xen/io/xenbus_xs.c

	xenbus_xs.c revision 7f0b8309074a5d8e9f9d8ffe7aad7bb0b1ee6b1f
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 *
 * xenbus_xs.c
 *
 * This is the kernel equivalent of the "xs" library.  We don't need everything
 * and we use xenbus_comms for communication.
 *
 * Copyright (C) 2005 Rusty Russell, IBM Corporation
 *
 * This file may be distributed separately from the Linux kernel, or
 * incorporated into other software packages, subject to the following license:
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this source file (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

/*
 * NOTE: To future maintainers of the Solaris version of this file:
 * I found the Linux version of this code to be very disgusting in
 * overloading pointers and error codes into void * return values.
 * The main difference you will find is that all such usage is changed
 * to pass pointers to void* to be filled in with return values and
 * the functions return error codes.
 */

#include <sys/errno.h>
#include <sys/types.h>
#include <sys/sysmacros.h>
#include <sys/uio.h>
#include <sys/mutex.h>
#include <sys/condvar.h>
#include <sys/rwlock.h>
#include <sys/disp.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>
#include <sys/avintr.h>
#include <sys/cmn_err.h>
#include <sys/mach_mmu.h>
#include <util/sscanf.h>
#define _XSD_ERRORS_DEFINED
#ifdef XPV_HVM_DRIVER
#include <sys/xpv_support.h>
#endif
#include <sys/hypervisor.h>
#include <sys/taskq.h>
#include <sys/sdt.h>
#include <xen/sys/xenbus_impl.h>
#include <xen/sys/xenbus_comms.h>
#include <xen/sys/xendev.h>
#include <xen/public/io/xs_wire.h>

#define streq(a, b) (strcmp((a), (b)) == 0)

#define list_empty(list) (list_head(list) == NULL)

struct xs_stored_msg {
    list_t list;

    struct xsd_sockmsg hdr;

    union {
        /* Queued replies. */
        struct {
            char *body;
        } reply;

        /* Queued watch events. */
        struct {
            struct xenbus_watch *handle;
            char **vec;
            unsigned int vec_size;
        } watch;
    } un;
};

static struct xs_handle {
    /* A list of replies. Currently only one will ever be outstanding. */
    list_t reply_list;
    kmutex_t reply_lock;
    kcondvar_t reply_cv;

    /* One request at a time. */
    kmutex_t request_mutex;

    /* Protect transactions against save/restore. */
    krwlock_t suspend_lock;
} xs_state;

static int last_req_id;

/*
 * List of clients wanting a xenstore up notification, and a lock to protect it
 */
static boolean_t xenstore_up;
static list_t notify_list;
static kmutex_t notify_list_lock;
static taskq_t *xenbus_taskq;

/* List of registered watches, and a lock to protect it. */
static list_t watches;
static kmutex_t watches_lock;

/* List of pending watch callback events, and a lock to protect it. */
static list_t watch_events;
static kmutex_t watch_events_lock;

/*
 * Details of the xenwatch callback kernel thread. The thread waits on the
 * watch_events_cv for work to do (queued on watch_events list). When it
 * wakes up it acquires the xenwatch_mutex before reading the list and
 * carrying out work.
 */
static kmutex_t xenwatch_mutex;
static kcondvar_t watch_events_cv;

static int process_msg(void);

static int
get_error(const char *errorstring)
{
    unsigned int i;

    for (i = 0; !streq(errorstring, xsd_errors[i].errstring); i++) {
        if (i == (sizeof (xsd_errors) / sizeof (xsd_errors[0])) - 1) {
            cmn_err(CE_WARN,
                "XENBUS xen store gave: unknown error %s",
                errorstring);
            return (EINVAL);
        }
    }
    return (xsd_errors[i].errnum);
}

