Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1339 insertions, 0 deletions

diff --git a/kernel/relay.c b/kernel/relay.c
new file mode 100644
index 000000000..735cb208f
--- /dev/null
+++ b/kernel/relay.c
@@ -0,0 +1,1339 @@
+/*
+ * Public API and common code for kernel->userspace relay file support.
+ *
+ * See Documentation/filesystems/relay.txt for an overview.
+ *
+ * Copyright (C) 2002-2005 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp
+ * Copyright (C) 1999-2005 - Karim Yaghmour (karim@opersys.com)
+ *
+ * Moved to kernel/relay.c by Paul Mundt, 2006.
+ * November 2006 - CPU hotplug support by Mathieu Desnoyers
+ * 	(mathieu.desnoyers@polymtl.ca)
+ *
+ * This file is released under the GPL.
+ */
+#include <linux/errno.h>
+#include <linux/stddef.h>
+#include <linux/slab.h>
+#include <linux/export.h>
+#include <linux/string.h>
+#include <linux/relay.h>
+#include <linux/vmalloc.h>
+#include <linux/mm.h>
+#include <linux/cpu.h>
+#include <linux/splice.h>
+
+/* list of open channels, for cpu hotplug */
+static DEFINE_MUTEX(relay_channels_mutex);
+static LIST_HEAD(relay_channels);
+
+/*
+ * close() vm_op implementation for relay file mapping.
+ */
+static void relay_file_mmap_close(struct vm_area_struct *vma)
+{
+	struct rchan_buf *buf = vma->vm_private_data;
+	buf->chan->cb->buf_unmapped(buf, vma->vm_file);
+}
+
+/*
+ * fault() vm_op implementation for relay file mapping.
+ */
+static vm_fault_t relay_buf_fault(struct vm_fault *vmf)
+{
+	struct page *page;
+	struct rchan_buf *buf = vmf->vma->vm_private_data;
+	pgoff_t pgoff = vmf->pgoff;
+
+	if (!buf)
+		return VM_FAULT_OOM;
+
+	page = vmalloc_to_page(buf->start + (pgoff << PAGE_SHIFT));
+	if (!page)
+		return VM_FAULT_SIGBUS;
+	get_page(page);
+	vmf->page = page;
+
+	return 0;
+}
+
+/*
+ * vm_ops for relay file mappings.
+ */
+static const struct vm_operations_struct relay_file_mmap_ops = {
+	.fault = relay_buf_fault,
+	.close = relay_file_mmap_close,
+};
+
+/*
+ * allocate an array of pointers of struct page
+ */
+static struct page **relay_alloc_page_array(unsigned int n_pages)
+{
+	const size_t pa_size = n_pages * sizeof(struct page *);
+	if (pa_size > PAGE_SIZE)
+		return vzalloc(pa_size);
+	return kzalloc(pa_size, GFP_KERNEL);
+}
+
+/*
+ * free an array of pointers of struct page
+ */
+static void relay_free_page_array(struct page **array)
+{
+	kvfree(array);
+}
+
+/**
+ *	relay_mmap_buf: - mmap channel buffer to process address space
+ *	@buf: relay channel buffer
+ *	@vma: vm_area_struct describing memory to be mapped
+ *
+ *	Returns 0 if ok, negative on error
+ *
+ *	Caller should already have grabbed mmap_sem.
+ */
+static int relay_mmap_buf(struct rchan_buf *buf, struct vm_area_struct *vma)
+{
+	unsigned long length = vma->vm_end - vma->vm_start;
+	struct file *filp = vma->vm_file;
+
+	if (!buf)
+		return -EBADF;
+
+	if (length != (unsigned long)buf->chan->alloc_size)
+		return -EINVAL;
+
+	vma->vm_ops = &relay_file_mmap_ops;
+	vma->vm_flags |= VM_DONTEXPAND;
+	vma->vm_private_data = buf;
+	buf->chan->cb->buf_mapped(buf, filp);
+
+	return 0;
+}
+
+/**
+ *	relay_alloc_buf - allocate a channel buffer
+ *	@buf: the buffer struct
+ *	@size: total size of the buffer
+ *
+ *	Returns a pointer to the resulting buffer, %NULL if unsuccessful. The
+ *	passed in size will get page aligned, if it isn't already.
+ */
+static void *relay_alloc_buf(struct rchan_buf *buf, size_t *size)
+{
+	void *mem;
+	unsigned int i, j, n_pages;
+
+	*size = PAGE_ALIGN(*size);
+	n_pages = *size >> PAGE_SHIFT;
+
+	buf->page_array = relay_alloc_page_array(n_pages);
+	if (!buf->page_array)
+		return NULL;
+
+	for (i = 0; i < n_pages; i++) {
+		buf->page_array[i] = alloc_page(GFP_KERNEL);
+		if (unlikely(!buf->page_array[i]))
+			goto depopulate;
+		set_page_private(buf->page_array[i], (unsigned long)buf);
+	}
+	mem = vmap(buf->page_array, n_pages, VM_MAP, PAGE_KERNEL);
+	if (!mem)
+		goto depopulate;
+
+	memset(mem, 0, *size);
+	buf->page_count = n_pages;
+	return mem;
+
+depopulate:
+	for (j = 0; j < i; j++)
+		__free_page(buf->page_array[j]);
+	relay_free_page_array(buf->page_array);
+	return NULL;
+}
+
+/**
+ *	relay_create_buf - allocate and initialize a channel buffer
+ *	@chan: the relay channel
+ *
+ *	Returns channel buffer if successful, %NULL otherwise.
