xen: Add Xen paravirtualized sink support.

A part of Xen's paravirtualized audio driver has been developed as a
pulseaudio module. This module acts as a tunnel over Xen's shared memory
mechanism and allows a domU guest to send audio data to a dom0 backend.

Reference: https://bugs.freedesktop.org/show_bug.cgi?id=43503

5 files changed, 1090 insertions, 0 deletions

diff --git a/configure.ac b/configure.ac
index 5474bc8d..8370546b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1079,6 +1079,31 @@ AS_IF([test "x$HAVE_SPEEX" = "x1"], AC_DEFINE([HAVE_SPEEX], 1, [Have speex]))
 AC_SUBST(LIBSPEEX_CFLAGS)
 AC_SUBST(LIBSPEEX_LIBS)
 
+#### Xen support (optional) ####
+
+AC_ARG_ENABLE([xen],
+    AS_HELP_STRING([--disable-xen],[Disable optional Xen paravirtualized driver]))
+
+XEN_CFLAGS=
+XEN_LIBS=
+
+AS_IF([test "x$enable_xen" != "xno"],
+    [
+        HAVE_XEN=1
+        AC_CHECK_HEADER(xenctrl.h, [], [HAVE_XEN=0])
+        AC_CHECK_HEADER(xs.h, [], [HAVE_XEN=0])
+        AC_CHECK_LIB(xenctrl, xc_interface_open, [XEN_LIBS="$XEN_LIBS -lxenctrl"], [HAVE_XEN=0])
+        AC_CHECK_LIB(xenstore, xs_domain_open, [XEN_LIBS="$XEN_LIBS -lxenstore"], [HAVE_XEN=0])
+    ],
+    HAVE_XEN=0)
+
+AS_IF([test "x$enable_xen" = "xyes" && test "x$HAVE_XEN" = "x0"],
+    [AC_MSG_ERROR([*** Xen development headers or libraries not found])])
+
+AC_SUBST(XEN_CFLAGS)
+AC_SUBST(XEN_LIBS)
+AM_CONDITIONAL([HAVE_XEN], [test "x$HAVE_XEN" = x1])
+
 #### ORC (optional) ####
 
 ORC_CHECK([0.4.11])
@@ -1332,6 +1357,7 @@ AS_IF([test "x$HAVE_AVAHI" = "x1"], ENABLE_AVAHI=yes, ENABLE_AVAHI=no)
 AS_IF([test "x$HAVE_JACK" = "x1"], ENABLE_JACK=yes, ENABLE_JACK=no)
 AS_IF([test "x$HAVE_LIBASYNCNS" = "x1"], ENABLE_LIBASYNCNS=yes, ENABLE_LIBASYNCNS=no)
 AS_IF([test "x$HAVE_LIRC" = "x1"], ENABLE_LIRC=yes, ENABLE_LIRC=no)
+AS_IF([test "x$HAVE_XEN" = "x1"], ENABLE_XEN=yes, ENABLE_XEN=no)
 AS_IF([test "x$HAVE_DBUS" = "x1"], ENABLE_DBUS=yes, ENABLE_DBUS=no)
 AS_IF([test "x$HAVE_HAL" = "x1"], ENABLE_HAL=yes, ENABLE_HAL=no)
 AS_IF([test "x$HAVE_UDEV" = "x1"], ENABLE_UDEV=yes, ENABLE_UDEV=no)
@@ -1383,6 +1409,7 @@ echo "
     Enable Jack:                   ${ENABLE_JACK}
     Enable Async DNS:              ${ENABLE_LIBASYNCNS}
     Enable LIRC:                   ${ENABLE_LIRC}
+    Enable Xen PV driver:          ${ENABLE_XEN}
     Enable D-Bus:                  ${ENABLE_DBUS}
       Enable HAL:                  ${ENABLE_HAL}
       Enable BlueZ:                ${ENABLE_BLUEZ}
diff --git a/src/Makefile.am b/src/Makefile.am
index b07c60a3..532770d5 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -1159,6 +1159,12 @@ modlibexec_LTLIBRARIES += \
 		module-lirc.la
 endif
 
+if HAVE_XEN
+modlibexec_LTLIBRARIES += \
+		module-xenpv-sink.la
+endif
+
+
 if HAVE_EVDEV
 modlibexec_LTLIBRARIES += \
 		module-mmkbd-evdev.la
@@ -1269,6 +1275,7 @@ SYMDEF_FILES = \
 		module-zeroconf-discover-symdef.h \
 		module-bonjour-publish-symdef.h \
 		module-lirc-symdef.h \
+		module-xenpv-sink-symdef.h \
 		module-mmkbd-evdev-symdef.h \
 		module-http-protocol-tcp-symdef.h \
 		module-http-protocol-unix-symdef.h \
@@ -1668,6 +1675,15 @@ module_lirc_la_LDFLAGS = $(MODULE_LDFLAGS)
 module_lirc_la_LIBADD = $(MODULE_LIBADD) $(LIRC_LIBS)
 module_lirc_la_CFLAGS = $(AM_CFLAGS) $(LIRC_CFLAGS)
 
+
+# Xen PV driver
+
+module_xenpv_sink_la_SOURCES = modules/xen/module-xenpv-sink.c modules/xen/gntalloc.h modules/xen/gntdev.h
+module_xenpv_sink_la_LDFLAGS = $(MODULE_LDFLAGS)
+module_xenpv_sink_la_LIBADD = $(MODULE_LIBADD) $(XEN_LIBS)
+module_xenpv_sink_la_CFLAGS = $(AM_CFLAGS) $(XEN_CFLAGS) -I$(top_srcdir)/src/modules/xen
+
+
 # Linux evdev
 
 module_mmkbd_evdev_la_SOURCES = modules/module-mmkbd-evdev.c
diff --git a/src/modules/xen/gntalloc.h b/src/modules/xen/gntalloc.h
new file mode 100644
index 00000000..4a9921ce
--- /dev/null
+++ b/src/modules/xen/gntalloc.h
@@ -0,0 +1,88 @@
+/*
+ * This file is copied from the linux kernel headers. It defines the standard
+ * interface to the xen/gntalloc device.