/*
 * Read a synchronous reply from xenstore.  Since we can return early before
 * reading a relevant reply, we discard any messages not matching the request
 * ID.  Caller must free returned message on success.
 */
static int
read_reply(struct xsd_sockmsg *req_hdr, struct xs_stored_msg **reply)
{
    extern int do_polled_io;

    mutex_enter(&xs_state.reply_lock);

    for (;;) {
        while (list_empty(&xs_state.reply_list)) {
            if (interrupts_unleashed && !do_polled_io) {
                if (cv_wait_sig(&xs_state.reply_cv,
                    &xs_state.reply_lock) == 0) {
                    mutex_exit(&xs_state.reply_lock);
                    *reply = NULL;
                    return (EINTR);
                }
            } else { /* polled mode needed for early probes */
                mutex_exit(&xs_state.reply_lock);
                (void) HYPERVISOR_yield();
                (void) process_msg();
                mutex_enter(&xs_state.reply_lock);
            }
        }

        *reply = list_head(&xs_state.reply_list);
        list_remove(&xs_state.reply_list, *reply);

        if ((*reply)->hdr.req_id == req_hdr->req_id)
            break;
    }

    mutex_exit(&xs_state.reply_lock);
    return (0);
}

/* Emergency write. */
void
xenbus_debug_write(const char *str, unsigned int count)
{
    struct xsd_sockmsg msg = { 0 };

    msg.type = XS_DEBUG;
    msg.len = sizeof ("print") + count + 1;

    mutex_enter(&xs_state.request_mutex);
    (void) xb_write(&msg, sizeof (msg));
    (void) xb_write("print", sizeof ("print"));
    (void) xb_write(str, count);
    (void) xb_write("", 1);
    mutex_exit(&xs_state.request_mutex);
}

/*
 * This is pretty unpleasant.  First off, there's the horrible logic around
 * suspend_lock and transactions.  Also, we can be interrupted either before we
 * write a message, or before we receive a reply.  A client that wants to
 * survive this can't know which case happened.  Luckily all clients don't care
 * about signals currently, and the alternative (a hard wait on a userspace
 * daemon) isn't exactly preferable.  Caller must free 'reply' on success.
 */
int
xenbus_dev_request_and_reply(struct xsd_sockmsg *msg, void **reply)
{
    struct xsd_sockmsg req_msg = *msg;
    struct xs_stored_msg *reply_msg = NULL;
    int err;

    if (req_msg.type == XS_TRANSACTION_START)
        rw_enter(&xs_state.suspend_lock, RW_READER);

    mutex_enter(&xs_state.request_mutex);

    msg->req_id = last_req_id++;

    err = xb_write(msg, sizeof (*msg) + msg->len);
    if (err) {
        if (req_msg.type == XS_TRANSACTION_START)
            rw_exit(&xs_state.suspend_lock);
        msg->type = XS_ERROR;
        *reply = NULL;
        goto out;
    }

    err = read_reply(msg, &reply_msg);

    if (err) {
        if (msg->type == XS_TRANSACTION_START)
            rw_exit(&xs_state.suspend_lock);
        *reply = NULL;
        goto out;
    }

    *reply = reply_msg->un.reply.body;
    *msg = reply_msg->hdr;

    if (reply_msg->hdr.type == XS_TRANSACTION_END)
        rw_exit(&xs_state.suspend_lock);

out:
    if (reply_msg != NULL)
        kmem_free(reply_msg, sizeof (*reply_msg));

    mutex_exit(&xs_state.request_mutex);
    return (err);
}

/*
 * Send message to xs, return errcode, rval filled in with pointer
 * to kmem_alloc'ed reply.
 */
static int
xs_talkv(xenbus_transaction_t t,
            enum xsd_sockmsg_type type,
            const iovec_t *iovec,
            unsigned int num_vecs,
            void **rval,
            unsigned int *len)
{
    struct xsd_sockmsg msg;
    struct xs_stored_msg *reply_msg;
    char *reply;
    unsigned int i;
    int err;

    msg.tx_id = (uint32_t)(unsigned long)t;
    msg.type = type;
    msg.len = 0;
    for (i = 0; i < num_vecs; i++)
        msg.len += iovec[i].iov_len;

