linux/drivers/xen/xenbus/xenbus_dev_frontend.c
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   1/*
   2 * Driver giving user-space access to the kernel's xenbus connection
   3 * to xenstore.
   4 *
   5 * Copyright (c) 2005, Christian Limpach
   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 * Changes:
  33 * 2008-10-07  Alex Zeffertt    Replaced /proc/xen/xenbus with xenfs filesystem
  34 *                              and /proc/xen compatibility mount point.
  35 *                              Turned xenfs into a loadable module.
  36 */
  37
  38#include <linux/kernel.h>
  39#include <linux/errno.h>
  40#include <linux/uio.h>
  41#include <linux/notifier.h>
  42#include <linux/wait.h>
  43#include <linux/fs.h>
  44#include <linux/poll.h>
  45#include <linux/mutex.h>
  46#include <linux/sched.h>
  47#include <linux/spinlock.h>
  48#include <linux/mount.h>
  49#include <linux/pagemap.h>
  50#include <linux/uaccess.h>
  51#include <linux/init.h>
  52#include <linux/namei.h>
  53#include <linux/string.h>
  54#include <linux/slab.h>
  55#include <linux/miscdevice.h>
  56#include <linux/module.h>
  57
  58#include "xenbus_comms.h"
  59
  60#include <xen/xenbus.h>
  61#include <xen/xen.h>
  62#include <asm/xen/hypervisor.h>
  63
  64MODULE_LICENSE("GPL");
  65
  66/*
  67 * An element of a list of outstanding transactions, for which we're
  68 * still waiting a reply.
  69 */
  70struct xenbus_transaction_holder {
  71        struct list_head list;
  72        struct xenbus_transaction handle;
  73};
  74
  75/*
  76 * A buffer of data on the queue.
  77 */
  78struct read_buffer {
  79        struct list_head list;
  80        unsigned int cons;
  81        unsigned int len;
  82        char msg[];
  83};
  84
  85struct xenbus_file_priv {
  86        /*
  87         * msgbuffer_mutex is held while partial requests are built up
  88         * and complete requests are acted on.  It therefore protects
  89         * the "transactions" and "watches" lists, and the partial
  90         * request length and buffer.
  91         *
  92         * reply_mutex protects the reply being built up to return to
  93         * usermode.  It nests inside msgbuffer_mutex but may be held
  94         * alone during a watch callback.
  95         */
  96        struct mutex msgbuffer_mutex;
  97
  98        /* In-progress transactions */
  99        struct list_head transactions;
 100
 101        /* Active watches. */
 102        struct list_head watches;
 103
 104        /* Partial request. */
 105        unsigned int len;
 106        union {
 107                struct xsd_sockmsg msg;
 108                char buffer[XENSTORE_PAYLOAD_MAX];
 109        } u;
 110
 111        /* Response queue. */
 112        struct mutex reply_mutex;
 113        struct list_head read_buffers;
 114        wait_queue_head_t read_waitq;
 115
 116};
 117
 118/* Read out any raw xenbus messages queued up. */
 119static ssize_t xenbus_file_read(struct file *filp,
 120                               char __user *ubuf,
 121                               size_t len, loff_t *ppos)
 122{
 123        struct xenbus_file_priv *u = filp->private_data;
 124        struct read_buffer *rb;
 125        unsigned i;
 126        int ret;
 127
 128        mutex_lock(&u->reply_mutex);
 129again:
 130        while (list_empty(&u->read_buffers)) {
 131                mutex_unlock(&u->reply_mutex);
 132                if (filp->f_flags & O_NONBLOCK)
 133                        return -EAGAIN;
 134
 135                ret = wait_event_interruptible(u->read_waitq,
 136                                               !list_empty(&u->read_buffers));
 137                if (ret)
 138                        return ret;
 139                mutex_lock(&u->reply_mutex);
 140        }
 141
 142        rb = list_entry(u->read_buffers.next, struct read_buffer, list);
 143        i = 0;
 144        while (i < len) {
 145                unsigned sz = min((unsigned)len - i, rb->len - rb->cons);
 146
