devmap.c

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/*
 * Copyright (c) 2007 Josef Cejka
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <ipc/services.h>
#include <ipc/ns.h>
#include <async.h>
#include <stdio.h>
#include <errno.h>
#include <bool.h>
#include <fibril_synch.h>
#include <stdlib.h>
#include <str.h>
#include <ipc/devmap.h>
#include <assert.h>

#define NAME          "devmap"
#define NULL_DEVICES  256

typedef struct {
        link_t drivers;
        link_t devices;
        sysarg_t phone;
        char *name;
        fibril_mutex_t devices_mutex;
} devmap_driver_t;

typedef struct {
        link_t namespaces;
        devmap_handle_t handle;
        char *name;
        size_t refcnt;
} devmap_namespace_t;

typedef struct {
        link_t devices;
        link_t driver_devices;
        devmap_handle_t handle;
        devmap_namespace_t *namespace;
        char *name;
        devmap_driver_t *driver;
        sysarg_t forward_interface;
} devmap_device_t;

LIST_INITIALIZE(devices_list);
LIST_INITIALIZE(namespaces_list);
LIST_INITIALIZE(drivers_list);

/* Locking order:
 *  drivers_list_mutex
 *  devices_list_mutex
 *  (devmap_driver_t *)->devices_mutex
 *  create_handle_mutex
 **/

static FIBRIL_MUTEX_INITIALIZE(devices_list_mutex);
static FIBRIL_CONDVAR_INITIALIZE(devices_list_cv);
static FIBRIL_MUTEX_INITIALIZE(drivers_list_mutex);
static FIBRIL_MUTEX_INITIALIZE(create_handle_mutex);
static FIBRIL_MUTEX_INITIALIZE(null_devices_mutex);

static devmap_handle_t last_handle = 0;
static devmap_device_t *null_devices[NULL_DEVICES];

/*
 * Dummy list for null devices. This is necessary so that null devices can
 * be used just as any other devices, e.g. in devmap_device_unregister_core().
 */
static LIST_INITIALIZE(dummy_null_driver_devices);

static devmap_handle_t devmap_create_handle(void)
{
        /* TODO: allow reusing old handles after their unregistration
         * and implement some version of LRU algorithm, avoid overflow
         */
        
        fibril_mutex_lock(&create_handle_mutex);
        last_handle++;
        fibril_mutex_unlock(&create_handle_mutex);
        
        return last_handle;
}

static bool devmap_fqdn_split(const char *fqdn, char **ns_name, char **name)
{
        size_t cnt = 0;
        size_t slash_offset = 0;
        size_t slash_after = 0;
        
        size_t offset = 0;
        size_t offset_prev = 0;
        wchar_t c;
        
        while ((c = str_decode(fqdn, &offset, STR_NO_LIMIT)) != 0) {
                if (c == '/') {
                        cnt++;
                        slash_offset = offset_prev;
                        slash_after = offset;
                }
                offset_prev = offset;
        }
        
        /* More than one slash */
        if (cnt > 1)
                return false;
        
        /* No slash -> namespace is empty */
        if (cnt == 0) {
                *ns_name = str_dup("");
                if (*ns_name == NULL)
                        return false;
                
                *name = str_dup(fqdn);
                if (*name == NULL) {
                        free(*ns_name);
                        return false;
                }
                
                if (str_cmp(*name, "") == 0) {
                        free(*name);
                        free(*ns_name);
                        return false;
                }
                
                return true;
        }
        
        /* Exactly one slash */
        *ns_name = str_ndup(fqdn, slash_offset);
        if (*ns_name == NULL)
                return false;
        
        *name = str_dup(fqdn + slash_after);
        if (*name == NULL) {
                free(*ns_name);
                return false;
        }
        
        if (str_cmp(*name, "") == 0) {
                free(*name);
                free(*ns_name);
                return false;
        }
        
        return true;
}

static devmap_namespace_t *devmap_namespace_find_name(const char *name)
{
        link_t *item;
        
        assert(fibril_mutex_is_locked(&devices_list_mutex));
        
        for (item = namespaces_list.next; item != &namespaces_list; item = item->next) {
                devmap_namespace_t *namespace =
                    list_get_instance(item, devmap_namespace_t, namespaces);
                if (str_cmp(namespace->name, name) == 0)
                        return namespace;
        }
        
