Message-ID: <20090814154302.26116.36314.stgit@dev.haskins.net>
Date:	Fri, 14 Aug 2009 11:43:03 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	alacrityvm-devel@...ts.sourceforge.net
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: [PATCH v3 2/6] ioq: Add basic definitions for a shared-memory,
	lockless queue

IOQ allows asynchronous communication between two end-points via a common
shared-memory region.  Memory is synchronized using pure barriers (i.e.
lockless), and updates are communicated via an embedded shm-signal.   The
design of the interface allows one code base to universally provide both
sides of a given channel.

We will use this mechanism later in the series to efficiently move data
in and out of a guest kernel from various sources, including both
infrastructure level and application level transports.

Signed-off-by: Gregory Haskins <ghaskins@...ell.com>
---

 MAINTAINERS          |    6 +
 include/linux/Kbuild |    1 
 include/linux/ioq.h  |  415 ++++++++++++++++++++++++++++++++++++++++++++++++++
 lib/Kconfig          |   12 +
 lib/Makefile         |    1 
 lib/ioq.c            |  294 +++++++++++++++++++++++++++++++++++
 6 files changed, 729 insertions(+), 0 deletions(-)
 create mode 100644 include/linux/ioq.h
 create mode 100644 lib/ioq.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 3e736fe..d0ea25c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2707,6 +2707,12 @@ L:	linux-mips@...ux-mips.org
 S:	Maintained
 F:	drivers/serial/ioc3_serial.c
 
+IOQ LIBRARY
+M:	Gregory Haskins <ghaskins@...ell.com>
+S:	Maintained
+F:	include/linux/ioq.h
+F:	lib/ioq.c
+
 IP MASQUERADING
 M:	Juanjo Ciarlante <jjciarla@...z.uncu.edu.ar>
 S:	Maintained
diff --git a/include/linux/Kbuild b/include/linux/Kbuild
index 01d67b6..32b3eb8 100644
--- a/include/linux/Kbuild
+++ b/include/linux/Kbuild
@@ -247,6 +247,7 @@ unifdef-y += in.h
 unifdef-y += in6.h
 unifdef-y += inotify.h
 unifdef-y += input.h
+unifdef-y += ioq.h
 unifdef-y += ip.h
 unifdef-y += ipc.h
 unifdef-y += ipmi.h
diff --git a/include/linux/ioq.h b/include/linux/ioq.h
new file mode 100644
index 0000000..f77e316
--- /dev/null
+++ b/include/linux/ioq.h
@@ -0,0 +1,415 @@
+/*
+ * Copyright 2009 Novell.  All Rights Reserved.
+ *
+ * IOQ is a generic shared-memory, lockless queue mechanism. It can be used
+ * in a variety of ways, though its intended purpose is to become the
+ * asynchronous communication path for virtual-bus drivers.
+ *
+ * The following are a list of key design points:
+ *
+ * #) All shared-memory is always allocated on explicitly one side of the
+ *    link.  This typically would be the guest side in a VM/VMM scenario.
+ * #) Each IOQ has the concept of "north" and "south" locales, where
+ *    north denotes the memory-owner side (e.g. guest).
+ * #) An IOQ is manipulated using an iterator idiom.
+ * #) Provides a bi-directional signaling/notification infrastructure on
+ *    a per-queue basis, which includes an event mitigation strategy
+ *    to reduce boundary switching.
+ * #) The signaling path is abstracted so that various technologies and
+ *    topologies can define their own specific implementation while sharing
+ *    the basic structures and code.
+ *
+ * Author:
+ *      Gregory Haskins <ghaskins@...ell.com>
+ *
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#ifndef _LINUX_IOQ_H
+#define _LINUX_IOQ_H
+
+#include <linux/types.h>
+#include <linux/shm_signal.h>
+
+/*
+ *---------
+ * The following structures represent data that is shared across boundaries
+ * which may be quite disparate from one another (e.g. Windows vs Linux,
+ * 32 vs 64 bit, etc).  Therefore, care has been taken to make sure they
+ * present data in a manner that is independent of the environment.