    mutex_enter(&xs_state.request_mutex);

    msg.req_id = last_req_id++;

    err = xb_write(&msg, sizeof (msg));
    if (err) {
        mutex_exit(&xs_state.request_mutex);
        return (err);
    }

    for (i = 0; i < num_vecs; i++) {
        err = xb_write(iovec[i].iov_base, iovec[i].iov_len);
        if (err) {
            mutex_exit(&xs_state.request_mutex);
            return (err);
        }
    }

    err = read_reply(&msg, &reply_msg);

    mutex_exit(&xs_state.request_mutex);

    if (err)
        return (err);

    reply = reply_msg->un.reply.body;

    if (reply_msg->hdr.type == XS_ERROR) {
        err = get_error(reply);
        kmem_free(reply, reply_msg->hdr.len + 1);
        goto out;
    }

    if (len != NULL)
        *len = reply_msg->hdr.len + 1;

    ASSERT(reply_msg->hdr.type == type);

    if (rval != NULL)
        *rval = reply;
    else
        kmem_free(reply, reply_msg->hdr.len + 1);

out:
    kmem_free(reply_msg, sizeof (*reply_msg));
    return (err);
}

/* Simplified version of xs_talkv: single message. */
static int
xs_single(xenbus_transaction_t t,
            enum xsd_sockmsg_type type,
            const char *string, void **ret,
            unsigned int *len)
{
    iovec_t iovec;

    iovec.iov_base = (char *)string;
    iovec.iov_len = strlen(string) + 1;
    return (xs_talkv(t, type, &iovec, 1, ret, len));
}

static unsigned int
count_strings(const char *strings, unsigned int len)
{
    unsigned int num;
    const char *p;

    for (p = strings, num = 0; p < strings + len; p += strlen(p) + 1)
        num++;

    return (num);
}

/* Return the path to dir with /name appended. Buffer must be kmem_free()'ed */
static char *
join(const char *dir, const char *name)
{
    char *buffer;
    size_t slashlen;

    slashlen = streq(name, "") ? 0 : 1;
    buffer = kmem_alloc(strlen(dir) + slashlen + strlen(name) + 1,
        KM_SLEEP);

    (void) strcpy(buffer, dir);
    if (slashlen != 0) {
        (void) strcat(buffer, "/");
        (void) strcat(buffer, name);
    }
    return (buffer);
}

static char **
split(char *strings, unsigned int len, unsigned int *num)
{
    char *p, **ret;

    /* Count the strings. */
    if ((*num = count_strings(strings, len - 1)) == 0)
        return (NULL);

    /* Transfer to one big alloc for easy freeing. */
    ret = kmem_alloc(*num * sizeof (char *) + (len - 1), KM_SLEEP);
    (void) memcpy(&ret[*num], strings, len - 1);
    kmem_free(strings, len);

    strings = (char *)&ret[*num];
    for (p = strings, *num = 0; p < strings + (len - 1);
        p += strlen(p) + 1) {
        ret[(*num)++] = p;
    }

    return (ret);
}

char **
xenbus_directory(xenbus_transaction_t t,
            const char *dir, const char *node, unsigned int *num)
{
    char *strings, *path;
    unsigned int len;
    int err;

    path = join(dir, node);
    err = xs_single(t, XS_DIRECTORY, path, (void **)&strings, &len);
    kmem_free(path, strlen(path) + 1);
    if (err != 0 || strings == NULL) {
        /* sigh, we lose error code info here */
        *num = 0;
        return (NULL);
    }

    return (split(strings, len, num));
}

/* Check if a path exists. */
boolean_t
xenbus_exists(const char *dir, const char *node)
{
    void    *p;
    uint_t  n;

    if (xenbus_read(XBT_NULL, dir, node, &p, &n) != 0)
        return (B_FALSE);
    kmem_free(p, n);
    return (B_TRUE);
}

