drivers/xen/xenbus/xenbus_comms.c

   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
  45 static int xenbus_irq;
  46
  47 static DECLARE_WORK(probe_work, xenbus_probe);
  48
  49 static DECLARE_WAIT_QUEUE_HEAD(xb_waitq);
  50
  51 static 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
  62 static int check_indexes(XENSTORE_RING_IDX cons, XENSTORE_RING_IDX prod)
  63 {
  64         return ((prod - cons) <= XENSTORE_RING_SIZE);
  65 }
  66
  67 static 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
  77 static 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  */
  94 int 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
 143 int 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
 149 int xb_wait_for_data_to_read(void)
 150 {
 151         return wait_event_interruptible(xb_waitq, xb_data_to_read());
 152 }
 153
 154 int 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  */
 205 int 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
 239 void xb_deinit_comms(void)
 240 {
 241         unbind_from_irqhandler(xenbus_irq, &xb_waitq);
 242         xenbus_irq = 0;
 243 }