source: mainline/uspace/srv/vfs/vfs_ops.c@ 4f9ab1e

/*
 * 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 <macros.h>
#include <stdint.h>
#include <async.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <str.h>
#include <stdbool.h>
#include <fibril_synch.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, service_id_t, fs_index_t,
    aoff64_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);

static size_t shared_path(char *a, char *b)
{
        size_t res = 0;
        
        while (a[res] == b[res] && a[res] != 0) {
                res++;
        }
        
        if (a[res] == b[res]) {
                return res;
        }
        
        res--;
        while (a[res] != '/') {
                res--;
        }
        return res;
}

/* This call destroys the file if and only if there are no hard links left. */
static void out_destroy(vfs_triplet_t *file)
{
        async_exch_t *exch = vfs_exchange_grab(file->fs_handle);
        async_msg_2(exch, VFS_OUT_DESTROY,
                (sysarg_t) file->service_id, (sysarg_t) file->index);
        vfs_exchange_release(exch);
}

int vfs_op_clone(int oldfd, bool desc)
{
        /* Lookup the file structure corresponding to fd. */
        vfs_file_t *oldfile = vfs_file_get(oldfd);
        if (oldfile == NULL) {
                return EBADF;
        }
        assert(oldfile->node != NULL);
        
        vfs_file_t *newfile;
        int newfd = vfs_fd_alloc(&newfile, desc);
        if (newfd >= 0) {
                newfile->node = oldfile->node;
                newfile->permissions = oldfile->permissions;
                vfs_node_addref(newfile->node);
        
                vfs_file_put(newfile);
        }
        vfs_file_put(oldfile);
        
        return newfd;
}

int vfs_op_close(int fd)
{
        return vfs_fd_free(fd);
}

int vfs_op_dup(int oldfd, int newfd)
{
        /* If the file descriptors are the same, do nothing. */
        if (oldfd == newfd) {
                return EOK;
        }
        
        /* Lookup the file structure corresponding to oldfd. */
        vfs_file_t *oldfile = vfs_file_get(oldfd);
        if (!oldfile) {
                return EBADF;
        }
        
        /* Make sure newfd is closed. */
        (void) vfs_fd_free(newfd);
        
        /* Assign the old file to newfd. */
        int ret = vfs_fd_assign(oldfile, newfd);
        vfs_file_put(oldfile);
        
        return ret;
}

int vfs_op_fstat_forward(int fd)
{
        vfs_file_t *file = vfs_file_get(fd);
        if (!file) {
                return EBADF;
        }
        assert(file->node);
        
        ipc_callid_t callid;
        if (!async_data_read_receive(&callid, NULL)) {
                vfs_file_put(file);
                async_answer_0(callid, EINVAL);
                return EINVAL;
        }

        async_exch_t *exch = vfs_exchange_grab(file->node->fs_handle);
        assert(exch);
        
        aid_t msg;
        msg = async_send_3(exch, VFS_OUT_STAT, file->node->service_id,
            file->node->index, true, NULL);
        assert(msg);
        async_forward_fast(callid, exch, 0, 0, 0, IPC_FF_ROUTE_FROM_ME);
        
        vfs_exchange_release(exch);
        
        sysarg_t rc;
        async_wait_for(msg, &rc);
        
        vfs_file_put(file);
        return rc;
}

static int vfs_connect_internal(service_id_t service_id, unsigned flags,
    unsigned instance, const char *options, const char *fsname,
    vfs_node_t **root)
{
        fs_handle_t fs_handle = 0;
        
        fibril_mutex_lock(&fs_list_lock);
        while (1) {
                fs_handle = fs_name_to_handle(instance, fsname, false);
                
                if (fs_handle != 0 || !(flags & VFS_MOUNT_BLOCKING)) {
                        break;
                }
                
                fibril_condvar_wait(&fs_list_cv, &fs_list_lock);
        }
        fibril_mutex_unlock(&fs_list_lock);

        if (fs_handle == 0) {
                return ENOENT;
        }
        
        /* Tell the mountee that it is being mounted. */
        ipc_call_t answer;
        async_exch_t *exch = vfs_exchange_grab(fs_handle);
        aid_t msg = async_send_1(exch, VFS_OUT_MOUNTED, (sysarg_t) service_id,
            &answer);
        /* Send the mount options */
        sysarg_t rc = async_data_write_start(exch, options, str_size(options));
        if (rc != EOK) {
                async_forget(msg);
                vfs_exchange_release(exch);
                return rc;
        }
        async_wait_for(msg, &rc);
        vfs_exchange_release(exch);
        
        if (rc != EOK) {
                return rc;
        }
        
        vfs_lookup_res_t res;
        res.triplet.fs_handle = fs_handle;
        res.triplet.service_id = service_id;
        res.triplet.index = (fs_index_t) IPC_GET_ARG1(answer);
        res.size = (int64_t) MERGE_LOUP32(IPC_GET_ARG2(answer),
            IPC_GET_ARG3(answer));
        res.type = VFS_NODE_DIRECTORY;
        