        return NULL;
}

static devmap_namespace_t *devmap_namespace_find_handle(devmap_handle_t handle)
{
        link_t *item;
        
        assert(fibril_mutex_is_locked(&devices_list_mutex));
        
        for (item = namespaces_list.next; item != &namespaces_list; item = item->next) {
                devmap_namespace_t *namespace =
                    list_get_instance(item, devmap_namespace_t, namespaces);
                if (namespace->handle == handle)
                        return namespace;
        }
        
        return NULL;
}

static devmap_device_t *devmap_device_find_name(const char *ns_name,
    const char *name)
{
        link_t *item;
        
        assert(fibril_mutex_is_locked(&devices_list_mutex));
        
        for (item = devices_list.next; item != &devices_list; item = item->next) {
                devmap_device_t *device =
                    list_get_instance(item, devmap_device_t, devices);
                if ((str_cmp(device->namespace->name, ns_name) == 0)
                    && (str_cmp(device->name, name) == 0))
                        return device;
        }
        
        return NULL;
}

static devmap_device_t *devmap_device_find_handle(devmap_handle_t handle)
{
        link_t *item;
        
        assert(fibril_mutex_is_locked(&devices_list_mutex));
        
        for (item = devices_list.next; item != &devices_list; item = item->next) {
                devmap_device_t *device =
                    list_get_instance(item, devmap_device_t, devices);
                if (device->handle == handle)
                        return device;
        }
        
        return NULL;
}

static devmap_namespace_t *devmap_namespace_create(const char *ns_name)
{
        devmap_namespace_t *namespace;
        
        assert(fibril_mutex_is_locked(&devices_list_mutex));
        
        namespace = devmap_namespace_find_name(ns_name);
        if (namespace != NULL)
                return namespace;
        
        namespace = (devmap_namespace_t *) malloc(sizeof(devmap_namespace_t));
        if (namespace == NULL)
                return NULL;
        
        namespace->name = str_dup(ns_name);
        if (namespace->name == NULL) {
                free(namespace);
                return NULL;
        }
        
        namespace->handle = devmap_create_handle();
        namespace->refcnt = 0;
        
        /*
         * Insert new namespace into list of registered namespaces
         */
        list_append(&(namespace->namespaces), &namespaces_list);
        
        return namespace;
}

static void devmap_namespace_destroy(devmap_namespace_t *namespace)
{
        assert(fibril_mutex_is_locked(&devices_list_mutex));

        if (namespace->refcnt == 0) {
                list_remove(&(namespace->namespaces));
                
                free(namespace->name);
                free(namespace);
        }
}

static void devmap_namespace_addref(devmap_namespace_t *namespace,
    devmap_device_t *device)
{
        assert(fibril_mutex_is_locked(&devices_list_mutex));

        device->namespace = namespace;
        namespace->refcnt++;
}

static void devmap_namespace_delref(devmap_namespace_t *namespace)
{
        assert(fibril_mutex_is_locked(&devices_list_mutex));

        namespace->refcnt--;
        devmap_namespace_destroy(namespace);
}

static void devmap_device_unregister_core(devmap_device_t *device)
{
        assert(fibril_mutex_is_locked(&devices_list_mutex));

        devmap_namespace_delref(device->namespace);
        list_remove(&(device->devices));
        list_remove(&(device->driver_devices));
        
        free(device->name);
        free(device);
}

static devmap_driver_t *devmap_driver_register(void)
{
        ipc_call_t icall;
        ipc_callid_t iid = async_get_call(&icall);
        
        if (IPC_GET_IMETHOD(icall) != DEVMAP_DRIVER_REGISTER) {
                async_answer_0(iid, EREFUSED);
                return NULL;
        }
        
        devmap_driver_t *driver =
            (devmap_driver_t *) malloc(sizeof(devmap_driver_t));
        if (driver == NULL) {
                async_answer_0(iid, ENOMEM);
                return NULL;
        }
        
        /*
         * Get driver name
         */
        int rc = async_data_write_accept((void **) &driver->name, true, 0,
            DEVMAP_NAME_MAXLEN, 0, NULL);
        if (rc != EOK) {
                free(driver);
                async_answer_0(iid, rc);
                return NULL;
        }
        
