10 files changed, 1887 insertions, 0 deletions

diff --git a/Documentation/filesystems/relayfs.txt b/Documentation/filesystems/relayfs.txt
new file mode 100644
index 000000000000..d24e1b0d4f39
--- /dev/null
+++ b/Documentation/filesystems/relayfs.txt
@@ -0,0 +1,362 @@
+
+relayfs - a high-speed data relay filesystem
+============================================
+
+relayfs is a filesystem designed to provide an efficient mechanism for
+tools and facilities to relay large and potentially sustained streams
+of data from kernel space to user space.
+
+The main abstraction of relayfs is the 'channel'.  A channel consists
+of a set of per-cpu kernel buffers each represented by a file in the
+relayfs filesystem.  Kernel clients write into a channel using
+efficient write functions which automatically log to the current cpu's
+channel buffer.  User space applications mmap() the per-cpu files and
+retrieve the data as it becomes available.
+
+The format of the data logged into the channel buffers is completely
+up to the relayfs client; relayfs does however provide hooks which
+allow clients to impose some stucture on the buffer data.  Nor does
+relayfs implement any form of data filtering - this also is left to
+the client.  The purpose is to keep relayfs as simple as possible.
+
+This document provides an overview of the relayfs API.  The details of
+the function parameters are documented along with the functions in the
+filesystem code - please see that for details.
+
+Semantics
+=========
+
+Each relayfs channel has one buffer per CPU, each buffer has one or
+more sub-buffers. Messages are written to the first sub-buffer until
+it is too full to contain a new message, in which case it it is
+written to the next (if available).  Messages are never split across
+sub-buffers.  At this point, userspace can be notified so it empties
+the first sub-buffer, while the kernel continues writing to the next.
+
+When notified that a sub-buffer is full, the kernel knows how many
+bytes of it are padding i.e. unused.  Userspace can use this knowledge
+to copy only valid data.
+
+After copying it, userspace can notify the kernel that a sub-buffer
+has been consumed.
+
+relayfs can operate in a mode where it will overwrite data not yet
+collected by userspace, and not wait for it to consume it.
+
+relayfs itself does not provide for communication of such data between
+userspace and kernel, allowing the kernel side to remain simple and not
+impose a single interface on userspace. It does provide a separate
+helper though, described below.
+
+klog, relay-app & librelay
+==========================
+
+relayfs itself is ready to use, but to make things easier, two
+additional systems are provided.  klog is a simple wrapper to make
+writing formatted text or raw data to a channel simpler, regardless of
+whether a channel to write into exists or not, or whether relayfs is
+compiled into the kernel or is configured as a module.  relay-app is
+the kernel counterpart of userspace librelay.c, combined these two
+files provide glue to easily stream data to disk, without having to
+bother with housekeeping.  klog and relay-app can be used together,
+with klog providing high-level logging functions to the kernel and
+relay-app taking care of kernel-user control and disk-logging chores.
+
+It is possible to use relayfs without relay-app & librelay, but you'll
+have to implement communication between userspace and kernel, allowing
+both to convey the state of buffers (full, empty, amount of padding).
+
+klog, relay-app and librelay can be found in the relay-apps tarball on
+http://relayfs.sourceforge.net
+
+The relayfs user space API
+==========================
+
+relayfs implements basic file operations for user space access to
+relayfs channel buffer data.  Here are the file operations that are
+available and some comments regarding their behavior:
+
+open()   enables user to open an _existing_ buffer.
+
+mmap()   results in channel buffer being mapped into the caller's
+         memory space. Note that you can't do a partial mmap - you must
+         map the entire file, which is NRBUF * SUBBUFSIZE.
+
+read()   read the contents of a channel buffer.  The bytes read are
+         'consumed' by the reader i.e. they won't be available again
+         to subsequent reads.  If the channel is being used in
+         no-overwrite mode (the default), it can be read at any time
+         even if there's an active kernel writer.  If the channel is
+         being used in overwrite mode and there are active channel
+         writers, results may be unpredictable - users should make
+         sure that all logging to the channel has ended before using
+         read() with overwrite mode.
+
+poll()   POLLIN/POLLRDNORM/POLLERR supported.  User applications are
+         notified when sub-buffer boundaries are crossed.
+
+close() decrements the channel buffer's refcount.  When the refcount
+        reaches 0 i.e. when no process or kernel client has the buffer
+        open, the channel buffer is freed.
+
+
+In order for a user application to make use of relayfs files, the
+relayfs filesystem must be mounted.  For example,
+
+        mount -t relayfs relayfs /mnt/relay
+
+NOTE:   relayfs doesn't need to be mounted for kernel clients to create
+        or use channels - it only needs to be mounted when user space
+        applications need access to the buffer data.
+
+
+The relayfs kernel API
+======================
+
+Here's a summary of the API relayfs provides to in-kernel clients:
+
+
+  channel management functions:
+
+    relay_open(base_filename, parent, subbuf_size, n_subbufs,
+               callbacks)
+    relay_close(chan)
+    relay_flush(chan)
+    relay_reset(chan)
+    relayfs_create_dir(name, parent)
+    relayfs_remove_dir(dentry)
+
+  channel management typically called on instigation of userspace:
+
+    relay_subbufs_consumed(chan, cpu, subbufs_consumed)
+
+  write functions:
+
+    relay_write(chan, data, length)
+    __relay_write(chan, data, length)
+    relay_reserve(chan, length)
+
+  callbacks:
+
+    subbuf_start(buf, subbuf, prev_subbuf, prev_padding)
+    buf_mapped(buf, filp)
+    buf_unmapped(buf, filp)
+
+  helper functions:
+
+    relay_buf_full(buf)
+    subbuf_start_reserve(buf, length)
+
+
+Creating a channel
+------------------
+
+relay_open() is used to create a channel, along with its per-cpu
+channel buffers.  Each channel buffer will have an associated file
+created for it in the relayfs filesystem, which can be opened and
+mmapped from user space if desired.  The files are named
+basename0...basenameN-1 where N is the number of online cpus, and by
+default will be created in the root of the filesystem.  If you want a
+directory structure to contain your relayfs files, you can create it
+with relayfs_create_dir() and pass the parent directory to
+relay_open().  Clients are responsible for cleaning up any directory
+structure they create when the channel is closed - use
+relayfs_remove_dir() for that.
