path: root/kdbus-add-connection-pool-implementation.patch

From: Daniel Mack <daniel@zonque.org>
Date: Thu, 11 Sep 2014 18:56:41 +0200
Subject: [PATCH] kdbus: add connection pool implementation

A pool for data received from the kernel is installed for every
connection of the bus, and it is used to copy data from the kernel to
userspace clients, for messages and other information.

It is accessed when one of the following ioctls is issued:

  * KDBUS_CMD_MSG_RECV, to receive a message
  * KDBUS_CMD_NAME_LIST, to dump the name registry
  * KDBUS_CMD_CONN_INFO, to retrieve information on a connection

The offsets returned by either one of the aforementioned ioctls
describe offsets inside the pool. Internally, the pool is organized in
slices, that are dynamically allocated on demand. The overall size of
the pool is chosen by the connection when it connects to the bus with
KDBUS_CMD_HELLO.

In order to make the slice available for subsequent calls,
KDBUS_CMD_FREE has to be called on the offset.

To access the memory, the caller is expected to mmap() it to its task.

Signed-off-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 ipc/kdbus/pool.c | 728 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 ipc/kdbus/pool.h |  46 ++++
 2 files changed, 774 insertions(+)
 create mode 100644 ipc/kdbus/pool.c
 create mode 100644 ipc/kdbus/pool.h

diff --git a/ipc/kdbus/pool.c b/ipc/kdbus/pool.c
new file mode 100644
index 000000000000..139bb77056b3
--- /dev/null
+++ b/ipc/kdbus/pool.c
@@ -0,0 +1,728 @@
+/*
+ * Copyright (C) 2013-2015 Kay Sievers
+ * Copyright (C) 2013-2015 Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+ * Copyright (C) 2013-2015 Daniel Mack <daniel@zonque.org>
+ * Copyright (C) 2013-2015 David Herrmann <dh.herrmann@gmail.com>
+ * Copyright (C) 2013-2015 Linux Foundation
+ * Copyright (C) 2014-2015 Djalal Harouni <tixxdz@opendz.org>
+ *
+ * kdbus is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation; either version 2.1 of the License, or (at
+ * your option) any later version.
+ */
+
+#include <linux/aio.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/highmem.h>
+#include <linux/init.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/pagemap.h>
+#include <linux/rbtree.h>
+#include <linux/sched.h>
+#include <linux/shmem_fs.h>
+#include <linux/sizes.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <linux/uio.h>
+
+#include "pool.h"
+#include "util.h"
+
+/**
+ * struct kdbus_pool - the receiver's buffer
+ * @f:			The backing shmem file
+ * @size:		The size of the file
+ * @accounted_size:	Currently accounted memory in bytes
+ * @lock:		Pool data lock
+ * @slices:		All slices sorted by address
+ * @slices_busy:	Tree of allocated slices
+ * @slices_free:	Tree of free slices
+ *
+ * The receiver's buffer, managed as a pool of allocated and free
+ * slices containing the queued messages.
+ *
+ * Messages sent with KDBUS_CMD_SEND are copied direcly by the
+ * sending process into the receiver's pool.
+ *
+ * Messages received with KDBUS_CMD_RECV just return the offset
+ * to the data placed in the pool.
+ *
+ * The internally allocated memory needs to be returned by the receiver
+ * with KDBUS_CMD_FREE.
+ */
+struct kdbus_pool {
+	struct file *f;
+	size_t size;
+	size_t accounted_size;
+	struct mutex lock;
+
+	struct list_head slices;
+	struct rb_root slices_busy;
+	struct rb_root slices_free;
+};
+
+/**
+ * struct kdbus_pool_slice - allocated element in kdbus_pool
+ * @pool:		Pool this slice belongs to
+ * @off:		Offset of slice in the shmem file
+ * @size:		Size of slice
+ * @entry:		Entry in "all slices" list
+ * @rb_node:		Entry in free or busy list
+ * @free:		Unused slice
+ * @accounted:		Accounted as queue slice
+ * @ref_kernel:		Kernel holds a reference
+ * @ref_user:		Userspace holds a reference
+ *
+ * The pool has one or more slices, always spanning the entire size of the
+ * pool.