        /*
         * Create connection to the driver
         */
        ipc_call_t call;
        ipc_callid_t callid = async_get_call(&call);
        
        if (IPC_GET_IMETHOD(call) != IPC_M_CONNECT_TO_ME) {
                free(driver->name);
                free(driver);
                async_answer_0(callid, ENOTSUP);
                async_answer_0(iid, ENOTSUP);
                return NULL;
        }
        
        driver->phone = IPC_GET_ARG5(call);
        async_answer_0(callid, EOK);
        
        /*
         * Initialize mutex for list of devices
         * owned by this driver
         */
        fibril_mutex_initialize(&driver->devices_mutex);
        
        /*
         * Initialize list of asociated devices
         */
        list_initialize(&driver->devices);

        link_initialize(&driver->drivers);
        
        fibril_mutex_lock(&drivers_list_mutex);
        
        /* TODO:
         * Check that no driver with name equal to
         * driver->name is registered
         */
        
        /*
         * Insert new driver into list of registered drivers
         */
        list_append(&(driver->drivers), &drivers_list);
        fibril_mutex_unlock(&drivers_list_mutex);
        
        async_answer_0(iid, EOK);
        
        return driver;
}

static int devmap_driver_unregister(devmap_driver_t *driver)
{
        if (driver == NULL)
                return EEXISTS;
        
        fibril_mutex_lock(&drivers_list_mutex);
        
        if (driver->phone != 0)
                async_hangup(driver->phone);
        
        /* Remove it from list of drivers */
        list_remove(&(driver->drivers));
        
        /* Unregister all its devices */
        fibril_mutex_lock(&devices_list_mutex);
        fibril_mutex_lock(&driver->devices_mutex);
        
        while (!list_empty(&(driver->devices))) {
                devmap_device_t *device = list_get_instance(driver->devices.next,
                    devmap_device_t, driver_devices);
                devmap_device_unregister_core(device);
        }
        
        fibril_mutex_unlock(&driver->devices_mutex);
        fibril_mutex_unlock(&devices_list_mutex);
        fibril_mutex_unlock(&drivers_list_mutex);
        
        /* Free name and driver */
        if (driver->name != NULL)
                free(driver->name);
        
        free(driver);
        
        return EOK;
}

static void devmap_device_register(ipc_callid_t iid, ipc_call_t *icall,
    devmap_driver_t *driver)
{
        if (driver == NULL) {
                async_answer_0(iid, EREFUSED);
                return;
        }
        
        /* Create new device entry */
        devmap_device_t *device =
            (devmap_device_t *) malloc(sizeof(devmap_device_t));
        if (device == NULL) {
                async_answer_0(iid, ENOMEM);
                return;
        }
        
        /* Set the interface, if any. */
        device->forward_interface = IPC_GET_ARG1(*icall);

        /* Get fqdn */
        char *fqdn;
        int rc = async_data_write_accept((void **) &fqdn, true, 0,
            DEVMAP_NAME_MAXLEN, 0, NULL);
        if (rc != EOK) {
                free(device);
                async_answer_0(iid, rc);
                return;
        }
        
        char *ns_name;
        if (!devmap_fqdn_split(fqdn, &ns_name, &device->name)) {
                free(fqdn);
                free(device);
                async_answer_0(iid, EINVAL);
                return;
        }
        
        free(fqdn);
        
        fibril_mutex_lock(&devices_list_mutex);
        
        devmap_namespace_t *namespace = devmap_namespace_create(ns_name);
        free(ns_name);
        if (namespace == NULL) {
                fibril_mutex_unlock(&devices_list_mutex);
                free(device->name);
                free(device);
                async_answer_0(iid, ENOMEM);
                return;
        }
        
        link_initialize(&device->devices);
        link_initialize(&device->driver_devices);
        
        /* Check that device is not already registered */
        if (devmap_device_find_name(namespace->name, device->name) != NULL) {
                printf("%s: Device '%s/%s' already registered\n", NAME,
                    namespace->name, device->name);
                devmap_namespace_destroy(namespace);
                fibril_mutex_unlock(&devices_list_mutex);
                free(device->name);
                free(device);
                async_answer_0(iid, EEXISTS);
                return;
        }
        
        /* Get unique device handle */
        device->handle = devmap_create_handle();

        devmap_namespace_addref(namespace, device);
        device->driver = driver;
        
        /* Insert device into list of all devices  */
        list_append(&device->devices, &devices_list);
        
