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/*

 * Copyright (c) 2008 Jakub Jermar

 * 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.

 */

/** @addtogroup fs

 * @{

 */

/**

 * @file    vfs_ops.c

 * @brief   Operations that VFS offers to its clients.

 */

#include "vfs.h"

#include <ipc/ipc.h>

#include <async.h>

#include <errno.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <bool.h>

#include <futex.h>

#include <rwlock.h>

#include <libadt/list.h>

#include <unistd.h>

#include <ctype.h>

#include <fcntl.h>

#include <assert.h>

#include <vfs/canonify.h>

/* Forward declarations of static functions. */

static int vfs_truncate_internal(fs_handle_t, dev_handle_t, fs_index_t, size_t);

/**

 * This rwlock prevents the race between a triplet-to-VFS-node resolution and a

 * concurrent VFS operation which modifies the file system namespace.

 */

RWLOCK_INITIALIZE(namespace_rwlock);

futex_t rootfs_futex = FUTEX_INITIALIZER;

vfs_triplet_t rootfs = {

    .fs_handle = 0,

    .dev_handle = 0,

    .index = 0,

};

static int

lookup_root(fs_handle_t fs_handle, dev_handle_t dev_handle,

    vfs_lookup_res_t *result)

{

    vfs_pair_t altroot = {

        .fs_handle = fs_handle,

        .dev_handle = dev_handle,

    };

    return vfs_lookup_internal("/", L_DIRECTORY, result, &altroot);

}

void vfs_mount(ipc_callid_t rid, ipc_call_t *request)

{

    dev_handle_t dev_handle;

    vfs_node_t *mp_node = NULL;

    /*

     * We expect the library to do the device-name to device-handle

     * translation for us, thus the device handle will arrive as ARG1

     * in the request.

     */

    dev_handle = (dev_handle_t)IPC_GET_ARG1(*request);

    /*

     * For now, don't make use of ARG2 and ARG3, but they can be used to

     * carry mount options in the future.

     */

    ipc_callid_t callid;

    size_t size;

    /*

     * Now, we expect the client to send us data with the name of the file

     * system.

     */

    if (!ipc_data_write_receive(&callid, &size)) {

        ipc_answer_0(callid, EINVAL);

        ipc_answer_0(rid, EINVAL);

        return;

    }

    /*

     * Don't receive more than is necessary for storing a full file system

     * name.

     */

    if (size < 1 || size > FS_NAME_MAXLEN) {

        ipc_answer_0(callid, EINVAL);

        ipc_answer_0(rid, EINVAL);

        return;

    }

    /* Deliver the file system name. */

    char fs_name[FS_NAME_MAXLEN + 1];

    (void) ipc_data_write_finalize(callid, fs_name, size);

    fs_name[size] = '\0';

    /*

     * Check if we know a file system with the same name as is in fs_name.

     * This will also give us its file system handle.

     */

    fs_handle_t fs_handle = fs_name_to_handle(fs_name, true);

    if (!fs_handle) {

        ipc_answer_0(rid, ENOENT);

        return;

    }

    /* Now, we want the client to send us the mount point. */

    if (!ipc_data_write_receive(&callid, &size)) {

        ipc_answer_0(callid, EINVAL);

        ipc_answer_0(rid, EINVAL);

        return;

    }

    /* Check whether size is reasonable wrt. the mount point. */

    if (size < 1 || size > MAX_PATH_LEN) {

        ipc_answer_0(callid, EINVAL);

        ipc_answer_0(rid, EINVAL);

        return;

    }

    /* Allocate buffer for the mount point data being received. */

    uint8_t *buf;

    buf = malloc(size + 1);

    if (!buf) {

        ipc_answer_0(callid, ENOMEM);

        ipc_answer_0(rid, ENOMEM);

        return;

    }

    /* Deliver the mount point. */

    (void) ipc_data_write_finalize(callid, buf, size);

    buf[size] = '\0';

    /*

     * Lookup the root node of the filesystem being mounted.

