Initial commit: OpenHarmony-v4.0-ReleaseOpenHarmony-v4.0-Release

1 files changed, 1335 insertions, 0 deletions

diff --git a/kernel/relay.c b/kernel/relay.c
new file mode 100644
index 000000000..f6826dec2
--- /dev/null
+++ b/kernel/relay.c
@@ -0,0 +1,1335 @@
+/*
+ * Public API and common code for kernel->userspace relay file support.
+ *
+ * See Documentation/filesystems/relay.rst 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_lock.
+ */
+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 subbuf_size = buf->chan->subbuf_size;
+        size_t n_subbufs = buf->chan->n_subbufs;
+        size_t produced = buf->subbufs_produced;
+        size_t consumed;
+
+        relay_file_read_consume(buf, 0, 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
+ *      @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(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;
+        size_t read_pos = (consumed * subbuf_size + buf->bytes_consumed)
+                        % (n_subbufs * subbuf_size);
+
+        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))
+                        break;
+
+                read_start = relay_file_read_start_pos(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 = {
+        .release        = relay_pipe_buf_release,
+        .try_steal      = generic_pipe_buf_try_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);