+ *
+ * Every slice is an element in a list sorted by the buffer address, to
+ * provide access to the next neighbor slice.
+ *
+ * Every slice is member in either the busy or the free tree. The free
+ * tree is organized by slice size, the busy tree organized by buffer
+ * offset.
+ */
+struct kdbus_pool_slice {
+	struct kdbus_pool *pool;
+	size_t off;
+	size_t size;
+
+	struct list_head entry;
+	struct rb_node rb_node;
+
+	bool free:1;
+	bool accounted:1;
+	bool ref_kernel:1;
+	bool ref_user:1;
+};
+
+static struct kdbus_pool_slice *kdbus_pool_slice_new(struct kdbus_pool *pool,
+						     size_t off, size_t size)
+{
+	struct kdbus_pool_slice *slice;
+
+	slice = kzalloc(sizeof(*slice), GFP_KERNEL);
+	if (!slice)
+		return NULL;
+
+	slice->pool = pool;
+	slice->off = off;
+	slice->size = size;
+	slice->free = true;
+	return slice;
+}
+
+/* insert a slice into the free tree */
+static void kdbus_pool_add_free_slice(struct kdbus_pool *pool,
+				      struct kdbus_pool_slice *slice)
+{
+	struct rb_node **n;
+	struct rb_node *pn = NULL;
+
+	n = &pool->slices_free.rb_node;
+	while (*n) {
+		struct kdbus_pool_slice *pslice;
+
+		pn = *n;
+		pslice = rb_entry(pn, struct kdbus_pool_slice, rb_node);
+		if (slice->size < pslice->size)
+			n = &pn->rb_left;
+		else
+			n = &pn->rb_right;
+	}
+
+	rb_link_node(&slice->rb_node, pn, n);
+	rb_insert_color(&slice->rb_node, &pool->slices_free);
+}
+
+/* insert a slice into the busy tree */
+static void kdbus_pool_add_busy_slice(struct kdbus_pool *pool,
+				      struct kdbus_pool_slice *slice)
+{
+	struct rb_node **n;
+	struct rb_node *pn = NULL;
+
+	n = &pool->slices_busy.rb_node;
+	while (*n) {
+		struct kdbus_pool_slice *pslice;
+
+		pn = *n;
+		pslice = rb_entry(pn, struct kdbus_pool_slice, rb_node);
+		if (slice->off < pslice->off)
+			n = &pn->rb_left;
+		else if (slice->off > pslice->off)
+			n = &pn->rb_right;
+		else
+			BUG();
+	}
+
+	rb_link_node(&slice->rb_node, pn, n);
+	rb_insert_color(&slice->rb_node, &pool->slices_busy);
+}
+
+static struct kdbus_pool_slice *kdbus_pool_find_slice(struct kdbus_pool *pool,
+						      size_t off)
+{
+	struct rb_node *n;
+
+	n = pool->slices_busy.rb_node;
+	while (n) {
+		struct kdbus_pool_slice *s;
+
+		s = rb_entry(n, struct kdbus_pool_slice, rb_node);
+		if (off < s->off)
+			n = n->rb_left;
+		else if (off > s->off)
+			n = n->rb_right;
+		else
+			return s;
+	}
+
+	return NULL;
+}
+
+/**
+ * kdbus_pool_slice_alloc() - allocate memory from a pool
+ * @pool:	The receiver's pool
+ * @size:	The number of bytes to allocate
+ * @accounted:	Whether this slice should be accounted for
+ *
+ * The returned slice is used for kdbus_pool_slice_release() to
+ * free the allocated memory. If either @kvec or @iovec is non-NULL, the data
+ * will be copied from kernel or userspace memory into the new slice at
+ * offset 0.
+ *
+ * Return: the allocated slice on success, ERR_PTR on failure.