/* Check if a directory path exists. */
boolean_t
xenbus_exists_dir(const char *dir, const char *node)
{
    char **d;
    unsigned int dir_n;
    int i, len;

    d = xenbus_directory(XBT_NULL, dir, node, &dir_n);
    if (d == NULL)
        return (B_FALSE);
    for (i = 0, len = 0; i < dir_n; i++)
        len += strlen(d[i]) + 1 + sizeof (char *);
    kmem_free(d, len);
    return (B_TRUE);
}

/*
 * Get the value of a single file.
 * Returns a kmem_alloced value in retp: call kmem_free() on it after use.
 * len indicates length in bytes.
 */
int
xenbus_read(xenbus_transaction_t t,
        const char *dir, const char *node, void **retp, unsigned int *len)
{
    char *path;
    int err;

    path = join(dir, node);
    err = xs_single(t, XS_READ, path, retp, len);
    kmem_free(path, strlen(path) + 1);
    return (err);
}

int
xenbus_read_str(const char *dir, const char *node, char **retp)
{
    uint_t  n;
    int err;
    char    *str;

    /*
     * Since we access the xenbus value immediatly we can't be
     * part of a transaction.
     */
    if ((err = xenbus_read(XBT_NULL, dir, node, (void **)&str, &n)) != 0)
        return (err);
    ASSERT((str != NULL) && (n > 0));

    /*
     * Why bother with this?  Because xenbus is truly annoying in the
     * fact that when it returns a string, it doesn't guarantee that
     * the memory that holds the string is of size strlen() + 1.
     * This forces callers to keep track of the size of the memory
     * containing the string.  Ugh.  We'll work around this by
     * re-allocate strings to always be of size strlen() + 1.
     */
    *retp = strdup(str);
    kmem_free(str, n);
    return (0);
}

/*
 * Write the value of a single file.
 * Returns err on failure.
 */
int
xenbus_write(xenbus_transaction_t t,
        const char *dir, const char *node, const char *string)
{
    char *path;
    iovec_t iovec[2];
    int ret;

    path = join(dir, node);

    iovec[0].iov_base = (void *)path;
    iovec[0].iov_len = strlen(path) + 1;
    iovec[1].iov_base = (void *)string;
    iovec[1].iov_len = strlen(string);

    ret = xs_talkv(t, XS_WRITE, iovec, 2, NULL, NULL);
    kmem_free(path, iovec[0].iov_len);
    return (ret);
}

/* Create a new directory. */
int
xenbus_mkdir(xenbus_transaction_t t, const char *dir, const char *node)
{
    char *path;
    int ret;

    path = join(dir, node);
    ret = xs_single(t, XS_MKDIR, path, NULL, NULL);
    kmem_free(path, strlen(path) + 1);
    return (ret);
}

/* Destroy a file or directory (directories must be empty). */
int
xenbus_rm(xenbus_transaction_t t, const char *dir, const char *node)
{
    char *path;
    int ret;

    path = join(dir, node);
    ret = xs_single(t, XS_RM, path, NULL, NULL);
    kmem_free(path, strlen(path) + 1);
    return (ret);
}

/*
 * Start a transaction: changes by others will not be seen during this
 * transaction, and changes will not be visible to others until end.
 */
int
xenbus_transaction_start(xenbus_transaction_t *t)
{
    void *id_str;
    unsigned long id;
    int err;
    unsigned int len;

    rw_enter(&xs_state.suspend_lock, RW_READER);

    err = xs_single(XBT_NULL, XS_TRANSACTION_START, "", &id_str, &len);
    if (err) {
        rw_exit(&xs_state.suspend_lock);
        return (err);
    }