+
+The total size of each per-cpu buffer is calculated by multiplying the
+number of sub-buffers by the sub-buffer size passed into relay_open().
+The idea behind sub-buffers is that they're basically an extension of
+double-buffering to N buffers, and they also allow applications to
+easily implement random-access-on-buffer-boundary schemes, which can
+be important for some high-volume applications.  The number and size
+of sub-buffers is completely dependent on the application and even for
+the same application, different conditions will warrant different
+values for these parameters at different times.  Typically, the right
+values to use are best decided after some experimentation; in general,
+though, it's safe to assume that having only 1 sub-buffer is a bad
+idea - you're guaranteed to either overwrite data or lose events
+depending on the channel mode being used.
+
+Channel 'modes'
+---------------
+
+relayfs channels can be used in either of two modes - 'overwrite' or
+'no-overwrite'.  The mode is entirely determined by the implementation
+of the subbuf_start() callback, as described below.  In 'overwrite'
+mode, also known as 'flight recorder' mode, writes continuously cycle
+around the buffer and will never fail, but will unconditionally
+overwrite old data regardless of whether it's actually been consumed.
+In no-overwrite mode, writes will fail i.e. data will be lost, if the
+number of unconsumed sub-buffers equals the total number of
+sub-buffers in the channel.  It should be clear that if there is no
+consumer or if the consumer can't consume sub-buffers fast enought,
+data will be lost in either case; the only difference is whether data
+is lost from the beginning or the end of a buffer.
+
+As explained above, a relayfs channel is made of up one or more
+per-cpu channel buffers, each implemented as a circular buffer
+subdivided into one or more sub-buffers.  Messages are written into
+the current sub-buffer of the channel's current per-cpu buffer via the
+write functions described below.  Whenever a message can't fit into
+the current sub-buffer, because there's no room left for it, the
+client is notified via the subbuf_start() callback that a switch to a
+new sub-buffer is about to occur.  The client uses this callback to 1)
+initialize the next sub-buffer if appropriate 2) finalize the previous
+sub-buffer if appropriate and 3) return a boolean value indicating
+whether or not to actually go ahead with the sub-buffer switch.
+
+To implement 'no-overwrite' mode, the userspace client would provide
+an implementation of the subbuf_start() callback something like the
+following:
+
+static int subbuf_start(struct rchan_buf *buf,
+                        void *subbuf,
+                        void *prev_subbuf,
+                        unsigned int prev_padding)
+{
+        if (prev_subbuf)
+                *((unsigned *)prev_subbuf) = prev_padding;
+
+        if (relay_buf_full(buf))
+                return 0;
+
+        subbuf_start_reserve(buf, sizeof(unsigned int));
+
+        return 1;
+}
+
+If the current buffer is full i.e. all sub-buffers remain unconsumed,
+the callback returns 0 to indicate that the buffer switch should not
+occur yet i.e. until the consumer has had a chance to read the current
+set of ready sub-buffers.  For the relay_buf_full() function to make
+sense, the consumer is reponsible for notifying relayfs when
+sub-buffers have been consumed via relay_subbufs_consumed().  Any
+subsequent attempts to write into the buffer will again invoke the
+subbuf_start() callback with the same parameters; only when the
+consumer has consumed one or more of the ready sub-buffers will
+relay_buf_full() return 0, in which case the buffer switch can
+continue.
+
+The implementation of the subbuf_start() callback for 'overwrite' mode
+would be very similar:
+
+static int subbuf_start(struct rchan_buf *buf,
+                        void *subbuf,
+                        void *prev_subbuf,
+                        unsigned int prev_padding)
+{
+        if (prev_subbuf)
+                *((unsigned *)prev_subbuf) = prev_padding;
+
+        subbuf_start_reserve(buf, sizeof(unsigned int));
+
+        return 1;
+}
+
+In this case, the relay_buf_full() check is meaningless and the
+callback always returns 1, causing the buffer switch to occur
+unconditionally.  It's also meaningless for the client to use the
+relay_subbufs_consumed() function in this mode, as it's never
+consulted.
+
+The default subbuf_start() implementation, used if the client doesn't
+define any callbacks, or doesn't define the subbuf_start() callback,
+implements the simplest possible 'no-overwrite' mode i.e. it does
+nothing but return 0.
+
+Header information can be reserved at the beginning of each sub-buffer
+by calling the subbuf_start_reserve() helper function from within the
+subbuf_start() callback.  This reserved area can be used to store
+whatever information the client wants.  In the example above, room is
+reserved in each sub-buffer to store the padding count for that
+sub-buffer.  This is filled in for the previous sub-buffer in the
+subbuf_start() implementation; the padding value for the previous
+sub-buffer is passed into the subbuf_start() callback along with a
+pointer to the previous sub-buffer, since the padding value isn't
+known until a sub-buffer is filled.  The subbuf_start() callback is
+also called for the first sub-buffer when the channel is opened, to
+give the client a chance to reserve space in it.  In this case the
+previous sub-buffer pointer passed into the callback will be NULL, so
+the client should check the value of the prev_subbuf pointer before
+writing into the previous sub-buffer.