        /* Insert device into list of devices that belog to one driver */
        fibril_mutex_lock(&device->driver->devices_mutex);
        
        list_append(&device->driver_devices, &device->driver->devices);
        
        fibril_mutex_unlock(&device->driver->devices_mutex);
        fibril_condvar_broadcast(&devices_list_cv);
        fibril_mutex_unlock(&devices_list_mutex);
        
        async_answer_1(iid, EOK, device->handle);
}

static int devmap_device_unregister(ipc_callid_t iid, ipc_call_t *icall, 
    devmap_driver_t *driver)
{
        /* TODO */
        return EOK;
}

static void devmap_forward(ipc_callid_t callid, ipc_call_t *call)
{
        fibril_mutex_lock(&devices_list_mutex);
        
        /*
         * Get handle from request
         */
        devmap_handle_t handle = IPC_GET_ARG2(*call);
        devmap_device_t *dev = devmap_device_find_handle(handle);
        
        if ((dev == NULL) || (dev->driver == NULL) || (dev->driver->phone == 0)) {
                fibril_mutex_unlock(&devices_list_mutex);
                async_answer_0(callid, ENOENT);
                return;
        }
        
        if (dev->forward_interface == 0) {
                async_forward_fast(callid, dev->driver->phone,
                    dev->handle, 0, 0,
                    IPC_FF_NONE);
        } else {
                async_forward_fast(callid, dev->driver->phone,
                    dev->forward_interface, dev->handle, 0,
                    IPC_FF_NONE);
        }
        
        fibril_mutex_unlock(&devices_list_mutex);
}

static void devmap_device_get_handle(ipc_callid_t iid, ipc_call_t *icall)
{
        char *fqdn;
        
        /* Get fqdn */
        int rc = async_data_write_accept((void **) &fqdn, true, 0,
            DEVMAP_NAME_MAXLEN, 0, NULL);
        if (rc != EOK) {
                async_answer_0(iid, rc);
                return;
        }
        
        char *ns_name;
        char *name;
        if (!devmap_fqdn_split(fqdn, &ns_name, &name)) {
                free(fqdn);
                async_answer_0(iid, EINVAL);
                return;
        }
        
        free(fqdn);
        
        fibril_mutex_lock(&devices_list_mutex);
        const devmap_device_t *dev;
        
recheck:
        
        /*
         * Find device name in the list of known devices.
         */
        dev = devmap_device_find_name(ns_name, name);
        
        /*
         * Device was not found.
         */
        if (dev == NULL) {
                if (IPC_GET_ARG1(*icall) & IPC_FLAG_BLOCKING) {
                        /* Blocking lookup */
                        fibril_condvar_wait(&devices_list_cv,
                            &devices_list_mutex);
                        goto recheck;
                }
                
                async_answer_0(iid, ENOENT);
                free(ns_name);
                free(name);
                fibril_mutex_unlock(&devices_list_mutex);
                return;
        }
        
        async_answer_1(iid, EOK, dev->handle);
        
        fibril_mutex_unlock(&devices_list_mutex);
        free(ns_name);
        free(name);
}

static void devmap_namespace_get_handle(ipc_callid_t iid, ipc_call_t *icall)
{
        char *name;
        
        /* Get device name */
        int rc = async_data_write_accept((void **) &name, true, 0,
            DEVMAP_NAME_MAXLEN, 0, NULL);
        if (rc != EOK) {
                async_answer_0(iid, rc);
                return;
        }
        
        fibril_mutex_lock(&devices_list_mutex);
        const devmap_namespace_t *namespace;
        
recheck:
        
        /*
         * Find namespace name in the list of known namespaces.
         */
        namespace = devmap_namespace_find_name(name);
        
        /*
         * Namespace was not found.
         */
        if (namespace == NULL) {
                if (IPC_GET_ARG1(*icall) & IPC_FLAG_BLOCKING) {
                        /* Blocking lookup */
                        fibril_condvar_wait(&devices_list_cv,
                            &devices_list_mutex);
                        goto recheck;
                }
                
                async_answer_0(iid, ENOENT);
                free(name);
                fibril_mutex_unlock(&devices_list_mutex);
                return;
        }
        
        async_answer_1(iid, EOK, namespace->handle);
        
        fibril_mutex_unlock(&devices_list_mutex);
        free(name);
}

static void devmap_handle_probe(ipc_callid_t iid, ipc_call_t *icall)
{
        fibril_mutex_lock(&devices_list_mutex);
        