 147                ret = copy_to_user(ubuf + i, &rb->msg[rb->cons], sz);
 148
 149                i += sz - ret;
 150                rb->cons += sz - ret;
 151
 152                if (ret != 0) {
 153                        if (i == 0)
 154                                i = -EFAULT;
 155                        goto out;
 156                }
 157
 158                /* Clear out buffer if it has been consumed */
 159                if (rb->cons == rb->len) {
 160                        list_del(&rb->list);
 161                        kfree(rb);
 162                        if (list_empty(&u->read_buffers))
 163                                break;
 164                        rb = list_entry(u->read_buffers.next,
 165                                        struct read_buffer, list);
 166                }
 167        }
 168        if (i == 0)
 169                goto again;
 170
 171out:
 172        mutex_unlock(&u->reply_mutex);
 173        return i;
 174}
 175
 176/*
 177 * Add a buffer to the queue.  Caller must hold the appropriate lock
 178 * if the queue is not local.  (Commonly the caller will build up
 179 * multiple queued buffers on a temporary local list, and then add it
 180 * to the appropriate list under lock once all the buffers have een
 181 * successfully allocated.)
 182 */
 183static int queue_reply(struct list_head *queue, const void *data, size_t len)
 184{
 185        struct read_buffer *rb;
 186
 187        if (len == 0)
 188                return 0;
 189
 190        rb = kmalloc(sizeof(*rb) + len, GFP_KERNEL);
 191        if (rb == NULL)
 192                return -ENOMEM;
 193
 194        rb->cons = 0;
 195        rb->len = len;
 196
 197        memcpy(rb->msg, data, len);
 198
 199        list_add_tail(&rb->list, queue);
 200        return 0;
 201}
 202
 203/*
 204 * Free all the read_buffer s on a list.
 205 * Caller must have sole reference to list.
 206 */
 207static void queue_cleanup(struct list_head *list)
 208{
 209        struct read_buffer *rb;
 210
 211        while (!list_empty(list)) {
 212                rb = list_entry(list->next, struct read_buffer, list);
 213                list_del(list->next);
 214                kfree(rb);
 215        }
 216}
 217
 218struct watch_adapter {
 219        struct list_head list;
 220        struct xenbus_watch watch;
 221        struct xenbus_file_priv *dev_data;
 222        char *token;
 223};
 224
 225static void free_watch_adapter(struct watch_adapter *watch)
 226{
 227        kfree(watch->watch.node);
 228        kfree(watch->token);
 229        kfree(watch);
 230}
 231
 232static struct watch_adapter *alloc_watch_adapter(const char *path,
 233                                                 const char *token)
 234{
 235        struct watch_adapter *watch;
 236
 237        watch = kzalloc(sizeof(*watch), GFP_KERNEL);
 238        if (watch == NULL)
 239                goto out_fail;
 240
 241        watch->watch.node = kstrdup(path, GFP_KERNEL);
 242        if (watch->watch.node == NULL)
 243                goto out_free;
 244
 245        watch->token = kstrdup(token, GFP_KERNEL);
 246        if (watch->token == NULL)
 247                goto out_free;
 248
 249        return watch;
 250
 251out_free:
 252        free_watch_adapter(watch);
 253
 254out_fail:
 255        return NULL;
 256}
 257
 258static void watch_fired(struct xenbus_watch *watch,
 259                        const char **vec,
 260                        unsigned int len)
 261{
 262        struct watch_adapter *adap;
 263        struct xsd_sockmsg hdr;
 264        const char *path, *token;
 265        int path_len, tok_len, body_len, data_len = 0;
 266        int ret;
 267        LIST_HEAD(staging_q);
 268
 269        adap = container_of(watch, struct watch_adapter, watch);
 270
 271        path = vec[XS_WATCH_PATH];
 272        token = adap->token;
 273
 274        path_len = strlen(path) + 1;
 275        tok_len = strlen(token) + 1;
 276        if (len > 2)
 277                data_len = vec[len] - vec[2] + 1;
