			list_splice_tail_init(this_queue, &to_queue);
+		}
+		spin_unlock(&fpq->lock);
+	}
+	spin_unlock(&fch->lock);
+
+	spin_lock(&fiq->lock);
+	if (!fiq->connected) {
+		spin_unlock(&fiq->lock);
+		fuse_dev_end_requests(&to_queue);
+		return;
+	}
+	/*
+	 * Remove interrupt entries for resent requests to prevent stale
+	 * intr_entry on fiq->interrupts after the request is re-queued.
+	 */
+	list_for_each_entry(req, &to_queue, list) {
+		set_bit(FR_PENDING, &req->flags);
+		/* mark the request as resend request */
+		req->in.h.unique |= FUSE_UNIQUE_RESEND;
+
+		if (test_bit(FR_INTERRUPTED, &req->flags))
+			list_del_init(&req->intr_entry);
+	}
+	/* iq and pq requests are both oldest to newest */
+	list_splice(&to_queue, &fiq->pending);
+	fuse_dev_wake_and_unlock(fiq, false);
+}
+
+/* Look up request on processing list by unique ID */
+struct fuse_req *fuse_request_find(struct fuse_pqueue *fpq, u64 unique)
+{
+	unsigned int hash = fuse_req_hash(unique);
+	struct fuse_req *req;
+
+	list_for_each_entry(req, &fpq->processing[hash], list) {
+		if (req->in.h.unique == unique)
+			return req;
+	}
+	return NULL;
+}
+
+int fuse_copy_out_args(struct fuse_copy_state *cs, struct fuse_args *args,
+		       unsigned nbytes)
+{
+
+	unsigned int reqsize = 0;
+
+	/*
+	 * Uring has all headers separated from args - args is payload only
+	 */
+	if (!cs->is_uring)
+		reqsize = sizeof(struct fuse_out_header);
+
+	reqsize += fuse_len_args(args->out_numargs, args->out_args);
+
+	if (reqsize < nbytes || (reqsize > nbytes && !args->out_argvar))
+		return -EINVAL;
+	else if (reqsize > nbytes) {
+		struct fuse_arg *lastarg = &args->out_args[args->out_numargs-1];
+		unsigned diffsize = reqsize - nbytes;
+
+		if (diffsize > lastarg->size)
+			return -EINVAL;
+		lastarg->size -= diffsize;
+	}
+	return fuse_copy_args(cs, args->out_numargs, args->out_pages,
+			      args->out_args, args->page_zeroing);
+}
+
+/*
+ * Write a single reply to a request.  First the header is copied from
+ * the write buffer.  The request is then searched on the processing
+ * list by the unique ID found in the header.  If found, then remove
+ * it from the list and copy the rest of the buffer to the request.
+ * The request is finished by calling fuse_request_end().
+ */
+static ssize_t fuse_dev_do_write(struct fuse_dev *fud,
+				 struct fuse_copy_state *cs, size_t nbytes)
+{
+	int err;
+	struct fuse_chan *fch = fud->chan;
+	struct fuse_pqueue *fpq = &fud->pq;
+	struct fuse_req *req;
+	struct fuse_out_header oh;
+
+	err = -EINVAL;
+	if (nbytes < sizeof(struct fuse_out_header))
+		goto out;
+
+	err = fuse_copy_one(cs, &oh, sizeof(oh));
+	if (err)
+		goto copy_finish;
+
+	err = -EINVAL;
+	if (oh.len != nbytes)
+		goto copy_finish;
+
+	/*
+	 * Zero oh.unique indicates unsolicited notification message
+	 * and error contains notification code.