     * In this case, we don't need to take the namespace_futex as the root

     * node cannot be removed. However, we do take a reference to it so

     * that we can track how many times it has been mounted.

     */

    int rc;

    vfs_lookup_res_t mr_res;

    rc = lookup_root(fs_handle, dev_handle, &mr_res);

    if (rc != EOK) {

        free(buf);

        ipc_answer_0(rid, rc);

        return;

    }

    vfs_node_t *mr_node = vfs_node_get(&mr_res);

    if (!mr_node) {

        free(buf);

        ipc_answer_0(rid, ENOMEM);

        return;

    }

    /* Finally, we need to resolve the path to the mountpoint. */

    vfs_lookup_res_t mp_res;

    futex_down(&rootfs_futex);

    if (rootfs.fs_handle) {

        /* We already have the root FS. */

        rwlock_write_lock(&namespace_rwlock);

        if ((size == 1) && (buf[0] == '/')) {

            /* Trying to mount root FS over root FS */

            rwlock_write_unlock(&namespace_rwlock);

            futex_up(&rootfs_futex);

            vfs_node_put(mr_node);

            free(buf);

            ipc_answer_0(rid, EBUSY);

            return;

        }

        rc = vfs_lookup_internal(buf, L_DIRECTORY, &mp_res, NULL);

        if (rc != EOK) {

            /* The lookup failed for some reason. */

            rwlock_write_unlock(&namespace_rwlock);

            futex_up(&rootfs_futex);

            vfs_node_put(mr_node);  /* failed -> drop reference */

            free(buf);

            ipc_answer_0(rid, rc);

            return;

        }

        mp_node = vfs_node_get(&mp_res);

        if (!mp_node) {

            rwlock_write_unlock(&namespace_rwlock);

            futex_up(&rootfs_futex);

            vfs_node_put(mr_node);  /* failed -> drop reference */

            free(buf);

            ipc_answer_0(rid, ENOMEM);

            return;

        }

        /*

         * Now we hold a reference to mp_node.

         * It will be dropped upon the corresponding VFS_UNMOUNT.

         * This prevents the mount point from being deleted.

         */

        rwlock_write_unlock(&namespace_rwlock);

    } else {

        /* We still don't have the root file system mounted. */

        if ((size == 1) && (buf[0] == '/')) {

            /* For this simple, but important case, we are done. */

            rootfs = mr_res.triplet;

            futex_up(&rootfs_futex);

            free(buf);

            ipc_answer_0(rid, EOK);

            return;

        } else {

            /*

             * We can't resolve this without the root filesystem

             * being mounted first.

             */

            futex_up(&rootfs_futex);

            free(buf);

            vfs_node_put(mr_node);  /* failed -> drop reference */

            ipc_answer_0(rid, ENOENT);

            return;

        }

    }

    futex_up(&rootfs_futex);

    free(buf);  /* The buffer is not needed anymore. */

    /*

     * At this point, we have all necessary pieces: file system and device

     * handles, and we know the mount point VFS node and also the root node

     * of the file system being mounted.

     */

    int phone = vfs_grab_phone(mp_res.triplet.fs_handle);

    /* Later we can use ARG3 to pass mode/flags. */

    aid_t req1 = async_send_3(phone, VFS_MOUNT,

        (ipcarg_t) mp_res.triplet.dev_handle,

        (ipcarg_t) mp_res.triplet.index, 0, NULL);

    /* The second call uses the same method. */

    aid_t req2 = async_send_3(phone, VFS_MOUNT,

        (ipcarg_t) mr_res.triplet.fs_handle,

        (ipcarg_t) mr_res.triplet.dev_handle,

        (ipcarg_t) mr_res.triplet.index, NULL);

    vfs_release_phone(phone);

    ipcarg_t rc1;

    ipcarg_t rc2;

    async_wait_for(req1, &rc1);

    async_wait_for(req2, &rc2);

    if ((rc1 != EOK) || (rc2 != EOK)) {

        /* Mount failed, drop references to mr_node and mp_node. */

        vfs_node_put(mr_node);

        if (mp_node)

            vfs_node_put(mp_node);

    }

    if (rc2 == EOK)

        ipc_answer_0(rid, rc1);

    else if (rc1 == EOK)

        ipc_answer_0(rid, rc2);

    else

        ipc_answer_0(rid, rc1);

}

void vfs_open(ipc_callid_t rid, ipc_call_t *request)

{

    if (!vfs_files_init()) {

        ipc_answer_0(rid, ENOMEM);

        return;

    }

    /*

     * The POSIX interface is open(path, oflag, mode).

