Subversion Repositories HelenOS

/*

 * 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 <fibril_sync.h>

#include <adt/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.

 */

FIBRIL_RWLOCK_INITIALIZE(namespace_rwlock);

vfs_pair_t rootfs = {

    .fs_handle = 0,

    .dev_handle = 0

};

static void vfs_mount_internal(ipc_callid_t rid, dev_handle_t dev_handle,

    fs_handle_t fs_handle, char *mp, char *opts)

{

    vfs_lookup_res_t mp_res;

    vfs_lookup_res_t mr_res;

    vfs_node_t *mp_node = NULL;

    vfs_node_t *mr_node;

    fs_index_t rindex;

    size_t rsize;

    unsigned rlnkcnt;

    ipcarg_t rc;

    int phone;

    aid_t msg;

    ipc_call_t answer;

    /* Resolve the path to the mountpoint. */

    fibril_rwlock_write_lock(&namespace_rwlock);

    if (rootfs.fs_handle) {

        /* We already have the root FS. */

        if (str_cmp(mp, "/") == 0) {

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

            fibril_rwlock_write_unlock(&namespace_rwlock);

            ipc_answer_0(rid, EBUSY);

            return;

        }

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

        if (rc != EOK) {

            /* The lookup failed for some reason. */

            fibril_rwlock_write_unlock(&namespace_rwlock);

            ipc_answer_0(rid, rc);

            return;

        }

        mp_node = vfs_node_get(&mp_res);

        if (!mp_node) {

            fibril_rwlock_write_unlock(&namespace_rwlock);

            ipc_answer_0(rid, ENOMEM);

            return;

        }

        /*

         * Now we hold a reference to mp_node.

         * It will be dropped upon the corresponding VFS_IN_UNMOUNT.

         * This prevents the mount point from being deleted.

         */

    } else {

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

        if (str_cmp(mp, "/") == 0) {

            /*

             * For this simple, but important case,

             * we are almost done.

             */

            /* Tell the mountee that it is being mounted. */

            phone = vfs_grab_phone(fs_handle);

            msg = async_send_1(phone, VFS_OUT_MOUNTED,

                (ipcarg_t) dev_handle, &answer);

            /* send the mount options */

            rc = ipc_data_write_start(phone, (void *)opts,

                str_size(opts));

            if (rc != EOK) {

                async_wait_for(msg, NULL);

                vfs_release_phone(phone);

                fibril_rwlock_write_unlock(&namespace_rwlock);

                ipc_answer_0(rid, rc);

                return;

            }

            async_wait_for(msg, &rc);

            vfs_release_phone(phone);

            if (rc != EOK) {

                fibril_rwlock_write_unlock(&namespace_rwlock);

                ipc_answer_0(rid, rc);

                return;

            }

            rindex = (fs_index_t) IPC_GET_ARG1(answer);

            rsize = (size_t) IPC_GET_ARG2(answer);

            rlnkcnt = (unsigned) IPC_GET_ARG3(answer);

            mr_res.triplet.fs_handle = fs_handle;

            mr_res.triplet.dev_handle = dev_handle;

            mr_res.triplet.index = rindex;

            mr_res.size = rsize;

            mr_res.lnkcnt = rlnkcnt;

            mr_res.type = VFS_NODE_DIRECTORY;

            rootfs.fs_handle = fs_handle;

            rootfs.dev_handle = dev_handle;

            /* Add reference to the mounted root. */

            mr_node = vfs_node_get(&mr_res);

            assert(mr_node);

            fibril_rwlock_write_unlock(&namespace_rwlock);

            ipc_answer_0(rid, rc);

            return;

        } else {

            /*

             * We can't resolve this without the root filesystem

             * being mounted first.

             */

            fibril_rwlock_write_unlock(&namespace_rwlock);

            ipc_answer_0(rid, ENOENT);

            return;

        }

    }

    /*

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

     * handles, and we know the mount point VFS node.

     */

    int mountee_phone = vfs_grab_phone(fs_handle);

    assert(mountee_phone >= 0);

    phone = vfs_grab_phone(mp_res.triplet.fs_handle);

    msg = async_send_4(phone, VFS_OUT_MOUNT,

        (ipcarg_t) mp_res.triplet.dev_handle,

        (ipcarg_t) mp_res.triplet.index,

        (ipcarg_t) fs_handle,

        (ipcarg_t) dev_handle, &answer);

    /* send connection */

    rc = async_req_1_0(phone, IPC_M_CONNECTION_CLONE, mountee_phone);

    if (rc != EOK) {

        async_wait_for(msg, NULL);

        vfs_release_phone(mountee_phone);

        vfs_release_phone(phone);

        /* Mount failed, drop reference to mp_node. */

        if (mp_node)

            vfs_node_put(mp_node);

        ipc_answer_0(rid, rc);

        fibril_rwlock_write_unlock(&namespace_rwlock);

        return;

    }

    vfs_release_phone(mountee_phone);

    /* send the mount options */

    rc = ipc_data_write_start(phone, (void *)opts, str_size(opts));

    if (rc != EOK) {

        async_wait_for(msg, NULL);

        vfs_release_phone(phone);