+
+Writing to a channel
+--------------------
+
+kernel clients write data into the current cpu's channel buffer using
+relay_write() or __relay_write().  relay_write() is the main logging
+function - it uses local_irqsave() to protect the buffer and should be
+used if you might be logging from interrupt context.  If you know
+you'll never be logging from interrupt context, you can use
+__relay_write(), which only disables preemption.  These functions
+don't return a value, so you can't determine whether or not they
+failed - the assumption is that you wouldn't want to check a return
+value in the fast logging path anyway, and that they'll always succeed
+unless the buffer is full and no-overwrite mode is being used, in
+which case you can detect a failed write in the subbuf_start()
+callback by calling the relay_buf_full() helper function.
+
+relay_reserve() is used to reserve a slot in a channel buffer which
+can be written to later.  This would typically be used in applications
+that need to write directly into a channel buffer without having to
+stage data in a temporary buffer beforehand.  Because the actual write
+may not happen immediately after the slot is reserved, applications
+using relay_reserve() can keep a count of the number of bytes actually
+written, either in space reserved in the sub-buffers themselves or as
+a separate array.  See the 'reserve' example in the relay-apps tarball
+at http://relayfs.sourceforge.net for an example of how this can be
+done.  Because the write is under control of the client and is
+separated from the reserve, relay_reserve() doesn't protect the buffer
+at all - it's up to the client to provide the appropriate
+synchronization when using relay_reserve().
+
+Closing a channel
+-----------------
+
+The client calls relay_close() when it's finished using the channel.
+The channel and its associated buffers are destroyed when there are no
+longer any references to any of the channel buffers.  relay_flush()
+forces a sub-buffer switch on all the channel buffers, and can be used
+to finalize and process the last sub-buffers before the channel is
+closed.
+
+Misc
+----
+
+Some applications may want to keep a channel around and re-use it
+rather than open and close a new channel for each use.  relay_reset()
+can be used for this purpose - it resets a channel to its initial
+state without reallocating channel buffer memory or destroying
+existing mappings.  It should however only be called when it's safe to
+do so i.e. when the channel isn't currently being written to.
+
+Finally, there are a couple of utility callbacks that can be used for
+different purposes.  buf_mapped() is called whenever a channel buffer
+is mmapped from user space and buf_unmapped() is called when it's
+unmapped.  The client can use this notification to trigger actions
+within the kernel application, such as enabling/disabling logging to
+the channel.
+
+
+Resources
+=========
+
+For news, example code, mailing list, etc. see the relayfs homepage:
+
+    http://relayfs.sourceforge.net
+
+
+Credits
+=======
+
+The ideas and specs for relayfs came about as a result of discussions
+on tracing involving the following:
+
+Michel Dagenais         <michel.dagenais@polymtl.ca>
+Richard Moore           <richardj_moore@uk.ibm.com>
+Bob Wisniewski          <bob@watson.ibm.com>
+Karim Yaghmour          <karim@opersys.com>
+Tom Zanussi             <zanussi@us.ibm.com>
+
+Also thanks to Hubertus Franke for a lot of useful suggestions and bug
+reports.
diff --git a/fs/Kconfig b/fs/Kconfig
index ed78d24ee426..740d6ff0367d 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -816,6 +816,18 @@ config RAMFS
           To compile this as a module, choose M here: the module will be called
           ramfs.
 
+config RELAYFS_FS
+        tristate "Relayfs file system support"
+        ---help---
+          Relayfs is a high-speed data relay filesystem designed to provide
+          an efficient mechanism for tools and facilities to relay large
+          amounts of data from kernel space to user space.
+
+          To compile this code as a module, choose M here: the module will be
+          called relayfs.
+
+          If unsure, say N.
+
 endmenu
 
 menu "Miscellaneous filesystems"
diff --git a/fs/Makefile b/fs/Makefile
index cf95eb894fd5..15158309dee4 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -90,6 +90,7 @@ obj-$(CONFIG_AUTOFS_FS)		+= autofs/
 obj-$(CONFIG_AUTOFS4_FS)        += autofs4/
 obj-$(CONFIG_ADFS_FS)           += adfs/
 obj-$(CONFIG_UDF_FS)            += udf/
+obj-$(CONFIG_RELAYFS_FS)        += relayfs/
 obj-$(CONFIG_SUN_OPENPROMFS)    += openpromfs/
 obj-$(CONFIG_JFS_FS)            += jfs/
 obj-$(CONFIG_XFS_FS)            += xfs/
diff --git a/fs/relayfs/Makefile b/fs/relayfs/Makefile
new file mode 100644
index 000000000000..e76e182cdb38
--- /dev/null
+++ b/fs/relayfs/Makefile
@@ -0,0 +1,4 @@
+obj-$(CONFIG_RELAYFS_FS) += relayfs.o
+
+relayfs-y := relay.o inode.o buffers.o
+
diff --git a/fs/relayfs/buffers.c b/fs/relayfs/buffers.c
new file mode 100644
index 000000000000..2aa8e2719999
--- /dev/null
+++ b/fs/relayfs/buffers.c
@@ -0,0 +1,189 @@
+/*
+ * RelayFS buffer management code.
+ *
+ * Copyright (C) 2002-2005 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp
+ * Copyright (C) 1999-2005 - Karim Yaghmour (karim@opersys.com)
+ *
+ * This file is released under the GPL.
