source: mainline/uspace/srv/vfs/vfs_ops.c@ ce7311fc

/*
 * 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;
        int rc;

        /*
         * 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.
         */
        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.
         */

        /**
         * @todo
         * Add more IPC parameters so that we can send mount mode/flags.
         */
        int phone = vfs_grab_phone(mp_res.triplet.fs_handle);
        rc = async_req_5_0(phone, VFS_MOUNT,
            (ipcarg_t) mp_res.triplet.dev_handle,
            (ipcarg_t) mp_res.triplet.index,
            (ipcarg_t) mr_res.triplet.fs_handle,
            (ipcarg_t) mr_res.triplet.dev_handle,
            (ipcarg_t) mr_res.triplet.index);
        vfs_release_phone(phone);

        if (rc != EOK) {
                /* Mount failed, drop references to mr_node and mp_node. */
                vfs_node_put(mr_node);
                if (mp_node)
                        vfs_node_put(mp_node);
        }
        
        ipc_answer_0(rid, rc);
}

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);
                free(old);
                free(new);
                return;
        }
        /* Lookup parent of the new file name. */
        rc = vfs_lookup_internal(newc, L_PARENT, &new_par_lr, NULL);
        if (rc != EOK) {
                rwlock_write_unlock(&namespace_rwlock);
                ipc_answer_0(rid, rc);
                free(old);
                free(new);
                return;
        }
        /* Check whether linking to the same file system instance. */
        if ((old_node->fs_handle != new_par_lr.triplet.fs_handle) ||
            (old_node->dev_handle != new_par_lr.triplet.dev_handle)) {
                rwlock_write_unlock(&namespace_rwlock);
                ipc_answer_0(rid, EXDEV);       /* different file systems */
                free(old);
                free(new);
                return;
        }
        /* Destroy the old link for the new name. */
        vfs_node_t *new_node = NULL;
        rc = vfs_lookup_internal(newc, L_UNLINK, &new_lr, NULL);
        switch (rc) {
        case ENOENT:
                /* simply not in our way */
                break;
        case EOK:
                new_node = vfs_node_get(&new_lr);
                if (!new_node) {
                        rwlock_write_unlock(&namespace_rwlock);
                        ipc_answer_0(rid, ENOMEM);
                        free(old);
                        free(new);
                        return;
                }
                futex_down(&nodes_futex);
                new_node->lnkcnt--;
                futex_up(&nodes_futex);
                break;
        default:
                rwlock_write_unlock(&namespace_rwlock);
                ipc_answer_0(rid, ENOTEMPTY);
                free(old);
                free(new);
                return;
        }
        /* Create the new link for the new name. */
        rc = vfs_lookup_internal(newc, L_LINK, NULL, NULL, old_node->index);
        if (rc != EOK) {
                rwlock_write_unlock(&namespace_rwlock);
                if (new_node)
                        vfs_node_put(new_node);
                ipc_answer_0(rid, rc);
                free(old);
                free(new);
                return;
        }
        futex_down(&nodes_futex);
        old_node->lnkcnt++;
        futex_up(&nodes_futex);
        /* Destroy the link for the old name. */
        rc = vfs_lookup_internal(oldc, L_UNLINK, NULL, NULL);
        if (rc != EOK) {
                rwlock_write_unlock(&namespace_rwlock);
                vfs_node_put(old_node);
                if (new_node)
                        vfs_node_put(new_node);
                ipc_answer_0(rid, rc);
                free(old);
                free(new);
                return;
        }
        futex_down(&nodes_futex);
        old_node->lnkcnt--;
        futex_up(&nodes_futex);
        rwlock_write_unlock(&namespace_rwlock);
        vfs_node_put(old_node);
        if (new_node)
                vfs_node_put(new_node);
        free(old);
        free(new);
        ipc_answer_0(rid, EOK);
}

/**
 * @}
 */