[wimlib] / src / mount.c

/*
 * mount.c
 *
 * This file implements mounting of WIM files using FUSE, which stands for
 * Filesystem in Userspace.  FUSE allows a filesystem to be implemented in a
 * userspace process by implementing the filesystem primitives--- read(),
 * write(), readdir(), etc.
 */

/*
 * Copyright (C) 2012 Eric Biggers
 *
 * This file is part of wimlib, a library for working with WIM files.
 *
 * wimlib is free software; you can redistribute it and/or modify it under the
 * terms of the GNU Lesser General Public License as published by the Free
 * Software Foundation; either version 2.1 of the License, or (at your option)
 * any later version.
 *
 * wimlib is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
 * A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
 * details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with wimlib; if not, see http://www.gnu.org/licenses/.
 */

#include "wimlib_internal.h"

#ifdef WITH_FUSE
#include "sha1.h"
#include "lookup_table.h"
#include "xml.h"
#include "io.h"
#include "timestamp.h"
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#define FUSE_USE_VERSION 26
#include <errno.h>
#include <string.h>
#include <sys/time.h>
#include <fuse.h>
#include <ftw.h>
#include <mqueue.h>

struct wimlib_fd {
        u16 idx;
        int staging_fd;
        u64 hard_link_group;
        struct lookup_table_entry *lte;
        struct dentry *dentry;
};

/* The WIMStruct for the mounted WIM. */
static WIMStruct *w;

/* Working directory when `imagex mount' is run. */
static const char *working_directory;

/* Name of the staging directory for a read-write mount.  Whenever a new file is
 * created, it is done so in the staging directory.  Furthermore, whenever a
 * file in the WIM is modified, it is extracted to the staging directory.  If
 * changes are commited when the WIM is unmounted, the file resources are merged
 * in from the staging directory when writing the new WIM. */
static char *staging_dir_name;
static size_t staging_dir_name_len;

/* Flags passed to wimlib_mount(). */
static int mount_flags;

/* Name of the directory on which the WIM file is mounted. */
static const char *mount_dir;


static inline int get_lookup_flags()
{
        if (mount_flags & WIMLIB_MOUNT_FLAG_STREAM_INTERFACE_WINDOWS)
                return LOOKUP_FLAG_ADS_OK;
        else
                return 0;
}

static inline int flags_writable(int open_flags)
{
        return open_flags & (O_RDWR | O_WRONLY);
}

static int alloc_wimlib_fd(struct lookup_table_entry *lte,
                           struct wimlib_fd **fd_ret)
{
        if (lte->num_opened_fds == lte->num_allocated_fds) {
                struct wimlib_fd **fds;
                if (lte->num_allocated_fds > 0xffff - 8)
                        return -ENFILE;
                
                fds = CALLOC(lte->num_allocated_fds + 8, sizeof(lte->fds[0]));
                if (!fds)
                        return -ENOMEM;
                memcpy(fds, lte->fds,
                       lte->num_allocated_fds * sizeof(lte->fds[0]));
                FREE(lte->fds);
                lte->fds = fds;
        }
        for (u16 i = 0; ; i++) {
                struct wimlib_fd *fd = lte->fds[i];
                if (!fd) {
                        fd = CALLOC(1, sizeof(*fd));
                        if (!fd)
                                return -ENOMEM;
                        fd->staging_fd = -1;
                        fd->idx        = i;
                        fd->lte        = lte;
                        lte->fds[i]    = fd;
                        *fd_ret        = fd;
                        return 0;
                }
        }
}

static int close_wimlib_fd(struct wimlib_fd *fd)
{
        struct lookup_table_entry *lte = fd->lte;

        wimlib_assert(lte);
        wimlib_assert(lte->num_opened_fds);

        if (lte->staging_file_name) {
                wimlib_assert(fd->staging_fd != -1);
                if (close(fd->staging_fd) != 0)
                        return -errno;
        }
        if (--lte->num_opened_fds == 0 && lte->refcnt == 0)
                free_lookup_table_entry(lte);
        lte->fds[fd->idx] = NULL;
        FREE(fd);
        return 0;
}