+ */
+static struct rchan_buf *relay_create_buf(struct rchan *chan)
+{
+	struct rchan_buf *buf;
+
+	if (chan->n_subbufs > KMALLOC_MAX_SIZE / sizeof(size_t *))
+		return NULL;
+
+	buf = kzalloc(sizeof(struct rchan_buf), GFP_KERNEL);
+	if (!buf)
+		return NULL;
+	buf->padding = kmalloc_array(chan->n_subbufs, sizeof(size_t *),
+				     GFP_KERNEL);
+	if (!buf->padding)
+		goto free_buf;
+
+	buf->start = relay_alloc_buf(buf, &chan->alloc_size);
+	if (!buf->start)
+		goto free_buf;
+
+	buf->chan = chan;
+	kref_get(&buf->chan->kref);
+	return buf;
+
+free_buf:
+	kfree(buf->padding);
+	kfree(buf);
+	return NULL;
+}
+
+/**
+ *	relay_destroy_channel - free the channel struct
+ *	@kref: target kernel reference that contains the relay channel
+ *
+ *	Should only be called from kref_put().
+ */
+static void relay_destroy_channel(struct kref *kref)
+{
+	struct rchan *chan = container_of(kref, struct rchan, kref);
+	free_percpu(chan->buf);
+	kfree(chan);
+}
+
+/**
+ *	relay_destroy_buf - destroy an rchan_buf struct and associated buffer
+ *	@buf: the buffer struct
+ */
+static void relay_destroy_buf(struct rchan_buf *buf)
+{
+	struct rchan *chan = buf->chan;
+	unsigned int i;
+
+	if (likely(buf->start)) {
+		vunmap(buf->start);
+		for (i = 0; i < buf->page_count; i++)
+			__free_page(buf->page_array[i]);
+		relay_free_page_array(buf->page_array);
+	}
+	*per_cpu_ptr(chan->buf, buf->cpu) = NULL;
+	kfree(buf->padding);
+	kfree(buf);
+	kref_put(&chan->kref, relay_destroy_channel);
+}
+
+/**
+ *	relay_remove_buf - remove a channel buffer
+ *	@kref: target kernel reference that contains the relay buffer
+ *
+ *	Removes the file from the filesystem, which also frees the
+ *	rchan_buf_struct and the channel buffer.  Should only be called from
+ *	kref_put().
+ */
+static void relay_remove_buf(struct kref *kref)
+{
+	struct rchan_buf *buf = container_of(kref, struct rchan_buf, kref);
+	relay_destroy_buf(buf);
+}
+
+/**
+ *	relay_buf_empty - boolean, is the channel buffer empty?
+ *	@buf: channel buffer
+ *
+ *	Returns 1 if the buffer is empty, 0 otherwise.
+ */
+static int relay_buf_empty(struct rchan_buf *buf)
+{
+	return (buf->subbufs_produced - buf->subbufs_consumed) ? 0 : 1;
+}
+
+/**
+ *	relay_buf_full - boolean, is the channel buffer full?
+ *	@buf: channel buffer
+ *
+ *	Returns 1 if the buffer is full, 0 otherwise.
+ */
+int relay_buf_full(struct rchan_buf *buf)
+{
+	size_t ready = buf->subbufs_produced - buf->subbufs_consumed;
+	return (ready >= buf->chan->n_subbufs) ? 1 : 0;
+}
+EXPORT_SYMBOL_GPL(relay_buf_full);
+
+/*
+ * High-level relay kernel API and associated functions.
+ */
+
+/*
+ * rchan_callback implementations defining default channel behavior.  Used
+ * in place of corresponding NULL values in client callback struct.
+ */
+
+/*
+ * subbuf_start() default callback.  Does nothing.
+ */
+static int subbuf_start_default_callback (struct rchan_buf *buf,
+					  void *subbuf,
+					  void *prev_subbuf,
+					  size_t prev_padding)
+{
+	if (relay_buf_full(buf))
+		return 0;
+
+	return 1;
+}
+
+/*
+ * buf_mapped() default callback.  Does nothing.
+ */
+static void buf_mapped_default_callback(struct rchan_buf *buf,
+					struct file *filp)
+{
+}
+
+/*
+ * buf_unmapped() default callback.  Does nothing.
+ */
+static void buf_unmapped_default_callback(struct rchan_buf *buf,
+					  struct file *filp)
+{
+}
+
+/*
+ * create_buf_file_create() default callback.  Does nothing.
+ */
+static struct dentry *create_buf_file_default_callback(const char *filename,
+						       struct dentry *parent,
+						       umode_t mode,
+						       struct rchan_buf *buf,
+						       int *is_global)
+{
+	return NULL;
+}
+
+/*
+ * remove_buf_file() default callback.  Does nothing.
+ */
+static int remove_buf_file_default_callback(struct dentry *dentry)
+{
+	return -EINVAL;
+}
+
+/* relay channel default callbacks */
+static struct rchan_callbacks default_channel_callbacks = {
+	.subbuf_start = subbuf_start_default_callback,
+	.buf_mapped = buf_mapped_default_callback,
+	.buf_unmapped = buf_unmapped_default_callback,
+	.create_buf_file = create_buf_file_default_callback,
+	.remove_buf_file = remove_buf_file_default_callback,
+};
+
+/**
+ *	wakeup_readers - wake up readers waiting on a channel
+ *	@work: contains the channel buffer
+ *
+ *	This is the function used to defer reader waking
+ */
+static void wakeup_readers(struct irq_work *work)
+{
+	struct rchan_buf *buf;
+
+	buf = container_of(work, struct rchan_buf, wakeup_work);
+	wake_up_interruptible(&buf->read_wait);
+}
+
+/**
+ *	__relay_reset - reset a channel buffer
+ *	@buf: the channel buffer
+ *	@init: 1 if this is a first-time initialization
+ *
+ *	See relay_reset() for description of effect.