     * We can receive oflags and mode along with the VFS_OPEN call; the path

     * will need to arrive in another call.

     *

     * We also receive one private, non-POSIX set of flags called lflag

     * used to pass information to vfs_lookup_internal().

     */

    int lflag = IPC_GET_ARG1(*request);

    int oflag = IPC_GET_ARG2(*request);

    int mode = IPC_GET_ARG3(*request);

    size_t len;

    if (oflag & O_CREAT)

        lflag |= L_CREATE;

    if (oflag & O_EXCL)

        lflag |= L_EXCLUSIVE;

    ipc_callid_t callid;

    if (!ipc_data_write_receive(&callid, &len)) {

        ipc_answer_0(callid, EINVAL);

        ipc_answer_0(rid, EINVAL);

        return;

    }

    char *path = malloc(len + 1);

    if (!path) {

        ipc_answer_0(callid, ENOMEM);

        ipc_answer_0(rid, ENOMEM);

        return;

    }

    int rc;

    if ((rc = ipc_data_write_finalize(callid, path, len))) {

        ipc_answer_0(rid, rc);

        free(path);

        return;

    }

    path[len] = '\0';

    /*

     * Avoid the race condition in which the file can be deleted before we

     * find/create-and-lock the VFS node corresponding to the looked-up

     * triplet.

     */

    if (lflag & L_CREATE)

        rwlock_write_lock(&namespace_rwlock);

    else

        rwlock_read_lock(&namespace_rwlock);

    /* The path is now populated and we can call vfs_lookup_internal(). */

    vfs_lookup_res_t lr;

    rc = vfs_lookup_internal(path, lflag, &lr, NULL);

    if (rc) {

        if (lflag & L_CREATE)

            rwlock_write_unlock(&namespace_rwlock);

        else

            rwlock_read_unlock(&namespace_rwlock);

        ipc_answer_0(rid, rc);

        free(path);

        return;

    }

    /* Path is no longer needed. */

    free(path);

    vfs_node_t *node = vfs_node_get(&lr);

    if (lflag & L_CREATE)

        rwlock_write_unlock(&namespace_rwlock);

    else

        rwlock_read_unlock(&namespace_rwlock);

    /* Truncate the file if requested and if necessary. */

    if (oflag & O_TRUNC) {

        rwlock_write_lock(&node->contents_rwlock);

        if (node->size) {

            rc = vfs_truncate_internal(node->fs_handle,

                node->dev_handle, node->index, 0);

            if (rc) {

                rwlock_write_unlock(&node->contents_rwlock);

                vfs_node_put(node);

                ipc_answer_0(rid, rc);

                return;

            }

            node->size = 0;

        }

        rwlock_write_unlock(&node->contents_rwlock);

    }

    /*

     * Get ourselves a file descriptor and the corresponding vfs_file_t

     * structure.

     */

    int fd = vfs_fd_alloc();

    if (fd < 0) {

        vfs_node_put(node);

        ipc_answer_0(rid, fd);

        return;

    }

    vfs_file_t *file = vfs_file_get(fd);

    file->node = node;

    if (oflag & O_APPEND)

        file->append = true;

    /*

     * The following increase in reference count is for the fact that the

     * file is being opened and that a file structure is pointing to it.

     * It is necessary so that the file will not disappear when

     * vfs_node_put() is called. The reference will be dropped by the

     * respective VFS_CLOSE.