+ *
+ */
+
+/******************************************************************************
+ * gntalloc.h
+ *
+ * Interface to /dev/xen/gntalloc.
+ *
+ * Author: Daniel De Graaf <dgdegra@tycho.nsa.gov>
+ *
+ * This file is in the public domain.
+ */
+
+#ifndef __LINUX_PUBLIC_GNTALLOC_H__
+#define __LINUX_PUBLIC_GNTALLOC_H__
+
+/*
+ * Allocates a new page and creates a new grant reference.
+ */
+#define IOCTL_GNTALLOC_ALLOC_GREF \
+_IOC(_IOC_NONE, 'G', 5, sizeof(struct ioctl_gntalloc_alloc_gref))
+struct ioctl_gntalloc_alloc_gref {
+	/* IN parameters */
+	/* The ID of the domain to be given access to the grants. */
+	uint16_t domid;
+	/* Flags for this mapping */
+	uint16_t flags;
+	/* Number of pages to map */
+	uint32_t count;
+	/* OUT parameters */
+	/* The offset to be used on a subsequent call to mmap(). */
+	uint64_t index;
+	/* The grant references of the newly created grant, one per page */
+	/* Variable size, depending on count */
+	uint32_t gref_ids[1];
+};
+
+#define GNTALLOC_FLAG_WRITABLE 1
+
+/*
+ * Deallocates the grant reference, allowing the associated page to be freed if
+ * no other domains are using it.
+ */
+#define IOCTL_GNTALLOC_DEALLOC_GREF \
+_IOC(_IOC_NONE, 'G', 6, sizeof(struct ioctl_gntalloc_dealloc_gref))
+struct ioctl_gntalloc_dealloc_gref {
+	/* IN parameters */
+	/* The offset returned in the map operation */
+	uint64_t index;
+	/* Number of references to unmap */
+	uint32_t count;
+};
+
+/*
+ * Sets up an unmap notification within the page, so that the other side can do
+ * cleanup if this side crashes. Required to implement cross-domain robust
+ * mutexes or close notification on communication channels.
+ *
+ * Each mapped page only supports one notification; multiple calls referring to
+ * the same page overwrite the previous notification. You must clear the
+ * notification prior to the IOCTL_GNTALLOC_DEALLOC_GREF if you do not want it
+ * to occur.
+ */
+#define IOCTL_GNTALLOC_SET_UNMAP_NOTIFY \
+_IOC(_IOC_NONE, 'G', 7, sizeof(struct ioctl_gntalloc_unmap_notify))
+struct ioctl_gntalloc_unmap_notify {
+	/* IN parameters */
+	/* Offset in the file descriptor for a byte within the page (same as
+	 * used in mmap). If using UNMAP_NOTIFY_CLEAR_BYTE, this is the byte to
+	 * be cleared. Otherwise, it can be any byte in the page whose
+	 * notification we are adjusting.
+	 */
+	uint64_t index;
+	/* Action(s) to take on unmap */
+	uint32_t action;
+	/* Event channel to notify */
+	uint32_t event_channel_port;
+};
+
+/* Clear (set to zero) the byte specified by index */
+#define UNMAP_NOTIFY_CLEAR_BYTE 0x1
+/* Send an interrupt on the indicated event channel */
+#define UNMAP_NOTIFY_SEND_EVENT 0x2
+
+#endif /* __LINUX_PUBLIC_GNTALLOC_H__ */
diff --git a/src/modules/xen/gntdev.h b/src/modules/xen/gntdev.h
new file mode 100644
index 00000000..7f65a381
--- /dev/null
+++ b/src/modules/xen/gntdev.h
@@ -0,0 +1,156 @@
+/*
+ * This file is copied from the linux kernel headers. It defines the standard
+ * interface to the xen/gntdev device.
+ *
+ */
+
+/******************************************************************************
+ * gntdev.h
+ *
+ * Interface to /dev/xen/gntdev.
+ *
+ * Copyright (c) 2007, D G Murray
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation; or, when distributed
+ * separately from the Linux kernel or incorporated into other
+ * software packages, subject to the following license:
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this source file (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy, modify,
+ * merge, publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#ifndef __LINUX_PUBLIC_GNTDEV_H__
+#define __LINUX_PUBLIC_GNTDEV_H__
+
+struct ioctl_gntdev_grant_ref {
+	/* The domain ID of the grant to be mapped. */
+	uint32_t domid;
+	/* The grant reference of the grant to be mapped. */
+	uint32_t ref;
+};
+
+/*
+ * Inserts the grant references into the mapping table of an instance
+ * of gntdev. N.B. This does not perform the mapping, which is deferred
+ * until mmap() is called with @index as the offset.