+ *-----------
+ */
+struct ioq_ring_desc {
+	__u64                 cookie; /* for arbitrary use by north-side */
+	__u64                 ptr;
+	__u64                 len;
+	__u8                  valid;
+	__u8                  sown; /* South owned = 1, North owned = 0 */
+};
+
+#define IOQ_RING_MAGIC 0x47fa2fe4
+#define IOQ_RING_VER   4
+
+struct ioq_ring_idx {
+	__u32                 head;    /* 0 based index to head of ptr array */
+	__u32                 tail;    /* 0 based index to tail of ptr array */
+	__u8                  full;
+};
+
+enum ioq_locality {
+	ioq_locality_north,
+	ioq_locality_south,
+};
+
+struct ioq_ring_head {
+	__u32                  magic;
+	__u32                  ver;
+	struct shm_signal_desc signal;
+	struct ioq_ring_idx    idx[2];
+	__u32                  count;
+	struct ioq_ring_desc   ring[1]; /* "count" elements will be allocated */
+};
+
+#define IOQ_HEAD_DESC_SIZE(count) \
+    (sizeof(struct ioq_ring_head) + sizeof(struct ioq_ring_desc) * (count - 1))
+
+/* --- END SHARED STRUCTURES --- */
+
+#ifdef __KERNEL__
+
+#include <linux/sched.h>
+#include <linux/wait.h>
+#include <linux/interrupt.h>
+#include <linux/shm_signal.h>
+#include <linux/kref.h>
+
+enum ioq_idx_type {
+	ioq_idxtype_valid,
+	ioq_idxtype_inuse,
+	ioq_idxtype_both,
+	ioq_idxtype_invalid,
+};
+
+enum ioq_seek_type {
+	ioq_seek_tail,
+	ioq_seek_next,
+	ioq_seek_head,
+	ioq_seek_set
+};
+
+struct ioq_iterator {
+	struct ioq            *ioq;
+	struct ioq_ring_idx   *idx;
+	u32                    pos;
+	struct ioq_ring_desc  *desc;
+	int                    update:1;
+	int                    dualidx:1;
+	int                    flipowner:1;
+};
+
+struct ioq_notifier {
+	void (*signal)(struct ioq_notifier *);
+};
+
+struct ioq_ops {
+	void     (*release)(struct ioq *ioq);
+};
+
+struct ioq {
+	struct ioq_ops *ops;
+
+	struct kref            kref;
+	enum ioq_locality      locale;
+	struct ioq_ring_head  *head_desc;
+	struct ioq_ring_desc  *ring;
+	struct shm_signal     *signal;
+	wait_queue_head_t      wq;
+	struct ioq_notifier   *notifier;
+	size_t                 count;
+	struct shm_signal_notifier shm_notifier;
+};
+
+#define IOQ_ITER_AUTOUPDATE  (1 << 0)
+#define IOQ_ITER_NOFLIPOWNER (1 << 1)
+
+/**
+ * ioq_init() - initialize an IOQ
+ * @ioq:        IOQ context
+ *
+ * Initializes IOQ context before first use
+ *
+ **/
+void ioq_init(struct ioq *ioq,
+	      struct ioq_ops *ops,
+	      enum ioq_locality locale,
+	      struct ioq_ring_head *head,
+	      struct shm_signal *signal,
+	      size_t count);
+
+/**
+ * ioq_get() - acquire an IOQ context reference
+ * @ioq:        IOQ context
+ *
+ **/
+static inline struct ioq *ioq_get(struct ioq *ioq)
+{
+	kref_get(&ioq->kref);
+
+	return ioq;
+}
+
+static inline void _ioq_kref_release(struct kref *kref)
+{
+	struct ioq *ioq = container_of(kref, struct ioq, kref);
+
+	shm_signal_put(ioq->signal);
+	ioq->ops->release(ioq);
+}
+
+/**
+ * ioq_put() - release an IOQ context reference
+ * @ioq:        IOQ context
+ *
+ **/
+static inline void ioq_put(struct ioq *ioq)
+{
+	kref_put(&ioq->kref, _ioq_kref_release);
+}
+
+/**
+ * ioq_notify_enable() - enables local notifications on an IOQ
+ * @ioq:        IOQ context
+ * @flags:      Reserved for future use, must be 0
+ *
+ * Enables/unmasks the registered ioq_notifier (if applicable) and waitq to
+ * receive wakeups whenever the remote side performs an ioq_signal() operation.
