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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 <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 < 0 || 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;
    
    /*
     * 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);

    /* Wait for reply from the FS server. */
    ipcarg_t rc;
    async_wait_for(msg, &rc);
    
    vfs_release_phone(fs_phone);
    
    size_t bytes = IPC_GET_ARG1(answer);

    if (file->node->type == VFS_NODE_DIRECTORY)
        fibril_rwlock_read_unlock(&namespace_rwlock);
    
    /* Unlock the VFS node. */
    if (read)
        fibril_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); 
        fibril_rwlock_write_unlock(&file->node->contents_rwlock);
    }
    
    /* Update the position pointer and unlock the open file. */
    if (rc == EOK)
        file->pos += bytes;
    fibril_mutex_unlock(&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;
    fibril_mutex_lock(&file->lock);
    if (whence == SEEK_SET) {
        file->pos = off;
        fibril_mutex_unlock(&file->lock);
        ipc_answer_1(rid, EOK, off);
        return;
    }
    if (whence == SEEK_CUR) {
        if (file->pos + off < file->pos) {
            fibril_mutex_unlock(&file->lock);
            ipc_answer_0(rid, EOVERFLOW);
            return;
        }
        file->pos += off;
        newpos = file->pos;
        fibril_mutex_unlock(&file->lock);
        ipc_answer_1(rid, EOK, newpos);
        return;
    }
    if (whence == SEEK_END) {
        fibril_rwlock_read_lock(&file->node->contents_rwlock);
        size_t size = file->node->size;
        fibril_rwlock_read_unlock(&file->node->contents_rwlock);
        if (size + off < size) {
            fibril_mutex_unlock(&file->lock);
            ipc_answer_0(rid, EOVERFLOW);
            return;
        }
        newpos = size + off;
        fibril_mutex_unlock(&file->lock);
        ipc_answer_1(rid, EOK, newpos);
        return;
    }
    fibril_mutex_unlock(&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_OUT_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;
    }
    fibril_mutex_lock(&file->lock);

    fibril_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;
    fibril_rwlock_write_unlock(&file->node->contents_rwlock);

    fibril_mutex_unlock(&file->lock);
    ipc_answer_0(rid, (ipcarg_t)rc);
}

void vfs_fstat(ipc_callid_t rid, ipc_call_t *request)
{
    int fd = IPC_GET_ARG1(*request);
    size_t size = IPC_GET_ARG2(*request);
    ipcarg_t rc;

    vfs_file_t *file = vfs_file_get(fd);
    if (!file) {
        ipc_answer_0(rid, ENOENT);
        return;
    }

    ipc_callid_t callid;
    if (!ipc_data_read_receive(&callid, NULL)) {
        ipc_answer_0(callid, EINVAL);
        ipc_answer_0(rid, EINVAL);
        return;
    }

    fibril_mutex_lock(&file->lock);

    int fs_phone = vfs_grab_phone(file->node->fs_handle);
    
    aid_t msg;
    msg = async_send_3(fs_phone, VFS_OUT_STAT, file->node->dev_handle,
        file->node->index, true, NULL);
    ipc_forward_fast(callid, fs_phone, 0, 0, 0, IPC_FF_ROUTE_FROM_ME);
    async_wait_for(msg, &rc);
    vfs_release_phone(fs_phone);

    fibril_mutex_unlock(&file->lock);
    ipc_answer_0(rid, rc);
}

void vfs_stat(ipc_callid_t rid, ipc_call_t *request)
{
}

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';
    
    fibril_rwlock_write_lock(&namespace_rwlock);
    int lflag = L_DIRECTORY | L_CREATE | L_EXCLUSIVE;
    rc = vfs_lookup_internal(path, lflag, NULL, NULL);
    fibril_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';
    
    fibril_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) {
        fibril_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_OUT_DESTROY'ed after the last reference to it is dropped.
     */
    vfs_node_t *node = vfs_node_get(&lr);
    fibril_mutex_lock(&nodes_mutex);
    node->lnkcnt--;
    fibril_mutex_unlock(&nodes_mutex);
    fibril_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 olen, nlen;
    ipc_callid_t callid;
    int rc;