        /* Add reference to the mounted root. */
        *root = vfs_node_get(&res); 
        assert(*root);
                        
        return EOK;
}

int vfs_op_mount(int mpfd, unsigned service_id, unsigned flags,
    unsigned instance, const char *opts, const char *fs_name, int *outfd)
{
        int rc;
        vfs_file_t *mp = NULL;
        vfs_file_t *file = NULL;
        int fd = -1;
        
        if (!(flags & VFS_MOUNT_CONNECT_ONLY)) {
                mp = vfs_file_get(mpfd);
                if (mp == NULL) {
                        rc = EBADF;
                        goto out;
                }
                
                if (mp->node->mount != NULL) {
                        rc = EBUSY;
                        goto out;
                }
                
                if (mp->node->type != VFS_NODE_DIRECTORY) {
                        rc = ENOTDIR;
                        goto out;
                }
                
                if (vfs_node_has_children(mp->node)) {
                        rc = ENOTEMPTY;
                        goto out;
                }
        }
        
        if (!(flags & VFS_MOUNT_NO_REF)) {
                fd = vfs_fd_alloc(&file, false);
                if (fd < 0) {
                        rc = fd;
                        goto out;
                }
        }
        
        vfs_node_t *root = NULL;
        
        fibril_rwlock_write_lock(&namespace_rwlock);

        rc = vfs_connect_internal(service_id, flags, instance, opts, fs_name,
             &root);
        if (rc == EOK && !(flags & VFS_MOUNT_CONNECT_ONLY)) {
                vfs_node_addref(mp->node);
                vfs_node_addref(root);
                mp->node->mount = root;
        }
        
        fibril_rwlock_write_unlock(&namespace_rwlock);
        
        if (rc != EOK) {
                goto out;
        }
        
        if (flags & VFS_MOUNT_NO_REF) {
                vfs_node_delref(root);
        } else {
                assert(file != NULL);
                
                file->node = root;
                file->permissions = MODE_READ | MODE_WRITE | MODE_APPEND;
                file->open_read = false;
                file->open_write = false;
        }
        
out:
        if (mp) {
                vfs_file_put(mp);
        }
        if (file) {
                vfs_file_put(file);
        }
        if (rc != EOK && fd >= 0) {
                vfs_fd_free(fd);
                fd = 0;
        }
        
        *outfd = fd;
        return rc;
}

int vfs_op_open2(int fd, int flags)
{
        if (flags == 0) {
                return EINVAL;
        }

        vfs_file_t *file = vfs_file_get(fd);
        if (!file) {
                return EBADF;
        }
        
        if ((flags & ~file->permissions) != 0) {
                vfs_file_put(file);
                return EPERM;
        }
        
        if (file->open_read || file->open_write) {
                vfs_file_put(file);
                return EBUSY;
        }
        
        file->open_read = (flags & MODE_READ) != 0;
        file->open_write = (flags & (MODE_WRITE | MODE_APPEND)) != 0;
        file->append = (flags & MODE_APPEND) != 0;
        
        if (!file->open_read && !file->open_write) {
                vfs_file_put(file);
                return EINVAL;
        }
        
        if (file->node->type == VFS_NODE_DIRECTORY && file->open_write) {
                file->open_read = file->open_write = false;
                vfs_file_put(file);
                return EINVAL;
        }
        
        int rc = vfs_open_node_remote(file->node);
        if (rc != EOK) {
                file->open_read = file->open_write = false;
                vfs_file_put(file);
                return rc;
        }
        
        vfs_file_put(file);
        return EOK;
}

typedef int (* rdwr_ipc_cb_t)(async_exch_t *, vfs_file_t *, ipc_call_t *,
    bool, void *);

static int rdwr_ipc_client(async_exch_t *exch, vfs_file_t *file,
    ipc_call_t *answer, bool read, void *data)
{
        size_t *bytes = (size_t *) data;
        int rc;