 278        body_len = path_len + tok_len + data_len;
 279
 280        hdr.type = XS_WATCH_EVENT;
 281        hdr.len = body_len;
 282
 283        mutex_lock(&adap->dev_data->reply_mutex);
 284
 285        ret = queue_reply(&staging_q, &hdr, sizeof(hdr));
 286        if (!ret)
 287                ret = queue_reply(&staging_q, path, path_len);
 288        if (!ret)
 289                ret = queue_reply(&staging_q, token, tok_len);
 290        if (!ret && len > 2)
 291                ret = queue_reply(&staging_q, vec[2], data_len);
 292
 293        if (!ret) {
 294                /* success: pass reply list onto watcher */
 295                list_splice_tail(&staging_q, &adap->dev_data->read_buffers);
 296                wake_up(&adap->dev_data->read_waitq);
 297        } else
 298                queue_cleanup(&staging_q);
 299
 300        mutex_unlock(&adap->dev_data->reply_mutex);
 301}
 302
 303static int xenbus_write_transaction(unsigned msg_type,
 304                                    struct xenbus_file_priv *u)
 305{
 306        int rc;
 307        void *reply;
 308        struct xenbus_transaction_holder *trans = NULL;
 309        LIST_HEAD(staging_q);
 310
 311        if (msg_type == XS_TRANSACTION_START) {
 312                trans = kmalloc(sizeof(*trans), GFP_KERNEL);
 313                if (!trans) {
 314                        rc = -ENOMEM;
 315                        goto out;
 316                }
 317        }
 318
 319        reply = xenbus_dev_request_and_reply(&u->u.msg);
 320        if (IS_ERR(reply)) {
 321                kfree(trans);
 322                rc = PTR_ERR(reply);
 323                goto out;
 324        }
 325
 326        if (msg_type == XS_TRANSACTION_START) {
 327                trans->handle.id = simple_strtoul(reply, NULL, 0);
 328
 329                list_add(&trans->list, &u->transactions);
 330        } else if (msg_type == XS_TRANSACTION_END) {
 331                list_for_each_entry(trans, &u->transactions, list)
 332                        if (trans->handle.id == u->u.msg.tx_id)
 333                                break;
 334                BUG_ON(&trans->list == &u->transactions);
 335                list_del(&trans->list);
 336
 337                kfree(trans);
 338        }
 339
 340        mutex_lock(&u->reply_mutex);
 341        rc = queue_reply(&staging_q, &u->u.msg, sizeof(u->u.msg));
 342        if (!rc)
 343                rc = queue_reply(&staging_q, reply, u->u.msg.len);
 344        if (!rc) {
 345                list_splice_tail(&staging_q, &u->read_buffers);
 346                wake_up(&u->read_waitq);
 347        } else {
 348                queue_cleanup(&staging_q);
 349        }
 350        mutex_unlock(&u->reply_mutex);
 351
 352        kfree(reply);
 353
 354out:
 355        return rc;
 356}
 357
 358static int xenbus_write_watch(unsigned msg_type, struct xenbus_file_priv *u)
 359{
 360        struct watch_adapter *watch, *tmp_watch;
 361        char *path, *token;
 362        int err, rc;
 363        LIST_HEAD(staging_q);
 364
 365        path = u->u.buffer + sizeof(u->u.msg);
 366        token = memchr(path, 0, u->u.msg.len);
 367        if (token == NULL) {
 368                rc = -EILSEQ;
 369                goto out;
 370        }
 371        token++;
 372        if (memchr(token, 0, u->u.msg.len - (token - path)) == NULL) {
 373                rc = -EILSEQ;
 374                goto out;
 375        }
 376
 377        if (msg_type == XS_WATCH) {
 378                watch = alloc_watch_adapter(path, token);
 379                if (watch == NULL) {
 380                        rc = -ENOMEM;
 381                        goto out;
 382                }
 383
 384                watch->watch.callback = watch_fired;
 385                watch->dev_data = u;
 386
 387                err = register_xenbus_watch(&watch->watch);
 388                if (err) {
 389                        free_watch_adapter(watch);
 390                        rc = err;
 391                        goto out;