+ */
+struct kdbus_pool_slice *kdbus_pool_slice_alloc(struct kdbus_pool *pool,
+						size_t size, bool accounted)
+{
+	size_t slice_size = KDBUS_ALIGN8(size);
+	struct rb_node *n, *found = NULL;
+	struct kdbus_pool_slice *s;
+	int ret = 0;
+
+	if (WARN_ON(!size))
+		return ERR_PTR(-EINVAL);
+
+	/* search a free slice with the closest matching size */
+	mutex_lock(&pool->lock);
+	n = pool->slices_free.rb_node;
+	while (n) {
+		s = rb_entry(n, struct kdbus_pool_slice, rb_node);
+		if (slice_size < s->size) {
+			found = n;
+			n = n->rb_left;
+		} else if (slice_size > s->size) {
+			n = n->rb_right;
+		} else {
+			found = n;
+			break;
+		}
+	}
+
+	/* no slice with the minimum size found in the pool */
+	if (!found) {
+		ret = -EXFULL;
+		goto exit_unlock;
+	}
+
+	/* no exact match, use the closest one */
+	if (!n) {
+		struct kdbus_pool_slice *s_new;
+
+		s = rb_entry(found, struct kdbus_pool_slice, rb_node);
+
+		/* split-off the remainder of the size to its own slice */
+		s_new = kdbus_pool_slice_new(pool, s->off + slice_size,
+					     s->size - slice_size);
+		if (!s_new) {
+			ret = -ENOMEM;
+			goto exit_unlock;
+		}
+
+		list_add(&s_new->entry, &s->entry);
+		kdbus_pool_add_free_slice(pool, s_new);
+
+		/* adjust our size now that we split-off another slice */
+		s->size = slice_size;
+	}
+
+	/* move slice from free to the busy tree */
+	rb_erase(found, &pool->slices_free);
+	kdbus_pool_add_busy_slice(pool, s);
+
+	WARN_ON(s->ref_kernel || s->ref_user);
+
+	s->ref_kernel = true;
+	s->free = false;
+	s->accounted = accounted;
+	if (accounted)
+		pool->accounted_size += s->size;
+	mutex_unlock(&pool->lock);
+
+	return s;
+
+exit_unlock:
+	mutex_unlock(&pool->lock);
+	return ERR_PTR(ret);
+}
+
+static void __kdbus_pool_slice_release(struct kdbus_pool_slice *slice)
+{
+	struct kdbus_pool *pool = slice->pool;
+
+	/* don't free the slice if either has a reference */
+	if (slice->ref_kernel || slice->ref_user)
+		return;
+
+	if (WARN_ON(slice->free))
+		return;
+
+	rb_erase(&slice->rb_node, &pool->slices_busy);
+
+	/* merge with the next free slice */
+	if (!list_is_last(&slice->entry, &pool->slices)) {
+		struct kdbus_pool_slice *s;
+
+		s = list_entry(slice->entry.next,
+			       struct kdbus_pool_slice, entry);
+		if (s->free) {
+			rb_erase(&s->rb_node, &pool->slices_free);
+			list_del(&s->entry);
+			slice->size += s->size;
+			kfree(s);
+		}
+	}
+
+	/* merge with previous free slice */
+	if (pool->slices.next != &slice->entry) {
+		struct kdbus_pool_slice *s;
+
+		s = list_entry(slice->entry.prev,
+			       struct kdbus_pool_slice, entry);
+		if (s->free) {
+			rb_erase(&s->rb_node, &pool->slices_free);
+			list_del(&slice->entry);
+			s->size += slice->size;
+			kfree(slice);
+			slice = s;
+		}
+	}
+
+	slice->free = true;
+	kdbus_pool_add_free_slice(pool, slice);
+}
+
+/**
+ * kdbus_pool_slice_release() - drop kernel-reference on allocated slice
+ * @slice:		Slice allocated from the pool
+ *
+ * This releases the kernel-reference on the given slice. If the
+ * kernel-reference and the user-reference on a slice are dropped, the slice is
+ * returned to the pool.
+ *
+ * So far, we do not implement full ref-counting on slices. Each, kernel and
+ * user-space can have exactly one reference to a slice. If both are dropped at
+ * the same time, the slice is released.