+ */
+static void __relay_reset(struct rchan_buf *buf, unsigned int init)
+{
+	size_t i;
+
+	if (init) {
+		init_waitqueue_head(&buf->read_wait);
+		kref_init(&buf->kref);
+		init_irq_work(&buf->wakeup_work, wakeup_readers);
+	} else {
+		irq_work_sync(&buf->wakeup_work);
+	}
+
+	buf->subbufs_produced = 0;
+	buf->subbufs_consumed = 0;
+	buf->bytes_consumed = 0;
+	buf->finalized = 0;
+	buf->data = buf->start;
+	buf->offset = 0;
+
+	for (i = 0; i < buf->chan->n_subbufs; i++)
+		buf->padding[i] = 0;
+
+	buf->chan->cb->subbuf_start(buf, buf->data, NULL, 0);
+}
+
+/**
+ *	relay_reset - reset the channel
+ *	@chan: the channel
+ *
+ *	This has the effect of erasing all data from all channel buffers
+ *	and restarting the channel in its initial state.  The buffers
+ *	are not freed, so any mappings are still in effect.
+ *
+ *	NOTE. Care should be taken that the channel isn't actually
+ *	being used by anything when this call is made.
+ */
+void relay_reset(struct rchan *chan)
+{
+	struct rchan_buf *buf;
+	unsigned int i;
+
+	if (!chan)
+		return;
+
+	if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0))) {
+		__relay_reset(buf, 0);
+		return;
+	}
+
+	mutex_lock(&relay_channels_mutex);
+	for_each_possible_cpu(i)
+		if ((buf = *per_cpu_ptr(chan->buf, i)))
+			__relay_reset(buf, 0);
+	mutex_unlock(&relay_channels_mutex);
+}
+EXPORT_SYMBOL_GPL(relay_reset);
+
+static inline void relay_set_buf_dentry(struct rchan_buf *buf,
+					struct dentry *dentry)
+{
+	buf->dentry = dentry;
+	d_inode(buf->dentry)->i_size = buf->early_bytes;
+}
+
+static struct dentry *relay_create_buf_file(struct rchan *chan,
+					    struct rchan_buf *buf,
+					    unsigned int cpu)
+{
+	struct dentry *dentry;
+	char *tmpname;
+
+	tmpname = kzalloc(NAME_MAX + 1, GFP_KERNEL);
+	if (!tmpname)
+		return NULL;
+	snprintf(tmpname, NAME_MAX, "%s%d", chan->base_filename, cpu);
+
+	/* Create file in fs */
+	dentry = chan->cb->create_buf_file(tmpname, chan->parent,
+					   S_IRUSR, buf,
+					   &chan->is_global);
+	if (IS_ERR(dentry))
+		dentry = NULL;
+
+	kfree(tmpname);
+
+	return dentry;
+}
+
+/*
+ *	relay_open_buf - create a new relay channel buffer
+ *
+ *	used by relay_open() and CPU hotplug.
+ */
+static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
+{
+ 	struct rchan_buf *buf = NULL;
+	struct dentry *dentry;
+
+ 	if (chan->is_global)
+		return *per_cpu_ptr(chan->buf, 0);
+
+	buf = relay_create_buf(chan);
+	if (!buf)
+		return NULL;
+
+	if (chan->has_base_filename) {
+		dentry = relay_create_buf_file(chan, buf, cpu);
+		if (!dentry)
+			goto free_buf;
+		relay_set_buf_dentry(buf, dentry);
+	} else {
+		/* Only retrieve global info, nothing more, nothing less */
+		dentry = chan->cb->create_buf_file(NULL, NULL,
+						   S_IRUSR, buf,
+						   &chan->is_global);
+		if (IS_ERR_OR_NULL(dentry))
+			goto free_buf;
+	}
+
+ 	buf->cpu = cpu;
+ 	__relay_reset(buf, 1);
+
+ 	if(chan->is_global) {
+		*per_cpu_ptr(chan->buf, 0) = buf;
+ 		buf->cpu = 0;
+  	}
+
+	return buf;
+
+free_buf:
+ 	relay_destroy_buf(buf);
+	return NULL;
+}
+
+/**
+ *	relay_close_buf - close a channel buffer
+ *	@buf: channel buffer
+ *
+ *	Marks the buffer finalized and restores the default callbacks.
+ *	The channel buffer and channel buffer data structure are then freed
+ *	automatically when the last reference is given up.