+ * A notification will be dispatched immediately if any pending signals have
+ * already been issued prior to invoking this call.
+ *
+ * This is synonymous with unmasking an interrupt.
+ *
+ * Returns: success = 0, <0 = ERRNO
+ *
+ **/
+static inline int ioq_notify_enable(struct ioq *ioq, int flags)
+{
+	return shm_signal_enable(ioq->signal, 0);
+}
+
+/**
+ * ioq_notify_disable() - disable local notifications on an IOQ
+ * @ioq:        IOQ context
+ * @flags:      Reserved for future use, must be 0
+ *
+ * Disables/masks the registered ioq_notifier (if applicable) and waitq
+ * from receiving any further notifications.  Any subsequent calls to
+ * ioq_signal() by the remote side will update the ring as dirty, but
+ * will not traverse the locale boundary and will not invoke the notifier
+ * callback or wakeup the waitq.  Signals delivered while masked will
+ * be deferred until ioq_notify_enable() is invoked
+ *
+ * This is synonymous with masking an interrupt
+ *
+ * Returns: success = 0, <0 = ERRNO
+ *
+ **/
+static inline int ioq_notify_disable(struct ioq *ioq, int flags)
+{
+	return shm_signal_disable(ioq->signal, 0);
+}
+
+/**
+ * ioq_signal() - notify the remote side about ring changes
+ * @ioq:        IOQ context
+ * @flags:      Reserved for future use, must be 0
+ *
+ * Marks the ring state as "dirty" and, if enabled, will traverse
+ * a locale boundary to invoke a remote notification.  The remote
+ * side controls whether the notification should be delivered via
+ * the ioq_notify_enable/disable() interface.
+ *
+ * The specifics of how to traverse a locale boundary are abstracted
+ * by the ioq_ops->signal() interface and provided by a particular
+ * implementation.  However, typically going north to south would be
+ * something like a syscall/hypercall, and going south to north would be
+ * something like a posix-signal/guest-interrupt.
+ *
+ * Returns: success = 0, <0 = ERRNO
+ *
+ **/
+static inline int ioq_signal(struct ioq *ioq, int flags)
+{
+	return shm_signal_inject(ioq->signal, 0);
+}
+
+/**
+ * ioq_count() - counts the number of outstanding descriptors in an index
+ * @ioq:        IOQ context
+ * @type:	Specifies the index type
+ *                 (*) valid: the descriptor is valid.  This is usually
+ *                     used to keep track of descriptors that may not
+ *                     be carrying a useful payload, but still need to
+ *                     be tracked carefully.
+ *                 (*) inuse: Descriptors that carry useful payload
+ *
+ * Returns:
+ *  (*) >=0: # of descriptors outstanding in the index
+ *  (*) <0 = ERRNO
+ *
+ **/
+int ioq_count(struct ioq *ioq, enum ioq_idx_type type);
+
+/**
+ * ioq_remain() - counts the number of remaining descriptors in an index
+ * @ioq:        IOQ context
+ * @type:	Specifies the index type
+ *                 (*) valid: the descriptor is valid.  This is usually
+ *                     used to keep track of descriptors that may not
+ *                     be carrying a useful payload, but still need to
+ *                     be tracked carefully.