    (void) ddi_strtoul((char *)id_str, NULL, 0, &id);
    *t = (xenbus_transaction_t)id;
    kmem_free(id_str, len);

    return (0);
}

/*
 * End a transaction.
 * If abandon is true, transaction is discarded instead of committed.
 */
int
xenbus_transaction_end(xenbus_transaction_t t, int abort)
{
    char abortstr[2];
    int err;

    if (abort)
        (void) strcpy(abortstr, "F");
    else
        (void) strcpy(abortstr, "T");

    err = xs_single(t, XS_TRANSACTION_END, abortstr, NULL, NULL);

    rw_exit(&xs_state.suspend_lock);

    return (err);
}

/*
 * Single read and scanf: returns errno or 0.  This can only handle a single
 * conversion specifier.
 */
/* SCANFLIKE4 */
int
xenbus_scanf(xenbus_transaction_t t,
        const char *dir, const char *node, const char *fmt, ...)
{
    va_list ap;
    int ret;
    char *val;
    unsigned int len;

    ret = xenbus_read(t, dir, node, (void **)&val, &len);
    if (ret)
        return (ret);

    va_start(ap, fmt);
    if (vsscanf(val, fmt, ap) != 1)
        ret = ERANGE;
    va_end(ap);
    kmem_free(val, len);
    return (ret);
}

/* Single printf and write: returns errno or 0. */
/* PRINTFLIKE4 */
int
xenbus_printf(xenbus_transaction_t t,
        const char *dir, const char *node, const char *fmt, ...)
{
    va_list ap;
    int ret;
#define PRINTF_BUFFER_SIZE 4096
    char *printf_buffer;

    printf_buffer = kmem_alloc(PRINTF_BUFFER_SIZE, KM_SLEEP);

    va_start(ap, fmt);
    ret = vsnprintf(printf_buffer, PRINTF_BUFFER_SIZE, fmt, ap);
    va_end(ap);

    ASSERT(ret <= PRINTF_BUFFER_SIZE-1);
    ret = xenbus_write(t, dir, node, printf_buffer);

    kmem_free(printf_buffer, PRINTF_BUFFER_SIZE);

    return (ret);
}


/* Takes tuples of names, scanf-style args, and void **, NULL terminated. */
int
xenbus_gather(xenbus_transaction_t t, const char *dir, ...)
{
    va_list ap;
    const char *name;
    int ret = 0;
    unsigned int len;

    va_start(ap, dir);
    while (ret == 0 && (name = va_arg(ap, char *)) != NULL) {
        const char *fmt = va_arg(ap, char *);
        void *result = va_arg(ap, void *);
        char *p;

        ret = xenbus_read(t, dir, name, (void **)&p, &len);
        if (ret)
            break;
        if (fmt) {
            ASSERT(result != NULL);
            if (sscanf(p, fmt, result) != 1)
                ret = EINVAL;
            kmem_free(p, len);
        } else
            *(char **)result = p;
    }
    va_end(ap);
    return (ret);
}

static int
xs_watch(const char *path, const char *token)
{
    iovec_t iov[2];

    iov[0].iov_base = (void *)path;
    iov[0].iov_len = strlen(path) + 1;
    iov[1].iov_base = (void *)token;
    iov[1].iov_len = strlen(token) + 1;

    return (xs_talkv(XBT_NULL, XS_WATCH, iov, 2, NULL, NULL));
}

static int
xs_unwatch(const char *path, const char *token)
{
    iovec_t iov[2];

    iov[0].iov_base = (char *)path;
    iov[0].iov_len = strlen(path) + 1;
    iov[1].iov_base = (char *)token;
    iov[1].iov_len = strlen(token) + 1;

    return (xs_talkv(XBT_NULL, XS_UNWATCH, iov, 2, NULL, NULL));
}

static struct xenbus_watch *
find_watch(const char *token)
{
    struct xenbus_watch *i, *cmp;