+ */
+void kdbus_pool_slice_release(struct kdbus_pool_slice *slice)
+{
+	struct kdbus_pool *pool;
+
+	if (!slice)
+		return;
+
+	/* @slice may be freed, so keep local ptr to @pool */
+	pool = slice->pool;
+
+	mutex_lock(&pool->lock);
+	/* kernel must own a ref to @slice to drop it */
+	WARN_ON(!slice->ref_kernel);
+	slice->ref_kernel = false;
+	/* no longer kernel-owned, de-account slice */
+	if (slice->accounted && !WARN_ON(pool->accounted_size < slice->size))
+		pool->accounted_size -= slice->size;
+	__kdbus_pool_slice_release(slice);
+	mutex_unlock(&pool->lock);
+}
+
+/**
+ * kdbus_pool_release_offset() - release a public offset
+ * @pool:		pool to operate on
+ * @off:		offset to release
+ *
+ * This should be called whenever user-space frees a slice given to them. It
+ * verifies the slice is available and public, and then drops it. It ensures
+ * correct locking and barriers against queues.
+ *
+ * Return: 0 on success, ENXIO if the offset is invalid or not public.
+ */
+int kdbus_pool_release_offset(struct kdbus_pool *pool, size_t off)
+{
+	struct kdbus_pool_slice *slice;
+	int ret = 0;
+
+	/* 'pool->size' is used as dummy offset for empty slices */
+	if (off == pool->size)
+		return 0;
+
+	mutex_lock(&pool->lock);
+	slice = kdbus_pool_find_slice(pool, off);
+	if (slice && slice->ref_user) {
+		slice->ref_user = false;
+		__kdbus_pool_slice_release(slice);
+	} else {
+		ret = -ENXIO;
+	}
+	mutex_unlock(&pool->lock);
+
+	return ret;
+}
+
+/**
+ * kdbus_pool_publish_empty() - publish empty slice to user-space
+ * @pool:		pool to operate on
+ * @off:		output storage for offset, or NULL
+ * @size:		output storage for size, or NULL
+ *
+ * This is the same as kdbus_pool_slice_publish(), but uses a dummy slice with
+ * size 0. The returned offset points to the end of the pool and is never
+ * returned on real slices.
+ */
+void kdbus_pool_publish_empty(struct kdbus_pool *pool, u64 *off, u64 *size)
+{
+	if (off)
+		*off = pool->size;
+	if (size)
+		*size = 0;
+}
+
+/**
+ * kdbus_pool_slice_publish() - publish slice to user-space
+ * @slice:		The slice
+ * @out_offset:		Output storage for offset, or NULL
+ * @out_size:		Output storage for size, or NULL
+ *
+ * This prepares a slice to be published to user-space.
+ *
+ * This call combines the following operations:
+ *   * the memory region is flushed so the user's memory view is consistent
+ *   * the slice is marked as referenced by user-space, so user-space has to
+ *     call KDBUS_CMD_FREE to release it
+ *   * the offset and size of the slice are written to the given output
+ *     arguments, if non-NULL
+ */
+void kdbus_pool_slice_publish(struct kdbus_pool_slice *slice,
+			      u64 *out_offset, u64 *out_size)
+{
+	mutex_lock(&slice->pool->lock);
+	/* kernel must own a ref to @slice to gain a user-space ref */
+	WARN_ON(!slice->ref_kernel);
+	slice->ref_user = true;
+	mutex_unlock(&slice->pool->lock);
+
+	if (out_offset)
+		*out_offset = slice->off;
+	if (out_size)
+		*out_size = slice->size;
+}
+
+/**
+ * kdbus_pool_slice_offset() - Get a slice's offset inside the pool
+ * @slice:	Slice to return the offset of
+ *
+ * Return: The internal offset @slice inside the pool.
