[PATCH] relay: migrate from relayfs to a generic relay API
Original patch from Paul Mundt, sysfs parts removed by me since they
were broken.
Signed-off-by: Jens Axboe <axboe@suse.de>
diff --git a/kernel/relay.c b/kernel/relay.c
new file mode 100644
index 0000000..9358e8e
--- /dev/null
+++ b/kernel/relay.c
@@ -0,0 +1,919 @@
+/*
+ * Public API and common code for kernel->userspace relay file support.
+ *
+ * See Documentation/filesystems/relayfs.txt for an overview of relayfs.
+ *
+ * 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.
+ *
+ * This file is released under the GPL.
+ */
+#include <linux/errno.h>
+#include <linux/stddef.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/relay.h>
+#include <linux/vmalloc.h>
+#include <linux/mm.h>
+
+/*
+ * 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);
+}
+
+/*
+ * nopage() vm_op implementation for relay file mapping.
+ */
+static struct page *relay_buf_nopage(struct vm_area_struct *vma,
+ unsigned long address,
+ int *type)
+{
+ struct page *page;
+ struct rchan_buf *buf = vma->vm_private_data;
+ unsigned long offset = address - vma->vm_start;
+
+ if (address > vma->vm_end)
+ return NOPAGE_SIGBUS; /* Disallow mremap */
+ if (!buf)
+ return NOPAGE_OOM;
+
+ page = vmalloc_to_page(buf->start + offset);
+ if (!page)
+ return NOPAGE_OOM;
+ get_page(page);
+
+ if (type)
+ *type = VM_FAULT_MINOR;
+
+ return page;
+}
+
+/*
+ * vm_ops for relay file mappings.
+ */
+static struct vm_operations_struct relay_file_mmap_ops = {
+ .nopage = relay_buf_nopage,
+ .close = relay_file_mmap_close,
+};
+
+/**
+ * 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.
+ */
+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_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
+ */
+static void *relay_alloc_buf(struct rchan_buf *buf, unsigned long size)
+{
+ void *mem;
+ unsigned int i, j, n_pages;
+
+ size = PAGE_ALIGN(size);
+ n_pages = size >> PAGE_SHIFT;
+
+ buf->page_array = kcalloc(n_pages, sizeof(struct page *), GFP_KERNEL);
+ 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;
+ }
+ 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]);
+ kfree(buf->page_array);
+ return NULL;
+}
+
+/**
+ * relay_create_buf - allocate and initialize a channel buffer
+ * @alloc_size: size of the buffer to allocate
+ * @n_subbufs: number of sub-buffers in the channel
+ *
+ * Returns channel buffer if successful, NULL otherwise
+ */
+struct rchan_buf *relay_create_buf(struct rchan *chan)
+{
+ struct rchan_buf *buf = kcalloc(1, sizeof(struct rchan_buf), GFP_KERNEL);
+ if (!buf)
+ return NULL;
+
+ buf->padding = kmalloc(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
+ *
+ * Should only be called from kref_put().
+ */
+void relay_destroy_channel(struct kref *kref)
+{
+ struct rchan *chan = container_of(kref, struct rchan, kref);
+ kfree(chan);
+}
+
+/**
+ * relay_destroy_buf - destroy an rchan_buf struct and associated buffer
+ * @buf: the buffer struct
+ */
+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]);
+ kfree(buf->page_array);
+ }
+ kfree(buf->padding);
+ kfree(buf);
+ kref_put(&chan->kref, relay_destroy_channel);
+}
+
+/**
+ * relay_remove_buf - remove a channel buffer
+ *
+ * Removes the file from the fileystem, which also frees the
+ * rchan_buf_struct and the channel buffer. Should only be called from
+ * kref_put().
+ */
+void relay_remove_buf(struct kref *kref)
+{
+ struct rchan_buf *buf = container_of(kref, struct rchan_buf, kref);
+ buf->chan->cb->remove_buf_file(buf->dentry);
+ 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.
+ */
+int relay_buf_empty(struct rchan_buf *buf)
+{
+ return (buf->subbufs_produced - buf->subbufs_consumed) ? 0 : 1;
+}
+EXPORT_SYMBOL_GPL(relay_buf_empty);
+
+/**
+ * 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,
+ int 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
+ * @private: the channel buffer
+ *
+ * This is the work function used to defer reader waking. The
+ * reason waking is deferred is that calling directly from write
+ * causes problems if you're writing from say the scheduler.
