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 #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
 207         if (intf->req_prod != intf->req_cons)
 208                 printk(KERN_ERR "XENBUS request ring is not quiescent "
 209                        "(%08x:%08x)!\n", intf->req_cons, intf->req_prod);
 210
 211         if (intf->rsp_prod != intf->rsp_cons) {
 212                 printk(KERN_WARNING "XENBUS response ring is not quiescent "
 213                        "(%08x:%08x): fixing up\n",
 214                        intf->rsp_cons, intf->rsp_prod);
 215                 intf->rsp_cons = intf->rsp_prod;
 216         }
 217
 218         if (xenbus_irq) {
 219                 /* Already have an irq; assume we're resuming */
 220                 rebind_evtchn_irq(xen_store_evtchn, xenbus_irq);
 221         } else {
 222                 int err;
 223                 err = bind_evtchn_to_irqhandler(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
 233         return 0;
 234 }