C++ xenbus_read函数代码示例

int pcifront_physical_to_virtual (struct pcifront_dev *dev,
                                  unsigned int *dom,
                                  unsigned int *bus,
                                  unsigned int *slot,
                                  unsigned long *fun)
{
    /* FIXME: the buffer sizing is a little lazy here. 10 extra bytes
       should be enough to hold the paths we need to construct, even
       if the number of devices is large */
    char path[strlen(dev->backend) + strlen("/num_devs") + 10 + 1];
    int i, n;
    char *s, *msg = NULL;
    unsigned int dom1, bus1, slot1, fun1;

    if (!dev)
        dev = pcidev;

    snprintf(path, sizeof(path), "%s/num_devs", dev->backend);
    n = xenbus_read_integer(path);

    for (i = 0; i < n; i++) {
        snprintf(path, sizeof(path), "%s/dev-%d", dev->backend, i);
        msg = xenbus_read(XBT_NIL, path, &s);
        if (msg) {
            printk("Error %s when reading the PCI root name at %s\n", msg, path);
            free(msg);
            continue;
        }

        if (sscanf(s, "%x:%x:%x.%x", &dom1, &bus1, &slot1, &fun1) != 4) {
            printk("\"%s\" does not look like a PCI device address\n", s);
            free(s);
            continue;
        }
        free(s);

        if (dom1 == *dom && bus1 == *bus && slot1 == *slot && fun1 == *fun) {
            snprintf(path, sizeof(path), "%s/vdev-%d", dev->backend, i);
            msg = xenbus_read(XBT_NIL, path, &s);
            if (msg) {
                printk("Error %s when reading the PCI root name at %s\n", msg, path);
                continue;
            }

            if (sscanf(s, "%x:%x:%x.%x", dom, bus, slot, fun) != 4) {
                printk("\"%s\" does not look like a PCI device address\n", s);
                free(s);
                continue;
            }
            free(s);

            return 0;
        }
    }
    return -1;
}

static void xen_net_read_rate(struct xenbus_device *dev,
			      unsigned long *bytes, unsigned long *usec)
{
	char *s, *e;
	unsigned long b, u;
	char *ratestr;

	/* Default to unlimited bandwidth. */
	*bytes = ~0UL;
	*usec = 0;

	ratestr = xenbus_read(XBT_NIL, dev->nodename, "rate", NULL);
	if (IS_ERR(ratestr))
		return;

	s = ratestr;
	b = simple_strtoul(s, &e, 10);
	if ((s == e) || (*e != ','))
		goto fail;

	s = e + 1;
	u = simple_strtoul(s, &e, 10);
	if ((s == e) || (*e != '\0'))
		goto fail;

	*bytes = b;
	*usec = u;

	kfree(ratestr);
	return;

 fail:
	pr_warn("Failed to parse network rate limit. Traffic unlimited.\n");
	kfree(ratestr);
}

/* Write a grant ref and ec port to xenstore in a transaction for whatever
 * your pThing is. Also some non-transaction read/write stuff.
 */
static NTSTATUS
GrantAndEventChannelInATransaction(CHAR *pFrontendPath, struct THING *pThing)
{
    NTSTATUS Status;
    CHAR *pMyData;
    xenbus_transaction_t Xbt;
    
    do {
        xenbus_transaction_start(&Xbt);
        xenbus_write_grant_ref(Xbt, pFrontendPath, "ring-ref",
                               pThing->RingGrantRef);

        xenbus_write_evtchn_port(Xbt, pFrontendPath, "event-channel",
                                 pThing->EvtchnPort);

        Status = xenbus_transaction_end(Xbt, 0);

    } while (Status == STATUS_RETRY);

    if (Status != STATUS_SUCCESS) {
        DbgPrint("Failed to end transaction, 0x%08x.\n", Status);
        /* Handle failure */
    }