+ */
+
+#include <linux/module.h>
+#include <linux/vmalloc.h>
+#include <linux/mm.h>
+#include <linux/relayfs_fs.h>
+#include "relay.h"
+#include "buffers.h"
+
+/*
+ * close() vm_op implementation for relayfs 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 relayfs 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, GFP_KERNEL, 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_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 relayfs 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);
+        relayfs_remove(buf->dentry);
+}
diff --git a/fs/relayfs/buffers.h b/fs/relayfs/buffers.h
new file mode 100644
index 000000000000..37a12493f641
--- /dev/null
+++ b/fs/relayfs/buffers.h
@@ -0,0 +1,12 @@
+#ifndef _BUFFERS_H
+#define _BUFFERS_H
+
+/* This inspired by rtai/shmem */
+#define FIX_SIZE(x) (((x) - 1) & PAGE_MASK) + PAGE_SIZE
+
+extern int relay_mmap_buf(struct rchan_buf *buf, struct vm_area_struct *vma);
+extern struct rchan_buf *relay_create_buf(struct rchan *chan);
+extern void relay_destroy_buf(struct rchan_buf *buf);
+extern void relay_remove_buf(struct kref *kref);
+
+#endif/* _BUFFERS_H */
diff --git a/fs/relayfs/inode.c b/fs/relayfs/inode.c
new file mode 100644
index 000000000000..0f7f88d067ad
--- /dev/null
+++ b/fs/relayfs/inode.c
@@ -0,0 +1,609 @@
+/*
+ * VFS-related code for RelayFS, a high-speed data relay filesystem.
+ *
+ * Copyright (C) 2003-2005 - Tom Zanussi <zanussi@us.ibm.com>, IBM Corp
+ * Copyright (C) 2003-2005 - Karim Yaghmour <karim@opersys.com>
+ *
+ * Based on ramfs, Copyright (C) 2002 - Linus Torvalds
+ *
+ * This file is released under the GPL.
+ */
+
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/mount.h>
+#include <linux/pagemap.h>
+#include <linux/init.h>
+#include <linux/string.h>
+#include <linux/backing-dev.h>
+#include <linux/namei.h>
+#include <linux/poll.h>
+#include <linux/relayfs_fs.h>
+#include "relay.h"
+#include "buffers.h"
+
+#define RELAYFS_MAGIC                   0xF0B4A981
+
+static struct vfsmount *                relayfs_mount;
+static int                              relayfs_mount_count;
+static kmem_cache_t *                   relayfs_inode_cachep;
+
+static struct backing_dev_info          relayfs_backing_dev_info = {
+        .ra_pages       = 0,    /* No readahead */
+        .capabilities   = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
+};
+
+static struct inode *relayfs_get_inode(struct super_block *sb, int mode,
+                                       struct rchan *chan)
+{
+        struct rchan_buf *buf = NULL;
+        struct inode *inode;
+
+        if (S_ISREG(mode)) {
+                BUG_ON(!chan);
+                buf = relay_create_buf(chan);
+                if (!buf)
+                        return NULL;
+        }
+
+        inode = new_inode(sb);
+        if (!inode) {
+                relay_destroy_buf(buf);
+                return NULL;
+        }
+
+        inode->i_mode = mode;
+        inode->i_uid = 0;
+        inode->i_gid = 0;
+        inode->i_blksize = PAGE_CACHE_SIZE;
+        inode->i_blocks = 0;
+        inode->i_mapping->backing_dev_info = &relayfs_backing_dev_info;
+        inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
+        switch (mode & S_IFMT) {
+        case S_IFREG:
+                inode->i_fop = &relayfs_file_operations;
+                RELAYFS_I(inode)->buf = buf;
+                break;
+        case S_IFDIR:
+                inode->i_op = &simple_dir_inode_operations;
+                inode->i_fop = &simple_dir_operations;
+
+                /* directory inodes start off with i_nlink == 2 (for "." entry) */
+                inode->i_nlink++;
+                break;
+        default:
+                break;
+        }
+
+        return inode;
+}
+
+/**
+ *      relayfs_create_entry - create a relayfs directory or file
+ *      @name: the name of the file to create
+ *      @parent: parent directory
+ *      @mode: mode
+ *      @chan: relay channel associated with the file
+ *
+ *      Returns the new dentry, NULL on failure
+ *
+ *      Creates a file or directory with the specifed permissions.
+ */
+static struct dentry *relayfs_create_entry(const char *name,
+                                           struct dentry *parent,
+                                           int mode,
+                                           struct rchan *chan)
+{
+        struct dentry *d;
+        struct inode *inode;
+        int error = 0;
+
+        BUG_ON(!name || !(S_ISREG(mode) || S_ISDIR(mode)));
+
+        error = simple_pin_fs("relayfs", &relayfs_mount, &relayfs_mount_count);
+        if (error) {
+                printk(KERN_ERR "Couldn't mount relayfs: errcode %d\n", error);
+                return NULL;
+        }
+
+        if (!parent && relayfs_mount && relayfs_mount->mnt_sb)
+                parent = relayfs_mount->mnt_sb->s_root;
+
+        if (!parent) {
+                simple_release_fs(&relayfs_mount, &relayfs_mount_count);
+                return NULL;
+        }
+
+        parent = dget(parent);
+        down(&parent->d_inode->i_sem);
+        d = lookup_one_len(name, parent, strlen(name));
+        if (IS_ERR(d)) {
+                d = NULL;
+                goto release_mount;
+        }
+
+        if (d->d_inode) {
+                d = NULL;
+                goto release_mount;
+        }
+
+        inode = relayfs_get_inode(parent->d_inode->i_sb, mode, chan);
+        if (!inode) {
+                d = NULL;
+                goto release_mount;
+        }
+
+        d_instantiate(d, inode);
+        dget(d);        /* Extra count - pin the dentry in core */
+
+        if (S_ISDIR(mode))
+                parent->d_inode->i_nlink++;
+
+        goto exit;
+
+release_mount:
+        simple_release_fs(&relayfs_mount, &relayfs_mount_count);
+
+exit:
+        up(&parent->d_inode->i_sem);
+        dput(parent);
+        return d;
+}
+
+/**
+ *      relayfs_create_file - create a file in the relay filesystem
+ *      @name: the name of the file to create
+ *      @parent: parent directory
+ *      @mode: mode, if not specied the default perms are used
+ *      @chan: channel associated with the file
+ *
+ *      Returns file dentry if successful, NULL otherwise.