    /* Retrieve the old path. */
    if (!ipc_data_write_receive(&callid, &olen)) {
        ipc_answer_0(callid, EINVAL);
        ipc_answer_0(rid, EINVAL);
        return;
    }
    char *old = malloc(olen + 1);
    if (!old) {
        ipc_answer_0(callid, ENOMEM);
        ipc_answer_0(rid, ENOMEM);
        return;
    }
    if ((rc = ipc_data_write_finalize(callid, old, olen))) {
        ipc_answer_0(rid, rc);
        free(old);
        return;
    }
    old[olen] = '\0';
    
    /* Retrieve the new path. */
    if (!ipc_data_write_receive(&callid, &nlen)) {
        ipc_answer_0(callid, EINVAL);
        ipc_answer_0(rid, EINVAL);
        free(old);
        return;
    }
    char *new = malloc(nlen + 1);
    if (!new) {
        ipc_answer_0(callid, ENOMEM);
        ipc_answer_0(rid, ENOMEM);
        free(old);
        return;
    }
    if ((rc = ipc_data_write_finalize(callid, new, nlen))) {
        ipc_answer_0(rid, rc);
        free(old);
        free(new);
        return;
    }
    new[nlen] = '\0';

    char *oldc = canonify(old, &olen);
    char *newc = canonify(new, &nlen);
    if (!oldc || !newc) {
        ipc_answer_0(rid, EINVAL);
        free(old);
        free(new);
        return;
    }
    oldc[olen] = '\0';
    newc[nlen] = '\0';
    if ((!str_lcmp(newc, oldc, str_length(oldc))) &&
        ((newc[str_length(oldc)] == '/') ||
        (str_length(oldc) == 1) ||
        (str_length(oldc) == str_length(newc)))) {
            /*
         * oldc is a prefix of newc and either
         * - newc continues with a / where oldc ends, or
         * - oldc was / itself, or
         * - oldc and newc are equal.
         */
        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;
    fibril_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) {
        fibril_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) {
        fibril_rwlock_write_unlock(&namespace_rwlock);
        ipc_answer_0(rid, ENOMEM);
        free(old);
        free(new);
        return;
    }
    /* Determine the path to the parent of the node with the new name. */
    char *parentc = str_dup(newc);
    if (!parentc) {
        fibril_rwlock_write_unlock(&namespace_rwlock);
        ipc_answer_0(rid, rc);
        free(old);
        free(new);
        return;
    }
    char *lastsl = str_rchr(parentc + 1, '/');
    if (lastsl)
        *lastsl = '\0';
    else
        parentc[1] = '\0';
    /* Lookup parent of the new file name. */
    rc = vfs_lookup_internal(parentc, L_NONE, &new_par_lr, NULL);
    free(parentc);  /* not needed anymore */
    if (rc != EOK) {
        fibril_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)) {
        fibril_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) {
            fibril_rwlock_write_unlock(&namespace_rwlock);
            ipc_answer_0(rid, ENOMEM);
            free(old);
            free(new);
            return;
        }
        fibril_mutex_lock(&nodes_mutex);
        new_node->lnkcnt--;
        fibril_mutex_unlock(&nodes_mutex);
        break;
    default:
        fibril_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) {
        fibril_rwlock_write_unlock(&namespace_rwlock);
        if (new_node)
            vfs_node_put(new_node);
        ipc_answer_0(rid, rc);
        free(old);
        free(new);
        return;
    }
    fibril_mutex_lock(&nodes_mutex);
    old_node->lnkcnt++;
    fibril_mutex_unlock(&nodes_mutex);
    /* Destroy the link for the old name. */
    rc = vfs_lookup_internal(oldc, L_UNLINK, NULL, NULL);
    if (rc != EOK) {
        fibril_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;
    }
    fibril_mutex_lock(&nodes_mutex);
    old_node->lnkcnt--;
    fibril_mutex_unlock(&nodes_mutex);
    fibril_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);
}

/**
 * @}
 */