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 #include <linux/wait.h>
34 #include <linux/interrupt.h>
35 #include <linux/sched.h>
36 #include <linux/err.h>
37 #include <xen/xenbus.h>
38 #include <asm/xen/hypervisor.h>
39 #include <xen/events.h>
40 #include <xen/page.h>
41 #include "xenbus_comms.h"
42
43 static int xenbus_irq;
44
45 static DECLARE_WORK(probe_work, xenbus_probe);
46
47 static DECLARE_WAIT_QUEUE_HEAD(xb_waitq);
48
49 static irqreturn_t wake_waiting(int irq, void *unused)
50 {
51 if (unlikely(xenstored_ready == 0)) {
52 xenstored_ready = 1;
53 schedule_work(&probe_work);
54 }
55
56 wake_up(&xb_waitq);
57 return IRQ_HANDLED;
58 }
59
60 static int check_indexes(XENSTORE_RING_IDX cons, XENSTORE_RING_IDX prod)
61 {
62 return ((prod - cons) <= XENSTORE_RING_SIZE);
63 }
64
65 static void *get_output_chunk(XENSTORE_RING_IDX cons,
66 XENSTORE_RING_IDX prod,
67 char *buf, uint32_t *len)
68 {
69 *len = XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(prod);
70 if ((XENSTORE_RING_SIZE - (prod - cons)) < *len)
71 *len = XENSTORE_RING_SIZE - (prod - cons);
72 return buf + MASK_XENSTORE_IDX(prod);
73 }
74
75 static const void *get_input_chunk(XENSTORE_RING_IDX cons,
76 XENSTORE_RING_IDX prod,
77 const char *buf, uint32_t *len)
78 {
79 *len = XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(cons);
80 if ((prod - cons) < *len)
81 *len = prod - cons;
82 return buf + MASK_XENSTORE_IDX(cons);
83 }
84
85 /**
86 * xb_write - low level write
87 * @data: buffer to send
88 * @len: length of buffer
89 *
90 * Returns 0 on success, error otherwise.
91 */
92 int xb_write(const void *data, unsigned len)
93 {
94 struct xenstore_domain_interface *intf = xen_store_interface;
95 XENSTORE_RING_IDX cons, prod;
96 int rc;
97
98 while (len != 0) {
99 void *dst;
100 unsigned int avail;
101
102 rc = wait_event_interruptible(
103 xb_waitq,
104 (intf->req_prod - intf->req_cons) !=
105 XENSTORE_RING_SIZE);
106 if (rc < 0)
107 return rc;
108
109 /* Read indexes, then verify. */
110 cons = intf->req_cons;
111 prod = intf->req_prod;
112 if (!check_indexes(cons, prod)) {
113 intf->req_cons = intf->req_prod = 0;
114 return -EIO;
115 }
116
117 dst = get_output_chunk(cons, prod, intf->req, &avail);
118 if (avail == 0)
119 continue;
120 if (avail > len)
121 avail = len;
122
123 /* Must write data /after/ reading the consumer index. */
124 mb();
125
126 memcpy(dst, data, avail);
127 data += avail;
128 len -= avail;
129
130 /* Other side must not see new producer until data is there. */
131 wmb();
132 intf->req_prod += avail;
133
134 /* Implies mb(): other side will see the updated producer. */
135 notify_remote_via_evtchn(xen_store_evtchn);
136 }
137
138 return 0;
139 }
140
141 int xb_data_to_read(void)
142 {
143 struct xenstore_domain_interface *intf = xen_store_interface;
144 return (intf->rsp_cons != intf->rsp_prod);
145 }
146
147 int xb_wait_for_data_to_read(void)
148 {
149 return wait_event_interruptible(xb_waitq, xb_data_to_read());
150 }
151
152 int xb_read(void *data, unsigned len)
153 {
154 struct xenstore_domain_interface *intf = xen_store_interface;
155 XENSTORE_RING_IDX cons, prod;
156 int rc;
157
158 while (len != 0) {
159 unsigned int avail;
160 const char *src;
161
162 rc = xb_wait_for_data_to_read();
163 if (rc < 0)
164 return rc;
165
166 /* Read indexes, then verify. */
167 cons = intf->rsp_cons;
168 prod = intf->rsp_prod;
169 if (!check_indexes(cons, prod)) {
170 intf->rsp_cons = intf->rsp_prod = 0;
171 return -EIO;
172 }
173
174 src = get_input_chunk(cons, prod, intf->rsp, &avail);
175 if (avail == 0)
176 continue;
177 if (avail > len)
178 avail = len;
179
180 /* Must read data /after/ reading the producer index. */
181 rmb();
182
183 memcpy(data, src, avail);
184 data += avail;
185 len -= avail;
186
187 /* Other side must not see free space until we've copied out */
188 mb();
189 intf->rsp_cons += avail;
190
191 pr_debug("Finished read of %i bytes (%i to go)\n", avail, len);
192
193 /* Implies mb(): other side will see the updated consumer. */
194 notify_remote_via_evtchn(xen_store_evtchn);
195 }
196
197 return 0;
198 }
199
200 /**
201 * xb_init_comms - Set up interrupt handler off store event channel.
202 */
203 int xb_init_comms(void)
204 {
205 struct xenstore_domain_interface *intf = xen_store_interface;
206 int err;
207
208 if (intf->req_prod != intf->req_cons)
209 printk(KERN_ERR "XENBUS request ring is not quiescent "
210 "(%08x:%08x)!\n", intf->req_cons, intf->req_prod);
211
212 if (intf->rsp_prod != intf->rsp_cons) {
213 printk(KERN_WARNING "XENBUS response ring is not quiescent "
214 "(%08x:%08x): fixing up\n",
215 intf->rsp_cons, intf->rsp_prod);
216 intf->rsp_cons = intf->rsp_prod;
217 }
218
219 if (xenbus_irq)
220 unbind_from_irqhandler(xenbus_irq, &xb_waitq);
221
222 err = bind_evtchn_to_irqhandler(
223 xen_store_evtchn, wake_waiting,
224 0, "xenbus", &xb_waitq);
225 if (err <= 0) {
226 printk(KERN_ERR "XENBUS request irq failed %i\n", err);
227 return err;
228 }
229
230 xenbus_irq = err;
231
232 return 0;
233 }
234
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