        devmap_namespace_t *namespace =
            devmap_namespace_find_handle(IPC_GET_ARG1(*icall));
        if (namespace == NULL) {
                devmap_device_t *dev =
                    devmap_device_find_handle(IPC_GET_ARG1(*icall));
                if (dev == NULL)
                        async_answer_1(iid, EOK, DEV_HANDLE_NONE);
                else
                        async_answer_1(iid, EOK, DEV_HANDLE_DEVICE);
        } else
                async_answer_1(iid, EOK, DEV_HANDLE_NAMESPACE);
        
        fibril_mutex_unlock(&devices_list_mutex);
}

static void devmap_get_namespace_count(ipc_callid_t iid, ipc_call_t *icall)
{
        fibril_mutex_lock(&devices_list_mutex);
        async_answer_1(iid, EOK, list_count(&namespaces_list));
        fibril_mutex_unlock(&devices_list_mutex);
}

static void devmap_get_device_count(ipc_callid_t iid, ipc_call_t *icall)
{
        fibril_mutex_lock(&devices_list_mutex);
        
        devmap_namespace_t *namespace =
            devmap_namespace_find_handle(IPC_GET_ARG1(*icall));
        if (namespace == NULL)
                async_answer_0(iid, EEXISTS);
        else
                async_answer_1(iid, EOK, namespace->refcnt);
        
        fibril_mutex_unlock(&devices_list_mutex);
}

static void devmap_get_namespaces(ipc_callid_t iid, ipc_call_t *icall)
{
        ipc_callid_t callid;
        size_t size;
        if (!async_data_read_receive(&callid, &size)) {
                async_answer_0(callid, EREFUSED);
                async_answer_0(iid, EREFUSED);
                return;
        }
        
        if ((size % sizeof(dev_desc_t)) != 0) {
                async_answer_0(callid, EINVAL);
                async_answer_0(iid, EINVAL);
                return;
        }
        
        fibril_mutex_lock(&devices_list_mutex);
        
        size_t count = size / sizeof(dev_desc_t);
        if (count != list_count(&namespaces_list)) {
                fibril_mutex_unlock(&devices_list_mutex);
                async_answer_0(callid, EOVERFLOW);
                async_answer_0(iid, EOVERFLOW);
                return;
        }
        
        dev_desc_t *desc = (dev_desc_t *) malloc(size);
        if (desc == NULL) {
                fibril_mutex_unlock(&devices_list_mutex);
                async_answer_0(callid, ENOMEM);
                async_answer_0(iid, ENOMEM);
                return;
        }
        
        link_t *item;
        size_t pos = 0;
        for (item = namespaces_list.next; item != &namespaces_list;
            item = item->next) {
                devmap_namespace_t *namespace =
                    list_get_instance(item, devmap_namespace_t, namespaces);
                
                desc[pos].handle = namespace->handle;
                str_cpy(desc[pos].name, DEVMAP_NAME_MAXLEN, namespace->name);
                pos++;
        }
        
        sysarg_t retval = async_data_read_finalize(callid, desc, size);
        
        free(desc);
        fibril_mutex_unlock(&devices_list_mutex);
        
        async_answer_0(iid, retval);
}

static void devmap_get_devices(ipc_callid_t iid, ipc_call_t *icall)
{
        /* FIXME: Use faster algorithm which can make better use
           of namespaces */
        
        ipc_callid_t callid;
        size_t size;
        if (!async_data_read_receive(&callid, &size)) {
                async_answer_0(callid, EREFUSED);
                async_answer_0(iid, EREFUSED);
                return;
        }
        
        if ((size % sizeof(dev_desc_t)) != 0) {
                async_answer_0(callid, EINVAL);
                async_answer_0(iid, EINVAL);
                return;
        }
        
        fibril_mutex_lock(&devices_list_mutex);
        
        devmap_namespace_t *namespace =
            devmap_namespace_find_handle(IPC_GET_ARG1(*icall));
        if (namespace == NULL) {
                fibril_mutex_unlock(&devices_list_mutex);
                async_answer_0(callid, ENOENT);
                async_answer_0(iid, ENOENT);
                return;
        }
        
        size_t count = size / sizeof(dev_desc_t);
        if (count != namespace->refcnt) {
                fibril_mutex_unlock(&devices_list_mutex);
                async_answer_0(callid, EOVERFLOW);
                async_answer_0(iid, EOVERFLOW);
                return;
        }
        