 392                }
 393                list_add(&watch->list, &u->watches);
 394        } else {
 395                list_for_each_entry_safe(watch, tmp_watch, &u->watches, list) {
 396                        if (!strcmp(watch->token, token) &&
 397                            !strcmp(watch->watch.node, path)) {
 398                                unregister_xenbus_watch(&watch->watch);
 399                                list_del(&watch->list);
 400                                free_watch_adapter(watch);
 401                                break;
 402                        }
 403                }
 404        }
 405
 406        /* Success.  Synthesize a reply to say all is OK. */
 407        {
 408                struct {
 409                        struct xsd_sockmsg hdr;
 410                        char body[3];
 411                } __packed reply = {
 412                        {
 413                                .type = msg_type,
 414                                .len = sizeof(reply.body)
 415                        },
 416                        "OK"
 417                };
 418
 419                mutex_lock(&u->reply_mutex);
 420                rc = queue_reply(&u->read_buffers, &reply, sizeof(reply));
 421                wake_up(&u->read_waitq);
 422                mutex_unlock(&u->reply_mutex);
 423        }
 424
 425out:
 426        return rc;
 427}
 428
 429static ssize_t xenbus_file_write(struct file *filp,
 430                                const char __user *ubuf,
 431                                size_t len, loff_t *ppos)
 432{
 433        struct xenbus_file_priv *u = filp->private_data;
 434        uint32_t msg_type;
 435        int rc = len;
 436        int ret;
 437        LIST_HEAD(staging_q);
 438
 439        /*
 440         * We're expecting usermode to be writing properly formed
 441         * xenbus messages.  If they write an incomplete message we
 442         * buffer it up.  Once it is complete, we act on it.
 443         */
 444
 445        /*
 446         * Make sure concurrent writers can't stomp all over each
 447         * other's messages and make a mess of our partial message
 448         * buffer.  We don't make any attemppt to stop multiple
 449         * writers from making a mess of each other's incomplete
 450         * messages; we're just trying to guarantee our own internal
 451         * consistency and make sure that single writes are handled
 452         * atomically.
 453         */
 454        mutex_lock(&u->msgbuffer_mutex);
 455
 456        /* Get this out of the way early to avoid confusion */
 457        if (len == 0)
 458                goto out;
 459
 460        /* Can't write a xenbus message larger we can buffer */
 461        if ((len + u->len) > sizeof(u->u.buffer)) {
 462                /* On error, dump existing buffer */
 463                u->len = 0;
 464                rc = -EINVAL;
 465                goto out;
 466        }
 467
 468        ret = copy_from_user(u->u.buffer + u->len, ubuf, len);
 469
 470        if (ret != 0) {
 471                rc = -EFAULT;
 472                goto out;
 473        }
 474
 475        /* Deal with a partial copy. */
 476        len -= ret;
 477        rc = len;
 478
 479        u->len += len;
 480
 481        /* Return if we haven't got a full message yet */
 482        if (u->len < sizeof(u->u.msg))
 483                goto out;       /* not even the header yet */
 484
 485        /* If we're expecting a message that's larger than we can
 486           possibly send, dump what we have and return an error. */
 487        if ((sizeof(u->u.msg) + u->u.msg.len) > sizeof(u->u.buffer)) {
 488                rc = -E2BIG;
 489                u->len = 0;
 490                goto out;
 491        }
 492
 493        if (u->len < (sizeof(u->u.msg) + u->u.msg.len))
 494                goto out;       /* incomplete data portion */
 495
 496        /*
 497         * OK, now we have a complete message.  Do something with it.