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

        if (read) {
                rc = async_data_read_forward_4_1(exch, VFS_OUT_READ,
                    file->node->service_id, file->node->index,
                    LOWER32(file->pos), UPPER32(file->pos), answer);
        } else {
                rc = async_data_write_forward_4_1(exch, VFS_OUT_WRITE,
                    file->node->service_id, file->node->index,
                    LOWER32(file->pos), UPPER32(file->pos), answer);
        }

        *bytes = IPC_GET_ARG1(*answer);
        return rc;
}

static int rdwr_ipc_internal(async_exch_t *exch, vfs_file_t *file,
    ipc_call_t *answer, bool read, void *data)
{
        rdwr_io_chunk_t *chunk = (rdwr_io_chunk_t *) data;

        if (exch == NULL)
                return ENOENT;
        
        aid_t msg = async_send_fast(exch, read ? VFS_OUT_READ : VFS_OUT_WRITE,
            file->node->service_id, file->node->index, LOWER32(file->pos),
            UPPER32(file->pos), answer);
        if (msg == 0)
                return EINVAL;

        int retval = async_data_read_start(exch, chunk->buffer, chunk->size);
        if (retval != EOK) {
                async_forget(msg);
                return retval;
        }
        
        sysarg_t rc;
        async_wait_for(msg, &rc);
        
        chunk->size = IPC_GET_ARG1(*answer); 

        return (int) rc;
}

static int vfs_rdwr(int fd, bool read, rdwr_ipc_cb_t ipc_cb, void *ipc_cb_data)
{
        /*
         * 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!
         */
        
        /* Lookup the file structure corresponding to the file descriptor. */
        vfs_file_t *file = vfs_file_get(fd);
        if (!file)
                return EBADF;
        
        if ((read && !file->open_read) || (!read && !file->open_write)) {
                vfs_file_put(file);
                return EINVAL;
        }
        
        vfs_info_t *fs_info = fs_handle_to_info(file->node->fs_handle);
        assert(fs_info);
        
        bool rlock = read ||
            (fs_info->concurrent_read_write && fs_info->write_retains_size);
        
        /*
         * Lock the file's node so that no other client can read/write to it at
         * the same time unless the FS supports concurrent reads/writes and its
         * write implementation does not modify the file size.
         */
        if (rlock) {
                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().
                 */
                
                if (!read) {
                        if (rlock) {
                                fibril_rwlock_read_unlock(
                                    &file->node->contents_rwlock);
                        } else {
                                fibril_rwlock_write_unlock(
                                    &file->node->contents_rwlock);
                        }
                        vfs_file_put(file);
                        return EINVAL;
                }
                
                fibril_rwlock_read_lock(&namespace_rwlock);
        }
        
        async_exch_t *fs_exch = vfs_exchange_grab(file->node->fs_handle);
        
        if (!read && file->append)
                file->pos = file->node->size;
        
        /*
         * Handle communication with the endpoint FS.
         */
        ipc_call_t answer;
        int rc = ipc_cb(fs_exch, file, &answer, read, ipc_cb_data);
        
        vfs_exchange_release(fs_exch);
        
        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 (rlock) {
                fibril_rwlock_read_unlock(&file->node->contents_rwlock);
        } else {
                /* Update the cached version of node's size. */
                if (rc == EOK) {
                        file->node->size = MERGE_LOUP32(IPC_GET_ARG2(answer),
                            IPC_GET_ARG3(answer));
                }
                fibril_rwlock_write_unlock(&file->node->contents_rwlock);
        }
        
        /* Update the position pointer and unlock the open file. */
        if (rc == EOK) {
                file->pos += bytes;
        }
        vfs_file_put(file);     

        return rc;
}

int vfs_rdwr_internal(int fd, bool read, rdwr_io_chunk_t *chunk)
{
        return vfs_rdwr(fd, read, rdwr_ipc_internal, chunk);
}

int vfs_op_read(int fd, size_t *out_bytes)
{
        return vfs_rdwr(fd, true, rdwr_ipc_client, out_bytes);
}

int vfs_op_rename(int basefd, char *old, char *new)
{
        vfs_file_t *base_file = vfs_file_get(basefd);
        if (!base_file) {
                return EBADF;
        }
        vfs_node_t *base = base_file->node;
        vfs_node_addref(base);
        vfs_file_put(base_file);
        
        vfs_lookup_res_t base_lr;
        vfs_lookup_res_t old_lr;
        vfs_lookup_res_t new_lr_orig;
        bool orig_unlinked = false;
        
        int rc;
        
        size_t shared = shared_path(old, new);
        