/* Creates a new staging file and returns its file descriptor opened for
 * writing.
 *
 * @name_ret: A location into which the a pointer to the newly allocated name of
 *                      the staging file is stored.
 * @return:  The file descriptor for the new file.  Returns -1 and sets errno on
 *              error, for any reason possible from the creat() function.
 */
static int create_staging_file(char **name_ret, int open_flags)
{
        size_t name_len;
        char *name;
        struct stat stbuf;
        int fd;
        int errno_save;

        name_len = staging_dir_name_len + 1 + WIM_HASH_SIZE;
        name = MALLOC(name_len + 1);
        if (!name) {
                errno = ENOMEM;
                return -1;
        }

        do {

                memcpy(name, staging_dir_name, staging_dir_name_len);
                name[staging_dir_name_len] = '/';
                randomize_char_array_with_alnum(name + staging_dir_name_len + 1,
                                                WIM_HASH_SIZE);
                name[name_len] = '\0';


        /* Just in case, verify that the randomly generated name doesn't name an
         * existing file, and try again if so  */
        } while (stat(name, &stbuf) == 0);

        if (errno != ENOENT)
                /* other error! */
                return -1;

        /* doesn't exist--- ok */

        DEBUG("Creating staging file `%s'", name);

        fd = open(name, open_flags | O_CREAT | O_TRUNC, 0600); 
        if (fd == -1) {
                errno_save = errno;
                FREE(name);
                errno = errno_save;
        } else {
                *name_ret = name;
        }
        return fd;
}

/* 
 * Extract a WIM resource to the staging directory.
 *
 * We need to:
 * - Create a staging file for the WIM resource
 * - Extract the resource to it
 * - Create a new lte for the file resource
 * - Transfer fds from the old lte to the new lte, but
 *   only if they share the same hard link group as this
 *   dentry
 */
static int extract_resource_to_staging_dir(struct dentry *dentry,
                                           struct lookup_table_entry **lte,
                                           off_t size)
{
        char *staging_file_name;
        int ret;
        int fd;
        struct lookup_table_entry *old_lte, *new_lte;
        size_t link_group_size;
        
        old_lte = *lte;
        fd = create_staging_file(&staging_file_name, O_WRONLY);
        if (fd == -1)
                return -errno;

        if (old_lte)
                ret = extract_resource_to_fd(w, &old_lte->resource_entry, fd,
                                             size);
        else
                ret = 0;
        if (ret != 0 || close(fd) != 0) {
                if (errno != 0)
                        ret = -errno;
                else
                        ret = -EIO;
                close(fd);
                unlink(staging_file_name);
                FREE(staging_file_name);
                return ret;
        }

        link_group_size = dentry_link_group_size(dentry);

        if (old_lte) {
                if (link_group_size == old_lte->refcnt) {
                        /* This hard link group is the only user of the lookup
                         * table entry, so we can re-use it. */
                        lookup_table_remove(w->lookup_table, old_lte);
                        new_lte = old_lte;
                } else {
                        /* Split a hard link group away from the "lookup table
                         * entry" hard link group (i.e. we had two hard link
                         * groups that were identical, but now we are changing
                         * one of them) */

                        /* XXX The ADS really complicate things here and not
                         * everything is going to work correctly yet.  For
                         * example it could be the same that a file contains two
                         * file streams that are identical and therefore share
                         * the same lookup table entry despite the fact that the
                         * streams themselves are not hardlinked. */
                        wimlib_assert(old_lte->refcnt > link_group_size);

                        new_lte = new_lookup_table_entry();
                        if (!new_lte)
                                return -ENOMEM;

                        u16 num_transferred_fds = 0;
                        for (u16 i = 0; i < old_lte->num_allocated_fds; i++) {
                                if (old_lte->fds[i] &&
                                    old_lte->fds[i]->dentry->hard_link ==
                                      dentry->hard_link)
                                {
                                        num_transferred_fds++;
                                }
                        }
                        new_lte->fds = MALLOC(num_transferred_fds *
                                              sizeof(new_lte->fds[0]));
                        if (!new_lte->fds) {
                                free_lookup_table_entry(new_lte);
                                return -ENOMEM;
                        }
                        u16 j = 0;
                        for (u16 i = 0; i < old_lte->num_allocated_fds; i++) {
                                if (old_lte->fds[i] &&
                                    old_lte->fds[i]->dentry->hard_link ==
                                      dentry->hard_link)
                                {
                                        struct wimlib_fd *fd = old_lte->fds[i];
                                        old_lte->fds[i] = NULL;
                                        fd->lte = new_lte;
                                        fd->idx = j;
                                        new_lte->fds[j] = fd;
                                }
                        }
                        old_lte->refcnt -= link_group_size;
                        old_lte->num_opened_fds -= j;
                        new_lte->num_opened_fds = j;