        /* Mount failed, drop reference to mp_node. */

        if (mp_node)

            vfs_node_put(mp_node);

        fibril_rwlock_write_unlock(&namespace_rwlock);

        ipc_answer_0(rid, rc);

        return;

    }

    async_wait_for(msg, &rc);

    vfs_release_phone(phone);

    if (rc == EOK) {

        rindex = (fs_index_t) IPC_GET_ARG1(answer);

        rsize = (size_t) IPC_GET_ARG2(answer);

        rlnkcnt = (unsigned) IPC_GET_ARG3(answer);

        mr_res.triplet.fs_handle = fs_handle;

        mr_res.triplet.dev_handle = dev_handle;

        mr_res.triplet.index = rindex;

        mr_res.size = rsize;

        mr_res.lnkcnt = rlnkcnt;

        mr_res.type = VFS_NODE_DIRECTORY;

        /* Add reference to the mounted root. */

        mr_node = vfs_node_get(&mr_res);

        assert(mr_node);

    } else {

        /* Mount failed, drop reference to mp_node. */

        if (mp_node)

            vfs_node_put(mp_node);

    }

    ipc_answer_0(rid, rc);

    fibril_rwlock_write_unlock(&namespace_rwlock);

}

void vfs_mount(ipc_callid_t rid, ipc_call_t *request)

{

    /*

     * 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_t dev_handle = (dev_handle_t) IPC_GET_ARG1(*request);

    /*

     * Mount flags are passed as ARG2.

     */

    unsigned int flags = (unsigned int) IPC_GET_ARG2(*request);

    /*

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

     * carry mount options in the future.

     */

    /* We want the client to send us the mount point. */

    ipc_callid_t callid;

    size_t size;

    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. */

    char *mp = malloc(size + 1);

    if (!mp) {

        ipc_answer_0(callid, ENOMEM);

        ipc_answer_0(rid, ENOMEM);

        return;

    }

    /* Deliver the mount point. */

    ipcarg_t retval = ipc_data_write_finalize(callid, mp, size);

    if (retval != EOK) {

        ipc_answer_0(rid, retval);

        free(mp);

        return;

    }

    mp[size] = '\0';

    /* Now we expect to receive the mount options. */

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

        ipc_answer_0(callid, EINVAL);

        ipc_answer_0(rid, EINVAL);

        free(mp);

        return;

    }

    /* Check the offered options size. */

    if (size > MAX_MNTOPTS_LEN) {

        ipc_answer_0(callid, EINVAL);

        ipc_answer_0(rid, EINVAL);

        free(mp);

        return;

    }

    /* Allocate buffer for the mount options. */

    char *opts = (char *) malloc(size + 1);

    if (!opts) {

        ipc_answer_0(callid, ENOMEM);

        ipc_answer_0(rid, ENOMEM);

        free(mp);

        return;

    }

    /* Deliver the mount options. */

    retval = ipc_data_write_finalize(callid, opts, size);

    if (retval != EOK) {

        ipc_answer_0(rid, retval);

        free(mp);

        free(opts);

        return;

    }

    opts[size] = '\0';

    /*

     * 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);

        free(mp);

        free(opts);

        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);

        free(mp);

        free(opts);

        return;

    }

    /*

     * Allocate buffer for file system name.

     */

    char *fs_name = (char *) malloc(size + 1);

    if (fs_name == NULL) {

        ipc_answer_0(callid, ENOMEM);

        ipc_answer_0(rid, ENOMEM);

        free(mp);

        free(opts);

        return;

    }

    /* Deliver the file system name. */

    retval = ipc_data_write_finalize(callid, fs_name, size);

    if (retval != EOK) {

        ipc_answer_0(rid, retval);

        free(mp);

        free(opts);

        free(fs_name);

        return;

    }

    fs_name[size] = '\0';

    /*

     * Wait for IPC_M_PING so that we can return an error if we don't know

     * fs_name.

     */

    ipc_call_t data;

    callid = async_get_call(&data);

    if (IPC_GET_METHOD(data) != IPC_M_PING) {

        ipc_answer_0(callid, ENOTSUP);

        ipc_answer_0(rid, ENOTSUP);

        free(mp);

        free(opts);

        free(fs_name);

        return;

    }

    /*

     * 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.

     */

    fibril_mutex_lock(&fs_head_lock);

    fs_handle_t fs_handle;

recheck:

    fs_handle = fs_name_to_handle(fs_name, false);

    if (!fs_handle) {

        if (flags & IPC_FLAG_BLOCKING) {

            fibril_condvar_wait(&fs_head_cv, &fs_head_lock);

            goto recheck;

        }

        fibril_mutex_unlock(&fs_head_lock);

        ipc_answer_0(callid, ENOENT);

        ipc_answer_0(rid, ENOENT);

        free(mp);

        free(fs_name);

        free(opts);

        return;

    }

    fibril_mutex_unlock(&fs_head_lock);

    /* Acknowledge that we know fs_name. */

    ipc_answer_0(callid, EOK);

    /* Do the mount */

    vfs_mount_internal(rid, dev_handle, fs_handle, mp, opts);

    free(mp);

    free(fs_name);

    free(opts);

}

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_IN_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;

    /* Ignore mode for now. */

    (void) mode;

    /*

     * Make sure that we are called with exactly one of L_FILE and

     * L_DIRECTORY. Make sure that the user does not pass L_OPEN.