+	 */
+	if (!oh.unique) {
+		/*
+		 * Only allow notifications during while the connection is in an
+		 * initialized and connected state
+		 */
+		err = -EINVAL;
+		/* Pairs with smp_store_release() in fuse_chan_set_initialized() */
+		if (!smp_load_acquire(&fch->initialized) || !fch->connected)
+			goto copy_finish;
+
+		/* Don't try to move folios (yet) */
+		cs->move_folios = false;
+
+		err = fuse_notify(fch->conn, oh.error, nbytes - sizeof(oh), cs);
+		goto copy_finish;
+	}
+
+	err = -EINVAL;
+	if (oh.error <= -512 || oh.error > 0)
+		goto copy_finish;
+
+	spin_lock(&fpq->lock);
+	req = NULL;
+	if (fpq->connected)
+		req = fuse_request_find(fpq, oh.unique & ~FUSE_INT_REQ_BIT);
+
+	err = -ENOENT;
+	if (!req) {
+		spin_unlock(&fpq->lock);
+		goto copy_finish;
+	}
+
+	/* Is it an interrupt reply ID? */
+	if (oh.unique & FUSE_INT_REQ_BIT) {
+		__fuse_get_request(req);
+		spin_unlock(&fpq->lock);
+
+		err = 0;
+		if (nbytes != sizeof(struct fuse_out_header))
+			err = -EINVAL;
+		else if (oh.error == -ENOSYS)
+			fch->no_interrupt = 1;
+		else if (oh.error == -EAGAIN)
+			err = queue_interrupt(req);
+
+		fuse_put_request(req);
+
+		goto copy_finish;
+	}
+
+	clear_bit(FR_SENT, &req->flags);
+	list_move(&req->list, &fpq->io);
+	req->out.h = oh;
+	set_bit(FR_LOCKED, &req->flags);
+	spin_unlock(&fpq->lock);
+	cs->req = req;
+	if (!req->args->page_replace)
+		cs->move_folios = false;
+
+	if (oh.error)
+		err = nbytes != sizeof(oh) ? -EINVAL : 0;
+	else
+		err = fuse_copy_out_args(cs, req->args, nbytes);
+	fuse_copy_finish(cs);
+
+	spin_lock(&fpq->lock);
+	clear_bit(FR_LOCKED, &req->flags);
+	if (!fpq->connected)
+		err = -ENOENT;
+	else if (err)
+		req->out.h.error = -EIO;
+	if (!test_bit(FR_PRIVATE, &req->flags))
+		list_del_init(&req->list);
+	spin_unlock(&fpq->lock);
+
+	fuse_request_end(req);
+out:
+	return err ? err : nbytes;
+
+copy_finish:
+	fuse_copy_finish(cs);
+	goto out;
+}
+
+static ssize_t fuse_dev_write(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct fuse_copy_state cs;
+	struct fuse_dev *fud = __fuse_get_dev(iocb->ki_filp);
+
+	if (!fud)
+		return -EPERM;
+
+	if (!user_backed_iter(from))
+		return -EINVAL;
+
+	fuse_copy_init(&cs, false, from);
+
+	return fuse_dev_do_write(fud, &cs, iov_iter_count(from));
+}
+
+static ssize_t fuse_dev_splice_write(struct pipe_inode_info *pipe,
+				     struct file *out, loff_t *ppos,
+				     size_t len, unsigned int flags)
+{
+	unsigned int head, tail, count;
+	unsigned nbuf;
+	unsigned idx;
+	struct pipe_buffer *bufs;
+	struct fuse_copy_state cs;
+	struct fuse_dev *fud = __fuse_get_dev(out);
+	size_t rem;
+	ssize_t ret;
+
+	if (!fud)
+		return -EPERM;
+
+	pipe_lock(pipe);
+
+	head = pipe->head;
+	tail = pipe->tail;
+	count = pipe_occupancy(head, tail);
+
+	bufs = kvmalloc_objs(struct pipe_buffer, count);
+	if (!bufs) {
+		pipe_unlock(pipe);
+		return -ENOMEM;
+	}
+
+	nbuf = 0;
+	rem = 0;
+	for (idx = tail; !pipe_empty(head, idx) && rem < len; idx++)
+		rem += pipe_buf(pipe, idx)->len;
+
+	ret = -EINVAL;
+	if (rem < len)
+		goto out_free;
+
+	rem = len;
+	while (rem) {
+		struct pipe_buffer *ibuf;
+		struct pipe_buffer *obuf;
+
+		if (WARN_ON(nbuf >= count || pipe_empty(head, tail)))
+			goto out_free;
+