+ *
+ *      The file will be created user r on behalf of current user.
+ */
+struct dentry *relayfs_create_file(const char *name, struct dentry *parent,
+                                   int mode, struct rchan *chan)
+{
+        if (!mode)
+                mode = S_IRUSR;
+        mode = (mode & S_IALLUGO) | S_IFREG;
+
+        return relayfs_create_entry(name, parent, mode, chan);
+}
+
+/**
+ *      relayfs_create_dir - create a directory in the relay filesystem
+ *      @name: the name of the directory to create
+ *      @parent: parent directory, NULL if parent should be fs root
+ *
+ *      Returns directory dentry if successful, NULL otherwise.
+ *
+ *      The directory will be created world rwx on behalf of current user.
+ */
+struct dentry *relayfs_create_dir(const char *name, struct dentry *parent)
+{
+        int mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
+        return relayfs_create_entry(name, parent, mode, NULL);
+}
+
+/**
+ *      relayfs_remove - remove a file or directory in the relay filesystem
+ *      @dentry: file or directory dentry
+ *
+ *      Returns 0 if successful, negative otherwise.
+ */
+int relayfs_remove(struct dentry *dentry)
+{
+        struct dentry *parent;
+        int error = 0;
+
+        if (!dentry)
+                return -EINVAL;
+        parent = dentry->d_parent;
+        if (!parent)
+                return -EINVAL;
+
+        parent = dget(parent);
+        down(&parent->d_inode->i_sem);
+        if (dentry->d_inode) {
+                if (S_ISDIR(dentry->d_inode->i_mode))
+                        error = simple_rmdir(parent->d_inode, dentry);
+                else
+                        error = simple_unlink(parent->d_inode, dentry);
+                if (!error)
+                        d_delete(dentry);
+        }
+        if (!error)
+                dput(dentry);
+        up(&parent->d_inode->i_sem);
+        dput(parent);
+
+        if (!error)
+                simple_release_fs(&relayfs_mount, &relayfs_mount_count);
+
+        return error;
+}
+
+/**
+ *      relayfs_remove_dir - remove a directory in the relay filesystem
+ *      @dentry: directory dentry
+ *
+ *      Returns 0 if successful, negative otherwise.
+ */
+int relayfs_remove_dir(struct dentry *dentry)
+{
+        return relayfs_remove(dentry);
+}
+
+/**
+ *      relayfs_open - open file op for relayfs files
+ *      @inode: the inode
+ *      @filp: the file
+ *
+ *      Increments the channel buffer refcount.
+ */
+static int relayfs_open(struct inode *inode, struct file *filp)
+{
+        struct rchan_buf *buf = RELAYFS_I(inode)->buf;
+        kref_get(&buf->kref);
+
+        return 0;
+}
+
+/**
+ *      relayfs_mmap - mmap file op for relayfs 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 relayfs_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+        struct inode *inode = filp->f_dentry->d_inode;
+        return relay_mmap_buf(RELAYFS_I(inode)->buf, vma);
+}
+
+/**
+ *      relayfs_poll - poll file op for relayfs files
+ *      @filp: the file
+ *      @wait: poll table
+ *
+ *      Poll implemention.
+ */
+static unsigned int relayfs_poll(struct file *filp, poll_table *wait)
+{
+        unsigned int mask = 0;
+        struct inode *inode = filp->f_dentry->d_inode;
+        struct rchan_buf *buf = RELAYFS_I(inode)->buf;
+
+        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;
+}
+
+/**
+ *      relayfs_release - release file op for relayfs files
+ *      @inode: the inode
+ *      @filp: the file
+ *
+ *      Decrements the channel refcount, as the filesystem is
+ *      no longer using it.
+ */
+static int relayfs_release(struct inode *inode, struct file *filp)
+{
+        struct rchan_buf *buf = RELAYFS_I(inode)->buf;
+        kref_put(&buf->kref, relay_remove_buf);
+
+        return 0;
+}
+
+/**
+ *      relayfs_read_consume - update the consumed count for the buffer
+ */
+static void relayfs_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;
+        }
+}
+
+/**
+ *      relayfs_read_avail - boolean, are there unconsumed bytes available?