+ */
+#define IOCTL_GNTDEV_MAP_GRANT_REF \
+_IOC(_IOC_NONE, 'G', 0, sizeof(struct ioctl_gntdev_map_grant_ref))
+struct ioctl_gntdev_map_grant_ref {
+	/* IN parameters */
+	/* The number of grants to be mapped. */
+	uint32_t count;
+	uint32_t pad;
+	/* OUT parameters */
+	/* The offset to be used on a subsequent call to mmap(). */
+	uint64_t index;
+	/* Variable IN parameter. */
+	/* Array of grant references, of size @count. */
+	struct ioctl_gntdev_grant_ref refs[1];
+};
+
+/*
+ * Removes the grant references from the mapping table of an instance of
+ * of gntdev. N.B. munmap() must be called on the relevant virtual address(es)
+ * before this ioctl is called, or an error will result.
+ */
+#define IOCTL_GNTDEV_UNMAP_GRANT_REF \
+_IOC(_IOC_NONE, 'G', 1, sizeof(struct ioctl_gntdev_unmap_grant_ref))
+struct ioctl_gntdev_unmap_grant_ref {
+	/* IN parameters */
+	/* The offset was returned by the corresponding map operation. */
+	uint64_t index;
+	/* The number of pages to be unmapped. */
+	uint32_t count;
+	uint32_t pad;
+};
+
+/*
+ * Returns the offset in the driver's address space that corresponds
+ * to @vaddr. This can be used to perform a munmap(), followed by an
+ * UNMAP_GRANT_REF ioctl, where no state about the offset is retained by
+ * the caller. The number of pages that were allocated at the same time as
+ * @vaddr is returned in @count.
+ *
+ * N.B. Where more than one page has been mapped into a contiguous range, the
+ *      supplied @vaddr must correspond to the start of the range; otherwise
+ *      an error will result. It is only possible to munmap() the entire
+ *      contiguously-allocated range at once, and not any subrange thereof.
+ */
+#define IOCTL_GNTDEV_GET_OFFSET_FOR_VADDR \
+_IOC(_IOC_NONE, 'G', 2, sizeof(struct ioctl_gntdev_get_offset_for_vaddr))
+struct ioctl_gntdev_get_offset_for_vaddr {
+	/* IN parameters */
+	/* The virtual address of the first mapped page in a range. */
+	uint64_t vaddr;
+	/* OUT parameters */
+	/* The offset that was used in the initial mmap() operation. */
+	uint64_t offset;
+	/* The number of pages mapped in the VM area that begins at @vaddr. */
+	uint32_t count;
+	uint32_t pad;
+};
+
+/*
+ * Sets the maximum number of grants that may mapped at once by this gntdev
+ * instance.
+ *
+ * N.B. This must be called before any other ioctl is performed on the device.
+ */
+#define IOCTL_GNTDEV_SET_MAX_GRANTS \
+_IOC(_IOC_NONE, 'G', 3, sizeof(struct ioctl_gntdev_set_max_grants))
+struct ioctl_gntdev_set_max_grants {
+	/* IN parameter */
+	/* The maximum number of grants that may be mapped at once. */
+	uint32_t count;
+};
+
+/*
+ * Sets up an unmap notification within the page, so that the other side can do
+ * cleanup if this side crashes. Required to implement cross-domain robust
+ * mutexes or close notification on communication channels.
+ *
+ * Each mapped page only supports one notification; multiple calls referring to
+ * the same page overwrite the previous notification. You must clear the
+ * notification prior to the IOCTL_GNTALLOC_DEALLOC_GREF if you do not want it
+ * to occur.
+ */
+#define IOCTL_GNTDEV_SET_UNMAP_NOTIFY \
+_IOC(_IOC_NONE, 'G', 7, sizeof(struct ioctl_gntdev_unmap_notify))
+struct ioctl_gntdev_unmap_notify {
+	/* IN parameters */
+	/* Offset in the file descriptor for a byte within the page (same as
+	 * used in mmap). If using UNMAP_NOTIFY_CLEAR_BYTE, this is the byte to
+	 * be cleared. Otherwise, it can be any byte in the page whose
+	 * notification we are adjusting.
+	 */
+	uint64_t index;
+	/* Action(s) to take on unmap */
+	uint32_t action;
+	/* Event channel to notify */
+	uint32_t event_channel_port;
+};
+
+/* Clear (set to zero) the byte specified by index */
+#define UNMAP_NOTIFY_CLEAR_BYTE 0x1
+/* Send an interrupt on the indicated event channel */
+#define UNMAP_NOTIFY_SEND_EVENT 0x2
+
+#endif /* __LINUX_PUBLIC_GNTDEV_H__ */
diff --git a/src/modules/xen/module-xenpv-sink.c b/src/modules/xen/module-xenpv-sink.c
new file mode 100644
index 00000000..086917c0
--- /dev/null
+++ b/src/modules/xen/module-xenpv-sink.c
@@ -0,0 +1,803 @@
+/***
+  This file is part of PulseAudio.
+
+  Copyright 2004-2006 Lennart Poettering
+  Copyright 2011 George Boutsioukis for Xen
+
+  PulseAudio 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.