        /* Do not allow one path to be a prefix of the other. */
        if (old[shared] == 0 || new[shared] == 0) {
                vfs_node_put(base);
                return EINVAL;
        }
        assert(old[shared] == '/');
        assert(new[shared] == '/');
        
        fibril_rwlock_write_lock(&namespace_rwlock);
        
        /* Resolve the shared portion of the path first. */
        if (shared != 0) {
                old[shared] = 0;
                rc = vfs_lookup_internal(base, old, L_DIRECTORY, &base_lr);
                if (rc != EOK) {
                        vfs_node_put(base);
                        fibril_rwlock_write_unlock(&namespace_rwlock);
                        return rc;
                }
                
                vfs_node_put(base);
                base = vfs_node_get(&base_lr);
                old[shared] = '/';
                old += shared;
                new += shared;
        }

        rc = vfs_lookup_internal(base, old, L_DISABLE_MOUNTS,
            &old_lr);
        if (rc != EOK) {
                vfs_node_put(base);
                fibril_rwlock_write_unlock(&namespace_rwlock);
                return rc;
        }
                
        rc = vfs_lookup_internal(base, new, L_UNLINK | L_DISABLE_MOUNTS,
            &new_lr_orig);
        if (rc == EOK) {
                orig_unlinked = true;
        } else if (rc != ENOENT) {
                vfs_node_put(base);
                fibril_rwlock_write_unlock(&namespace_rwlock);
                return rc;
        }

        rc = vfs_link_internal(base, new, &old_lr.triplet);
        if (rc != EOK) {
                vfs_link_internal(base, old, &old_lr.triplet);
                if (orig_unlinked) {
                        vfs_link_internal(base, new, &new_lr_orig.triplet);
                }
                vfs_node_put(base);
                fibril_rwlock_write_unlock(&namespace_rwlock);
                return rc;
        }

        rc = vfs_lookup_internal(base, old, L_UNLINK | L_DISABLE_MOUNTS,
            &old_lr);
        if (rc != EOK) {
                if (orig_unlinked) {
                        vfs_link_internal(base, new, &new_lr_orig.triplet);
                }
                vfs_node_put(base);
                fibril_rwlock_write_unlock(&namespace_rwlock);
                return rc;
        }
        
        /* If the node is not held by anyone, try to destroy it. */
        if (orig_unlinked) {
                vfs_node_t *node = vfs_node_peek(&new_lr_orig);
                if (!node)
                        out_destroy(&new_lr_orig.triplet);
                else
                        vfs_node_put(node);
        }
        
        vfs_node_put(base);
        fibril_rwlock_write_unlock(&namespace_rwlock);
        return EOK;
}

int vfs_op_seek(int fd, int64_t offset, int whence, int64_t *out_offset)
{
        vfs_file_t *file = vfs_file_get(fd);
        if (!file) {
                return EBADF;
        }
        
        switch (whence) {
        case SEEK_SET:
                if (offset < 0) {
                        vfs_file_put(file);
                        return EINVAL;
                }
                file->pos = offset;
                *out_offset = offset;
                vfs_file_put(file);
                return EOK;
        case SEEK_CUR:
                if (offset > 0 && file->pos > (INT64_MAX - offset)) {
                        vfs_file_put(file);
                        return EOVERFLOW;
                }
                
                if (offset < 0 && -file->pos > offset) {
                        vfs_file_put(file);
                        return EOVERFLOW;
                }
                
                file->pos += offset;
                *out_offset = file->pos;
                vfs_file_put(file);
                return EOK;
        case SEEK_END:
                fibril_rwlock_read_lock(&file->node->contents_rwlock);
                int64_t size = vfs_node_get_size(file->node);
                fibril_rwlock_read_unlock(&file->node->contents_rwlock);
                
                if (offset > 0 && size > (INT64_MAX - offset)) {
                        vfs_file_put(file);
                        return EOVERFLOW;
                }
                
                if (offset < 0 && -size > offset) {
                        vfs_file_put(file);
                        return EOVERFLOW;
                }
                
                file->pos = size + offset;
                *out_offset = file->pos;
                vfs_file_put(file);
                return EOK;
        }
        
        vfs_file_put(file);
        return EINVAL;
}

int vfs_op_statfs(int fd)
{
        ipc_callid_t callid;
        
        if (!async_data_read_receive(&callid, NULL)) {
                async_answer_0(callid, EINVAL);
                return EINVAL;
        }