    (void) ddi_strtoul(token, NULL, 16, (unsigned long *)&cmp);

    for (i = list_head(&watches); i != NULL; i = list_next(&watches, i))
        if (i == cmp)
            break;

    return (i);
}

/* Register a xenstore state notify callback */
int
xs_register_xenbus_callback(void (*callback)(int))
{
    struct xenbus_notify *xbn, *xnp;

    xbn = kmem_alloc(sizeof (struct xenbus_notify), KM_SLEEP);
    xbn->notify_func = callback;
    mutex_enter(&notify_list_lock);
    /*
     * Make sure not already on the list
     */
    xnp = list_head(&notify_list);
    for (; xnp != NULL; xnp = list_next(&notify_list, xnp)) {
        if (xnp->notify_func == callback) {
            kmem_free(xbn, sizeof (struct xenbus_notify));
            mutex_exit(&notify_list_lock);
            return (EEXIST);
        }
    }
    xnp = xbn;
    list_insert_tail(&notify_list, xbn);
done:
    if (xenstore_up)
        xnp->notify_func(XENSTORE_UP);
    mutex_exit(&notify_list_lock);
    return (0);
}

/*
 * Notify clients of xenstore state
 */
static void
do_notify_callbacks(void *arg)
{
    struct xenbus_notify *xnp;

    mutex_enter(&notify_list_lock);
    xnp = list_head(&notify_list);
    for (; xnp != NULL; xnp = list_next(&notify_list, xnp)) {
        xnp->notify_func((int)((uintptr_t)arg));
    }
    mutex_exit(&notify_list_lock);
}

void
xs_notify_xenstore_up(void)
{
    xenstore_up = B_TRUE;
    (void) taskq_dispatch(xenbus_taskq, do_notify_callbacks,
        (void *)XENSTORE_UP, 0);
}

void
xs_notify_xenstore_down(void)
{
    xenstore_up = B_FALSE;
    (void) taskq_dispatch(xenbus_taskq, do_notify_callbacks,
        (void *)XENSTORE_DOWN, 0);
}

/* Register callback to watch this node. */
int
register_xenbus_watch(struct xenbus_watch *watch)
{
    /* Pointer in ascii is the token. */
    char token[sizeof (watch) * 2 + 1];
    int err;

    ASSERT(xenstore_up);
    (void) snprintf(token, sizeof (token), "%lX", (long)watch);

    rw_enter(&xs_state.suspend_lock, RW_READER);

    mutex_enter(&watches_lock);
    /*
     * May be re-registering a watch if xenstore daemon was restarted
     */
    if (find_watch(token) == NULL)
        list_insert_tail(&watches, watch);
    mutex_exit(&watches_lock);

    DTRACE_XPV3(xenbus__register__watch, const char *, watch->node,
        uintptr_t, watch->callback, struct xenbus_watch *, watch);

    err = xs_watch(watch->node, token);

    /* Ignore errors due to multiple registration. */
    if ((err != 0) && (err != EEXIST)) {
        mutex_enter(&watches_lock);
        list_remove(&watches, watch);
        mutex_exit(&watches_lock);
    }

    rw_exit(&xs_state.suspend_lock);

    return (err);
}

static void
free_stored_msg(struct xs_stored_msg *msg)
{
    int i, len = 0;

    for (i = 0; i < msg->un.watch.vec_size; i++)
        len += strlen(msg->un.watch.vec[i]) + 1 + sizeof (char *);
    kmem_free(msg->un.watch.vec, len);
    kmem_free(msg, sizeof (*msg));
}

void
unregister_xenbus_watch(struct xenbus_watch *watch)
{
    struct xs_stored_msg *msg;
    char token[sizeof (watch) * 2 + 1];
    int err;

    (void) snprintf(token, sizeof (token), "%lX", (long)watch);

    rw_enter(&xs_state.suspend_lock, RW_READER);

    mutex_enter(&watches_lock);
    ASSERT(find_watch(token));
    list_remove(&watches, watch);
    mutex_exit(&watches_lock);

    DTRACE_XPV3(xenbus__unregister__watch, const char *, watch->node,
        uintptr_t, watch->callback, struct xenbus_watch *, watch);

    err = xs_unwatch(watch->node, token);
    if (err)
        cmn_err(CE_WARN, "XENBUS Failed to release watch %s: %d",
            watch->node, err);

    rw_exit(&xs_state.suspend_lock);