+ */
+static void wakeup_readers(void *private)
+{
+ struct rchan_buf *buf = private;
+ 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 inline 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_WORK(&buf->wake_readers, NULL, NULL);
+ } else {
+ cancel_delayed_work(&buf->wake_readers);
+ flush_scheduled_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)
+{
+ unsigned int i;
+ struct rchan_buf *prev = NULL;
+
+ if (!chan)
+ return;
+
+ for (i = 0; i < NR_CPUS; i++) {
+ if (!chan->buf[i] || chan->buf[i] == prev)
+ break;
+ __relay_reset(chan->buf[i], 0);
+ prev = chan->buf[i];
+ }
+}
+EXPORT_SYMBOL_GPL(relay_reset);
+
+/**
+ * relay_open_buf - create a new relay channel buffer
+ *
+ * Internal - used by relay_open().
+ */
+static struct rchan_buf *relay_open_buf(struct rchan *chan,
+ const char *filename,
+ struct dentry *parent,
+ int *is_global)
+{
+ struct rchan_buf *buf;
+ struct dentry *dentry;
+
+ if (*is_global)
+ return chan->buf[0];
+
+ buf = relay_create_buf(chan);
+ if (!buf)
+ return NULL;
+
+ /* Create file in fs */
+ dentry = chan->cb->create_buf_file(filename, parent, S_IRUSR,
+ buf, is_global);
+ if (!dentry) {
+ relay_destroy_buf(buf);
+ return NULL;
+ }
+
+ buf->dentry = dentry;
+ __relay_reset(buf, 1);
+
+ return buf;
+}
+
+/**
+ * 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 inline void relay_close_buf(struct rchan_buf *buf)
+{
+ buf->finalized = 1;
+ cancel_delayed_work(&buf->wake_readers);
+ flush_scheduled_work();
+ kref_put(&buf->kref, relay_remove_buf);
+}
+
+static inline 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;
+}
+
+/**
+ * relay_open - create a new relay channel
+ * @base_filename: base name of files to create
+ * @parent: dentry of parent directory, NULL for root directory
+ * @subbuf_size: size of sub-buffers
+ * @n_subbufs: number of sub-buffers
+ * @cb: client callback functions
+ *
+ * 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.
+ */
+struct rchan *relay_open(const char *base_filename,
+ struct dentry *parent,
+ size_t subbuf_size,
+ size_t n_subbufs,
+ struct rchan_callbacks *cb)
+{
+ unsigned int i;
+ struct rchan *chan;
+ char *tmpname;
+ int is_global = 0;
+
+ if (!base_filename)
+ return NULL;
+
+ if (!(subbuf_size && n_subbufs))
+ return NULL;
+
+ chan = kcalloc(1, sizeof(struct rchan), GFP_KERNEL);
+ if (!chan)
+ return NULL;
+
+ chan->version = RELAYFS_CHANNEL_VERSION;
+ chan->n_subbufs = n_subbufs;
+ chan->subbuf_size = subbuf_size;
+ chan->alloc_size = FIX_SIZE(subbuf_size * n_subbufs);
+ setup_callbacks(chan, cb);
+ kref_init(&chan->kref);
+
+ tmpname = kmalloc(NAME_MAX + 1, GFP_KERNEL);
+ if (!tmpname)
+ goto free_chan;
+
+ for_each_online_cpu(i) {
+ sprintf(tmpname, "%s%d", base_filename, i);
+ chan->buf[i] = relay_open_buf(chan, tmpname, parent,
+ &is_global);
+ if (!chan->buf[i])
+ goto free_bufs;
+
+ chan->buf[i]->cpu = i;
+ }
+
+ kfree(tmpname);
+ return chan;
+
+free_bufs:
+ for (i = 0; i < NR_CPUS; i++) {
+ if (!chan->buf[i])
+ break;
+ relay_close_buf(chan->buf[i]);
+ if (is_global)
+ break;
+ }
+ kfree(tmpname);
+
+free_chan:
+ kref_put(&chan->kref, relay_destroy_channel);
+ return NULL;
+}
+EXPORT_SYMBOL_GPL(relay_open);
+
+/**
+ * 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 (waitqueue_active(&buf->read_wait)) {
+ PREPARE_WORK(&buf->wake_readers, wakeup_readers, buf);
+ schedule_delayed_work(&buf->wake_readers, 1);
+ }
+ }
+
+ 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)
+ return;
+
+ if (cpu >= NR_CPUS || !chan->buf[cpu])
+ return;
+
+ buf = chan->buf[cpu];
+ buf->subbufs_consumed += subbufs_consumed;
+ if (buf->subbufs_consumed > buf->subbufs_produced)
+ buf->subbufs_consumed = buf->subbufs_produced;
+}
+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)
+{
+ unsigned int i;
+ struct rchan_buf *prev = NULL;
+