+ */
+static void relay_close_buf(struct rchan_buf *buf)
+{
+	buf->finalized = 1;
+	irq_work_sync(&buf->wakeup_work);
+	buf->chan->cb->remove_buf_file(buf->dentry);
+	kref_put(&buf->kref, relay_remove_buf);
+}
+
+static void setup_callbacks(struct rchan *chan,
+				   struct rchan_callbacks *cb)
+{
+	if (!cb) {
+		chan->cb = &default_channel_callbacks;
+		return;
+	}
+
+	if (!cb->subbuf_start)
+		cb->subbuf_start = subbuf_start_default_callback;
+	if (!cb->buf_mapped)
+		cb->buf_mapped = buf_mapped_default_callback;
+	if (!cb->buf_unmapped)
+		cb->buf_unmapped = buf_unmapped_default_callback;
+	if (!cb->create_buf_file)
+		cb->create_buf_file = create_buf_file_default_callback;
+	if (!cb->remove_buf_file)
+		cb->remove_buf_file = remove_buf_file_default_callback;
+	chan->cb = cb;
+}
+
+int relay_prepare_cpu(unsigned int cpu)
+{
+	struct rchan *chan;
+	struct rchan_buf *buf;
+
+	mutex_lock(&relay_channels_mutex);
+	list_for_each_entry(chan, &relay_channels, list) {
+		if ((buf = *per_cpu_ptr(chan->buf, cpu)))
+			continue;
+		buf = relay_open_buf(chan, cpu);
+		if (!buf) {
+			pr_err("relay: cpu %d buffer creation failed\n", cpu);
+			mutex_unlock(&relay_channels_mutex);
+			return -ENOMEM;
+		}
+		*per_cpu_ptr(chan->buf, cpu) = buf;
+	}
+	mutex_unlock(&relay_channels_mutex);
+	return 0;
+}
+
+/**
+ *	relay_open - create a new relay channel
+ *	@base_filename: base name of files to create, %NULL for buffering only
+ *	@parent: dentry of parent directory, %NULL for root directory or buffer
+ *	@subbuf_size: size of sub-buffers
+ *	@n_subbufs: number of sub-buffers
+ *	@cb: client callback functions
+ *	@private_data: user-defined data
+ *
+ *	Returns channel pointer if successful, %NULL otherwise.
+ *
+ *	Creates a channel buffer for each cpu using the sizes and
+ *	attributes specified.  The created channel buffer files
+ *	will be named base_filename0...base_filenameN-1.  File
+ *	permissions will be %S_IRUSR.
+ *
+ *	If opening a buffer (@parent = NULL) that you later wish to register
+ *	in a filesystem, call relay_late_setup_files() once the @parent dentry
+ *	is available.
+ */
+struct rchan *relay_open(const char *base_filename,
+			 struct dentry *parent,
+			 size_t subbuf_size,
+			 size_t n_subbufs,
+			 struct rchan_callbacks *cb,
+			 void *private_data)
+{
+	unsigned int i;
+	struct rchan *chan;
+	struct rchan_buf *buf;
+
+	if (!(subbuf_size && n_subbufs))
+		return NULL;
+	if (subbuf_size > UINT_MAX / n_subbufs)
+		return NULL;
+
+	chan = kzalloc(sizeof(struct rchan), GFP_KERNEL);
+	if (!chan)
+		return NULL;
+
+	chan->buf = alloc_percpu(struct rchan_buf *);
+	if (!chan->buf) {
+		kfree(chan);
+		return NULL;
+	}
+
+	chan->version = RELAYFS_CHANNEL_VERSION;
+	chan->n_subbufs = n_subbufs;
+	chan->subbuf_size = subbuf_size;
+	chan->alloc_size = PAGE_ALIGN(subbuf_size * n_subbufs);
+	chan->parent = parent;
+	chan->private_data = private_data;
+	if (base_filename) {
+		chan->has_base_filename = 1;
+		strlcpy(chan->base_filename, base_filename, NAME_MAX);
+	}
+	setup_callbacks(chan, cb);
+	kref_init(&chan->kref);
+
+	mutex_lock(&relay_channels_mutex);
+	for_each_online_cpu(i) {
+		buf = relay_open_buf(chan, i);
+		if (!buf)
+			goto free_bufs;
+		*per_cpu_ptr(chan->buf, i) = buf;
+	}
+	list_add(&chan->list, &relay_channels);
+	mutex_unlock(&relay_channels_mutex);
+
+	return chan;
+
+free_bufs:
+	for_each_possible_cpu(i) {
+		if ((buf = *per_cpu_ptr(chan->buf, i)))
+			relay_close_buf(buf);
+	}
+
+	kref_put(&chan->kref, relay_destroy_channel);
+	mutex_unlock(&relay_channels_mutex);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(relay_open);
+
+struct rchan_percpu_buf_dispatcher {
+	struct rchan_buf *buf;
+	struct dentry *dentry;
+};
+
+/* Called in atomic context. */
+static void __relay_set_buf_dentry(void *info)
+{
+	struct rchan_percpu_buf_dispatcher *p = info;
+
+	relay_set_buf_dentry(p->buf, p->dentry);
+}
+
+/**
+ *	relay_late_setup_files - triggers file creation
+ *	@chan: channel to operate on
+ *	@base_filename: base name of files to create
+ *	@parent: dentry of parent directory, %NULL for root directory
+ *
+ *	Returns 0 if successful, non-zero otherwise.
+ *
+ *	Use to setup files for a previously buffer-only channel created
+ *	by relay_open() with a NULL parent dentry.
+ *
+ *	For example, this is useful for perfomring early tracing in kernel,
+ *	before VFS is up and then exposing the early results once the dentry
+ *	is available.