+		ibuf = pipe_buf(pipe, tail);
+		obuf = &bufs[nbuf];
+
+		if (rem >= ibuf->len) {
+			*obuf = *ibuf;
+			ibuf->ops = NULL;
+			tail++;
+			pipe->tail = tail;
+		} else {
+			if (!pipe_buf_get(pipe, ibuf))
+				goto out_free;
+
+			*obuf = *ibuf;
+			obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
+			obuf->len = rem;
+			ibuf->offset += obuf->len;
+			ibuf->len -= obuf->len;
+		}
+		nbuf++;
+		rem -= obuf->len;
+	}
+	pipe_unlock(pipe);
+
+	fuse_copy_init(&cs, false, NULL);
+	cs.pipebufs = bufs;
+	cs.nr_segs = nbuf;
+	cs.pipe = pipe;
+
+	if (flags & SPLICE_F_MOVE)
+		cs.move_folios = true;
+
+	ret = fuse_dev_do_write(fud, &cs, len);
+
+	pipe_lock(pipe);
+out_free:
+	for (idx = 0; idx < nbuf; idx++) {
+		struct pipe_buffer *buf = &bufs[idx];
+
+		if (buf->ops)
+			pipe_buf_release(pipe, buf);
+	}
+	pipe_unlock(pipe);
+
+	kvfree(bufs);
+	return ret;
+}
+
+static __poll_t fuse_dev_poll(struct file *file, poll_table *wait)
+{
+	__poll_t mask = EPOLLOUT | EPOLLWRNORM;
+	struct fuse_iqueue *fiq;
+	struct fuse_dev *fud = fuse_get_dev(file);
+
+	if (IS_ERR(fud))
+		return EPOLLERR;
+
+	fiq = &fud->chan->iq;
+	poll_wait(file, &fiq->waitq, wait);
+
+	spin_lock(&fiq->lock);
+	if (!fiq->connected)
+		mask = EPOLLERR;
+	else if (request_pending(fiq))
+		mask |= EPOLLIN | EPOLLRDNORM;
+	spin_unlock(&fiq->lock);
+
+	return mask;
+}
+
+/* Abort all requests on the given list (pending or processing) */
+void fuse_dev_end_requests(struct list_head *head)
+{
+	while (!list_empty(head)) {
+		struct fuse_req *req;
+		req = list_entry(head->next, struct fuse_req, list);
+		req->out.h.error = -ECONNABORTED;
+		clear_bit(FR_SENT, &req->flags);
+		list_del_init(&req->list);
+		fuse_request_end(req);
+	}
+}
+
+/*
+ * Abort all requests.
+ *
+ * Emergency exit in case of a malicious or accidental deadlock, or just a hung
+ * filesystem.
+ *
+ * The same effect is usually achievable through killing the filesystem daemon
+ * and all users of the filesystem.  The exception is the combination of an
+ * asynchronous request and the tricky deadlock (see
+ * Documentation/filesystems/fuse/fuse.rst).
+ *
+ * Aborting requests under I/O goes as follows: 1: Separate out unlocked
+ * requests, they should be finished off immediately.  Locked requests will be
+ * finished after unlock; see unlock_request(). 2: Finish off the unlocked
+ * requests.  It is possible that some request will finish before we can.  This
+ * is OK, the request will in that case be removed from the list before we touch
+ * it.
+ */
+void fuse_chan_abort(struct fuse_chan *fch, bool abort_with_err)
+{
+	struct fuse_iqueue *fiq = &fch->iq;
+
+	fch->abort_with_err = abort_with_err;
+
+	spin_lock(&fch->lock);
+	if (fch->connected) {
+		struct fuse_dev *fud;
+		struct fuse_req *req, *next;
+		LIST_HEAD(to_end);
+		unsigned int i;
+
+		if (fch->timeout.req_timeout)
+			cancel_delayed_work(&fch->timeout.work);
+
+		/* Background queuing checks fch->connected under bg_lock */
+		spin_lock(&fch->bg_lock);
+		fch->connected = 0;
+		spin_unlock(&fch->bg_lock);
+
+		fuse_chan_set_initialized(fch, NULL);
+		list_for_each_entry(fud, &fch->devices, entry) {
+			struct fuse_pqueue *fpq = &fud->pq;
+
+			spin_lock(&fpq->lock);
+			fpq->connected = 0;