    /* A write and read w/o a transaction */
    xenbus_write(XBT_NIL, "drivers/mydriver", "1.2.3.4");

    Status = xenbus_read(XBT_NIL, "drivers/mydriver/mydata", &pMyData);
    if (NT_SUCCESS(Status)) {
        DbgPrint("Read MyData: %s\n", pMyData);
        XmFreeMemory(pMyData);
    }

    /* ... */
}

static void shutdown_thread(void *p)
{
    const char *path = "control/shutdown";
    const char *token = path;
    xenbus_event_queue events = NULL;
    char *shutdown = NULL, *err;
    unsigned int shutdown_reason;
    xenbus_watch_path_token(XBT_NIL, path, token, &events);
    while ((err = xenbus_read(XBT_NIL, path, &shutdown)) != NULL || !strcmp(shutdown, ""))
    {
        free(err);
        free(shutdown);
        shutdown = NULL;
        xenbus_wait_for_watch(&events);
    }
    err = xenbus_unwatch_path_token(XBT_NIL, path, token);
    free(err);
    err = xenbus_write(XBT_NIL, path, "");
    free(err);
    printk("Shutting down (%s)\n", shutdown);

    if (!strcmp(shutdown, "poweroff"))
        shutdown_reason = SHUTDOWN_poweroff;
    else if (!strcmp(shutdown, "reboot"))
        shutdown_reason = SHUTDOWN_reboot;
    else
        /* Unknown */
        shutdown_reason = SHUTDOWN_crash;
    app_shutdown(shutdown_reason);
    free(shutdown);
}

int fork_xenbus(void)
{
	char path[50];
    char *flag = "fork", *err;
    xenbus_event_queue events = NULL;

    sprintf(path,"fork/requests");
    xenbus_watch_path_token(XBT_NIL, path, path, &events);
	xenbus_write(XBT_NIL, path, "fork");

    while(1){

        xenbus_wait_for_watch(&events);

        if ((err = xenbus_read(XBT_NIL, path, &flag))) {
            free(err);
            continue;
        }

        if (!strcmp(flag, "") || !strcmp(flag, "fork")) {
            free(flag);
            flag = NULL;
            continue;
        }else if (!strcmp(flag, "0"))
        	return 0;
        else if (!strcmp(flag, "1"))
            return 1;

        err = xenbus_write(XBT_NIL, path, "");
        free(err);
        free(flag);
        flag = NULL;
    }
    return -1;
}

/**
 * Handle the creation of the hotplug script environment.  We add the script
 * and vif variables to the environment, for the benefit of the vif-* hotplug
 * scripts.
 */
static int netback_uevent(struct xenbus_device *xdev, char **envp,
			  int num_envp, char *buffer, int buffer_size)
{
	struct backend_info *be = xdev->dev.driver_data;
	netif_t *netif = be->netif;
	int i = 0, length = 0;
	char *val;

	DPRINTK("netback_uevent");

	val = xenbus_read(XBT_NIL, xdev->nodename, "script", NULL);
	if (IS_ERR(val)) {
		int err = PTR_ERR(val);
		xenbus_dev_fatal(xdev, err, "reading script");
		return err;
	}
	else {
		add_uevent_var(envp, num_envp, &i, buffer, buffer_size,
			       &length, "script=%s", val);
		kfree(val);
	}

	add_uevent_var(envp, num_envp, &i, buffer, buffer_size, &length,
		       "vif=%s", netif->dev->name);

	envp[i] = NULL;

	return 0;
}

void pcifront_scan(struct pcifront_dev *dev, void (*func)(unsigned int domain, unsigned int bus, unsigned slot, unsigned int fun))
{
    char path[strlen(dev->backend) + 1 + 5 + 10 + 1];
    int i, n;
    char *s, *msg;
    unsigned int domain, bus, slot, fun;

    snprintf(path, sizeof(path), "%s/num_devs", dev->backend);
    n = xenbus_read_integer(path);