+ */
+int relay_late_setup_files(struct rchan *chan,
+			   const char *base_filename,
+			   struct dentry *parent)
+{
+	int err = 0;
+	unsigned int i, curr_cpu;
+	unsigned long flags;
+	struct dentry *dentry;
+	struct rchan_buf *buf;
+	struct rchan_percpu_buf_dispatcher disp;
+
+	if (!chan || !base_filename)
+		return -EINVAL;
+
+	strlcpy(chan->base_filename, base_filename, NAME_MAX);
+
+	mutex_lock(&relay_channels_mutex);
+	/* Is chan already set up? */
+	if (unlikely(chan->has_base_filename)) {
+		mutex_unlock(&relay_channels_mutex);
+		return -EEXIST;
+	}
+	chan->has_base_filename = 1;
+	chan->parent = parent;
+
+	if (chan->is_global) {
+		err = -EINVAL;
+		buf = *per_cpu_ptr(chan->buf, 0);
+		if (!WARN_ON_ONCE(!buf)) {
+			dentry = relay_create_buf_file(chan, buf, 0);
+			if (dentry && !WARN_ON_ONCE(!chan->is_global)) {
+				relay_set_buf_dentry(buf, dentry);
+				err = 0;
+			}
+		}
+		mutex_unlock(&relay_channels_mutex);
+		return err;
+	}
+
+	curr_cpu = get_cpu();
+	/*
+	 * The CPU hotplug notifier ran before us and created buffers with
+	 * no files associated. So it's safe to call relay_setup_buf_file()
+	 * on all currently online CPUs.
+	 */
+	for_each_online_cpu(i) {
+		buf = *per_cpu_ptr(chan->buf, i);
+		if (unlikely(!buf)) {
+			WARN_ONCE(1, KERN_ERR "CPU has no buffer!\n");
+			err = -EINVAL;
+			break;
+		}
+
+		dentry = relay_create_buf_file(chan, buf, i);
+		if (unlikely(!dentry)) {
+			err = -EINVAL;
+			break;
+		}
+
+		if (curr_cpu == i) {
+			local_irq_save(flags);
+			relay_set_buf_dentry(buf, dentry);
+			local_irq_restore(flags);
+		} else {
+			disp.buf = buf;
+			disp.dentry = dentry;
+			smp_mb();
+			/* relay_channels_mutex must be held, so wait. */
+			err = smp_call_function_single(i,
+						       __relay_set_buf_dentry,
+						       &disp, 1);
+		}
+		if (unlikely(err))
+			break;
+	}
+	put_cpu();
+	mutex_unlock(&relay_channels_mutex);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(relay_late_setup_files);
+
+/**
+ *	relay_switch_subbuf - switch to a new sub-buffer
+ *	@buf: channel buffer
+ *	@length: size of current event
+ *
+ *	Returns either the length passed in or 0 if full.
+ *
+ *	Performs sub-buffer-switch tasks such as invoking callbacks,
+ *	updating padding counts, waking up readers, etc.
+ */
+size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
+{
+	void *old, *new;
+	size_t old_subbuf, new_subbuf;
+
+	if (unlikely(length > buf->chan->subbuf_size))
+		goto toobig;
+
+	if (buf->offset != buf->chan->subbuf_size + 1) {
+		buf->prev_padding = buf->chan->subbuf_size - buf->offset;
+		old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
+		buf->padding[old_subbuf] = buf->prev_padding;
+		buf->subbufs_produced++;
+		if (buf->dentry)
+			d_inode(buf->dentry)->i_size +=
+				buf->chan->subbuf_size -
+				buf->padding[old_subbuf];
+		else
+			buf->early_bytes += buf->chan->subbuf_size -
+					    buf->padding[old_subbuf];
+		smp_mb();
+		if (waitqueue_active(&buf->read_wait)) {
+			/*
+			 * Calling wake_up_interruptible() from here
+			 * will deadlock if we happen to be logging
+			 * from the scheduler (trying to re-grab
+			 * rq->lock), so defer it.
+			 */
+			irq_work_queue(&buf->wakeup_work);
+		}
+	}
+
+	old = buf->data;
+	new_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
+	new = buf->start + new_subbuf * buf->chan->subbuf_size;
+	buf->offset = 0;
+	if (!buf->chan->cb->subbuf_start(buf, new, old, buf->prev_padding)) {
+		buf->offset = buf->chan->subbuf_size + 1;
+		return 0;
+	}
+	buf->data = new;
+	buf->padding[new_subbuf] = 0;
+
+	if (unlikely(length + buf->offset > buf->chan->subbuf_size))
+		goto toobig;
+
+	return length;
+
+toobig:
+	buf->chan->last_toobig = length;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(relay_switch_subbuf);
+
+/**
+ *	relay_subbufs_consumed - update the buffer's sub-buffers-consumed count
+ *	@chan: the channel
+ *	@cpu: the cpu associated with the channel buffer to update
+ *	@subbufs_consumed: number of sub-buffers to add to current buf's count
+ *
+ *	Adds to the channel buffer's consumed sub-buffer count.
+ *	subbufs_consumed should be the number of sub-buffers newly consumed,
+ *	not the total consumed.
+ *
+ *	NOTE. Kernel clients don't need to call this function if the channel
+ *	mode is 'overwrite'.
+ */
+void relay_subbufs_consumed(struct rchan *chan,
+			    unsigned int cpu,
+			    size_t subbufs_consumed)
+{
+	struct rchan_buf *buf;
+
+	if (!chan || cpu >= NR_CPUS)
+		return;
+
+	buf = *per_cpu_ptr(chan->buf, cpu);
+	if (!buf || subbufs_consumed > chan->n_subbufs)
+		return;
+
+	if (subbufs_consumed > buf->subbufs_produced - buf->subbufs_consumed)
+		buf->subbufs_consumed = buf->subbufs_produced;
+	else
+		buf->subbufs_consumed += subbufs_consumed;
+}
+EXPORT_SYMBOL_GPL(relay_subbufs_consumed);
+
+/**
+ *	relay_close - close the channel
+ *	@chan: the channel
+ *
+ *	Closes all channel buffers and frees the channel.