+			list_for_each_entry_safe(req, next, &fpq->io, list) {
+				req->out.h.error = -ECONNABORTED;
+				spin_lock(&req->waitq.lock);
+				set_bit(FR_ABORTED, &req->flags);
+				if (!test_bit(FR_LOCKED, &req->flags)) {
+					set_bit(FR_PRIVATE, &req->flags);
+					__fuse_get_request(req);
+					list_move(&req->list, &to_end);
+				}
+				spin_unlock(&req->waitq.lock);
+			}
+			for (i = 0; i < FUSE_PQ_HASH_SIZE; i++)
+				list_splice_tail_init(&fpq->processing[i],
+						      &to_end);
+			spin_unlock(&fpq->lock);
+		}
+		spin_lock(&fch->bg_lock);
+		fch->blocked = 0;
+		fch->max_background = UINT_MAX;
+		flush_bg_queue(fch);
+		spin_unlock(&fch->bg_lock);
+
+		spin_lock(&fiq->lock);
+		fiq->connected = 0;
+		list_for_each_entry(req, &fiq->pending, list)
+			clear_bit(FR_PENDING, &req->flags);
+		list_splice_tail_init(&fiq->pending, &to_end);
+		while (forget_pending(fiq))
+			kfree(fuse_dequeue_forget(fiq, 1, NULL));
+		wake_up_all(&fiq->waitq);
+		spin_unlock(&fiq->lock);
+		kill_fasync(&fiq->fasync, SIGIO, POLL_IN);
+		fuse_end_polls(fch->conn);
+		wake_up_all(&fch->blocked_waitq);
+		spin_unlock(&fch->lock);
+
+		fuse_dev_end_requests(&to_end);
+
+		/*
+		 * fch->lock must not be taken to avoid conflicts with io-uring
+		 * locks
+		 */
+		fuse_uring_abort(fch);
+	} else {
+		spin_unlock(&fch->lock);
+	}
+}
+EXPORT_SYMBOL_GPL(fuse_chan_abort);
+
+void fuse_chan_wait_aborted(struct fuse_chan *fch)
+{
+	/* matches implicit memory barrier in fuse_drop_waiting() */
+	smp_mb();
+	wait_event(fch->blocked_waitq, fuse_chan_num_waiting(fch) == 0);
+
+	fuse_uring_wait_stopped_queues(fch);
+}
+
+int fuse_dev_release(struct inode *inode, struct file *file)
+{
+	struct fuse_dev *fud = fuse_file_to_fud(file);
+	/* Pairs with cmpxchg() in fuse_dev_install() */
+	struct fuse_chan *fch = xchg(&fud->chan, FUSE_DEV_CHAN_DISCONNECTED);
+
+	if (fch) {
+		struct fuse_pqueue *fpq = &fud->pq;
+		LIST_HEAD(to_end);
+		unsigned int i;
+		bool last;
+
+		/* Make sure fuse_dev_install_with_pq() has finished */
+		spin_lock(&fch->lock);
+		spin_lock(&fpq->lock);
+		WARN_ON(!list_empty(&fpq->io));
+		for (i = 0; i < FUSE_PQ_HASH_SIZE; i++)
+			list_splice_init(&fpq->processing[i], &to_end);
+		spin_unlock(&fpq->lock);
+
+		list_del(&fud->entry);
+		/* Are we the last open device? */
+		last = list_empty(&fch->devices);
+		spin_unlock(&fch->lock);
+
+		fuse_dev_end_requests(&to_end);
+
+		if (last) {
+			WARN_ON(fch->iq.fasync != NULL);
+			fuse_chan_abort(fch, false);
+		}
+		fuse_conn_put(fch->conn);
+	}
+	fuse_dev_put(fud);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(fuse_dev_release);
+
+static int fuse_dev_fasync(int fd, struct file *file, int on)
+{
+	struct fuse_dev *fud = fuse_get_dev(file);
+
+	if (IS_ERR(fud))
+		return PTR_ERR(fud);
+
+	/* No locking - fasync_helper does its own locking */
+	return fasync_helper(fd, file, on, &fud->chan->iq.fasync);
+}
+
+static long fuse_dev_ioctl_clone(struct file *file, __u32 __user *argp)
+{
+	int oldfd;
+	struct fuse_dev *fud, *new_fud;
+	struct list_head *pq;
+
+	if (get_user(oldfd, argp))
+		return -EFAULT;
+
+	CLASS(fd, f)(oldfd);
+	if (fd_empty(f))
+		return -EINVAL;
+
+	/*
+	 * Check against file->f_op because CUSE
+	 * uses the same ioctl handler.