    for (i = 0; i < n; i++) {
        snprintf(path, sizeof(path), "%s/vdev-%d", dev->backend, i);
        msg = xenbus_read(XBT_NIL, path, &s);
        if (msg) {
            printk("Error %s when reading the PCI root name at %s\n", path);
            continue;
        }

        if (sscanf(s, "%x:%x:%x.%x", &domain, &bus, &slot, &fun) != 4) {
            printk("\"%s\" does not look like a PCI device address\n", s);
            free(s);
            continue;
        }
        free(s);

        func(domain, bus, slot, fun);
    }
}

static PCHAR
XenLowerReadXenstoreValue(
    PCHAR Path,
    PCHAR Value)
{
    ULONG plen, vlen;
    PCHAR path;
    PCHAR res = NULL;
    NTSTATUS status;

    plen = (ULONG)strlen(Path);
    vlen = (ULONG)strlen(Value);
    path = (PCHAR)XmAllocateMemory(plen + vlen + 2);
    if (path == NULL)
    {
        return NULL;
    }

    memcpy(path, Path, plen);
    path[plen] = '/';
    memcpy(path + plen + 1, Value, vlen + 1);
    status = xenbus_read(XBT_NIL, path, &res);
    XmFreeMemory(path);
    if (!NT_SUCCESS(status))
    {
        return NULL;
    }

    return res;
}

int xenbus_read_uuid(const char* path, unsigned char uuid[16]) {
   char * res, *buf;
   res = xenbus_read(XBT_NIL, path, &buf);
   if(res) {
      printk("Failed to read %s.\n", path);
      free(res);
      return 0;
   }
   if(strlen(buf) != ((2*16)+4) /* 16 hex bytes and 4 hyphens */
         || sscanf(buf,
            "%2hhx%2hhx%2hhx%2hhx-"
            "%2hhx%2hhx-"
            "%2hhx%2hhx-"
            "%2hhx%2hhx-"
            "%2hhx%2hhx%2hhx%2hhx%2hhx%2hhx",
            uuid, uuid + 1, uuid + 2, uuid + 3,
            uuid + 4, uuid + 5, uuid + 6, uuid + 7,
            uuid + 8, uuid + 9, uuid + 10, uuid + 11,
            uuid + 12, uuid + 13, uuid + 14, uuid + 15) != 16) {
      printk("Xenbus path %s value %s is not a uuid!\n", path, buf);
      free(buf);
      return 0;
   }
   free(buf);
   return 1;
}

/*ARGSUSED*/
static void
xen_shutdown_handler(struct xenbus_watch *watch, const char **vec,
	unsigned int len)
{
	char *str;
	xenbus_transaction_t xbt;
	int err, shutdown_code = SHUTDOWN_INVALID;
	unsigned int slen;

again:
	err = xenbus_transaction_start(&xbt);
	if (err)
		return;
	if (xenbus_read(xbt, "control", "shutdown", (void *)&str, &slen)) {
		(void) xenbus_transaction_end(xbt, 1);
		return;
	}

	SUSPEND_DEBUG("%d: xen_shutdown_handler: \"%s\"\n", CPU->cpu_id, str);

	/*
	 * If this is a watch fired from our write below, check out early to
	 * avoid an infinite loop.
	 */
	if (strcmp(str, "") == 0) {
		(void) xenbus_transaction_end(xbt, 0);
		kmem_free(str, slen);
		return;
	} else if (strcmp(str, "poweroff") == 0) {
		shutdown_code = SHUTDOWN_POWEROFF;
	} else if (strcmp(str, "reboot") == 0) {
		shutdown_code = SHUTDOWN_REBOOT;
	} else if (strcmp(str, "suspend") == 0) {
		shutdown_code = SHUTDOWN_SUSPEND;
	} else if (strcmp(str, "halt") == 0) {
		shutdown_code = SHUTDOWN_HALT;
	} else {
		printf("Ignoring shutdown request: %s\n", str);
	}