+ */
+off_t kdbus_pool_slice_offset(const struct kdbus_pool_slice *slice)
+{
+	return slice->off;
+}
+
+/**
+ * kdbus_pool_slice_size() - get size of a pool slice
+ * @slice:	slice to query
+ *
+ * Return: size of the given slice
+ */
+size_t kdbus_pool_slice_size(const struct kdbus_pool_slice *slice)
+{
+	return slice->size;
+}
+
+/**
+ * kdbus_pool_new() - create a new pool
+ * @name:		Name of the (deleted) file which shows up in
+ *			/proc, used for debugging
+ * @size:		Maximum size of the pool
+ *
+ * Return: a new kdbus_pool on success, ERR_PTR on failure.
+ */
+struct kdbus_pool *kdbus_pool_new(const char *name, size_t size)
+{
+	struct kdbus_pool_slice *s;
+	struct kdbus_pool *p;
+	struct file *f;
+	char *n = NULL;
+	int ret;
+
+	p = kzalloc(sizeof(*p), GFP_KERNEL);
+	if (!p)
+		return ERR_PTR(-ENOMEM);
+
+	if (name) {
+		n = kasprintf(GFP_KERNEL, KBUILD_MODNAME "-conn:%s", name);
+		if (!n) {
+			ret = -ENOMEM;
+			goto exit_free;
+		}
+	}
+
+	f = shmem_file_setup(n ?: KBUILD_MODNAME "-conn", size, 0);
+	kfree(n);
+
+	if (IS_ERR(f)) {
+		ret = PTR_ERR(f);
+		goto exit_free;
+	}
+
+	ret = get_write_access(file_inode(f));
+	if (ret < 0)
+		goto exit_put_shmem;
+
+	/* allocate first slice spanning the entire pool */
+	s = kdbus_pool_slice_new(p, 0, size);
+	if (!s) {
+		ret = -ENOMEM;
+		goto exit_put_write;
+	}
+
+	p->f = f;
+	p->size = size;
+	p->slices_free = RB_ROOT;
+	p->slices_busy = RB_ROOT;
+	mutex_init(&p->lock);
+
+	INIT_LIST_HEAD(&p->slices);
+	list_add(&s->entry, &p->slices);
+
+	kdbus_pool_add_free_slice(p, s);
+	return p;
+
+exit_put_write:
+	put_write_access(file_inode(f));
+exit_put_shmem:
+	fput(f);
+exit_free:
+	kfree(p);
+	return ERR_PTR(ret);
+}
+
+/**
+ * kdbus_pool_free() - destroy pool
+ * @pool:		The receiver's pool
+ */
+void kdbus_pool_free(struct kdbus_pool *pool)
+{
+	struct kdbus_pool_slice *s, *tmp;
+
+	if (!pool)
+		return;
+
+	list_for_each_entry_safe(s, tmp, &pool->slices, entry) {
+		list_del(&s->entry);
+		kfree(s);
+	}
+
+	put_write_access(file_inode(pool->f));
+	fput(pool->f);
+	kfree(pool);
+}
+
+/**
+ * kdbus_pool_accounted() - retrieve accounting information
+ * @pool:		pool to query
+ * @size:		output for overall pool size
+ * @acc:		output for currently accounted size
+ *
+ * This returns accounting information of the pool. Note that the data might
+ * change after the function returns, as the pool lock is dropped. You need to
+ * protect the data via other means, if you need reliable accounting.
+ */
+void kdbus_pool_accounted(struct kdbus_pool *pool, size_t *size, size_t *acc)
+{
+	mutex_lock(&pool->lock);
+	if (size)
+		*size = pool->size;
+	if (acc)
+		*acc = pool->accounted_size;
+	mutex_unlock(&pool->lock);
+}
+
+/**
+ * kdbus_pool_slice_copy_iovec() - copy user memory to a slice
+ * @slice:		The slice to write to
+ * @off:		Offset in the slice to write to
+ * @iov:		iovec array, pointing to data to copy
+ * @iov_len:		Number of elements in @iov
+ * @total_len:		Total number of bytes described in members of @iov
+ *
+ * User memory referenced by @iov will be copied into @slice at offset @off.
+ *
+ * Return: the numbers of bytes copied, negative errno on failure.