        dev_desc_t *desc = (dev_desc_t *) malloc(size);
        if (desc == NULL) {
                fibril_mutex_unlock(&devices_list_mutex);
                async_answer_0(callid, ENOMEM);
                async_answer_0(iid, EREFUSED);
                return;
        }
        
        link_t *item;
        size_t pos = 0;
        for (item = devices_list.next; item != &devices_list; item = item->next) {
                devmap_device_t *device =
                    list_get_instance(item, devmap_device_t, devices);
                
                if (device->namespace == namespace) {
                        desc[pos].handle = device->handle;
                        str_cpy(desc[pos].name, DEVMAP_NAME_MAXLEN, device->name);
                        pos++;
                }
        }
        
        sysarg_t retval = async_data_read_finalize(callid, desc, size);
        
        free(desc);
        fibril_mutex_unlock(&devices_list_mutex);
        
        async_answer_0(iid, retval);
}

static void devmap_null_create(ipc_callid_t iid, ipc_call_t *icall)
{
        fibril_mutex_lock(&null_devices_mutex);
        
        unsigned int i;
        bool fnd = false;
        
        for (i = 0; i < NULL_DEVICES; i++) {
                if (null_devices[i] == NULL) {
                        fnd = true;
                        break;
                }
        }
        
        if (!fnd) {
                fibril_mutex_unlock(&null_devices_mutex);
                async_answer_0(iid, ENOMEM);
                return;
        }
        
        char null[DEVMAP_NAME_MAXLEN];
        snprintf(null, DEVMAP_NAME_MAXLEN, "%u", i);
        
        char *dev_name = str_dup(null);
        if (dev_name == NULL) {
                fibril_mutex_unlock(&null_devices_mutex);
                async_answer_0(iid, ENOMEM);
                return;
        }
        
        devmap_device_t *device =
            (devmap_device_t *) malloc(sizeof(devmap_device_t));
        if (device == NULL) {
                fibril_mutex_unlock(&null_devices_mutex);
                async_answer_0(iid, ENOMEM);
                return;
        }
        
        fibril_mutex_lock(&devices_list_mutex);
        
        devmap_namespace_t *namespace = devmap_namespace_create("null");
        if (namespace == NULL) {
                fibril_mutex_lock(&devices_list_mutex);
                fibril_mutex_unlock(&null_devices_mutex);
                async_answer_0(iid, ENOMEM);
                return;
        }
        
        link_initialize(&device->devices);
        link_initialize(&device->driver_devices);
        
        /* Get unique device handle */
        device->handle = devmap_create_handle();
        device->driver = NULL;
        
        devmap_namespace_addref(namespace, device);
        device->name = dev_name;
        
        /*
         * Insert device into list of all devices and into null devices array.
         * Insert device into a dummy list of null driver's devices so that it
         * can be safely removed later.
         */
        list_append(&device->devices, &devices_list);
        list_append(&device->driver_devices, &dummy_null_driver_devices);
        null_devices[i] = device;
        
        fibril_mutex_unlock(&devices_list_mutex);
        fibril_mutex_unlock(&null_devices_mutex);
        
        async_answer_1(iid, EOK, (sysarg_t) i);
}

static void devmap_null_destroy(ipc_callid_t iid, ipc_call_t *icall)
{
        sysarg_t i = IPC_GET_ARG1(*icall);
        if (i >= NULL_DEVICES) {
                async_answer_0(iid, ELIMIT);
                return;
        }
        
        fibril_mutex_lock(&null_devices_mutex);
        
        if (null_devices[i] == NULL) {
                fibril_mutex_unlock(&null_devices_mutex);
                async_answer_0(iid, ENOENT);
                return;
        }
        
        fibril_mutex_lock(&devices_list_mutex);
        devmap_device_unregister_core(null_devices[i]);
        fibril_mutex_unlock(&devices_list_mutex);
        
        null_devices[i] = NULL;
        
        fibril_mutex_unlock(&null_devices_mutex);
        async_answer_0(iid, EOK);
}

static bool devmap_init(void)
{
        fibril_mutex_lock(&null_devices_mutex);
        
        unsigned int i;
        for (i = 0; i < NULL_DEVICES; i++)
                null_devices[i] = NULL;
        
        fibril_mutex_unlock(&null_devices_mutex);
        