     */

    vfs_node_addref(node);

    vfs_node_put(node);

    /* Success! Return the new file descriptor to the client. */

    ipc_answer_1(rid, EOK, fd);

}

void vfs_close(ipc_callid_t rid, ipc_call_t *request)

{

    int fd = IPC_GET_ARG1(*request);

    if (fd >= MAX_OPEN_FILES) {

        ipc_answer_0(rid, EBADF);

        return;

    }

    vfs_fd_free(fd);

    ipc_answer_0(rid, EOK);

}

static void vfs_rdwr(ipc_callid_t rid, ipc_call_t *request, bool read)

{

    /*

     * The following code strongly depends on the fact that the files data

     * structure can be only accessed by a single fibril and all file

     * operations are serialized (i.e. the reads and writes cannot

     * interleave and a file cannot be closed while it is being read).

     *

     * Additional synchronization needs to be added once the table of

     * open files supports parallel access!

     */

    int fd = IPC_GET_ARG1(*request);

    /* Lookup the file structure corresponding to the file descriptor. */

    vfs_file_t *file = vfs_file_get(fd);

    if (!file) {

        ipc_answer_0(rid, ENOENT);

        return;

    }

    /*

     * Now we need to receive a call with client's

     * IPC_M_DATA_READ/IPC_M_DATA_WRITE request.

     */

    ipc_callid_t callid;

    int res;

    if (read)

        res = ipc_data_read_receive(&callid, NULL);

    else

        res = ipc_data_write_receive(&callid, NULL);

    if (!res) {

        ipc_answer_0(callid, EINVAL);

        ipc_answer_0(rid, EINVAL);

        return;

    }

    /*

     * Lock the open file structure so that no other thread can manipulate

     * the same open file at a time.

     */

    futex_down(&file->lock);

    /*

     * Lock the file's node so that no other client can read/write to it at

     * the same time.

     */

    if (read)

        rwlock_read_lock(&file->node->contents_rwlock);

    else

        rwlock_write_lock(&file->node->contents_rwlock);

    int fs_phone = vfs_grab_phone(file->node->fs_handle);  

    /* Make a VFS_READ/VFS_WRITE request at the destination FS server. */

    aid_t msg;

    ipc_call_t answer;

    if (!read && file->append)

        file->pos = file->node->size;

    msg = async_send_3(fs_phone, IPC_GET_METHOD(*request),

        file->node->dev_handle, file->node->index, file->pos, &answer);

    /*

     * Forward the IPC_M_DATA_READ/IPC_M_DATA_WRITE request to the

     * destination FS server. The call will be routed as if sent by

     * ourselves. Note that call arguments are immutable in this case so we

     * don't have to bother.

     */

    ipc_forward_fast(callid, fs_phone, 0, 0, 0, IPC_FF_ROUTE_FROM_ME);

    vfs_release_phone(fs_phone);

    /* Wait for reply from the FS server. */

    ipcarg_t rc;

    async_wait_for(msg, &rc);

    size_t bytes = IPC_GET_ARG1(answer);

    /* Unlock the VFS node. */

    if (read)

        rwlock_read_unlock(&file->node->contents_rwlock);

    else {

        /* Update the cached version of node's size. */

        if (rc == EOK)

            file->node->size = IPC_GET_ARG2(answer);

        rwlock_write_unlock(&file->node->contents_rwlock);

    }

    /* Update the position pointer and unlock the open file. */

    if (rc == EOK)

        file->pos += bytes;

    futex_up(&file->lock);

    /*

     * FS server's reply is the final result of the whole operation we

     * return to the client.