+ */
+ssize_t
+kdbus_pool_slice_copy_iovec(const struct kdbus_pool_slice *slice, loff_t off,
+			    struct iovec *iov, size_t iov_len, size_t total_len)
+{
+	struct iov_iter iter;
+	ssize_t len;
+
+	if (WARN_ON(off + total_len > slice->size))
+		return -EFAULT;
+
+	off += slice->off;
+	iov_iter_init(&iter, WRITE, iov, iov_len, total_len);
+	len = vfs_iter_write(slice->pool->f, &iter, &off);
+
+	return (len >= 0 && len != total_len) ? -EFAULT : len;
+}
+
+/**
+ * kdbus_pool_slice_copy_kvec() - copy kernel memory to a slice
+ * @slice:		The slice to write to
+ * @off:		Offset in the slice to write to
+ * @kvec:		kvec array, pointing to data to copy
+ * @kvec_len:		Number of elements in @kvec
+ * @total_len:		Total number of bytes described in members of @kvec
+ *
+ * Kernel memory referenced by @kvec will be copied into @slice at offset @off.
+ *
+ * Return: the numbers of bytes copied, negative errno on failure.
+ */
+ssize_t kdbus_pool_slice_copy_kvec(const struct kdbus_pool_slice *slice,
+				   loff_t off, struct kvec *kvec,
+				   size_t kvec_len, size_t total_len)
+{
+	struct iov_iter iter;
+	mm_segment_t old_fs;
+	ssize_t len;
+
+	if (WARN_ON(off + total_len > slice->size))
+		return -EFAULT;
+
+	off += slice->off;
+	iov_iter_kvec(&iter, WRITE | ITER_KVEC, kvec, kvec_len, total_len);
+
+	old_fs = get_fs();
+	set_fs(get_ds());
+	len = vfs_iter_write(slice->pool->f, &iter, &off);
+	set_fs(old_fs);
+
+	return (len >= 0 && len != total_len) ? -EFAULT : len;
+}
+
+/**
+ * kdbus_pool_slice_copy() - copy data from one slice into another
+ * @slice_dst:		destination slice
+ * @slice_src:		source slice
+ *
+ * Return: 0 on success, negative error number on failure.
+ */
+int kdbus_pool_slice_copy(const struct kdbus_pool_slice *slice_dst,
+			  const struct kdbus_pool_slice *slice_src)
+{
+	struct file *f_src = slice_src->pool->f;
+	struct file *f_dst = slice_dst->pool->f;
+	struct inode *i_dst = file_inode(f_dst);
+	struct address_space *mapping_dst = f_dst->f_mapping;
+	const struct address_space_operations *aops = mapping_dst->a_ops;
+	unsigned long len = slice_src->size;
+	loff_t off_src = slice_src->off;
+	loff_t off_dst = slice_dst->off;
+	mm_segment_t old_fs;
+	int ret = 0;
+
+	if (WARN_ON(slice_src->size != slice_dst->size) ||
+	    WARN_ON(slice_src->free || slice_dst->free))
+		return -EINVAL;
+
+	mutex_lock(&i_dst->i_mutex);
+	old_fs = get_fs();
+	set_fs(get_ds());
+	while (len > 0) {
+		unsigned long page_off;
+		unsigned long copy_len;
+		char __user *kaddr;
+		struct page *page;
+		ssize_t n_read;
+		void *fsdata;
+		long status;
+
+		page_off = off_dst & (PAGE_CACHE_SIZE - 1);
+		copy_len = min_t(unsigned long,
+				 PAGE_CACHE_SIZE - page_off, len);
+
+		status = aops->write_begin(f_dst, mapping_dst, off_dst,
+					   copy_len, 0, &page, &fsdata);
+		if (unlikely(status < 0)) {
+			ret = status;
+			break;
+		}
+
+		kaddr = (char __force __user *)kmap(page) + page_off;
+		n_read = f_src->f_op->read(f_src, kaddr, copy_len, &off_src);
+		kunmap(page);
+		mark_page_accessed(page);
+		flush_dcache_page(page);
+
+		if (unlikely(n_read != copy_len)) {
+			ret = -EFAULT;
+			break;
+		}
+
+		status = aops->write_end(f_dst, mapping_dst, off_dst,
+					 copy_len, copy_len, page, fsdata);
+		if (unlikely(status != copy_len)) {
+			ret = -EFAULT;
+			break;
+		}
+
+		off_dst += copy_len;
+		len -= copy_len;
+	}
+	set_fs(old_fs);
+	mutex_unlock(&i_dst->i_mutex);
+
+	return ret;
+}
+
+/**
+ * kdbus_pool_mmap() -  map the pool into the process
+ * @pool:		The receiver's pool
+ * @vma:		passed by mmap() syscall
+ *
+ * Return: the result of the mmap() call, negative errno on failure.