     */

    if (((lflag & (L_FILE | L_DIRECTORY)) == 0) ||

        ((lflag & (L_FILE | L_DIRECTORY)) == (L_FILE | L_DIRECTORY)) ||

        ((lflag & L_OPEN) != 0)) {

        ipc_answer_0(rid, EINVAL);

        return;

    }

    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)

        fibril_rwlock_write_lock(&namespace_rwlock);

    else

        fibril_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 | L_OPEN, &lr, NULL);

    if (rc != EOK) {

        if (lflag & L_CREATE)

            fibril_rwlock_write_unlock(&namespace_rwlock);

        else

            fibril_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)

        fibril_rwlock_write_unlock(&namespace_rwlock);

    else

        fibril_rwlock_read_unlock(&namespace_rwlock);

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

    if (oflag & O_TRUNC) {

        fibril_rwlock_write_lock(&node->contents_rwlock);

        if (node->size) {

            rc = vfs_truncate_internal(node->fs_handle,

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

            if (rc) {

                fibril_rwlock_write_unlock(&node->contents_rwlock);

                vfs_node_put(node);

                ipc_answer_0(rid, rc);

                return;

            }

            node->size = 0;

        }

        fibril_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_IN_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_open_node(ipc_callid_t rid, ipc_call_t *request)

{

    // FIXME: check for sanity of the supplied fs, dev and index

    if (!vfs_files_init()) {

        ipc_answer_0(rid, ENOMEM);

        return;

    }

    /*

     * The interface is open_node(fs, dev, index, oflag).

     */

    vfs_lookup_res_t lr;

    lr.triplet.fs_handle = IPC_GET_ARG1(*request);

    lr.triplet.dev_handle = IPC_GET_ARG2(*request);

    lr.triplet.index = IPC_GET_ARG3(*request);

    int oflag = IPC_GET_ARG4(*request);

    fibril_rwlock_read_lock(&namespace_rwlock);

    int rc = vfs_open_node_internal(&lr);

    if (rc != EOK) {

        fibril_rwlock_read_unlock(&namespace_rwlock);

        ipc_answer_0(rid, rc);

        return;

    }

    vfs_node_t *node = vfs_node_get(&lr);

    fibril_rwlock_read_unlock(&namespace_rwlock);

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

    if (oflag & O_TRUNC) {

        fibril_rwlock_write_lock(&node->contents_rwlock);

        if (node->size) {

            rc = vfs_truncate_internal(node->fs_handle,

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

            if (rc) {

                fibril_rwlock_write_unlock(&node->contents_rwlock);

                vfs_node_put(node);

                ipc_answer_0(rid, rc);

                return;

            }

            node->size = 0;

        }

        fibril_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_IN_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_sync(ipc_callid_t rid, ipc_call_t *request)

{

    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;

    }

    /*

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

     * the same open file at a time.

     */

    fibril_mutex_lock(&file->lock);

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

    /* Make a VFS_OUT_SYMC request at the destination FS server. */

    aid_t msg;

    ipc_call_t answer;

    msg = async_send_2(fs_phone, VFS_OUT_SYNC, file->node->dev_handle,

        file->node->index, &answer);

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

    ipcarg_t rc;

    async_wait_for(msg, &rc);

    vfs_release_phone(fs_phone);

    fibril_mutex_unlock(&file->lock);

    ipc_answer_0(rid, rc);

}

void vfs_close(ipc_callid_t rid, ipc_call_t *request)

{

    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;

    }

    /*

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

     * the same open file at a time.

     */

    fibril_mutex_lock(&file->lock);

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

    /* Make a VFS_OUT_CLOSE request at the destination FS server. */

    aid_t msg;

    ipc_call_t answer;

    msg = async_send_2(fs_phone, VFS_OUT_CLOSE, file->node->dev_handle,

        file->node->index, &answer);

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

    ipcarg_t rc;

    async_wait_for(msg, &rc);

    vfs_release_phone(fs_phone);

    fibril_mutex_unlock(&file->lock);

    int retval = IPC_GET_ARG1(answer);

    if (retval != EOK)

        ipc_answer_0(rid, retval);

    retval = vfs_fd_free(fd);

    ipc_answer_0(rid, retval);

}

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.

     */

    fibril_mutex_lock(&file->lock);

    /*

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

     * the same time.

     */

    if (read)

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

    else

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

    if (file->node->type == VFS_NODE_DIRECTORY) {

        /*

         * Make sure that no one is modifying the namespace

         * while we are in readdir().

         */

        assert(read);

        fibril_rwlock_read_lock(&namespace_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, read ? VFS_OUT_READ : VFS_OUT_WRITE,

        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);