+
+  PulseAudio 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 Lesser General Public License
+  along with PulseAudio; if not, write to the Free Software
+  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+  USA.
+***/
+
+#include "config.h"
+
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <limits.h>
+#include <sys/ioctl.h>
+#include <poll.h>
+#include <time.h>
+
+#include <pulse/xmalloc.h>
+
+#include <pulsecore/core-error.h>
+#include <pulsecore/sink.h>
+#include <pulsecore/module.h>
+#include <pulsecore/core-util.h>
+#include <pulsecore/modargs.h>
+#include <pulsecore/log.h>
+#include <pulsecore/thread.h>
+#include <pulsecore/thread-mq.h>
+#include <pulsecore/rtpoll.h>
+
+#include <sys/select.h>
+#include <sys/mman.h>
+#include <xenctrl.h>
+#include <xs.h>
+
+#include "module-xenpv-sink-symdef.h"
+#include "gntalloc.h"
+#include "gntdev.h"
+
+PA_MODULE_AUTHOR("Giorgos Boutsioukis");
+PA_MODULE_DESCRIPTION("Xen PV audio sink");
+PA_MODULE_VERSION(PACKAGE_VERSION);
+PA_MODULE_LOAD_ONCE(FALSE);
+PA_MODULE_USAGE(
+        "sink_name=<name for the sink> "
+        "sink_properties=<properties for the sink> "
+        "format=<sample format> "
+        "rate=<sample rate>"
+        "channels=<number of channels> "
+        "channel_map=<channel map>");
+
+#define DEFAULT_SINK_NAME "xenpv_output"
+#define DEFAULT_FILE_NAME "xenpv_output"
+
+#define STATE_UNDEFINED 9999
+
+int device_id = -1;
+enum xenbus_state {
+	XenbusStateUnknown      = 0,
+	XenbusStateInitialising = 1,
+	XenbusStateInitWait     = 2,
+	XenbusStateInitialised  = 3,
+	XenbusStateConnected    = 4,
+	XenbusStateClosing      = 5,
+	XenbusStateClosed       = 6,
+	XenbusStateReconfiguring = 7,
+	XenbusStateReconfigured  = 8
+};
+
+static const char* xenbus_names[] = {
+    "XenbusStateUnknown",
+    "XenbusStateInitialising",
+    "XenbusStateInitWait",
+    "XenbusStateInitialised",
+    "XenbusStateConnected",
+    "XenbusStateClosing",
+    "XenbusStateClosed",
+    "XenbusStateReconfiguring",
+    "XenbusStateReconfigured"
+};
+
+struct userdata {
+    pa_core *core;
+    pa_module *module;
+    pa_sink *sink;
+
+    pa_thread *thread;
+    pa_thread_mq thread_mq;
+    pa_rtpoll *rtpoll;
+
+    pa_memchunk memchunk;
+
+    pa_rtpoll_item *rtpoll_item;
+
+    int write_type;
+};
+
+pa_sample_spec ss;
+pa_channel_map map;
+
+/* just to test non- frame-aligned size */
+#define BUFSIZE 2047
+
+struct ring {
+    uint32_t cons_indx, prod_indx;
+    uint32_t usable_buffer_space; /* kept here for convenience */
+    uint8_t buffer[BUFSIZE];
+} *ioring;
+
+static const char* const valid_modargs[] = {
+    "sink_name",
+    "sink_properties",
+    "file",
+    "format",
+    "rate",
+    "channels",
+    "channel_map",
+    NULL
+};
+
+/* Xen globals*/
+xc_interface* xch;
+xc_evtchn* xce;
+evtchn_port_or_error_t xen_evtchn_port;
+static struct xs_handle *xsh;
+struct ioctl_gntalloc_alloc_gref gref;
+
+static int register_backend_state_watch(void);
+static int wait_for_backend_state_change(void);
+static int alloc_gref(struct ioctl_gntalloc_alloc_gref *gref, void **addr);
+static int ring_write(struct ring *r, void *src, int length);
+static int publish_spec(pa_sample_spec *ss);
+static int read_backend_default_spec(pa_sample_spec *ss);
+static int publish_param(const char *paramname, const char *value);
+static int publish_param_int(const char *paramname, const int value);
+static char* read_param(const char *paramname);
+
+static int set_state(int state) {
+    static int current_state = 0;
+    pa_log_debug("State transition %s->%s\n",
+            xenbus_names[current_state], xenbus_names[state]);
+
+    publish_param_int("state", state);
+    current_state = state;
+    return state;
+}
+#define NEGOTIATION_ERROR 2
+#define NEGOTIATION_OK 1
+
+/* negotiation callbacks */
+static int state_unknown_cb() {
+    pa_log_debug("Xen audio sink: Backend state was XenbusStateUnknown\n");
+    set_state(XenbusStateInitialising);
+
+    return 0;
+}
+
+static int state_initialising_cb() {
+    pa_log_debug("Xen audio sink: Backend state was XenbusStateInitialising\n");
+    set_state(XenbusStateInitialised);
+    return 0;
+}
+
+static int state_initwait_cb() {
+    pa_log_debug("Xen audio sink: Backend state was XenbusStateInitWait\n");
+    return 0;
+}
+
+static int state_initialised_cb() {