        return true;
}

static void devmap_connection_driver(ipc_callid_t iid, ipc_call_t *icall)
{
        /* Accept connection */
        async_answer_0(iid, EOK);
        
        devmap_driver_t *driver = devmap_driver_register();
        if (driver == NULL)
                return;
        
        bool cont = true;
        while (cont) {
                ipc_call_t call;
                ipc_callid_t callid = async_get_call(&call);
                
                switch (IPC_GET_IMETHOD(call)) {
                case IPC_M_PHONE_HUNGUP:
                        cont = false;
                        continue;
                case DEVMAP_DRIVER_UNREGISTER:
                        if (NULL == driver)
                                async_answer_0(callid, ENOENT);
                        else
                                async_answer_0(callid, EOK);
                        break;
                case DEVMAP_DEVICE_REGISTER:
                        /* Register one instance of device */
                        devmap_device_register(callid, &call, driver);
                        break;
                case DEVMAP_DEVICE_UNREGISTER:
                        /* Remove instance of device identified by handler */
                        devmap_device_unregister(callid, &call, driver);
                        break;
                case DEVMAP_DEVICE_GET_HANDLE:
                        devmap_device_get_handle(callid, &call);
                        break;
                case DEVMAP_NAMESPACE_GET_HANDLE:
                        devmap_namespace_get_handle(callid, &call);
                        break;
                default:
                        async_answer_0(callid, ENOENT);
                }
        }
        
        if (driver != NULL) {
                /*
                 * Unregister the device driver and all its devices.
                 */
                devmap_driver_unregister(driver);
                driver = NULL;
        }
}

static void devmap_connection_client(ipc_callid_t iid, ipc_call_t *icall)
{
        /* Accept connection */
        async_answer_0(iid, EOK);
        
        bool cont = true;
        while (cont) {
                ipc_call_t call;
                ipc_callid_t callid = async_get_call(&call);
                
                switch (IPC_GET_IMETHOD(call)) {
                case IPC_M_PHONE_HUNGUP:
                        cont = false;
                        continue;
                case DEVMAP_DEVICE_GET_HANDLE:
                        devmap_device_get_handle(callid, &call);
                        break;
                case DEVMAP_NAMESPACE_GET_HANDLE:
                        devmap_namespace_get_handle(callid, &call);
                        break;
                case DEVMAP_HANDLE_PROBE:
                        devmap_handle_probe(callid, &call);
                        break;
                case DEVMAP_NULL_CREATE:
                        devmap_null_create(callid, &call);
                        break;
                case DEVMAP_NULL_DESTROY:
                        devmap_null_destroy(callid, &call);
                        break;
                case DEVMAP_GET_NAMESPACE_COUNT:
                        devmap_get_namespace_count(callid, &call);
                        break;
                case DEVMAP_GET_DEVICE_COUNT:
                        devmap_get_device_count(callid, &call);
                        break;
                case DEVMAP_GET_NAMESPACES:
                        devmap_get_namespaces(callid, &call);
                        break;
                case DEVMAP_GET_DEVICES:
                        devmap_get_devices(callid, &call);
                        break;
                default:
                        async_answer_0(callid, ENOENT);
                }
        }
}

static void devmap_connection(ipc_callid_t iid, ipc_call_t *icall)
{
        /* Select interface */
        switch ((sysarg_t) (IPC_GET_ARG1(*icall))) {
        case DEVMAP_DRIVER:
                devmap_connection_driver(iid, icall);
                break;
        case DEVMAP_CLIENT:
                devmap_connection_client(iid, icall);
                break;
        case DEVMAP_CONNECT_TO_DEVICE:
                /* Connect client to selected device */
                devmap_forward(iid, icall);
                break;
        default:
                /* No such interface */
                async_answer_0(iid, ENOENT);
        }
}

int main(int argc, char *argv[])
{
        printf("%s: HelenOS Device Mapper\n", NAME);
        
        if (!devmap_init()) {
                printf("%s: Error while initializing service\n", NAME);
                return -1;
        }
        
        /* Set a handler of incomming connections */
        async_set_client_connection(devmap_connection);
        
        /* Register device mapper at naming service */
        if (service_register(SERVICE_DEVMAP) != EOK)
                return -1;
        
        printf("%s: Accepting connections\n", NAME);
        async_manager();
        
        /* Never reached */
        return 0;
}

---