     */

    ipc_answer_1(rid, rc, bytes);

}

void vfs_read(ipc_callid_t rid, ipc_call_t *request)

{

    vfs_rdwr(rid, request, true);

}

void vfs_write(ipc_callid_t rid, ipc_call_t *request)

{

    vfs_rdwr(rid, request, false);

}

void vfs_seek(ipc_callid_t rid, ipc_call_t *request)

{

    int fd = (int) IPC_GET_ARG1(*request);

    off_t off = (off_t) IPC_GET_ARG2(*request);

    int whence = (int) IPC_GET_ARG3(*request);

    /* Lookup the file structure corresponding to the file descriptor. */

    vfs_file_t *file = vfs_file_get(fd);

    if (!file) {

        ipc_answer_0(rid, ENOENT);

        return;

    }

    off_t newpos;

    futex_down(&file->lock);

    if (whence == SEEK_SET) {

        file->pos = off;

        futex_up(&file->lock);

        ipc_answer_1(rid, EOK, off);

        return;

    }

    if (whence == SEEK_CUR) {

        if (file->pos + off < file->pos) {

            futex_up(&file->lock);

            ipc_answer_0(rid, EOVERFLOW);

            return;

        }

        file->pos += off;

        newpos = file->pos;

        futex_up(&file->lock);

        ipc_answer_1(rid, EOK, newpos);

        return;

    }

    if (whence == SEEK_END) {

        rwlock_read_lock(&file->node->contents_rwlock);

        size_t size = file->node->size;

        rwlock_read_unlock(&file->node->contents_rwlock);

        if (size + off < size) {

            futex_up(&file->lock);

            ipc_answer_0(rid, EOVERFLOW);

            return;

        }

        newpos = size + off;

        futex_up(&file->lock);

        ipc_answer_1(rid, EOK, newpos);

        return;

    }

    futex_up(&file->lock);

    ipc_answer_0(rid, EINVAL);

}

int

vfs_truncate_internal(fs_handle_t fs_handle, dev_handle_t dev_handle,

    fs_index_t index, size_t size)

{

    ipcarg_t rc;

    int fs_phone;

    fs_phone = vfs_grab_phone(fs_handle);

    rc = async_req_3_0(fs_phone, VFS_TRUNCATE, (ipcarg_t)dev_handle,

        (ipcarg_t)index, (ipcarg_t)size);

    vfs_release_phone(fs_phone);

    return (int)rc;

}

void vfs_truncate(ipc_callid_t rid, ipc_call_t *request)

{

    int fd = IPC_GET_ARG1(*request);

    size_t size = IPC_GET_ARG2(*request);

    int rc;

    vfs_file_t *file = vfs_file_get(fd);

    if (!file) {

        ipc_answer_0(rid, ENOENT);

        return;

    }

    futex_down(&file->lock);

    rwlock_write_lock(&file->node->contents_rwlock);

    rc = vfs_truncate_internal(file->node->fs_handle,

        file->node->dev_handle, file->node->index, size);

    if (rc == EOK)

        file->node->size = size;

    rwlock_write_unlock(&file->node->contents_rwlock);

    futex_up(&file->lock);

    ipc_answer_0(rid, (ipcarg_t)rc);

}

void vfs_mkdir(ipc_callid_t rid, ipc_call_t *request)

{

    int mode = IPC_GET_ARG1(*request);

    size_t len;

    ipc_callid_t callid;

    if (!ipc_data_write_receive(&callid, &len)) {

        ipc_answer_0(callid, EINVAL);

        ipc_answer_0(rid, EINVAL);

        return;

    }

    char *path = malloc(len + 1);

    if (!path) {

        ipc_answer_0(callid, ENOMEM);

        ipc_answer_0(rid, ENOMEM);

        return;

    }

    int rc;

    if ((rc = ipc_data_write_finalize(callid, path, len))) {

        ipc_answer_0(rid, rc);

        free(path);

        return;

    }

    path[len] = '\0';

    rwlock_write_lock(&namespace_rwlock);

    int lflag = L_DIRECTORY | L_CREATE | L_EXCLUSIVE;

    rc = vfs_lookup_internal(path, lflag, NULL, NULL);

    rwlock_write_unlock(&namespace_rwlock);

    free(path);

    ipc_answer_0(rid, rc);

}

void vfs_unlink(ipc_callid_t rid, ipc_call_t *request)

