1/******************************************************************************
2 * xenbus_comms.c
3 *
4 * Low level code to talks to Xen Store: ringbuffer and event channel.
5 *
6 * Copyright (C) 2005 Rusty Russell, IBM Corporation
7 *
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License version 2
10 * as published by the Free Software Foundation; or, when distributed
11 * separately from the Linux kernel or incorporated into other
12 * software packages, subject to the following license:
13 *
14 * Permission is hereby granted, free of charge, to any person obtaining a copy
15 * of this source file (the "Software"), to deal in the Software without
16 * restriction, including without limitation the rights to use, copy, modify,
17 * merge, publish, distribute, sublicense, and/or sell copies of the Software,
18 * and to permit persons to whom the Software is furnished to do so, subject to
19 * the following conditions:
20 *
21 * The above copyright notice and this permission notice shall be included in
22 * all copies or substantial portions of the Software.
23 *
24 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
25 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
26 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
27 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
28 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
29 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
30 * IN THE SOFTWARE.
31 */
32
33#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
34
35#include <linux/wait.h>
36#include <linux/interrupt.h>
37#include <linux/sched.h>
38#include <linux/err.h>
39#include <xen/xenbus.h>
40#include <asm/xen/hypervisor.h>
41#include <xen/events.h>
42#include <xen/page.h>
43#include "xenbus_comms.h"
44
45static int xenbus_irq;
46
47static DECLARE_WORK(probe_work, xenbus_probe);
48
49static DECLARE_WAIT_QUEUE_HEAD(xb_waitq);
50
51static irqreturn_t wake_waiting(int irq, void *unused)
52{
53	if (unlikely(xenstored_ready == 0)) {
54		xenstored_ready = 1;
55		schedule_work(&probe_work);
56	}
57
58	wake_up(&xb_waitq);
59	return IRQ_HANDLED;
60}
61
62static int check_indexes(XENSTORE_RING_IDX cons, XENSTORE_RING_IDX prod)
63{
64	return ((prod - cons) <= XENSTORE_RING_SIZE);
65}
66
67static void *get_output_chunk(XENSTORE_RING_IDX cons,
68			      XENSTORE_RING_IDX prod,
69			      char *buf, uint32_t *len)
70{
71	*len = XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(prod);
72	if ((XENSTORE_RING_SIZE - (prod - cons)) < *len)
73		*len = XENSTORE_RING_SIZE - (prod - cons);
74	return buf + MASK_XENSTORE_IDX(prod);
75}
76
77static const void *get_input_chunk(XENSTORE_RING_IDX cons,
78				   XENSTORE_RING_IDX prod,
79				   const char *buf, uint32_t *len)
80{
81	*len = XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(cons);
82	if ((prod - cons) < *len)
83		*len = prod - cons;
84	return buf + MASK_XENSTORE_IDX(cons);
85}
86
87/**
88 * xb_write - low level write
89 * @data: buffer to send
90 * @len: length of buffer
91 *
92 * Returns 0 on success, error otherwise.
93 */
94int xb_write(const void *data, unsigned len)
95{
96	struct xenstore_domain_interface *intf = xen_store_interface;
97	XENSTORE_RING_IDX cons, prod;
98	int rc;
99
100	while (len != 0) {
101		void *dst;
102		unsigned int avail;
103
104		rc = wait_event_interruptible(
105			xb_waitq,
106			(intf->req_prod - intf->req_cons) !=
107			XENSTORE_RING_SIZE);
108		if (rc < 0)
109			return rc;
110
111		/* Read indexes, then verify. */
112		cons = intf->req_cons;
113		prod = intf->req_prod;
114		if (!check_indexes(cons, prod)) {
115			intf->req_cons = intf->req_prod = 0;
116			return -EIO;
117		}
118
119		dst = get_output_chunk(cons, prod, intf->req, &avail);
120		if (avail == 0)
121			continue;
122		if (avail > len)
123			avail = len;
124
125		/* Must write data /after/ reading the consumer index. */
126		mb();
127
128		memcpy(dst, data, avail);
129		data += avail;
130		len -= avail;
131
132		/* Other side must not see new producer until data is there. */
133		wmb();
134		intf->req_prod += avail;
135
136		/* Implies mb(): other side will see the updated producer. */
137		notify_remote_via_evtchn(xen_store_evtchn);
138	}
139
140	return 0;
141}
142
143int xb_data_to_read(void)
144{
145	struct xenstore_domain_interface *intf = xen_store_interface;
146	return (intf->rsp_cons != intf->rsp_prod);
147}
148
149int xb_wait_for_data_to_read(void)
150{
151	return wait_event_interruptible(xb_waitq, xb_data_to_read());
152}
153
154int xb_read(void *data, unsigned len)
155{
156	struct xenstore_domain_interface *intf = xen_store_interface;
157	XENSTORE_RING_IDX cons, prod;
158	int rc;
159
160	while (len != 0) {
161		unsigned int avail;
162		const char *src;
163
164		rc = xb_wait_for_data_to_read();
165		if (rc < 0)
166			return rc;
167
168		/* Read indexes, then verify. */
169		cons = intf->rsp_cons;
170		prod = intf->rsp_prod;
171		if (!check_indexes(cons, prod)) {
172			intf->rsp_cons = intf->rsp_prod = 0;
173			return -EIO;
174		}
175
176		src = get_input_chunk(cons, prod, intf->rsp, &avail);
177		if (avail == 0)
178			continue;
179		if (avail > len)
180			avail = len;
181
182		/* Must read data /after/ reading the producer index. */
183		rmb();
184
185		memcpy(data, src, avail);
186		data += avail;
187		len -= avail;
188
189		/* Other side must not see free space until we've copied out */
190		mb();
191		intf->rsp_cons += avail;
192
193		pr_debug("Finished read of %i bytes (%i to go)\n", avail, len);
194
195		/* Implies mb(): other side will see the updated consumer. */
196		notify_remote_via_evtchn(xen_store_evtchn);
197	}
198
199	return 0;
200}
201
202/**
203 * xb_init_comms - Set up interrupt handler off store event channel.
204 */
205int xb_init_comms(void)
206{
207	struct xenstore_domain_interface *intf = xen_store_interface;
208
209	if (intf->req_prod != intf->req_cons)
210		pr_err("request ring is not quiescent (%08x:%08x)!\n",
211		       intf->req_cons, intf->req_prod);
212
213	if (intf->rsp_prod != intf->rsp_cons) {
214		pr_warn("response ring is not quiescent (%08x:%08x): fixing up\n",
215			intf->rsp_cons, intf->rsp_prod);
216		/* breaks kdump */
217		if (!reset_devices)
218			intf->rsp_cons = intf->rsp_prod;
219	}
220
221	if (xenbus_irq) {
222		/* Already have an irq; assume we're resuming */
223		rebind_evtchn_irq(xen_store_evtchn, xenbus_irq);
224	} else {
225		int err;
226		err = bind_evtchn_to_irqhandler(xen_store_evtchn, wake_waiting,
227						0, "xenbus", &xb_waitq);
228		if (err < 0) {
229			pr_err("request irq failed %i\n", err);
230			return err;
231		}
232
233		xenbus_irq = err;
234	}
235
236	return 0;
237}
238
239void xb_deinit_comms(void)
240{
241	unbind_from_irqhandler(xenbus_irq, &xb_waitq);
242	xenbus_irq = 0;
243}
244