	/*
	 * XXPV	Should we check the value of xenbus_write() too, or are all
	 *	errors automatically folded into xenbus_transaction_end() ??
	 */
	(void) xenbus_write(xbt, "control", "shutdown", "");
	err = xenbus_transaction_end(xbt, 0);
	if (err == EAGAIN) {
		SUSPEND_DEBUG("%d: trying again\n", CPU->cpu_id);
		kmem_free(str, slen);
		goto again;
	}

	kmem_free(str, slen);
	if (shutdown_code != SHUTDOWN_INVALID) {
		(void) taskq_dispatch(xen_shutdown_tq, xen_shutdown,
		    (void *)(intptr_t)shutdown_code, 0);
	}
}

static void shutdown_handler(struct xenbus_watch *watch,
			     const char **vec, unsigned int len)
{
	char *str;
	struct xenbus_transaction xbt;
	int err;
	static struct shutdown_handler handlers[] = {
		{ "poweroff",	do_poweroff },
		{ "halt",	do_poweroff },
		{ "reboot",	do_reboot   },
#ifdef CONFIG_HIBERNATE_CALLBACKS
		{ "suspend",	do_suspend  },
#endif
		{NULL, NULL},
	};
	static struct shutdown_handler *handler;

	if (shutting_down != SHUTDOWN_INVALID)
		return;

 again:
	err = xenbus_transaction_start(&xbt);
	if (err)
		return;

	str = (char *)xenbus_read(xbt, "control", "shutdown", NULL);
	/* Ignore read errors and empty reads. */
	if (XENBUS_IS_ERR_READ(str)) {
		xenbus_transaction_end(xbt, 1);
		return;
	}

	for (handler = &handlers[0]; handler->command; handler++) {
		if (strcmp(str, handler->command) == 0)
			break;
	}

	/* Only acknowledge commands which we are prepared to handle. */
	if (handler->cb)
		xenbus_write(xbt, "control", "shutdown", "");

	err = xenbus_transaction_end(xbt, 0);
	if (err == -EAGAIN) {
		kfree(str);
		goto again;
	}

	if (handler->cb) {
		handler->cb();
	} else {
		pr_info("Ignoring shutdown request: %s\n", str);
		shutting_down = SHUTDOWN_INVALID;
	}

	kfree(str);
}

domid_t xenbus_get_self_id(void)
{
    char *dom_id;
    domid_t ret;

    BUG_ON(xenbus_read(XBT_NIL, "domid", &dom_id));
    sscanf(dom_id, "%u", (unsigned int*)&ret);

    return ret;
}

static ssize_t uuid_show(struct hyp_sysfs_attr *attr, char *buffer)
{
	char *vm, *val;
	int ret;

	if (!is_xenstored_ready())
		return -EBUSY;

	vm = xenbus_read(XBT_NIL, "vm", "", NULL);
	if (IS_ERR(vm))
		return PTR_ERR(vm);
	val = xenbus_read(XBT_NIL, vm, "uuid", NULL);
	kfree(vm);
	if (IS_ERR(val))
		return PTR_ERR(val);
	ret = sprintf(buffer, "%s\n", val);
	kfree(val);
	return ret;
}

static int read_nicname(struct xenbus_device *dev, struct netback_accel *bend)
{
	int len;

	/* nic name used to select interface used for acceleration */
	bend->nicname = xenbus_read(XBT_NIL, dev->nodename, "accel", &len);
	if (IS_ERR(bend->nicname))
		return PTR_ERR(bend->nicname);

	return 0;
}

static void do_read_test(const char *path)
{
    char *res, *msg;
    printk("Read %s...\n", path);
    msg = xenbus_read(XBT_NIL, path, &res);
    if (msg) {
	printk("Error in xenbus read: %s\n", msg);
	free(msg);
	return;
    }
    printk("Read %s -> %s.\n", path, res);
    free(res);
}