                } 
        }
        new_lte->resource_entry.original_size = size;
        new_lte->refcnt = link_group_size;
        randomize_byte_array(new_lte->hash, WIM_HASH_SIZE);
        new_lte->staging_file_name = staging_file_name;

        lookup_table_insert(w->lookup_table, new_lte);
        *lte = new_lte;
        return 0;
}

/* 
 * Creates a randomly named staging directory and returns its name into the
 * static variable staging_dir_name.
 *
 * If the staging directory cannot be created, staging_dir_name is set to NULL.
 * */
static void make_staging_dir()
{
        /* XXX Give the user an option of where to stage files */

        static char prefix[] = "wimlib-staging-";
        static const size_t prefix_len = 15;
        static const size_t suffix_len = 10;

        size_t pwd_len = strlen(working_directory);

        staging_dir_name_len = pwd_len + 1 + prefix_len + suffix_len;

        staging_dir_name = MALLOC(staging_dir_name_len + 1);
        if (!staging_dir_name) {
                ERROR("Out of memory");
                return;
        }

        memcpy(staging_dir_name, working_directory, pwd_len);
        staging_dir_name[pwd_len] = '/';
        memcpy(staging_dir_name + pwd_len + 1, prefix, prefix_len);
        randomize_char_array_with_alnum(staging_dir_name + pwd_len + 1 + prefix_len,
                                suffix_len);
        staging_dir_name[staging_dir_name_len] = '\0';

        if (mkdir(staging_dir_name, 0700) != 0) {
                ERROR_WITH_ERRNO("Failed to create temporary directory `%s'",
                                 staging_dir_name);
                FREE(staging_dir_name);
                staging_dir_name = NULL;
        }
}

static int remove_file_or_directory(const char *fpath, const struct stat *sb,
                int typeflag, struct FTW *ftwbuf)
{
        if (remove(fpath) == 0)
                return 0;
        else
                return WIMLIB_ERR_DELETE_STAGING_DIR;
}


/* 
 * Deletes the staging directory and all the files contained in it. 
 */
static inline int delete_staging_dir()
{
        int ret;
        
        ret = nftw(staging_dir_name, remove_file_or_directory,10, FTW_DEPTH);
        staging_dir_name = NULL;
        return ret;
}

/* Name and message queue descriptors for message queues between the filesystem
 * daemon process and the unmount process.  These are used when the filesystem
 * is unmounted and the process running wimlib_mount() (i.e. the `imagex
 * unmount' command) needs to communicate with the filesystem daemon running
 * fuse_main() (i.e. that spawned by the `imagex mount' or `imagex mountrw'
 * commands */
static char *unmount_to_daemon_mq_name;
static char *daemon_to_unmount_mq_name;
static int unmount_to_daemon_mq;
static int daemon_to_unmount_mq;

/* Simple function that returns the concatenation of 4 strings. */
static char *strcat_dup(const char *s1, const char *s2, const char *s3, 
                                                        const char *s4)
{
        size_t len = strlen(s1) + strlen(s2) + strlen(s3) + strlen(s4) + 1;
        char *p = MALLOC(len);
        if (!p)
                return NULL;
        *p = '\0';
        strcat(p, s1);
        strcat(p, s2);
        strcat(p, s3);
        strcat(p, s4);
        return p;
}

/* Removes trailing forward slashes in a string. */
static void remove_trailing_slashes(char *s)
{
        long len = strlen(s);
        for (long i = len - 1; i >= 1; i--) {
                if (s[i] == '/')
                        s[i] = '\0';
                else
                        break;
        }
}

/* Changes forward slashes to underscores in a string. */
static void s_slashes_underscores_g(char *s)
{
        while (*s) {
                if (*s == '/')
                        *s = '_';
                s++;
        }
}