+ */
+void relay_close(struct rchan *chan)
+{
+	struct rchan_buf *buf;
+	unsigned int i;
+
+	if (!chan)
+		return;
+
+	mutex_lock(&relay_channels_mutex);
+	if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0)))
+		relay_close_buf(buf);
+	else
+		for_each_possible_cpu(i)
+			if ((buf = *per_cpu_ptr(chan->buf, i)))
+				relay_close_buf(buf);
+
+	if (chan->last_toobig)
+		printk(KERN_WARNING "relay: one or more items not logged "
+		       "[item size (%zd) > sub-buffer size (%zd)]\n",
+		       chan->last_toobig, chan->subbuf_size);
+
+	list_del(&chan->list);
+	kref_put(&chan->kref, relay_destroy_channel);
+	mutex_unlock(&relay_channels_mutex);
+}
+EXPORT_SYMBOL_GPL(relay_close);
+
+/**
+ *	relay_flush - close the channel
+ *	@chan: the channel
+ *
+ *	Flushes all channel buffers, i.e. forces buffer switch.
+ */
+void relay_flush(struct rchan *chan)
+{
+	struct rchan_buf *buf;
+	unsigned int i;
+
+	if (!chan)
+		return;
+
+	if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0))) {
+		relay_switch_subbuf(buf, 0);
+		return;
+	}
+
+	mutex_lock(&relay_channels_mutex);
+	for_each_possible_cpu(i)
+		if ((buf = *per_cpu_ptr(chan->buf, i)))
+			relay_switch_subbuf(buf, 0);
+	mutex_unlock(&relay_channels_mutex);
+}
+EXPORT_SYMBOL_GPL(relay_flush);
+
+/**
+ *	relay_file_open - open file op for relay files
+ *	@inode: the inode
+ *	@filp: the file
+ *
+ *	Increments the channel buffer refcount.
+ */
+static int relay_file_open(struct inode *inode, struct file *filp)
+{
+	struct rchan_buf *buf = inode->i_private;
+	kref_get(&buf->kref);
+	filp->private_data = buf;
+
+	return nonseekable_open(inode, filp);
+}
+
+/**
+ *	relay_file_mmap - mmap file op for relay files
+ *	@filp: the file
+ *	@vma: the vma describing what to map
+ *
+ *	Calls upon relay_mmap_buf() to map the file into user space.
+ */
+static int relay_file_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+	struct rchan_buf *buf = filp->private_data;
+	return relay_mmap_buf(buf, vma);
+}
+
+/**
+ *	relay_file_poll - poll file op for relay files
+ *	@filp: the file
+ *	@wait: poll table
+ *
+ *	Poll implemention.
+ */
+static __poll_t relay_file_poll(struct file *filp, poll_table *wait)
+{
+	__poll_t mask = 0;
+	struct rchan_buf *buf = filp->private_data;
+
+	if (buf->finalized)
+		return EPOLLERR;
+
+	if (filp->f_mode & FMODE_READ) {
+		poll_wait(filp, &buf->read_wait, wait);
+		if (!relay_buf_empty(buf))
+			mask |= EPOLLIN | EPOLLRDNORM;
+	}
+
+	return mask;
+}
+
+/**
+ *	relay_file_release - release file op for relay files
+ *	@inode: the inode
+ *	@filp: the file
+ *
+ *	Decrements the channel refcount, as the filesystem is
+ *	no longer using it.
+ */
+static int relay_file_release(struct inode *inode, struct file *filp)
+{
+	struct rchan_buf *buf = filp->private_data;
+	kref_put(&buf->kref, relay_remove_buf);
+
+	return 0;
+}
+
+/*
+ *	relay_file_read_consume - update the consumed count for the buffer
+ */
+static void relay_file_read_consume(struct rchan_buf *buf,
+				    size_t read_pos,
+				    size_t bytes_consumed)
+{
+	size_t subbuf_size = buf->chan->subbuf_size;
+	size_t n_subbufs = buf->chan->n_subbufs;
+	size_t read_subbuf;
+
+	if (buf->subbufs_produced == buf->subbufs_consumed &&
+	    buf->offset == buf->bytes_consumed)
+		return;
+
+	if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
+		relay_subbufs_consumed(buf->chan, buf->cpu, 1);
+		buf->bytes_consumed = 0;
+	}
+
+	buf->bytes_consumed += bytes_consumed;
+	if (!read_pos)
+		read_subbuf = buf->subbufs_consumed % n_subbufs;
+	else
+		read_subbuf = read_pos / buf->chan->subbuf_size;
+	if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
+		if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
+		    (buf->offset == subbuf_size))
+			return;
+		relay_subbufs_consumed(buf->chan, buf->cpu, 1);
+		buf->bytes_consumed = 0;
+	}
+}
+
+/*
+ *	relay_file_read_avail - boolean, are there unconsumed bytes available?