+ */
+static int relayfs_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;
+
+        relayfs_read_consume(buf, read_pos, 0);
+
+        return 1;
+}
+
+/**
+ *      relayfs_read_subbuf_avail - return bytes available in sub-buffer
+ */
+static size_t relayfs_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;
+}
+
+/**
+ *      relayfs_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 relayfs_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;
+}
+
+/**
+ *      relayfs_read_end_pos - return the new read position
+ */
+static size_t relayfs_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;
+}
+
+/**
+ *      relayfs_read - read file op for relayfs 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 relayfs_read(struct file *filp,
+                            char __user *buffer,
+                            size_t count,
+                            loff_t *ppos)
+{
+        struct inode *inode = filp->f_dentry->d_inode;
+        struct rchan_buf *buf = RELAYFS_I(inode)->buf;
+        size_t read_start, avail;
+        ssize_t ret = 0;
+        void *from;
+
+        down(&inode->i_sem);
+        if(!relayfs_read_avail(buf, *ppos))
+                goto out;
+
+        read_start = relayfs_read_start_pos(*ppos, buf);
+        avail = relayfs_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;
+        }
+        relayfs_read_consume(buf, read_start, count);
+        *ppos = relayfs_read_end_pos(buf, read_start, count);
+out:
+        up(&inode->i_sem);
+        return ret;
+}
+
+/**
+ *      relayfs alloc_inode() implementation
+ */
+static struct inode *relayfs_alloc_inode(struct super_block *sb)
+{
+        struct relayfs_inode_info *p = kmem_cache_alloc(relayfs_inode_cachep, SLAB_KERNEL);
+        if (!p)
+                return NULL;
+        p->buf = NULL;
+
+        return &p->vfs_inode;
+}
+
+/**
+ *      relayfs destroy_inode() implementation
+ */
+static void relayfs_destroy_inode(struct inode *inode)
+{
+        if (RELAYFS_I(inode)->buf)
+                relay_destroy_buf(RELAYFS_I(inode)->buf);
+
+        kmem_cache_free(relayfs_inode_cachep, RELAYFS_I(inode));
+}
+
+static void init_once(void *p, kmem_cache_t *cachep, unsigned long flags)
+{
+        struct relayfs_inode_info *i = p;
+        if ((flags & (SLAB_CTOR_VERIFY | SLAB_CTOR_CONSTRUCTOR)) == SLAB_CTOR_CONSTRUCTOR)
+                inode_init_once(&i->vfs_inode);
+}
+
+struct file_operations relayfs_file_operations = {
+        .open           = relayfs_open,
+        .poll           = relayfs_poll,
+        .mmap           = relayfs_mmap,
+        .read           = relayfs_read,
+        .llseek         = no_llseek,
+        .release        = relayfs_release,
+};
+
+static struct super_operations relayfs_ops = {
+        .statfs         = simple_statfs,
+        .drop_inode     = generic_delete_inode,
+        .alloc_inode    = relayfs_alloc_inode,
+        .destroy_inode  = relayfs_destroy_inode,
+};
+
+static int relayfs_fill_super(struct super_block * sb, void * data, int silent)
+{
+        struct inode *inode;
+        struct dentry *root;
+        int mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
+
+        sb->s_blocksize = PAGE_CACHE_SIZE;
+        sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
+        sb->s_magic = RELAYFS_MAGIC;
+        sb->s_op = &relayfs_ops;
+        inode = relayfs_get_inode(sb, mode, NULL);
+
+        if (!inode)
+                return -ENOMEM;
+
+        root = d_alloc_root(inode);
+        if (!root) {
+                iput(inode);
+                return -ENOMEM;
+        }
+        sb->s_root = root;
+
+        return 0;
+}
+
+static struct super_block * relayfs_get_sb(struct file_system_type *fs_type,
+                                           int flags, const char *dev_name,
+                                           void *data)
+{
+        return get_sb_single(fs_type, flags, data, relayfs_fill_super);
+}
+
+static struct file_system_type relayfs_fs_type = {
+        .owner          = THIS_MODULE,
+        .name           = "relayfs",
+        .get_sb         = relayfs_get_sb,
+        .kill_sb        = kill_litter_super,
+};
+
+static int __init init_relayfs_fs(void)
+{
+        int err;
+
+        relayfs_inode_cachep = kmem_cache_create("relayfs_inode_cache",
+                                sizeof(struct relayfs_inode_info), 0,
+                                0, init_once, NULL);
+        if (!relayfs_inode_cachep)
+                return -ENOMEM;
+
+        err = register_filesystem(&relayfs_fs_type);
+        if (err)
+                kmem_cache_destroy(relayfs_inode_cachep);
+
+        return err;
+}
+
+static void __exit exit_relayfs_fs(void)
+{
+        unregister_filesystem(&relayfs_fs_type);
+        kmem_cache_destroy(relayfs_inode_cachep);
+}
+
+module_init(init_relayfs_fs)
+module_exit(exit_relayfs_fs)
+
+EXPORT_SYMBOL_GPL(relayfs_file_operations);
+EXPORT_SYMBOL_GPL(relayfs_create_dir);
+EXPORT_SYMBOL_GPL(relayfs_remove_dir);
+
+MODULE_AUTHOR("Tom Zanussi <zanussi@us.ibm.com> and Karim Yaghmour <karim@opersys.com>");
+MODULE_DESCRIPTION("Relay Filesystem");
+MODULE_LICENSE("GPL");
+
diff --git a/fs/relayfs/relay.c b/fs/relayfs/relay.c
new file mode 100644
index 000000000000..16446a15c96d
--- /dev/null
+++ b/fs/relayfs/relay.c
@@ -0,0 +1,431 @@
+/*
+ * Public API and common code for RelayFS.
+ *
+ * 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)
+ *
+ * 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/relayfs_fs.h>
+#include "relay.h"
+#include "buffers.h"
+
+/**
+ *      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;
+}
+
+/**
+ *      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;
+}
+
+/*
+ * High-level relayfs 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)
+{
+}
+
+/* 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,
+};
+
+/**
+ *      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;
+
+        if (!chan)
+                return;
+
+        for (i = 0; i < NR_CPUS; i++) {
+                if (!chan->buf[i])
+                        continue;
+                __relay_reset(chan->buf[i], 0);
+        }
+}
+
+/**
+ *      relay_open_buf - create a new channel buffer in relayfs
+ *
+ *      Internal - used by relay_open().
+ */
+static struct rchan_buf *relay_open_buf(struct rchan *chan,
+                                        const char *filename,
+                                        struct dentry *parent)
+{
+        struct rchan_buf *buf;
+        struct dentry *dentry;
+
+        /* Create file in fs */
+        dentry = relayfs_create_file(filename, parent, S_IRUSR, chan);
+        if (!dentry)
+                return NULL;
+
+        buf = RELAYFS_I(dentry->d_inode)->buf;
+        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;
+        buf->chan->cb = &default_channel_callbacks;
+        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;
+        chan->cb = cb;
+}
+
+/**
+ *      relay_open - create a new relayfs 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;
+
+        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);
+                chan->buf[i]->cpu = i;
+                if (!chan->buf[i])
+                        goto free_bufs;
+        }
+
+        kfree(tmpname);
+        return chan;
+
+free_bufs:
+        for (i = 0; i < NR_CPUS; i++) {
+                if (!chan->buf[i])
+                        break;
+                relay_close_buf(chan->buf[i]);
+        }
+        kfree(tmpname);
+
+free_chan:
+        kref_put(&chan->kref, relay_destroy_channel);
+        return NULL;
+}
+
+/**
+ *      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:
+        printk(KERN_WARNING "relayfs: event too large (%Zd)\n", length);
+        WARN_ON(1);
+        return 0;
+}
+
+/**
+ *      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;
+}
+
+/**
+ *      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_close - close the channel
+ *      @chan: the channel
+ *
+ *      Closes all channel buffers and frees the channel.