+ if (!chan)
+ return;
+
+ for (i = 0; i < NR_CPUS; i++) {
+ if (!chan->buf[i] || chan->buf[i] == prev)
+ break;
+ relay_close_buf(chan->buf[i]);
+ prev = chan->buf[i];
+ }
+
+ 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);
+
+ kref_put(&chan->kref, relay_destroy_channel);
+}
+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)
+{
+ unsigned int i;
+ struct rchan_buf *prev = NULL;
+
+ if (!chan)
+ return;
+
+ for (i = 0; i < NR_CPUS; i++) {
+ if (!chan->buf[i] || chan->buf[i] == prev)
+ break;
+ relay_switch_subbuf(chan->buf[i], 0);
+ prev = chan->buf[i];
+ }
+}
+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->u.generic_ip;
+ kref_get(&buf->kref);
+ filp->private_data = buf;
+
+ return 0;
+}
+
+/**
+ * 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 unsigned int relay_file_poll(struct file *filp, poll_table *wait)
+{
+ unsigned int mask = 0;
+ struct rchan_buf *buf = filp->private_data;
+
+ if (buf->finalized)
+ return POLLERR;
+
+ if (filp->f_mode & FMODE_READ) {
+ poll_wait(filp, &buf->read_wait, wait);
+ if (!relay_buf_empty(buf))
+ mask |= POLLIN | POLLRDNORM;
+ }
+
+ 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->bytes_consumed + bytes_consumed > subbuf_size) {
+ relay_subbufs_consumed(buf->chan, buf->cpu, 1);
+ buf->bytes_consumed = 0;
+ }
+
+ buf->bytes_consumed += bytes_consumed;
+ 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 bytes_produced, bytes_consumed, write_offset;
+ size_t subbuf_size = buf->chan->subbuf_size;
+ size_t n_subbufs = buf->chan->n_subbufs;
+ size_t produced = buf->subbufs_produced % n_subbufs;
+ size_t consumed = buf->subbufs_consumed % n_subbufs;
+
+ write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
+
+ if (consumed > produced) {
+ if ((produced > n_subbufs) &&
+ (produced + n_subbufs - consumed <= n_subbufs))
+ produced += n_subbufs;
+ } else if (consumed == produced) {
+ if (buf->offset > subbuf_size) {
+ produced += n_subbufs;
+ if (buf->subbufs_produced == buf->subbufs_consumed)
+ consumed += n_subbufs;
+ }
+ }
+
+ if (buf->offset > subbuf_size)
+ bytes_produced = (produced - 1) * subbuf_size + write_offset;
+ else
+ bytes_produced = produced * subbuf_size + write_offset;
+ bytes_consumed = consumed * subbuf_size + buf->bytes_consumed;
+
+ if (bytes_produced == bytes_consumed)
+ return 0;
+
+ relay_file_read_consume(buf, read_pos, 0);
+
+ return 1;
+}
+
+/**
+ * relay_file_read_subbuf_avail - return bytes available in sub-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
+ *
+ * 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;
+
+ 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
+ */
+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;
+}
+
+/**
+ * relay_file_read - read file op for relay files
+ * @filp: the file
+ * @buffer: the userspace buffer
+ * @count: number of bytes to read
+ * @ppos: position to read from
+ *
+ * Reads count bytes or the number of bytes available in the
+ * current sub-buffer being read, whichever is smaller.
+ */
+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;
+ struct inode *inode = filp->f_dentry->d_inode;
+ size_t read_start, avail;
+ ssize_t ret = 0;
+ void *from;
+
+ mutex_lock(&inode->i_mutex);
+ if(!relay_file_read_avail(buf, *ppos))
+ goto out;
+
+ read_start = relay_file_read_start_pos(*ppos, buf);
+ avail = relay_file_read_subbuf_avail(read_start, buf);
+ if (!avail)
+ goto out;
+
+ from = buf->start + read_start;
+ ret = count = min(count, avail);
+ if (copy_to_user(buffer, from, count)) {
+ ret = -EFAULT;
+ goto out;
+ }
+ relay_file_read_consume(buf, read_start, count);
+ *ppos = relay_file_read_end_pos(buf, read_start, count);
+out:
+ mutex_unlock(&inode->i_mutex);
+ return ret;
+}
+
+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,
+};
+EXPORT_SYMBOL_GPL(relay_file_operations);