+    pa_log_debug("Xen audio sink: Backend state was XenbusStateInitialised\n");
+    /*Remind the backend we are ready*/
+    set_state(XenbusStateInitialised);
+    return 0;
+}
+
+static int state_connected_cb() {
+    /* The backend accepted our parameters, sweet! */
+    set_state(XenbusStateConnected);
+    pa_log_debug("Xen audio sink: Backend state was XenbusStateConnected\n");
+    return NEGOTIATION_OK;
+}
+
+static int state_closing_cb() {
+    pa_log_debug("Xen audio sink: Backend state was XenbusStateClosing\n");
+    return 0;
+}
+
+static int state_closed_cb() {
+    pa_log_debug("Xen audio sink: Backend state was XenbusStateClosed\n");
+    return 0;
+}
+
+static int state_reconfiguring_cb() {
+    /* The backend rejected our sample spec */
+    pa_log_debug("Xen audio sink: Backend state was XenbusStateReconfiguring\n");
+    /* fall back to the backend's default parameters*/
+    read_backend_default_spec(&ss);
+    /* backend should accept these now */
+    publish_spec(&ss);
+    set_state(XenbusStateInitialised);
+    return 0;
+}
+
+static int state_reconfigured_cb() {
+    pa_log_debug("Xen audio sink: Backend state was XenbusStateReconfigured\n");
+    return 0;
+}
+
+int (*state_callbacks[9])(void) = {
+    state_unknown_cb,
+    state_initialising_cb,
+    state_initwait_cb,
+    state_initialised_cb,
+    state_connected_cb,
+    state_closing_cb,
+    state_closed_cb,
+    state_reconfiguring_cb,
+    state_reconfigured_cb
+};
+
+static void xen_cleanup() {
+    char keybuf[64];
+    /*XXX hardcoded*/
+    munmap((void*)gref.index, 4096);
+
+    set_state(XenbusStateClosing);
+    /* send one last event to unblock the backend */
+    xc_evtchn_notify(xce, xen_evtchn_port);
+    /* close xen interfaces */
+    xc_evtchn_close(xce);
+    xc_interface_close(xch);
+
+    /* delete xenstore keys */
+    publish_param_int("state", XenbusStateClosed);
+    snprintf(keybuf, sizeof(keybuf), "device/audio/%d", device_id);
+    xs_rm(xsh, 0, keybuf);
+    xs_daemon_close(xsh);
+}
+
+static int sink_process_msg(pa_msgobject *o, int code, void *data, int64_t offset, pa_memchunk *chunk) {
+    struct userdata *u = PA_SINK(o)->userdata;
+
+    switch (code) {
+
+        case PA_SINK_MESSAGE_GET_LATENCY: {
+            size_t n = 0;
+
+            n += u->memchunk.length;
+
+            *((pa_usec_t*) data) = pa_bytes_to_usec(n, &u->sink->sample_spec);
+            return 0;
+        }
+    }
+
+    return pa_sink_process_msg(o, code, data, offset, chunk);
+}
+
+static int process_render(struct userdata *u) {
+    pa_assert(u);
+
+
+    if (u->memchunk.length <= 0)
+        pa_sink_render(u->sink, ioring->usable_buffer_space, &u->memchunk);
+
+
+    pa_assert(u->memchunk.length > 0);
+
+    xc_evtchn_notify(xce, xen_evtchn_port);
+    for (;;) {
+        ssize_t l;
+        void *p;
+
+        p = pa_memblock_acquire(u->memchunk.memblock);
+	    /* xen: write data to ring buffer & notify backend */
+        l = ring_write(ioring, (uint8_t*)p + u->memchunk.index, u->memchunk.length);
+
+        pa_memblock_release(u->memchunk.memblock);
+
+        pa_assert(l != 0);
+
+        if (l < 0) {
+            if (errno == EINTR)
+                continue;
+            else if (errno == EAGAIN)
+                return 0;
+            else {
+                pa_log("Failed to write data to FIFO: %s", pa_cstrerror(errno));
+                return -1;
+            }
+
+        } else {
+
+            u->memchunk.index += (size_t) l;
+            u->memchunk.length -= (size_t) l;
+
+            if (u->memchunk.length <= 0) {
+                pa_memblock_unref(u->memchunk.memblock);
+                pa_memchunk_reset(&u->memchunk);
+            }
+        }
+
+        return 0;
+    }
+}
+
+static void thread_func(void *userdata) {
+    struct userdata *u = userdata;
+
+    pa_assert(u);
+
+    pa_log_debug("Thread starting up");
+
+    pa_thread_mq_install(&u->thread_mq);
+
+    for(;;){
+        struct pollfd *pollfd;
+        int ret;
+
+        pollfd = pa_rtpoll_item_get_pollfd(u->rtpoll_item, NULL);
+
+        /* Render some data and write it to the fifo */
+        if (PA_SINK_IS_OPENED(u->sink->thread_info.state)) {
+
+            if (u->sink->thread_info.rewind_requested)
+                pa_sink_process_rewind(u->sink, 0);
+
+            if (pollfd->revents) {
+                if (process_render(u) < 0)
+                    goto fail;