+ */
+void relay_close(struct rchan *chan)
+{
+        unsigned int i;
+
+        if (!chan)
+                return;
+
+        for (i = 0; i < NR_CPUS; i++) {
+                if (!chan->buf[i])
+                        continue;
+                relay_close_buf(chan->buf[i]);
+        }
+
+        kref_put(&chan->kref, relay_destroy_channel);
+}
+
+/**
+ *      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;
+
+        if (!chan)
+                return;
+
+        for (i = 0; i < NR_CPUS; i++) {
+                if (!chan->buf[i])
+                        continue;
+                relay_switch_subbuf(chan->buf[i], 0);
+        }
+}
+
+EXPORT_SYMBOL_GPL(relay_open);
+EXPORT_SYMBOL_GPL(relay_close);
+EXPORT_SYMBOL_GPL(relay_flush);
+EXPORT_SYMBOL_GPL(relay_reset);
+EXPORT_SYMBOL_GPL(relay_subbufs_consumed);
+EXPORT_SYMBOL_GPL(relay_switch_subbuf);
+EXPORT_SYMBOL_GPL(relay_buf_full);
diff --git a/fs/relayfs/relay.h b/fs/relayfs/relay.h
new file mode 100644
index 000000000000..703503fa22b6
--- /dev/null
+++ b/fs/relayfs/relay.h
@@ -0,0 +1,12 @@
+#ifndef _RELAY_H
+#define _RELAY_H
+
+struct dentry *relayfs_create_file(const char *name,
+                                   struct dentry *parent,
+                                   int mode,
+                                   struct rchan *chan);
+extern int relayfs_remove(struct dentry *dentry);
+extern int relay_buf_empty(struct rchan_buf *buf);
+extern void relay_destroy_channel(struct kref *kref);
+
+#endif /* _RELAY_H */
diff --git a/include/linux/relayfs_fs.h b/include/linux/relayfs_fs.h
new file mode 100644
index 000000000000..cfafc3e76bc2
--- /dev/null
+++ b/include/linux/relayfs_fs.h
@@ -0,0 +1,255 @@
+/*
+ * linux/include/linux/relayfs_fs.h
+ *
+ * Copyright (C) 2002, 2003 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp
+ * Copyright (C) 1999, 2000, 2001, 2002 - Karim Yaghmour (karim@opersys.com)
+ *
+ * RelayFS definitions and declarations
+ */
+
+#ifndef _LINUX_RELAYFS_FS_H
+#define _LINUX_RELAYFS_FS_H
+
+#include <linux/config.h>
+#include <linux/types.h>
+#include <linux/sched.h>
+#include <linux/wait.h>
+#include <linux/list.h>
+#include <linux/fs.h>
+#include <linux/poll.h>
+#include <linux/kref.h>
+
+/*
+ * Tracks changes to rchan_buf struct
+ */
+#define RELAYFS_CHANNEL_VERSION         5
+
+/*
+ * Per-cpu relay channel buffer
+ */
+struct rchan_buf
+{
+        void *start;                    /* start of channel buffer */
+        void *data;                     /* start of current sub-buffer */
+        size_t offset;                  /* current offset into sub-buffer */
+        size_t subbufs_produced;        /* count of sub-buffers produced */
+        size_t subbufs_consumed;        /* count of sub-buffers consumed */
+        struct rchan *chan;             /* associated channel */
+        wait_queue_head_t read_wait;    /* reader wait queue */
+        struct work_struct wake_readers; /* reader wake-up work struct */
+        struct dentry *dentry;          /* channel file dentry */
+        struct kref kref;               /* channel buffer refcount */
+        struct page **page_array;       /* array of current buffer pages */
+        unsigned int page_count;        /* number of current buffer pages */
+        unsigned int finalized;         /* buffer has been finalized */
+        size_t *padding;                /* padding counts per sub-buffer */
+        size_t prev_padding;            /* temporary variable */
+        size_t bytes_consumed;          /* bytes consumed in cur read subbuf */
+        unsigned int cpu;               /* this buf's cpu */
+} ____cacheline_aligned;
+
+/*
+ * Relay channel data structure
+ */
+struct rchan
+{
+        u32 version;                    /* the version of this struct */
+        size_t subbuf_size;             /* sub-buffer size */
+        size_t n_subbufs;               /* number of sub-buffers per buffer */
+        size_t alloc_size;              /* total buffer size allocated */
+        struct rchan_callbacks *cb;     /* client callbacks */
+        struct kref kref;               /* channel refcount */
+        void *private_data;             /* for user-defined data */
+        struct rchan_buf *buf[NR_CPUS]; /* per-cpu channel buffers */
+};
+
+/*
+ * Relayfs inode
+ */
+struct relayfs_inode_info
+{
+        struct inode vfs_inode;
+        struct rchan_buf *buf;
+};
+
+static inline struct relayfs_inode_info *RELAYFS_I(struct inode *inode)
+{
+        return container_of(inode, struct relayfs_inode_info, vfs_inode);
+}
+
+/*
+ * Relay channel client callbacks
+ */
+struct rchan_callbacks
+{
+        /*
+         * subbuf_start - called on buffer-switch to a new sub-buffer
+         * @buf: the channel buffer containing the new sub-buffer
+         * @subbuf: the start of the new sub-buffer
+         * @prev_subbuf: the start of the previous sub-buffer
+         * @prev_padding: unused space at the end of previous sub-buffer
+         *
+         * The client should return 1 to continue logging, 0 to stop
+         * logging.