+	 */
+	if (fd_file(f)->f_op != file->f_op)
+		return -EINVAL;
+
+	fud = fuse_get_dev(fd_file(f));
+	if (IS_ERR(fud))
+		return PTR_ERR(fud);
+
+	pq = fuse_pqueue_alloc();
+	if (!pq)
+		return -ENOMEM;
+
+	new_fud = fuse_file_to_fud(file);
+	if (!fuse_dev_install_with_pq(new_fud, fud->chan, pq))
+		return -EINVAL;
+
+	return 0;
+}
+
+static long fuse_dev_ioctl_backing_open(struct file *file,
+					struct fuse_backing_map __user *argp)
+{
+	struct fuse_dev *fud = fuse_get_dev(file);
+	struct fuse_backing_map map;
+
+	if (IS_ERR(fud))
+		return PTR_ERR(fud);
+
+	if (!IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
+		return -EOPNOTSUPP;
+
+	if (copy_from_user(&map, argp, sizeof(map)))
+		return -EFAULT;
+
+	return fuse_backing_open(fud->chan->conn, &map);
+}
+
+static long fuse_dev_ioctl_backing_close(struct file *file, __u32 __user *argp)
+{
+	struct fuse_dev *fud = fuse_get_dev(file);
+	int backing_id;
+
+	if (IS_ERR(fud))
+		return PTR_ERR(fud);
+
+	if (!IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
+		return -EOPNOTSUPP;
+
+	if (get_user(backing_id, argp))
+		return -EFAULT;
+
+	return fuse_backing_close(fud->chan->conn, backing_id);
+}
+
+static long fuse_dev_ioctl_sync_init(struct file *file)
+{
+	struct fuse_dev *fud = fuse_file_to_fud(file);
+
+	if (fuse_dev_chan_get(fud))
+		return -EINVAL;
+
+	fud->sync_init = true;
+	return 0;
+}
+
+static long fuse_dev_ioctl(struct file *file, unsigned int cmd,
+			   unsigned long arg)
+{
+	void __user *argp = (void __user *)arg;
+
+	switch (cmd) {
+	case FUSE_DEV_IOC_CLONE:
+		return fuse_dev_ioctl_clone(file, argp);
+
+	case FUSE_DEV_IOC_BACKING_OPEN:
+		return fuse_dev_ioctl_backing_open(file, argp);
+
+	case FUSE_DEV_IOC_BACKING_CLOSE:
+		return fuse_dev_ioctl_backing_close(file, argp);
+
+	case FUSE_DEV_IOC_SYNC_INIT:
+		return fuse_dev_ioctl_sync_init(file);
+
+	default:
+		return -ENOTTY;
+	}
+}
+
+#ifdef CONFIG_PROC_FS
+static void fuse_dev_show_fdinfo(struct seq_file *seq, struct file *file)
+{
+	struct fuse_dev *fud = __fuse_get_dev(file);
+	if (!fud)
+		return;
+
+	seq_printf(seq, "fuse_connection:\t%u\n", fuse_conn_get_id(fud->chan->conn));
+}
+#endif
+
+const struct file_operations fuse_dev_operations = {
+	.owner		= THIS_MODULE,
+	.open		= fuse_dev_open,
+	.read_iter	= fuse_dev_read,
+	.splice_read	= fuse_dev_splice_read,
+	.write_iter	= fuse_dev_write,
+	.splice_write	= fuse_dev_splice_write,
+	.poll		= fuse_dev_poll,
+	.release	= fuse_dev_release,
+	.fasync		= fuse_dev_fasync,
+	.unlocked_ioctl = fuse_dev_ioctl,
+	.compat_ioctl   = compat_ptr_ioctl,
+#ifdef CONFIG_FUSE_IO_URING
+	.uring_cmd	= fuse_uring_cmd,
+#endif
+#ifdef CONFIG_PROC_FS
+	.show_fdinfo	= fuse_dev_show_fdinfo,
+#endif
+};
+EXPORT_SYMBOL_GPL(fuse_dev_operations);
+
+static struct miscdevice fuse_miscdevice = {
+	.minor = FUSE_MINOR,
+	.name  = "fuse",
+	.fops = &fuse_dev_operations,
+};
+
+int __init fuse_dev_init(void)
+{
+	int err = -ENOMEM;
+	fuse_req_cachep = kmem_cache_create("fuse_request",
+					    sizeof(struct fuse_req),
+					    0, 0, NULL);
+	if (!fuse_req_cachep)
+		goto out;
+
+	err = misc_register(&fuse_miscdevice);
+	if (err)
+		goto out_cache_clean;
+
+	return 0;
+
+ out_cache_clean:
+	kmem_cache_destroy(fuse_req_cachep);
+ out:
+	return err;
+}
+
+void fuse_dev_cleanup(void)
+{
+	misc_deregister(&fuse_miscdevice);
+	kmem_cache_destroy(fuse_req_cachep);
+}