+ */
+static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
+{
+	size_t subbuf_size = buf->chan->subbuf_size;
+	size_t n_subbufs = buf->chan->n_subbufs;
+	size_t produced = buf->subbufs_produced;
+	size_t consumed = buf->subbufs_consumed;
+
+	relay_file_read_consume(buf, read_pos, 0);
+
+	consumed = buf->subbufs_consumed;
+
+	if (unlikely(buf->offset > subbuf_size)) {
+		if (produced == consumed)
+			return 0;
+		return 1;
+	}
+
+	if (unlikely(produced - consumed >= n_subbufs)) {
+		consumed = produced - n_subbufs + 1;
+		buf->subbufs_consumed = consumed;
+		buf->bytes_consumed = 0;
+	}
+
+	produced = (produced % n_subbufs) * subbuf_size + buf->offset;
+	consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
+
+	if (consumed > produced)
+		produced += n_subbufs * subbuf_size;
+
+	if (consumed == produced) {
+		if (buf->offset == subbuf_size &&
+		    buf->subbufs_produced > buf->subbufs_consumed)
+			return 1;
+		return 0;
+	}
+
+	return 1;
+}
+
+/**
+ *	relay_file_read_subbuf_avail - return bytes available in sub-buffer
+ *	@read_pos: file read position
+ *	@buf: relay channel buffer
+ */
+static size_t relay_file_read_subbuf_avail(size_t read_pos,
+					   struct rchan_buf *buf)
+{
+	size_t padding, avail = 0;
+	size_t read_subbuf, read_offset, write_subbuf, write_offset;
+	size_t subbuf_size = buf->chan->subbuf_size;
+
+	write_subbuf = (buf->data - buf->start) / subbuf_size;
+	write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
+	read_subbuf = read_pos / subbuf_size;
+	read_offset = read_pos % subbuf_size;
+	padding = buf->padding[read_subbuf];
+
+	if (read_subbuf == write_subbuf) {
+		if (read_offset + padding < write_offset)
+			avail = write_offset - (read_offset + padding);
+	} else
+		avail = (subbuf_size - padding) - read_offset;
+
+	return avail;
+}
+
+/**
+ *	relay_file_read_start_pos - find the first available byte to read
+ *	@read_pos: file read position
+ *	@buf: relay channel buffer
+ *
+ *	If the @read_pos is in the middle of padding, return the
+ *	position of the first actually available byte, otherwise
+ *	return the original value.
+ */
+static size_t relay_file_read_start_pos(size_t read_pos,
+					struct rchan_buf *buf)
+{
+	size_t read_subbuf, padding, padding_start, padding_end;
+	size_t subbuf_size = buf->chan->subbuf_size;
+	size_t n_subbufs = buf->chan->n_subbufs;
+	size_t consumed = buf->subbufs_consumed % n_subbufs;
+
+	if (!read_pos)
+		read_pos = consumed * subbuf_size + buf->bytes_consumed;
+	read_subbuf = read_pos / subbuf_size;
+	padding = buf->padding[read_subbuf];
+	padding_start = (read_subbuf + 1) * subbuf_size - padding;
+	padding_end = (read_subbuf + 1) * subbuf_size;
+	if (read_pos >= padding_start && read_pos < padding_end) {
+		read_subbuf = (read_subbuf + 1) % n_subbufs;
+		read_pos = read_subbuf * subbuf_size;
+	}
+
+	return read_pos;
+}
+
+/**
+ *	relay_file_read_end_pos - return the new read position
+ *	@read_pos: file read position
+ *	@buf: relay channel buffer
+ *	@count: number of bytes to be read
+ */
+static size_t relay_file_read_end_pos(struct rchan_buf *buf,
+				      size_t read_pos,
+				      size_t count)
+{
+	size_t read_subbuf, padding, end_pos;
+	size_t subbuf_size = buf->chan->subbuf_size;
+	size_t n_subbufs = buf->chan->n_subbufs;
+
+	read_subbuf = read_pos / subbuf_size;
+	padding = buf->padding[read_subbuf];
+	if (read_pos % subbuf_size + count + padding == subbuf_size)
+		end_pos = (read_subbuf + 1) * subbuf_size;
+	else
+		end_pos = read_pos + count;
+	if (end_pos >= subbuf_size * n_subbufs)
+		end_pos = 0;
+
+	return end_pos;
+}
+
+static ssize_t relay_file_read(struct file *filp,
+			       char __user *buffer,
+			       size_t count,
+			       loff_t *ppos)
+{
+	struct rchan_buf *buf = filp->private_data;
+	size_t read_start, avail;
+	size_t written = 0;
+	int ret;
+
+	if (!count)
+		return 0;
+
+	inode_lock(file_inode(filp));
+	do {
+		void *from;
+
+		if (!relay_file_read_avail(buf, *ppos))
+			break;
+
+		read_start = relay_file_read_start_pos(*ppos, buf);
+		avail = relay_file_read_subbuf_avail(read_start, buf);
+		if (!avail)
+			break;
+
+		avail = min(count, avail);
+		from = buf->start + read_start;
+		ret = avail;
+		if (copy_to_user(buffer, from, avail))
+			break;
+
+		buffer += ret;
+		written += ret;
+		count -= ret;
+
+		relay_file_read_consume(buf, read_start, ret);
+		*ppos = relay_file_read_end_pos(buf, read_start, ret);
+	} while (count);
+	inode_unlock(file_inode(filp));
+