+ *                 (*) inuse: Descriptors that carry useful payload
+ *
+ * This is the converse of ioq_count().  This function returns the number
+ * of "free" descriptors left in a particular index
+ *
+ * Returns:
+ *  (*) >=0: # of descriptors remaining in the index
+ *  (*) <0 = ERRNO
+ *
+ **/
+int ioq_remain(struct ioq *ioq, enum ioq_idx_type type);
+
+/**
+ * ioq_size() - counts the maximum number of descriptors in an ring
+ * @ioq:        IOQ context
+ *
+ * This function returns the maximum number of descriptors supported in
+ * a ring, regardless of their current state (free or inuse).
+ *
+ * Returns:
+ *  (*) >=0: total # of descriptors in the ring
+ *  (*) <0 = ERRNO
+ *
+ **/
+int ioq_size(struct ioq *ioq);
+
+/**
+ * ioq_full() - determines if a specific index is "full"
+ * @ioq:        IOQ context
+ * @type:	Specifies the index type
+ *                 (*) valid: the descriptor is valid.  This is usually
+ *                     used to keep track of descriptors that may not
+ *                     be carrying a useful payload, but still need to
+ *                     be tracked carefully.
+ *                 (*) inuse: Descriptors that carry useful payload
+ *
+ * Returns:
+ *  (*) 0: index is not full
+ *  (*) 1: index is full
+ *  (*) <0 = ERRNO
+ *
+ **/
+int ioq_full(struct ioq *ioq, enum ioq_idx_type type);
+
+/**
+ * ioq_empty() - determines if a specific index is "empty"
+ * @ioq:        IOQ context
+ * @type:	Specifies the index type
+ *                 (*) valid: the descriptor is valid.  This is usually
+ *                     used to keep track of descriptors that may not
+ *                     be carrying a useful payload, but still need to
+ *                     be tracked carefully.
+ *                 (*) inuse: Descriptors that carry useful payload
+ *
+ * Returns:
+ *  (*) 0: index is not empty
+ *  (*) 1: index is empty
+ *  (*) <0 = ERRNO
+ *
+ **/
+static inline int ioq_empty(struct ioq *ioq, enum ioq_idx_type type)
+{
+    return !ioq_count(ioq, type);
+}
+
+/**
+ * ioq_iter_init() - initialize an iterator for IOQ descriptor traversal
+ * @ioq:        IOQ context to iterate on
+ * @iter:	Iterator context to init (usually from stack)
+ * @type:	Specifies the index type to iterate against
+ *                 (*) valid: iterate against the "valid" index
+ *                 (*) inuse: iterate against the "inuse" index
+ *                 (*) both: iterate against both indexes simultaneously
+ * @flags:      Bitfield with 0 or more bits set to alter behavior
+ *                 (*) autoupdate: automatically signal the remote side
+ *                     whenever the iterator pushes/pops to a new desc
+ *                 (*) noflipowner: do not flip the ownership bit during
+ *                     a push/pop operation
+ *
+ * Returns: success = 0, <0 = ERRNO
+ *
+ **/
+int ioq_iter_init(struct ioq *ioq, struct ioq_iterator *iter,
+		  enum ioq_idx_type type, int flags);
+
+/**
+ * ioq_iter_seek() - seek to a specific location in the IOQ ring
+ * @iter:	Iterator context (must be initialized with ioq_iter_init)
+ * @type:	Specifies the type of seek operation
+ *                 (*) tail: seek to the absolute tail, offset is ignored
+ *                 (*) next: seek to the relative next, offset is ignored
+ *                 (*) head: seek to the absolute head, offset is ignored
+ *                 (*) set: seek to the absolute offset
+ * @offset:     Offset for ioq_seek_set operations
+ * @flags:      Reserved for future use, must be 0
+ *
+ * Returns: success = 0, <0 = ERRNO
+ *
+ **/
+int  ioq_iter_seek(struct ioq_iterator *iter, enum ioq_seek_type type,
+		   long offset, int flags);
+
+/**
+ * ioq_iter_push() - push the tail pointer forward
+ * @iter:	Iterator context (must be initialized with ioq_iter_init)
+ * @flags:      Reserved for future use, must be 0
+ *
+ * This function will simultaneously advance the tail ptr in the current
+ * index (valid/inuse, as specified in the ioq_iter_init) as well as
+ * perform a seek(next) operation.  This effectively "pushes" a new pointer
+ * onto the tail of the index.