/* 
 * Opens two POSIX message queue: one for sending messages from the unmount
 * process to the daemon process, and one to go the other way.  The names of the
 * message queues, which must be system-wide unique, are be based on the mount
 * point.  (There of course is still a possibility of a collision if one were to
 * unmount two identically named directories simultaneously...)
 *
 * @daemon specifies whether the calling process is the filesystem daemon or the
 * unmount process.
 */
static int open_message_queues(bool daemon)
{
        static const char *slash = "/";
        static const char *prefix = "wimlib-";
        static const char *u2d_suffix = "unmount-to-daemon-mq";
        static const char *d2u_suffix = "daemon-to-unmount-mq";

        const char *mount_dir_basename = path_basename(mount_dir);
        int flags;
        int ret;

        unmount_to_daemon_mq_name = strcat_dup(slash, mount_dir_basename,
                                                prefix, u2d_suffix);
        if (!unmount_to_daemon_mq_name) {
                ERROR("Out of memory");
                return WIMLIB_ERR_NOMEM;
        }
        daemon_to_unmount_mq_name = strcat_dup(slash, mount_dir_basename,
                                                prefix, d2u_suffix);
        if (!daemon_to_unmount_mq_name) {
                ERROR("Out of memory");
                ret = WIMLIB_ERR_NOMEM;
                goto err1;
        }

        remove_trailing_slashes(unmount_to_daemon_mq_name);
        remove_trailing_slashes(daemon_to_unmount_mq_name);
        s_slashes_underscores_g(unmount_to_daemon_mq_name + 1);
        s_slashes_underscores_g(daemon_to_unmount_mq_name + 1);

        if (daemon)
                flags = O_RDONLY | O_CREAT;
        else
                flags = O_WRONLY | O_CREAT;

        unmount_to_daemon_mq = mq_open(unmount_to_daemon_mq_name, flags, 
                                       0700, NULL);

        if (unmount_to_daemon_mq == -1) {
                ERROR_WITH_ERRNO("mq_open()");
                ret = WIMLIB_ERR_MQUEUE;
                goto err2;
        }

        if (daemon)
                flags = O_WRONLY | O_CREAT;
        else
                flags = O_RDONLY | O_CREAT;

        daemon_to_unmount_mq = mq_open(daemon_to_unmount_mq_name, flags, 
                                       0700, NULL);

        if (daemon_to_unmount_mq == -1) {
                ERROR_WITH_ERRNO("mq_open()");
                ret = WIMLIB_ERR_MQUEUE;
                goto err3;
        }
        return 0;
err3:
        mq_close(unmount_to_daemon_mq);
        mq_unlink(unmount_to_daemon_mq_name);
err2:
        FREE(daemon_to_unmount_mq_name);
err1:
        FREE(unmount_to_daemon_mq_name);
        return ret;
}

static int mq_get_msgsize(mqd_t mq)
{
        static const char *msgsize_max_file = "/proc/sys/fs/mqueue/msgsize_max";
        FILE *fp;
        struct mq_attr attr;
        int msgsize;

        if (mq_getattr(unmount_to_daemon_mq, &attr) == 0) {
                msgsize = attr.mq_msgsize;
        } else {
                ERROR_WITH_ERRNO("mq_getattr()");
                ERROR("Attempting to read %s", msgsize_max_file);
                fp = fopen(msgsize_max_file, "rb");
                if (fp) {
                        if (fscanf(fp, "%d", &msgsize) != 1) {
                                ERROR("Assuming message size of 8192");
                                msgsize = 8192;
                        }
                        fclose(fp);
                } else {
                        ERROR_WITH_ERRNO("Failed to open the file `%s'",
                                         msgsize_max_file);
                        ERROR("Assuming message size of 8192");
                        msgsize = 8192;
                }
        }
        return msgsize;
}

/* Closes the message queues, which are allocated in static variables */
static void close_message_queues()
{
        mq_close(unmount_to_daemon_mq);
        mq_close(daemon_to_unmount_mq);
        mq_unlink(unmount_to_daemon_mq_name);
        mq_unlink(daemon_to_unmount_mq_name);
}

static int wimfs_access(const char *path, int mask)
{
        /* XXX Permissions not implemented */
        return 0;
}