+	return written;
+}
+
+static void relay_consume_bytes(struct rchan_buf *rbuf, int bytes_consumed)
+{
+	rbuf->bytes_consumed += bytes_consumed;
+
+	if (rbuf->bytes_consumed >= rbuf->chan->subbuf_size) {
+		relay_subbufs_consumed(rbuf->chan, rbuf->cpu, 1);
+		rbuf->bytes_consumed %= rbuf->chan->subbuf_size;
+	}
+}
+
+static void relay_pipe_buf_release(struct pipe_inode_info *pipe,
+				   struct pipe_buffer *buf)
+{
+	struct rchan_buf *rbuf;
+
+	rbuf = (struct rchan_buf *)page_private(buf->page);
+	relay_consume_bytes(rbuf, buf->private);
+}
+
+static const struct pipe_buf_operations relay_pipe_buf_ops = {
+	.can_merge = 0,
+	.confirm = generic_pipe_buf_confirm,
+	.release = relay_pipe_buf_release,
+	.steal = generic_pipe_buf_steal,
+	.get = generic_pipe_buf_get,
+};
+
+static void relay_page_release(struct splice_pipe_desc *spd, unsigned int i)
+{
+}
+
+/*
+ *	subbuf_splice_actor - splice up to one subbuf's worth of data
+ */
+static ssize_t subbuf_splice_actor(struct file *in,
+			       loff_t *ppos,
+			       struct pipe_inode_info *pipe,
+			       size_t len,
+			       unsigned int flags,
+			       int *nonpad_ret)
+{
+	unsigned int pidx, poff, total_len, subbuf_pages, nr_pages;
+	struct rchan_buf *rbuf = in->private_data;
+	unsigned int subbuf_size = rbuf->chan->subbuf_size;
+	uint64_t pos = (uint64_t) *ppos;
+	uint32_t alloc_size = (uint32_t) rbuf->chan->alloc_size;
+	size_t read_start = (size_t) do_div(pos, alloc_size);
+	size_t read_subbuf = read_start / subbuf_size;
+	size_t padding = rbuf->padding[read_subbuf];
+	size_t nonpad_end = read_subbuf * subbuf_size + subbuf_size - padding;
+	struct page *pages[PIPE_DEF_BUFFERS];
+	struct partial_page partial[PIPE_DEF_BUFFERS];
+	struct splice_pipe_desc spd = {
+		.pages = pages,
+		.nr_pages = 0,
+		.nr_pages_max = PIPE_DEF_BUFFERS,
+		.partial = partial,
+		.ops = &relay_pipe_buf_ops,
+		.spd_release = relay_page_release,
+	};
+	ssize_t ret;
+
+	if (rbuf->subbufs_produced == rbuf->subbufs_consumed)
+		return 0;
+	if (splice_grow_spd(pipe, &spd))
+		return -ENOMEM;
+
+	/*
+	 * Adjust read len, if longer than what is available
+	 */
+	if (len > (subbuf_size - read_start % subbuf_size))
+		len = subbuf_size - read_start % subbuf_size;
+
+	subbuf_pages = rbuf->chan->alloc_size >> PAGE_SHIFT;
+	pidx = (read_start / PAGE_SIZE) % subbuf_pages;
+	poff = read_start & ~PAGE_MASK;
+	nr_pages = min_t(unsigned int, subbuf_pages, spd.nr_pages_max);
+
+	for (total_len = 0; spd.nr_pages < nr_pages; spd.nr_pages++) {
+		unsigned int this_len, this_end, private;
+		unsigned int cur_pos = read_start + total_len;
+
+		if (!len)
+			break;
+
+		this_len = min_t(unsigned long, len, PAGE_SIZE - poff);
+		private = this_len;
+
+		spd.pages[spd.nr_pages] = rbuf->page_array[pidx];
+		spd.partial[spd.nr_pages].offset = poff;
+
+		this_end = cur_pos + this_len;
+		if (this_end >= nonpad_end) {
+			this_len = nonpad_end - cur_pos;
+			private = this_len + padding;
+		}
+		spd.partial[spd.nr_pages].len = this_len;
+		spd.partial[spd.nr_pages].private = private;
+
+		len -= this_len;
+		total_len += this_len;
+		poff = 0;
+		pidx = (pidx + 1) % subbuf_pages;
+
+		if (this_end >= nonpad_end) {
+			spd.nr_pages++;
+			break;
+		}
+	}
+
+	ret = 0;
+	if (!spd.nr_pages)
+		goto out;
+
+	ret = *nonpad_ret = splice_to_pipe(pipe, &spd);
+	if (ret < 0 || ret < total_len)
+		goto out;
+
+        if (read_start + ret == nonpad_end)
+                ret += padding;
+
+out:
+	splice_shrink_spd(&spd);
+	return ret;
+}
+
+static ssize_t relay_file_splice_read(struct file *in,
+				      loff_t *ppos,
+				      struct pipe_inode_info *pipe,
+				      size_t len,
+				      unsigned int flags)
+{
+	ssize_t spliced;
+	int ret;
+	int nonpad_ret = 0;
+
+	ret = 0;
+	spliced = 0;
+
+	while (len && !spliced) {
+		ret = subbuf_splice_actor(in, ppos, pipe, len, flags, &nonpad_ret);
+		if (ret < 0)
+			break;
+		else if (!ret) {
+			if (flags & SPLICE_F_NONBLOCK)
+				ret = -EAGAIN;
+			break;
+		}
+
+		*ppos += ret;
+		if (ret > len)
+			len = 0;
+		else
+			len -= ret;
+		spliced += nonpad_ret;
+		nonpad_ret = 0;
+	}
+
+	if (spliced)
+		return spliced;
+
+	return ret;
+}
+
+const struct file_operations relay_file_operations = {
+	.open		= relay_file_open,
+	.poll		= relay_file_poll,
+	.mmap		= relay_file_mmap,
+	.read		= relay_file_read,
+	.llseek		= no_llseek,
+	.release	= relay_file_release,
+	.splice_read	= relay_file_splice_read,
+};
+EXPORT_SYMBOL_GPL(relay_file_operations);