+ *
+ * Returns: success = 0, <0 = ERRNO
+ *
+ **/
+int  ioq_iter_push(struct ioq_iterator *iter, int flags);
+
+/**
+ * ioq_iter_pop() - pop the head pointer from the ring
+ * @iter:	Iterator context (must be initialized with ioq_iter_init)
+ * @flags:      Reserved for future use, must be 0
+ *
+ * This function will simultaneously advance the head ptr in the current
+ * index (valid/inuse, as specified in the ioq_iter_init) as well as
+ * perform a seek(next) operation.  This effectively "pops" a pointer
+ * from the head of the index.
+ *
+ * Returns: success = 0, <0 = ERRNO
+ *
+ **/
+int  ioq_iter_pop(struct ioq_iterator *iter,  int flags);
+
+#endif /* __KERNEL__ */
+
+#endif /* _LINUX_IOQ_H */
diff --git a/lib/Kconfig b/lib/Kconfig
index 136da19..255778d 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -209,4 +209,16 @@ config SHM_SIGNAL
 
 	 If unsure, say N
 
+config IOQ
+	tristate "IO-Queue library - Generic shared-memory queue"
+	select SHM_SIGNAL
+	default n
+	help
+	 IOQ is a generic shared-memory-queue mechanism that happens to be
+	 friendly to virtualization boundaries. It can be used in a variety
+	 of ways, though its intended purpose is to become a low-level
+	 communication path for paravirtualized drivers.
+
+	 If unsure, say N
+
 endmenu
diff --git a/lib/Makefile b/lib/Makefile
index 503bf7b..215f0c9 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -77,6 +77,7 @@ obj-$(CONFIG_TEXTSEARCH_FSM) += ts_fsm.o
 obj-$(CONFIG_SMP) += percpu_counter.o
 obj-$(CONFIG_AUDIT_GENERIC) += audit.o
 obj-$(CONFIG_SHM_SIGNAL) += shm_signal.o
+obj-$(CONFIG_IOQ) += ioq.o
 
 obj-$(CONFIG_SWIOTLB) += swiotlb.o
 obj-$(CONFIG_IOMMU_HELPER) += iommu-helper.o
diff --git a/lib/ioq.c b/lib/ioq.c
new file mode 100644
index 0000000..af3090f
--- /dev/null
+++ b/lib/ioq.c
@@ -0,0 +1,294 @@
+/*
+ * Copyright 2009 Novell.  All Rights Reserved.