+
+                pollfd->revents = 0;
+            }
+        }
+
+        /* Hmm, nothing to do. Let's sleep */
+
+        pollfd->events = (short) (u->sink->thread_info.state == PA_SINK_RUNNING ? POLLOUT : 0);
+
+        if ((ret = pa_rtpoll_run(u->rtpoll, TRUE)) < 0)
+            goto fail;
+
+        if (ret == 0)
+            goto finish;
+
+        pollfd = pa_rtpoll_item_get_pollfd(u->rtpoll_item, NULL);
+
+        if (pollfd->revents & ~POLLOUT) {
+            pa_log("FIFO shutdown.");
+            goto fail;
+        }
+    }
+
+fail:
+    /* If this was no regular exit from the loop we have to continue
+     * processing messages until we received PA_MESSAGE_SHUTDOWN */
+    pa_asyncmsgq_post(u->thread_mq.outq, PA_MSGOBJECT(u->core), PA_CORE_MESSAGE_UNLOAD_MODULE, u->module, 0, NULL, NULL);
+    pa_asyncmsgq_wait_for(u->thread_mq.inq, PA_MESSAGE_SHUTDOWN);
+    pa_log_debug("Shutting down Xen...");
+    xen_cleanup();
+finish:
+    pa_log_debug("Thread shutting down");
+}
+
+int pa__init(pa_module*m) {
+
+    struct userdata *u;
+    pa_modargs *ma;
+    pa_sink_new_data data;
+    int backend_state;
+    int ret;
+    char strbuf[100];
+
+    pa_assert(m);
+
+    if (!(ma = pa_modargs_new(m->argument, valid_modargs))) {
+        pa_log("Failed to parse module arguments.");
+        goto fail;
+    }
+
+    ss = m->core->default_sample_spec;
+    map = m->core->default_channel_map;
+
+    /* user arguments override these */
+    if (pa_modargs_get_sample_spec_and_channel_map(ma, &ss, &map, PA_CHANNEL_MAP_DEFAULT) < 0) {
+        pa_log("Invalid sample format specification or channel map");
+        return 1;
+    }
+
+    /* Xen Basic init */
+    xsh = xs_domain_open();
+    if (xsh==NULL) {
+        pa_log("xs_domain_open failed");
+        goto fail;
+    }
+    set_state(XenbusStateUnknown);
+
+    xch = xc_interface_open(NULL, NULL, 0);
+    if (xch==0) {
+        pa_log("xc_interface_open failed");
+        goto fail;
+    }
+
+    xce = xc_evtchn_open(NULL, 0);
+    if (xce==0) {
+        pa_log("xc_evtchn_open failed");
+        goto fail;
+    }
+
+    /* use only dom0 as the backend for now */
+    xen_evtchn_port = xc_evtchn_bind_unbound_port(xce, 0);
+    if (xen_evtchn_port == 0) {
+        pa_log("xc_evtchn_bind_unbound_port failed");
+    }
+
+    /* get grant reference & map locally */
+    if (alloc_gref(&gref, (void**)&ioring)) {
+       pa_log("alloc_gref failed");
+    };
+    device_id = 0; /* hardcoded for now */
+
+    if (register_backend_state_watch()) {
+        pa_log("Xen sink: register xenstore watch failed");
+    };
+
+    publish_param_int("event-channel", xen_evtchn_port);
+    publish_param_int("ring-ref", gref.gref_ids[0]);
+
+    /* let's ask for something absurd and deal with rejection */
+    ss.rate = 192000;
+
+    publish_spec(&ss);
+
+    ret=0;
+    while (!ret) {
+        backend_state = wait_for_backend_state_change();
+        if (backend_state == STATE_UNDEFINED) {
+            pa_log("Xen Backend is taking long to respond, still waiting...");
+            continue;
+        } else if (backend_state == -1) {
+            pa_log("Error while waiting for backend: %s", strerror(errno));
+            break;
+            goto fail;
+        }
+        ret = state_callbacks[backend_state]();
+    }
+    if (ret!=NEGOTIATION_OK) {
+        pa_log("Negotiation with Xen backend failed!");
+        return 1;
+    }
+
+    pa_sample_spec_snprint(strbuf, 100, &ss);
+    pa_log_debug("Negotiation ended, the result was: %s", strbuf);
+
+    /* End of Phase 2, begin playback cycle */
+
+    u = pa_xnew0(struct userdata, 1);
+    u->core = m->core;
+    u->module = m;
+    m->userdata = u;
+    pa_memchunk_reset(&u->memchunk);
+    u->rtpoll = pa_rtpoll_new();
+    pa_thread_mq_init(&u->thread_mq, m->core->mainloop, u->rtpoll);
+    u->write_type = 0;
+
+    /* init ring buffer */
+    ioring->prod_indx = ioring->cons_indx = 0;
+    ioring->usable_buffer_space = BUFSIZE - BUFSIZE % pa_frame_size(&ss);
+
+    pa_sink_new_data_init(&data);
+    data.driver = __FILE__;
+    data.module = m;
+    pa_sink_new_data_set_name(&data, pa_modargs_get_value(ma, "sink_name", DEFAULT_SINK_NAME));
+    pa_proplist_sets(data.proplist, PA_PROP_DEVICE_STRING, "xensink");
+    pa_proplist_setf(data.proplist, PA_PROP_DEVICE_DESCRIPTION, "Xen PV audio sink");