        vfs_file_t *file = vfs_file_get(fd);
        if (!file) {
                async_answer_0(callid, EBADF);
                return EBADF;
        }

        vfs_node_t *node = file->node;

        async_exch_t *exch = vfs_exchange_grab(node->fs_handle);
                                                                
        aid_t msg;
        msg = async_send_3(exch, VFS_OUT_STATFS, node->service_id,
        node->index, false, NULL);
        async_forward_fast(callid, exch, 0, 0, 0, IPC_FF_ROUTE_FROM_ME);

        vfs_exchange_release(exch);

        sysarg_t rv;
        async_wait_for(msg, &rv);

        vfs_file_put(file);
        return rv;
}

int vfs_op_sync(int fd)
{
        vfs_file_t *file = vfs_file_get(fd);
        if (!file) {
                return EBADF;
        }
        
        async_exch_t *fs_exch = vfs_exchange_grab(file->node->fs_handle);
        
        aid_t msg;
        ipc_call_t answer;
        msg = async_send_2(fs_exch, VFS_OUT_SYNC, file->node->service_id,
                file->node->index, &answer);
        
        vfs_exchange_release(fs_exch);
        
        sysarg_t rc;
        async_wait_for(msg, &rc);
        
        vfs_file_put(file);
        return rc;
        
}

static int vfs_truncate_internal(fs_handle_t fs_handle, service_id_t service_id,
    fs_index_t index, aoff64_t size)
{
        async_exch_t *exch = vfs_exchange_grab(fs_handle);
        sysarg_t rc = async_req_4_0(exch, VFS_OUT_TRUNCATE,
            (sysarg_t) service_id, (sysarg_t) index, LOWER32(size),
            UPPER32(size));
        vfs_exchange_release(exch);
        
        return (int) rc;
}

int vfs_op_truncate(int fd, int64_t size)
{
        vfs_file_t *file = vfs_file_get(fd);
        if (!file) {
                return EBADF;
        }

        fibril_rwlock_write_lock(&file->node->contents_rwlock);
        
        int rc = vfs_truncate_internal(file->node->fs_handle,
                file->node->service_id, file->node->index, size);
        if (rc == EOK) {
                file->node->size = size;
        }
        
        fibril_rwlock_write_unlock(&file->node->contents_rwlock);
        vfs_file_put(file);
        return rc;
}

int vfs_op_unlink2(int parentfd, int expectfd, int wflag, char *path)
{
        int rc = EOK;
        vfs_file_t *parent = NULL;
        vfs_file_t *expect = NULL;
        
        if (parentfd == expectfd) {
                return EINVAL;
        }
        
        fibril_rwlock_write_lock(&namespace_rwlock);
        
        int lflag = (wflag&WALK_DIRECTORY) ? L_DIRECTORY: 0;

        /* 
         * Files are retrieved in order of file descriptors, to prevent
         * deadlock.
         */
        if (parentfd < expectfd) {
                parent = vfs_file_get(parentfd);
                if (!parent) {
                        rc = EBADF;
                        goto exit;
                }
        }
        
        if (expectfd >= 0) {
                expect = vfs_file_get(expectfd);
                if (!expect) {
                        rc = EBADF;
                        goto exit;
                }
        }
        
        if (parentfd > expectfd) {
                parent = vfs_file_get(parentfd);
                if (!parent) {
                        rc = EBADF;
                        goto exit;
                }
        }
        
        assert(parent != NULL);
        
        if (expectfd >= 0) {
                vfs_lookup_res_t lr;
                rc = vfs_lookup_internal(parent->node, path, lflag, &lr);
                if (rc != EOK) {
                        goto exit;
                }
                
                vfs_node_t *found_node = vfs_node_peek(&lr);
                vfs_node_put(found_node);
                if (expect->node != found_node) {
                        rc = ENOENT;
                        goto exit;
                }
                
                vfs_file_put(expect);
                expect = NULL;
        }
        
        vfs_lookup_res_t lr;
        rc = vfs_lookup_internal(parent->node, path, lflag | L_UNLINK, &lr);
        if (rc != EOK) {
                goto exit;
        }