+ *
+ * See include/linux/ioq.h for documentation
+ *
+ * Author:
+ *      Gregory Haskins <ghaskins@...ell.com>
+ *
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#include <linux/sched.h>
+#include <linux/ioq.h>
+#include <linux/bitops.h>
+#include <linux/module.h>
+
+#ifndef NULL
+#define NULL 0
+#endif
+
+static int ioq_iter_setpos(struct ioq_iterator *iter, u32 pos)
+{
+	struct ioq *ioq = iter->ioq;
+
+	BUG_ON(pos >= ioq->count);
+
+	iter->pos  = pos;
+	iter->desc = &ioq->ring[pos];
+
+	return 0;
+}
+
+static inline u32 modulo_inc(u32 val, u32 mod)
+{
+	BUG_ON(val >= mod);
+
+	if (val == (mod - 1))
+		return 0;
+
+	return val + 1;
+}
+
+static inline int idx_full(struct ioq_ring_idx *idx)
+{
+	return idx->full && (idx->head == idx->tail);
+}
+
+int ioq_iter_seek(struct ioq_iterator *iter, enum ioq_seek_type type,
+		  long offset, int flags)
+{
+	struct ioq_ring_idx *idx = iter->idx;
+	u32 pos;
+
+	switch (type) {
+	case ioq_seek_next:
+		pos = modulo_inc(iter->pos, iter->ioq->count);
+		break;
+	case ioq_seek_tail:
+		pos = idx->tail;
+		break;
+	case ioq_seek_head:
+		pos = idx->head;
+		break;
+	case ioq_seek_set:
+		if (offset >= iter->ioq->count)
+			return -1;
+		pos = offset;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return ioq_iter_setpos(iter, pos);
+}
+EXPORT_SYMBOL_GPL(ioq_iter_seek);
+
+static int ioq_ring_count(struct ioq_ring_idx *idx, int count)
+{
+	if (idx->full && (idx->head == idx->tail))
+		return count;
+	else if (idx->tail >= idx->head)
+		return idx->tail - idx->head;
+	else
+		return (idx->tail + count) - idx->head;
+}
+
+static void idx_tail_push(struct ioq_ring_idx *idx, int count)
+{
+	u32 tail = modulo_inc(idx->tail, count);
+
+	if (idx->head == tail) {
+		rmb();
+
+		/*
+		 * Setting full here may look racy, but note that we havent
+		 * flipped the owner bit yet.  So it is impossible for the
+		 * remote locale to move head in such a way that this operation
+		 * becomes invalid
+		 */
+		idx->full = 1;
+		wmb();
+	}
+
+	idx->tail = tail;
+}
+
+int ioq_iter_push(struct ioq_iterator *iter, int flags)
+{
+	struct ioq_ring_head *head_desc = iter->ioq->head_desc;
+	struct ioq_ring_idx  *idx  = iter->idx;
+	int ret;
+
+	/*
+	 * Its only valid to push if we are currently pointed at the tail
+	 */
+	if (iter->pos != idx->tail || iter->desc->sown != iter->ioq->locale)
+		return -EINVAL;
+
+	idx_tail_push(idx, iter->ioq->count);
+	if (iter->dualidx) {
+		idx_tail_push(&head_desc->idx[ioq_idxtype_inuse],
+			      iter->ioq->count);
+		if (head_desc->idx[ioq_idxtype_inuse].tail !=
+		    head_desc->idx[ioq_idxtype_valid].tail) {
+			SHM_SIGNAL_FAULT(iter->ioq->signal,
+					 "Tails not synchronized");
+			return -EINVAL;
+		}
+	}
+
+	wmb(); /* the index must be visible before the sown, or signal */
+
+	if (iter->flipowner) {
+		iter->desc->sown = !iter->ioq->locale;
+		wmb(); /* sown must be visible before we signal */
+	}
+
+	ret = ioq_iter_seek(iter, ioq_seek_next, 0, flags);
+
+	if (iter->update)
+		ioq_signal(iter->ioq, 0);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ioq_iter_push);
+
+int ioq_iter_pop(struct ioq_iterator *iter,  int flags)
+{
+	struct ioq_ring_idx *idx = iter->idx;
+	int ret;