/* Closes the staging file descriptor associated with the lookup table entry, if
 * it is opened. */
static int close_lte_fds(struct lookup_table_entry *lte, void *ignore)
{
        for (u16 i = 0; i < lte->num_opened_fds; i++) {
                if (lte->fds[i] && lte->fds[i]->staging_fd != -1) {
                        if (close(lte->fds[i]->staging_fd) != 0) {
                                ERROR_WITH_ERRNO("Failed close file `%s'",
                                                 lte->staging_file_name);
                                return WIMLIB_ERR_WRITE;
                        }
                }
        }
        return 0;
}


/* Calculates the SHA1 sum for @dentry if its file resource is in a staging
 * file.  Updates the SHA1 sum in the dentry and the lookup table entry.  If
 * there is already a lookup table entry with the same checksum, increment its
 * reference count and destroy the lookup entry with the updated checksum. */
static int calculate_sha1sum_for_staging_file(struct dentry *dentry,
                                              void *_lookup_table)
{
        struct lookup_table *lookup_table =  _lookup_table;
        u8 *hash = dentry->hash;
        u16 i = 0;
        while (1) {
                struct lookup_table_entry *lte = __lookup_resource(lookup_table, hash);
                if (lte && lte->staging_file_name) {
                        struct lookup_table_entry *existing;
                        int ret;

                        DEBUG("Calculating SHA1 hash for file `%s'",
                              dentry->file_name_utf8);
                        ret = sha1sum(lte->staging_file_name, lte->hash);
                        if (ret != 0)
                                return ret;

                        lookup_table_unlink(lookup_table, lte);
                        memcpy(hash, lte->hash, WIM_HASH_SIZE);
                        existing = __lookup_resource(lookup_table, hash);
                        if (existing) {
                                DEBUG("Merging duplicate lookup table entries for file "
                                      "`%s'", dentry->file_name_utf8);
                                free_lookup_table_entry(lte);
                                existing->refcnt++;
                        } else {
                                lookup_table_insert(lookup_table, lte);
                        }
                }
                if (i == dentry->num_ads)
                        break;
                hash = dentry->ads_entries[i].hash;
                i++;
        }
        return 0;
}

/* Overwrites the WIM file, with changes saved. */
static int rebuild_wim(WIMStruct *w, bool check_integrity)
{
        int ret;
        struct dentry *root;

        root = wim_root_dentry(w);

        DEBUG("Closing all staging file descriptors.");
        /* Close all the staging file descriptors. */
        ret = for_lookup_table_entry(w->lookup_table, close_lte_fds, NULL);
        if (ret != 0) {
                ERROR("Failed to close all staging files");
                return ret;
        }

        DEBUG("Calculating SHA1 checksums for all new staging files.");
        /* Calculate SHA1 checksums for all staging files, and merge unnecessary
         * lookup table entries. */
        ret = for_dentry_in_tree(root, calculate_sha1sum_for_staging_file,
                                 w->lookup_table);
        if (ret != 0) {
                ERROR("Failed to calculate new SHA1 checksums");
                return ret;
        }

        xml_update_image_info(w, w->current_image);

        ret = wimlib_overwrite(w, check_integrity);
        if (ret != 0) {
                ERROR("Failed to commit changes");
                return ret;
        }
        return ret;
}

/* Called when the filesystem is unmounted. */
static void wimfs_destroy(void *p)
{

        /* For read-write mounts, the `imagex unmount' command, which is
         * running in a separate process and is executing the
         * wimlib_unmount() function, will send this process a byte
         * through a message queue that indicates whether the --commit
         * option was specified or not. */

        int msgsize;
        struct timespec timeout;
        struct timeval now;
        ssize_t bytes_received;
        int ret;
        char commit;
        char check_integrity;
        char status;

        ret = open_message_queues(true);
        if (ret != 0)
                exit(1);

        msgsize = mq_get_msgsize(unmount_to_daemon_mq);
        char msg[msgsize];
        msg[0] = 0;
        msg[1] = 0;