    /* Cancel pending watch events. */
    mutex_enter(&watch_events_lock);
    msg = list_head(&watch_events);

    while (msg != NULL) {
        struct xs_stored_msg *tmp = list_next(&watch_events, msg);
        if (msg->un.watch.handle == watch) {
            list_remove(&watch_events, msg);
            free_stored_msg(msg);
        }
        msg = tmp;
    }

    mutex_exit(&watch_events_lock);

    /* Flush any currently-executing callback, unless we are it. :-) */
    if (mutex_owner(&xenwatch_mutex) != curthread) {
        mutex_enter(&xenwatch_mutex);
        mutex_exit(&xenwatch_mutex);
    }
}

void
xenbus_suspend(void)
{
    rw_enter(&xs_state.suspend_lock, RW_WRITER);
    mutex_enter(&xs_state.request_mutex);

    xb_suspend();
}

void
xenbus_resume(void)
{
    struct xenbus_watch *watch;
    char token[sizeof (watch) * 2 + 1];

    mutex_exit(&xs_state.request_mutex);

    xb_init();
    xb_setup_intr();

    /* No need for watches_lock: the suspend_lock is sufficient. */
    for (watch = list_head(&watches); watch != NULL;
        watch = list_next(&watches, watch)) {
        (void) snprintf(token, sizeof (token), "%lX", (long)watch);
        (void) xs_watch(watch->node, token);
    }

    rw_exit(&xs_state.suspend_lock);
}

static void
xenwatch_thread(void)
{
    struct xs_stored_msg *msg;
    struct xenbus_watch *watch;

    for (;;) {
        mutex_enter(&watch_events_lock);
        while (list_empty(&watch_events))
            cv_wait(&watch_events_cv, &watch_events_lock);
        msg = list_head(&watch_events);
        ASSERT(msg != NULL);
        list_remove(&watch_events, msg);
        watch = msg->un.watch.handle;
        mutex_exit(&watch_events_lock);

        mutex_enter(&xenwatch_mutex);

        DTRACE_XPV4(xenbus__fire__watch,
            const char *, watch->node,
            uintptr_t, watch->callback,
            struct xenbus_watch *, watch,
            const char *, msg->un.watch.vec[XS_WATCH_PATH]);

        watch->callback(watch, (const char **)msg->un.watch.vec,
            msg->un.watch.vec_size);

        free_stored_msg(msg);
        mutex_exit(&xenwatch_mutex);
    }
}

static int
process_msg(void)
{
    struct xs_stored_msg *msg;
    char *body;
    int err, mlen;

    msg = kmem_alloc(sizeof (*msg), KM_SLEEP);

    err = xb_read(&msg->hdr, sizeof (msg->hdr));
    if (err) {
        kmem_free(msg, sizeof (*msg));
        return (err);
    }

    mlen = msg->hdr.len + 1;
    body = kmem_alloc(mlen, KM_SLEEP);

    err = xb_read(body, msg->hdr.len);
    if (err) {
        kmem_free(body, mlen);
        kmem_free(msg, sizeof (*msg));
        return (err);
    }

    body[mlen - 1] = '\0';

    if (msg->hdr.type == XS_WATCH_EVENT) {
        const char *token;
        msg->un.watch.vec = split(body, msg->hdr.len + 1,
            &msg->un.watch.vec_size);
        if (msg->un.watch.vec == NULL) {
            kmem_free(msg, sizeof (*msg));
            return (EIO);
        }

        mutex_enter(&watches_lock);
        token = msg->un.watch.vec[XS_WATCH_TOKEN];
        if ((msg->un.watch.handle = find_watch(token)) != NULL) {
            mutex_enter(&watch_events_lock);