 498         */
 499
 500        msg_type = u->u.msg.type;
 501
 502        switch (msg_type) {
 503        case XS_WATCH:
 504        case XS_UNWATCH:
 505                /* (Un)Ask for some path to be watched for changes */
 506                ret = xenbus_write_watch(msg_type, u);
 507                break;
 508
 509        default:
 510                /* Send out a transaction */
 511                ret = xenbus_write_transaction(msg_type, u);
 512                break;
 513        }
 514        if (ret != 0)
 515                rc = ret;
 516
 517        /* Buffered message consumed */
 518        u->len = 0;
 519
 520 out:
 521        mutex_unlock(&u->msgbuffer_mutex);
 522        return rc;
 523}
 524
 525static int xenbus_file_open(struct inode *inode, struct file *filp)
 526{
 527        struct xenbus_file_priv *u;
 528
 529        if (xen_store_evtchn == 0)
 530                return -ENOENT;
 531
 532        nonseekable_open(inode, filp);
 533
 534        u = kzalloc(sizeof(*u), GFP_KERNEL);
 535        if (u == NULL)
 536                return -ENOMEM;
 537
 538        INIT_LIST_HEAD(&u->transactions);
 539        INIT_LIST_HEAD(&u->watches);
 540        INIT_LIST_HEAD(&u->read_buffers);
 541        init_waitqueue_head(&u->read_waitq);
 542
 543        mutex_init(&u->reply_mutex);
 544        mutex_init(&u->msgbuffer_mutex);
 545
 546        filp->private_data = u;
 547
 548        return 0;
 549}
 550
 551static int xenbus_file_release(struct inode *inode, struct file *filp)
 552{
 553        struct xenbus_file_priv *u = filp->private_data;
 554        struct xenbus_transaction_holder *trans, *tmp;
 555        struct watch_adapter *watch, *tmp_watch;
 556        struct read_buffer *rb, *tmp_rb;
 557
 558        /*
 559         * No need for locking here because there are no other users,
 560         * by definition.
 561         */
 562
 563        list_for_each_entry_safe(trans, tmp, &u->transactions, list) {
 564                xenbus_transaction_end(trans->handle, 1);
 565                list_del(&trans->list);
 566                kfree(trans);
 567        }
 568
 569        list_for_each_entry_safe(watch, tmp_watch, &u->watches, list) {
 570                unregister_xenbus_watch(&watch->watch);
 571                list_del(&watch->list);
 572                free_watch_adapter(watch);
 573        }
 574
 575        list_for_each_entry_safe(rb, tmp_rb, &u->read_buffers, list) {
 576                list_del(&rb->list);
 577                kfree(rb);
 578        }
 579        kfree(u);
 580
 581        return 0;
 582}
 583
 584static unsigned int xenbus_file_poll(struct file *file, poll_table *wait)
 585{
 586        struct xenbus_file_priv *u = file->private_data;
 587
 588        poll_wait(file, &u->read_waitq, wait);
 589        if (!list_empty(&u->read_buffers))
 590                return POLLIN | POLLRDNORM;
 591        return 0;
 592}
 593
 594const struct file_operations xen_xenbus_fops = {
 595        .read = xenbus_file_read,
 596        .write = xenbus_file_write,
 597        .open = xenbus_file_open,
 598        .release = xenbus_file_release,
 599        .poll = xenbus_file_poll,
 600        .llseek = no_llseek,
 601};
 602EXPORT_SYMBOL_GPL(xen_xenbus_fops);
 603
 604static struct miscdevice xenbus_dev = {
 605        .minor = MISC_DYNAMIC_MINOR,
 606        .name = "xen/xenbus",
 607        .fops = &xen_xenbus_fops,
 608};
 609
 610static int __init xenbus_init(void)
 611{
 612        int err;
 613
 614        if (!xen_domain())
 615                return -ENODEV;
 616
 617        err = misc_register(&xenbus_dev);
 618        if (err)
 619                printk(KERN_ERR "Could not register xenbus frontend device\n");
 620        return err;
 621}
 622
 623static void __exit xenbus_exit(void)
 624{
 625        misc_deregister(&xenbus_dev);
 626}
 627
 628module_init(xenbus_init);
 629module_exit(xenbus_exit);
 630
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