        /* If the node is not held by anyone, try to destroy it. */
        vfs_node_t *node = vfs_node_peek(&lr);
        if (!node)
                out_destroy(&lr.triplet);
        else
                vfs_node_put(node);

exit:
        if (path) {
                free(path);
        }
        if (parent) {
                vfs_file_put(parent);
        }
        if (expect) {
                vfs_file_put(expect);
        }
        fibril_rwlock_write_unlock(&namespace_rwlock);
        return rc;
}

int vfs_op_unmount(int mpfd)
{
        vfs_file_t *mp = vfs_file_get(mpfd);
        if (mp == NULL) {
                return EBADF;
        }
        
        if (mp->node->mount == NULL) {
                vfs_file_put(mp);
                return ENOENT;
        }
        
        fibril_rwlock_write_lock(&namespace_rwlock);
        
        /*
         * Count the total number of references for the mounted file system. We
         * are expecting at least one, which is held by the mount point.
         * If we find more, it means that
         * the file system cannot be gracefully unmounted at the moment because
         * someone is working with it.
         */
        if (vfs_nodes_refcount_sum_get(mp->node->mount->fs_handle,
            mp->node->mount->service_id) != 1) {
                vfs_file_put(mp);
                fibril_rwlock_write_unlock(&namespace_rwlock);
                return EBUSY;
        }
        
        async_exch_t *exch = vfs_exchange_grab(mp->node->mount->fs_handle);
        int rc = async_req_1_0(exch, VFS_OUT_UNMOUNTED,
            mp->node->mount->service_id);
        vfs_exchange_release(exch);
        
        if (rc != EOK) {
                vfs_file_put(mp);
                fibril_rwlock_write_unlock(&namespace_rwlock);
                return rc;
        }
        
        vfs_node_forget(mp->node->mount);
        vfs_node_put(mp->node);
        mp->node->mount = NULL;
        
        fibril_rwlock_write_unlock(&namespace_rwlock);
        
        vfs_file_put(mp);
        return EOK;
}

int vfs_op_wait_handle(bool high_fd)
{
        return vfs_wait_handle_internal(high_fd);
}

static inline bool walk_flags_valid(int flags)
{
        if ((flags & ~WALK_ALL_FLAGS) != 0) {
                return false;
        }
        if ((flags & WALK_MAY_CREATE) && (flags & WALK_MUST_CREATE)) {
                return false;
        }
        if ((flags & WALK_REGULAR) && (flags & WALK_DIRECTORY)) {
                return false;
        }
        if ((flags & WALK_MAY_CREATE) || (flags & WALK_MUST_CREATE)) {
                if (!(flags & WALK_DIRECTORY) && !(flags & WALK_REGULAR)) {
                        return false;
                }
        }
        return true;
}

static inline int walk_lookup_flags(int flags)
{
        int lflags = 0;
        if ((flags & WALK_MAY_CREATE) || (flags & WALK_MUST_CREATE)) {
                lflags |= L_CREATE;
        }
        if (flags & WALK_MUST_CREATE) {
                lflags |= L_EXCLUSIVE;
        }
        if (flags & WALK_REGULAR) {
                lflags |= L_FILE;
        }
        if (flags & WALK_DIRECTORY) {
                lflags |= L_DIRECTORY;
        }
        if (flags & WALK_MOUNT_POINT) {
                lflags |= L_MP;
        }
        return lflags;
}

int vfs_op_walk(int parentfd, int flags, char *path, int *out_fd)
{
        if (!walk_flags_valid(flags)) {
                return EINVAL;
        }
        
        vfs_file_t *parent = vfs_file_get(parentfd);
        if (!parent) {
                return EBADF;
        }
        
        fibril_rwlock_read_lock(&namespace_rwlock);
        
        vfs_lookup_res_t lr;
        int rc = vfs_lookup_internal(parent->node, path,
            walk_lookup_flags(flags), &lr);

        if (rc != EOK) {
                fibril_rwlock_read_unlock(&namespace_rwlock);
                vfs_file_put(parent);
                return rc;
        }
        
        vfs_node_t *node = vfs_node_get(&lr);
        
        vfs_file_t *file;
        int fd = vfs_fd_alloc(&file, false);
        if (fd < 0) {
                vfs_node_put(node);
                vfs_file_put(parent);
                return fd;
        }
        assert(file != NULL);
        
        file->node = node;
        file->permissions = parent->permissions;
        file->open_read = false;
        file->open_write = false;
        
        vfs_file_put(file);
        vfs_file_put(parent);
        
        fibril_rwlock_read_unlock(&namespace_rwlock);

        *out_fd = fd;
        return EOK;
}

int vfs_op_write(int fd, size_t *out_bytes)
{
        return vfs_rdwr(fd, false, rdwr_ipc_client, out_bytes);
}

/**
 * @}
 */