+    pa_sink_new_data_set_sample_spec(&data, &ss);
+    pa_sink_new_data_set_channel_map(&data, &map);
+
+    if (pa_modargs_get_proplist(ma, "sink_properties", data.proplist, PA_UPDATE_REPLACE) < 0) {
+        pa_log("Invalid properties");
+        pa_sink_new_data_done(&data);
+        goto fail;
+    }
+
+    u->sink = pa_sink_new(m->core, &data, PA_SINK_LATENCY);
+    pa_sink_new_data_done(&data);
+
+    if (!u->sink) {
+        pa_log("Failed to create sink.");
+        goto fail;
+    }
+
+    u->sink->parent.process_msg = sink_process_msg;
+    u->sink->userdata = u;
+
+    pa_sink_set_asyncmsgq(u->sink, u->thread_mq.inq);
+    pa_sink_set_rtpoll(u->sink, u->rtpoll);
+    pa_sink_set_max_request(u->sink, ioring->usable_buffer_space);
+    pa_sink_set_fixed_latency(u->sink, pa_bytes_to_usec(ioring->usable_buffer_space, &u->sink->sample_spec));
+
+    u->rtpoll_item = pa_rtpoll_item_new(u->rtpoll, PA_RTPOLL_NEVER, 1);
+
+    if (!(u->thread = pa_thread_new("xenpv-sink", thread_func, u))) {
+        pa_log("Failed to create thread.");
+        goto fail;
+    }
+
+    pa_sink_put(u->sink);
+
+    pa_modargs_free(ma);
+
+    return 0;
+
+fail:
+    if (ma)
+        pa_modargs_free(ma);
+
+    pa__done(m);
+
+    return -1;
+}
+
+int pa__get_n_used(pa_module *m) {
+    struct userdata *u;
+
+    pa_assert(m);
+    pa_assert_se(u = m->userdata);
+
+    return pa_sink_linked_by(u->sink);
+}
+
+void pa__done(pa_module*m) {
+    struct userdata *u;
+
+    pa_assert(m);
+
+    if (!(u = m->userdata))
+        return;
+
+    if (u->sink)
+        pa_sink_unlink(u->sink);
+
+    if (u->thread) {
+        pa_asyncmsgq_send(u->thread_mq.inq, NULL, PA_MESSAGE_SHUTDOWN, NULL, 0, NULL);
+        pa_thread_free(u->thread);
+    }
+
+    pa_thread_mq_done(&u->thread_mq);
+
+    if (u->sink)
+        pa_sink_unref(u->sink);
+
+    if (u->memchunk.memblock)
+       pa_memblock_unref(u->memchunk.memblock);
+
+    if (u->rtpoll_item)
+        pa_rtpoll_item_free(u->rtpoll_item);
+
+    if (u->rtpoll)
+        pa_rtpoll_free(u->rtpoll);
+
+    pa_xfree(u);
+
+    xen_cleanup();
+
+}
+
+
+static int alloc_gref(struct ioctl_gntalloc_alloc_gref *gref_, void **addr) {
+    int alloc_fd, dev_fd, rv;
+
+    alloc_fd = open("/dev/xen/gntalloc", O_RDWR);
+    if (alloc_fd<=0) {
+        perror("Could not open /dev/xen/gntalloc! Have you loaded the xen_gntalloc module?");
+        return 1;
+    }
+
+    dev_fd = open("/dev/xen/gntdev", O_RDWR);
+    if (dev_fd<=0) {
+        perror("Could not open /dev/xen/gntdev! Have you loaded the xen_gntdev module?");
+        return 1;
+    }
+
+    /* use dom0 */
+    gref_->domid = 0;
+    gref_->flags = GNTALLOC_FLAG_WRITABLE;
+    gref_->count = 1;
+
+    rv = ioctl(alloc_fd, IOCTL_GNTALLOC_ALLOC_GREF, gref_);
+    if (rv) {
+        pa_log_debug("Xen audio sink: src-add error: %s (rv=%d)\n", strerror(errno), rv);
+        return rv;
+    }
+
+    /*addr=NULL(default),length, prot,             flags,    fd,         offset*/
+    *addr = mmap(0, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, alloc_fd, gref_->index);
+    if (*addr == MAP_FAILED) {
+        *addr = 0;
+        pa_log_debug("Xen audio sink: mmap'ing shared page failed\n");
+        return rv;
+    }
+
+    pa_log_debug("Xen audio sink: Got grant #%d. Mapped locally at %Ld=%p\n",
+            gref_->gref_ids[0], (long long)gref_->index, *addr);
+
+    /* skip this for now
+       struct ioctl_gntalloc_unmap_notify uarg = {
+       .index = gref->index + offsetof(struct shr_page, notifies[0]),
+       .action = UNMAP_NOTIFY_CLEAR_BYTE
+       };
+
+       rv = ioctl(a_fd, IOCTL_GNTALLOC_SET_UNMAP_NOTIFY, &uarg);
+       if (rv)
+       pa_log_debug("gntalloc unmap notify error: %s (rv=%d)\n", strerror(errno), rv);
+       */
+
+    close(alloc_fd);
+    close(dev_fd);
+
+    return rv;
+}
+
+#define RING_FREE_BYTES ((r->usable_buffer_space - (r->prod_indx-r->cons_indx) -1) % r->usable_buffer_space)
+static int ring_write(struct ring *r, void *src, int length) {
+    int full = 0;
+    for (;;) {
+        /* free space may be split over the end of the buffer */
+        int first_chunk_size = (r->usable_buffer_space-r->prod_indx);
+        int second_chunk_size = (r->cons_indx>=r->prod_indx)? (r->cons_indx) : 0;
+        int l, fl, sl;
+
+        /* full? */
+        if (RING_FREE_BYTES==0) {
