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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 /*
  * 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);
 
 /*
  * 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,
 };
 
 /*
  * 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;
 
     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;
 
     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.
  */
 
 static int relay_subbuf_start(struct rchan_buf *buf, void *subbuf,
                   void *prev_subbuf, size_t prev_padding)
 {
     if (!buf->chan->cb->subbuf_start)
         return !relay_buf_full(buf);
 
     return buf->chan->cb->subbuf_start(buf, subbuf,
                        prev_subbuf, prev_padding);
 }
 
 /**
  *  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;
 
     relay_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);
 }
 
 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 (*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,
              const 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;
     if (!cb || !cb->create_buf_file || !cb->remove_buf_file)
         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);
     }
     chan->cb = 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 (!relay_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;
 
     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);

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