{

    int lflag = IPC_GET_ARG1(*request);

    size_t len;

    ipc_callid_t callid;

    if (!ipc_data_write_receive(&callid, &len)) {

        ipc_answer_0(callid, EINVAL);

        ipc_answer_0(rid, EINVAL);

        return;

    }

    char *path = malloc(len + 1);

    if (!path) {

        ipc_answer_0(callid, ENOMEM);

        ipc_answer_0(rid, ENOMEM);

        return;

    }

    int rc;

    if ((rc = ipc_data_write_finalize(callid, path, len))) {

        ipc_answer_0(rid, rc);

        free(path);

        return;

    }

    path[len] = '\0';

    rwlock_write_lock(&namespace_rwlock);

    lflag &= L_DIRECTORY;   /* sanitize lflag */

    vfs_lookup_res_t lr;

    rc = vfs_lookup_internal(path, lflag | L_UNLINK, &lr, NULL);

    free(path);

    if (rc != EOK) {

        rwlock_write_unlock(&namespace_rwlock);

        ipc_answer_0(rid, rc);

        return;

    }

    /*

     * The name has already been unlinked by vfs_lookup_internal().

     * We have to get and put the VFS node to ensure that it is

     * VFS_DESTROY'ed after the last reference to it is dropped.

     */

    vfs_node_t *node = vfs_node_get(&lr);

    futex_down(&nodes_futex);

    node->lnkcnt--;

    futex_up(&nodes_futex);

    rwlock_write_unlock(&namespace_rwlock);

    vfs_node_put(node);

    ipc_answer_0(rid, EOK);

}

void vfs_rename(ipc_callid_t rid, ipc_call_t *request)

{

    size_t len;

    ipc_callid_t callid;

    int rc;

    /* Retrieve the old path. */

    if (!ipc_data_write_receive(&callid, &len)) {

        ipc_answer_0(callid, EINVAL);

        ipc_answer_0(rid, EINVAL);

        return;

    }

    char *old = malloc(len + 1);

    if (!old) {

        ipc_answer_0(callid, ENOMEM);

        ipc_answer_0(rid, ENOMEM);

        return;

    }

    if ((rc = ipc_data_write_finalize(callid, old, len))) {

        ipc_answer_0(rid, rc);

        free(old);

        return;

    }

    old[len] = '\0';

    /* Retrieve the new path. */

    if (!ipc_data_write_receive(&callid, &len)) {

        ipc_answer_0(callid, EINVAL);

        ipc_answer_0(rid, EINVAL);

        free(old);

        return;

    }

    char *new = malloc(len + 1);

    if (!new) {

        ipc_answer_0(callid, ENOMEM);

        ipc_answer_0(rid, ENOMEM);

        free(old);

        return;

    }

    if ((rc = ipc_data_write_finalize(callid, new, len))) {

        ipc_answer_0(rid, rc);

        free(old);

        free(new);

        return;

    }

    new[len] = '\0';

    char *oldc = canonify(old, &len);

    char *newc = canonify(new, NULL);

    if (!oldc || !newc) {

        ipc_answer_0(rid, EINVAL);

        free(old);

        free(new);

        return;

    }

    if (!strncmp(newc, oldc, len)) {

        /* oldc is a prefix of newc */

        ipc_answer_0(rid, EINVAL);

        free(old);

        free(new);

        return;

    }

    vfs_lookup_res_t old_lr;

    vfs_lookup_res_t new_lr;

    vfs_lookup_res_t new_par_lr;

    rwlock_write_lock(&namespace_rwlock);

    /* Lookup the node belonging to the old file name. */

    rc = vfs_lookup_internal(oldc, L_NONE, &old_lr, NULL);

    if (rc != EOK) {

        rwlock_write_unlock(&namespace_rwlock);

        ipc_answer_0(rid, rc);

        free(old);

        free(new);

        return;

    }

    vfs_node_t *old_node = vfs_node_get(&old_lr);

    if (!old_node) {

        rwlock_write_unlock(&namespace_rwlock);

        ipc_answer_0(rid, ENOMEM);