+            /*XXX hardcoded*/
+            if (full>=100) {
+                errno = EINTR;
+                return -1;
+            }
+            /*XXX hardcoded */
+            usleep(1000);
+            /* should return in 100ms max; definitely not midstream */
+            full++;
+            continue;
+        }
+
+        /* calculate lengths in case of a split buffer */
+        l = PA_MIN((int)RING_FREE_BYTES, length);
+        fl = PA_MIN(l, first_chunk_size);
+        sl = PA_MIN(l-fl, second_chunk_size);
+
+        memcpy(r->buffer+r->prod_indx, src, fl);
+        if (sl)
+            memcpy(r->buffer, ((char*)src)+fl, sl);
+        r->prod_indx = (r->prod_indx+fl+sl) % r->usable_buffer_space;
+
+        return sl+fl;
+    }
+}
+
+static int publish_param(const char *paramname, const char *value) {
+    char keybuf[128], valbuf[32];
+
+    snprintf(keybuf, sizeof keybuf, "device/audio/%d/%s", device_id, paramname);
+    snprintf(valbuf, sizeof valbuf, "%s", value);
+    return xs_write(xsh, 0, keybuf, valbuf, strlen(valbuf));
+}
+
+static int publish_param_int(const char *paramname, const int value) {
+    char keybuf[128], valbuf[32];
+    snprintf(keybuf, sizeof keybuf, "device/audio/%d/%s", device_id, paramname);
+    snprintf(valbuf, sizeof valbuf, "%d", value);
+    return xs_write(xsh, 0, keybuf, valbuf, strlen(valbuf));
+}
+
+static char* read_param(const char *paramname) {
+    char keybuf[128];
+    unsigned int len;
+    int my_domid;
+
+    my_domid = atoi(xs_read(xsh, 0, "domid", &len));
+    snprintf(keybuf, sizeof(keybuf), "/local/domain/0/backend/audio/%d/%d/%s", my_domid, device_id, paramname);
+    /* remember to free lvalue! */
+    return xs_read(xsh, 0, keybuf, &len);
+}
+
+
+static int publish_spec(pa_sample_spec *sample_spec) {
+    /* Publish spec and set state to XenbusStateInitWait*/
+    int ret;
+
+    ret = publish_param("format", pa_sample_format_to_string(sample_spec->format));
+    ret += publish_param_int("rate", sample_spec->rate);
+    ret += publish_param_int("channels", sample_spec->channels);
+
+    return ret;
+}
+
+
+static int read_backend_default_spec(pa_sample_spec *sample_spec) {
+    /* Read spec from backend */
+    char *out;
+
+    out = read_param("default-format");
+    sample_spec->format = pa_parse_sample_format(out);
+    free(out);
+
+    out = read_param("default-rate");
+    sample_spec->rate = atoi(out);
+    free(out);
+
+    out = read_param("default-channels");
+    sample_spec->channels = atoi(out);
+    free(out);
+
+    return 0;
+}
+
+static int register_backend_state_watch() {
+    char keybuf[128];
+    int my_domid;
+    unsigned int len;
+
+    my_domid = atoi(xs_read(xsh, 0, "domid", &len));
+    snprintf(keybuf, sizeof(keybuf), "/local/domain/0/backend/audio/%d/%d/state", my_domid, device_id);
+    if (!xs_watch(xsh, keybuf, "xenpvaudiofrontendsinktoken")) {
+        perror("xs_watch failed");
+        return -EINVAL;
+    }
+    return 0;
+}
+
+static int wait_for_backend_state_change() {
+    char keybuf[128];
+    int my_domid;
+    unsigned int len;
+
+    int backend_state;
+    int seconds;
+    char *buf, **vec;
+    int ret;
+
+    int xs_fd;
+    struct timeval tv;
+	fd_set watch_fdset;
+    int start, now;
+
+    backend_state = STATE_UNDEFINED;
+    xs_fd = xs_fileno(xsh);
+    start = now = time(NULL);
+
+    my_domid = atoi(xs_read(xsh, 0, "domid", &len));
+    snprintf(keybuf, sizeof(keybuf), "/local/domain/0/backend/audio/%d/%d/state", my_domid, device_id);
+
+    /*XXX: hardcoded */
+    seconds = 10;
+	do {
+		tv.tv_usec = 0;
+		tv.tv_sec = (start + seconds) - now;
+		FD_ZERO(&watch_fdset);
+		FD_SET(xs_fd, &watch_fdset);
+        ret=select(xs_fd + 1, &watch_fdset, NULL, NULL, &tv);
+
+        if (ret==-1)
+            /* error */
+            return -1;
+        else if (ret) {
+
+			/* Read the watch to drain the buffer */
+			vec = xs_read_watch(xsh, &len);
+
+            buf = xs_read(xsh, XBT_NULL, vec[0], &len);
+            if (buf == 0) {
+                /* usually means that the backend isn't there yet */
+                continue;
+            };
+            backend_state = atoi(buf);
+
+            free(buf);
+            free(vec);
+		}
+        /* else: timeout */
+	} while (backend_state == STATE_UNDEFINED && \
+            (now = time(NULL)) < start + seconds);
+
+    return backend_state;
+}