+
+	/*
+	 * Its only valid to pop if we are currently pointed at the head
+	 */
+	if (iter->pos != idx->head || iter->desc->sown != iter->ioq->locale)
+		return -EINVAL;
+
+	idx->head = modulo_inc(idx->head, iter->ioq->count);
+	wmb(); /* head must be visible before full */
+
+	if (idx->full) {
+		idx->full = 0;
+		wmb(); /* full must be visible before sown */
+	}
+
+	if (iter->flipowner) {
+		iter->desc->sown = !iter->ioq->locale;
+		wmb(); /* sown must be visible before we signal */
+	}
+
+	ret = ioq_iter_seek(iter, ioq_seek_next, 0, flags);
+
+	if (iter->update)
+		ioq_signal(iter->ioq, 0);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ioq_iter_pop);
+
+static struct ioq_ring_idx *idxtype_to_idx(struct ioq *ioq,
+					   enum ioq_idx_type type)
+{
+	struct ioq_ring_idx *idx;
+
+	switch (type) {
+	case ioq_idxtype_valid:
+	case ioq_idxtype_inuse:
+		idx = &ioq->head_desc->idx[type];
+		break;
+	default:
+		panic("IOQ: illegal index type: %d", type);
+		break;
+	}
+
+	return idx;
+}
+
+int ioq_iter_init(struct ioq *ioq, struct ioq_iterator *iter,
+		  enum ioq_idx_type type, int flags)
+{
+	iter->ioq        = ioq;
+	iter->update     = (flags & IOQ_ITER_AUTOUPDATE);
+	iter->flipowner  = !(flags & IOQ_ITER_NOFLIPOWNER);
+	iter->pos        = -1;
+	iter->desc       = NULL;
+	iter->dualidx    = 0;
+
+	if (type == ioq_idxtype_both) {
+		/*
+		 * "both" is a special case, so we set the dualidx flag.
+		 *
+		 * However, we also just want to use the valid-index
+		 * for normal processing, so override that here
+		 */
+		type = ioq_idxtype_valid;
+		iter->dualidx = 1;
+	}
+
+	iter->idx = idxtype_to_idx(ioq, type);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ioq_iter_init);
+
+int ioq_count(struct ioq *ioq, enum ioq_idx_type type)
+{
+	return ioq_ring_count(idxtype_to_idx(ioq, type), ioq->count);
+}
+EXPORT_SYMBOL_GPL(ioq_count);
+
+int ioq_remain(struct ioq *ioq, enum ioq_idx_type type)
+{
+	int count = ioq_ring_count(idxtype_to_idx(ioq, type), ioq->count);
+
+	return ioq->count - count;
+}
+EXPORT_SYMBOL_GPL(ioq_remain);
+
+int ioq_size(struct ioq *ioq)
+{
+	return ioq->count;
+}
+EXPORT_SYMBOL_GPL(ioq_size);
+
+int ioq_full(struct ioq *ioq, enum ioq_idx_type type)
+{
+	struct ioq_ring_idx *idx = idxtype_to_idx(ioq, type);
+
+	return idx_full(idx);
+}
+EXPORT_SYMBOL_GPL(ioq_full);
+
+static void ioq_shm_signal(struct shm_signal_notifier *notifier)
+{
+	struct ioq *ioq = container_of(notifier, struct ioq, shm_notifier);
+
+	wake_up(&ioq->wq);
+	if (ioq->notifier)
+		ioq->notifier->signal(ioq->notifier);
+}
+
+void ioq_init(struct ioq *ioq,
+	      struct ioq_ops *ops,
+	      enum ioq_locality locale,
+	      struct ioq_ring_head *head,
+	      struct shm_signal *signal,
+	      size_t count)
+{
+	memset(ioq, 0, sizeof(*ioq));
+	kref_init(&ioq->kref);
+	init_waitqueue_head(&ioq->wq);
+
+	ioq->ops         = ops;
+	ioq->locale      = locale;
+	ioq->head_desc   = head;
+	ioq->ring        = &head->ring[0];
+	ioq->count       = count;
+	ioq->signal      = signal;
+
+	ioq->shm_notifier.signal = &ioq_shm_signal;
+	signal->notifier         = &ioq->shm_notifier;
+}
+EXPORT_SYMBOL_GPL(ioq_init);

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