+ */
+int kdbus_pool_mmap(const struct kdbus_pool *pool, struct vm_area_struct *vma)
+{
+	/* deny write access to the pool */
+	if (vma->vm_flags & VM_WRITE)
+		return -EPERM;
+	vma->vm_flags &= ~VM_MAYWRITE;
+
+	/* do not allow to map more than the size of the file */
+	if ((vma->vm_end - vma->vm_start) > pool->size)
+		return -EFAULT;
+
+	/* replace the connection file with our shmem file */
+	if (vma->vm_file)
+		fput(vma->vm_file);
+	vma->vm_file = get_file(pool->f);
+
+	return pool->f->f_op->mmap(pool->f, vma);
+}
diff --git a/ipc/kdbus/pool.h b/ipc/kdbus/pool.h
new file mode 100644
index 000000000000..a9038213aa4d
--- /dev/null
+++ b/ipc/kdbus/pool.h
@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2013-2015 Kay Sievers
+ * Copyright (C) 2013-2015 Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+ * Copyright (C) 2013-2015 Daniel Mack <daniel@zonque.org>
+ * Copyright (C) 2013-2015 David Herrmann <dh.herrmann@gmail.com>
+ * Copyright (C) 2013-2015 Linux Foundation
+ * Copyright (C) 2014-2015 Djalal Harouni <tixxdz@opendz.org>
+ *
+ * kdbus is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation; either version 2.1 of the License, or (at
+ * your option) any later version.
+ */
+
+#ifndef __KDBUS_POOL_H
+#define __KDBUS_POOL_H
+
+#include <linux/uio.h>
+
+struct kdbus_pool;
+struct kdbus_pool_slice;
+
+struct kdbus_pool *kdbus_pool_new(const char *name, size_t size);
+void kdbus_pool_free(struct kdbus_pool *pool);
+void kdbus_pool_accounted(struct kdbus_pool *pool, size_t *size, size_t *acc);
+int kdbus_pool_mmap(const struct kdbus_pool *pool, struct vm_area_struct *vma);
+int kdbus_pool_release_offset(struct kdbus_pool *pool, size_t off);
+void kdbus_pool_publish_empty(struct kdbus_pool *pool, u64 *off, u64 *size);
+
+struct kdbus_pool_slice *kdbus_pool_slice_alloc(struct kdbus_pool *pool,
+						size_t size, bool accounted);
+void kdbus_pool_slice_release(struct kdbus_pool_slice *slice);
+void kdbus_pool_slice_publish(struct kdbus_pool_slice *slice,
+			      u64 *out_offset, u64 *out_size);
+off_t kdbus_pool_slice_offset(const struct kdbus_pool_slice *slice);
+size_t kdbus_pool_slice_size(const struct kdbus_pool_slice *slice);
+int kdbus_pool_slice_copy(const struct kdbus_pool_slice *slice_dst,
+			  const struct kdbus_pool_slice *slice_src);
+ssize_t kdbus_pool_slice_copy_kvec(const struct kdbus_pool_slice *slice,
+				   loff_t off, struct kvec *kvec,
+				   size_t kvec_count, size_t total_len);
+ssize_t kdbus_pool_slice_copy_iovec(const struct kdbus_pool_slice *slice,
+				    loff_t off, struct iovec *iov,
+				    size_t iov_count, size_t total_len);
+
+#endif