            DTRACE_XPV4(xenbus__enqueue__watch,
                const char *, msg->un.watch.handle->node,
                uintptr_t, msg->un.watch.handle->callback,
                struct xenbus_watch *, msg->un.watch.handle,
                const char *, msg->un.watch.vec[XS_WATCH_PATH]);

            list_insert_tail(&watch_events, msg);
            cv_broadcast(&watch_events_cv);
            mutex_exit(&watch_events_lock);
        } else {
            free_stored_msg(msg);
        }
        mutex_exit(&watches_lock);
    } else {
        msg->un.reply.body = body;
        mutex_enter(&xs_state.reply_lock);
        list_insert_tail(&xs_state.reply_list, msg);
        mutex_exit(&xs_state.reply_lock);
        cv_signal(&xs_state.reply_cv);
    }

    return (0);
}

static void
xenbus_thread(void)
{
    int err;

    for (; interrupts_unleashed != 0; ) {
        err = process_msg();
        if (err)
            cmn_err(CE_WARN, "XENBUS error %d while reading "
                "message", err);
    }
}

/*
 * When setting up xenbus, dom0 and domU have to take different paths, which
 * makes this code a little confusing. For dom0:
 *
 * xs_early_init - mutex init only
 * xs_dom0_init - called on xenbus dev attach: set up our xenstore page and
 * event channel; start xenbus threads for responding to interrupts.
 *
 * And for domU:
 *
 * xs_early_init - mutex init; set up our xenstore page and event channel
 * xs_domu_init - installation of IRQ handler; start xenbus threads.
 *
 * We need an early init on domU so we can use xenbus in polled mode to
 * discover devices, VCPUs etc.
 *
 * On resume, we use xb_init() and xb_setup_intr() to restore xenbus to a
 * working state.
 */

void
xs_early_init(void)
{
    list_create(&xs_state.reply_list, sizeof (struct xs_stored_msg),
        offsetof(struct xs_stored_msg, list));
    list_create(&watch_events, sizeof (struct xs_stored_msg),
        offsetof(struct xs_stored_msg, list));
    list_create(&watches, sizeof (struct xenbus_watch),
        offsetof(struct xenbus_watch, list));
    list_create(&notify_list, sizeof (struct xenbus_notify),
        offsetof(struct xenbus_notify, list));
    mutex_init(&xs_state.reply_lock, NULL, MUTEX_DEFAULT, NULL);
    mutex_init(&xs_state.request_mutex, NULL, MUTEX_DEFAULT, NULL);
    mutex_init(&notify_list_lock, NULL, MUTEX_DEFAULT, NULL);
    rw_init(&xs_state.suspend_lock, NULL, RW_DEFAULT, NULL);
    cv_init(&xs_state.reply_cv, NULL, CV_DEFAULT, NULL);

    if (DOMAIN_IS_INITDOMAIN(xen_info))
        return;

    xb_init();
    xenstore_up = B_TRUE;
}

static void
xs_thread_init(void)
{
    (void) thread_create(NULL, 0, xenwatch_thread, NULL, 0, &p0,
        TS_RUN, minclsyspri);
    (void) thread_create(NULL, 0, xenbus_thread, NULL, 0, &p0,
        TS_RUN, minclsyspri);
    xenbus_taskq = taskq_create("xenbus_taskq", 1,
        maxclsyspri - 1, 1, 1, TASKQ_PREPOPULATE);
    ASSERT(xenbus_taskq != NULL);
}

void
xs_domu_init(void)
{
    if (DOMAIN_IS_INITDOMAIN(xen_info))
        return;

    /*
     * Add interrupt handler for xenbus now, must wait till after
     * psm module is loaded.  All use of xenbus is in polled mode
     * until xs_init is called since it is what kicks off the xs
     * server threads.
     */
    xs_thread_init();
    xb_setup_intr();
}


void
xs_dom0_init(void)
{
    static boolean_t initialized = B_FALSE;

    ASSERT(DOMAIN_IS_INITDOMAIN(xen_info));

    /*
     * The xenbus driver might be re-attaching.
     */
    if (initialized)
        return;

    xb_init();
    xs_thread_init();
    xb_setup_intr();

    initialized = B_TRUE;
}