+         *
+         * NOTE: subbuf_start will also be invoked when the buffer is
+         *       created, so that the first sub-buffer can be initialized
+         *       if necessary.  In this case, prev_subbuf will be NULL.
+         *
+         * NOTE: the client can reserve bytes at the beginning of the new
+         *       sub-buffer by calling subbuf_start_reserve() in this callback.
+         */
+        int (*subbuf_start) (struct rchan_buf *buf,
+                             void *subbuf,
+                             void *prev_subbuf,
+                             size_t prev_padding);
+
+        /*
+         * buf_mapped - relayfs buffer mmap notification
+         * @buf: the channel buffer
+         * @filp: relayfs file pointer
+         *
+         * Called when a relayfs file is successfully mmapped
+         */
+        void (*buf_mapped)(struct rchan_buf *buf,
+                           struct file *filp);
+
+        /*
+         * buf_unmapped - relayfs buffer unmap notification
+         * @buf: the channel buffer
+         * @filp: relayfs file pointer
+         *
+         * Called when a relayfs file is successfully unmapped
+         */
+        void (*buf_unmapped)(struct rchan_buf *buf,
+                             struct file *filp);
+};
+
+/*
+ * relayfs kernel API, fs/relayfs/relay.c
+ */
+
+struct rchan *relay_open(const char *base_filename,
+                         struct dentry *parent,
+                         size_t subbuf_size,
+                         size_t n_subbufs,
+                         struct rchan_callbacks *cb);
+extern void relay_close(struct rchan *chan);
+extern void relay_flush(struct rchan *chan);
+extern void relay_subbufs_consumed(struct rchan *chan,
+                                   unsigned int cpu,
+                                   size_t consumed);
+extern void relay_reset(struct rchan *chan);
+extern int relay_buf_full(struct rchan_buf *buf);
+
+extern size_t relay_switch_subbuf(struct rchan_buf *buf,
+                                  size_t length);
+extern struct dentry *relayfs_create_dir(const char *name,
+                                         struct dentry *parent);
+extern int relayfs_remove_dir(struct dentry *dentry);
+
+/**
+ *      relay_write - write data into the channel
+ *      @chan: relay channel
+ *      @data: data to be written
+ *      @length: number of bytes to write
+ *
+ *      Writes data into the current cpu's channel buffer.
+ *
+ *      Protects the buffer by disabling interrupts.  Use this
+ *      if you might be logging from interrupt context.  Try
+ *      __relay_write() if you know you won't be logging from
+ *      interrupt context.
+ */
+static inline void relay_write(struct rchan *chan,
+                               const void *data,
+                               size_t length)
+{
+        unsigned long flags;
+        struct rchan_buf *buf;
+
+        local_irq_save(flags);
+        buf = chan->buf[smp_processor_id()];
+        if (unlikely(buf->offset + length > chan->subbuf_size))
+                length = relay_switch_subbuf(buf, length);
+        memcpy(buf->data + buf->offset, data, length);
+        buf->offset += length;
+        local_irq_restore(flags);
+}
+
+/**
+ *      __relay_write - write data into the channel
+ *      @chan: relay channel
+ *      @data: data to be written
+ *      @length: number of bytes to write
+ *
+ *      Writes data into the current cpu's channel buffer.
+ *
+ *      Protects the buffer by disabling preemption.  Use
+ *      relay_write() if you might be logging from interrupt
+ *      context.
+ */
+static inline void __relay_write(struct rchan *chan,
+                                 const void *data,
+                                 size_t length)
+{
+        struct rchan_buf *buf;
+
+        buf = chan->buf[get_cpu()];
+        if (unlikely(buf->offset + length > buf->chan->subbuf_size))
+                length = relay_switch_subbuf(buf, length);
+        memcpy(buf->data + buf->offset, data, length);
+        buf->offset += length;
+        put_cpu();
+}
+
+/**
+ *      relay_reserve - reserve slot in channel buffer
+ *      @chan: relay channel
+ *      @length: number of bytes to reserve
+ *
+ *      Returns pointer to reserved slot, NULL if full.
+ *
+ *      Reserves a slot in the current cpu's channel buffer.
+ *      Does not protect the buffer at all - caller must provide
+ *      appropriate synchronization.
+ */
+static inline void *relay_reserve(struct rchan *chan, size_t length)
+{
+        void *reserved;
+        struct rchan_buf *buf = chan->buf[smp_processor_id()];
+
+        if (unlikely(buf->offset + length > buf->chan->subbuf_size)) {
+                length = relay_switch_subbuf(buf, length);
+                if (!length)
+                        return NULL;
+        }
+        reserved = buf->data + buf->offset;
+        buf->offset += length;
+
+        return reserved;
+}
+
+/**
+ *      subbuf_start_reserve - reserve bytes at the start of a sub-buffer
+ *      @buf: relay channel buffer
+ *      @length: number of bytes to reserve
+ *
+ *      Helper function used to reserve bytes at the beginning of
+ *      a sub-buffer in the subbuf_start() callback.
+ */
+static inline void subbuf_start_reserve(struct rchan_buf *buf,
+                                        size_t length)
+{
+        BUG_ON(length >= buf->chan->subbuf_size - 1);
+        buf->offset = length;
+}
+
+/*
+ * exported relayfs file operations, fs/relayfs/inode.c
+ */
+
+extern struct file_operations relayfs_file_operations;
+
+#endif /* _LINUX_RELAYFS_FS_H */
+