        /* Wait at most 3 seconds before giving up and discarding changes. */
        gettimeofday(&now, NULL);
        timeout.tv_sec = now.tv_sec + 3;
        timeout.tv_nsec = now.tv_usec * 1000;
        DEBUG("Waiting for message telling us whether to commit or not, and "
              "whether to include integrity checks.");

        bytes_received = mq_timedreceive(unmount_to_daemon_mq, msg, 
                                         msgsize, NULL, &timeout);
        commit = msg[0];
        check_integrity = msg[1];
        if (bytes_received == -1) {
                if (errno == ETIMEDOUT) {
                        ERROR("Timed out.");
                } else {
                        ERROR_WITH_ERRNO("mq_timedreceive()");
                }
                ERROR("Not committing.");
        } else {
                DEBUG("Received message: [%d %d]", msg[0], msg[1]);
        }

        status = 0;
        if (mount_flags & WIMLIB_MOUNT_FLAG_READWRITE) {
                if (commit) {
                        status = chdir(working_directory);
                        if (status != 0) {
                                ERROR_WITH_ERRNO("chdir()");
                                status = WIMLIB_ERR_NOTDIR;
                                goto done;
                        }
                        status = rebuild_wim(w, (check_integrity != 0));
                }
                ret = delete_staging_dir();
                if (ret != 0) {
                        ERROR_WITH_ERRNO("Failed to delete the staging "
                                         "directory");
                        if (status == 0)
                                status = ret;
                }
        }
done:
        ret = mq_send(daemon_to_unmount_mq, &status, 1, 1);
        if (ret == -1)
                ERROR_WITH_ERRNO("Failed to send status to unmount process");
        close_message_queues();
}

static int wimfs_ftruncate(const char *path, off_t size,
                           struct fuse_file_info *fi)
{
        struct wimlib_fd *fd = (struct wimlib_fd*)fi->fh;
        int ret = ftruncate(fd->staging_fd, size);
        if (ret != 0)
                return ret;
        fd->lte->resource_entry.original_size = size;
        return 0;
}

/*
 * Fills in a `struct stat' that corresponds to a file or directory in the WIM.
 */
static int wimfs_getattr(const char *path, struct stat *stbuf)
{
        struct dentry *dentry = get_dentry(w, path);
        if (!dentry)
                return -ENOENT;
        dentry_to_stbuf(dentry, stbuf, w->lookup_table);
        return 0;
}

/* 
 * Create a directory in the WIM.  
 * @mode is currently ignored.
 */
static int wimfs_mkdir(const char *path, mode_t mode)
{
        struct dentry *parent;
        struct dentry *newdir;
        const char *basename;
        
        parent = get_parent_dentry(w, path);
        if (!parent)
                return -ENOENT;

        if (!dentry_is_directory(parent))
                return -ENOTDIR;

        basename = path_basename(path);
        if (get_dentry_child_with_name(parent, basename))
                return -EEXIST;

        newdir = new_dentry(basename);
        newdir->attributes |= FILE_ATTRIBUTE_DIRECTORY;
        link_dentry(newdir, parent);
        return 0;
}


/* Creates a regular file. */
static int wimfs_mknod(const char *path, mode_t mode, dev_t rdev)
{
        const char *stream_name;
        if ((mount_flags & WIMLIB_MOUNT_FLAG_STREAM_INTERFACE_WINDOWS)
             && (stream_name = path_stream_name(path))) {
                struct ads_entry *new_entry;
                struct dentry *dentry;

                dentry = get_dentry(w, path);
                if (!dentry || !dentry_is_regular_file(dentry))
                        return -ENOENT;
                if (dentry_get_ads_entry(dentry, stream_name))
                        return -EEXIST;
                new_entry = dentry_add_ads(dentry, stream_name);
                if (!new_entry)
                        return -ENOENT;
        } else {
                struct dentry *dentry, *parent;
                const char *basename;

                /* Make sure that the parent of @path exists and is a directory, and
                 * that the dentry named by @path does not already exist.  */
                parent = get_parent_dentry(w, path);
                if (!parent)
                        return -ENOENT;
                if (!dentry_is_directory(parent))
                        return -ENOTDIR;
                basename = path_basename(path);
                if (get_dentry_child_with_name(parent, path))
                        return -EEXIST;

                dentry = new_dentry(basename);
                link_dentry(dentry, parent);
        }
        return 0;
}


/* Open a file.  */
static int wimfs_open(const char *path, struct fuse_file_info *fi)
{
        struct dentry *dentry;
        struct lookup_table_entry *lte;
        u8 *dentry_hash;
        int ret;
        struct wimlib_fd *fd;

        ret = lookup_resource(w, path, get_lookup_flags(), &dentry, &lte,
                              &dentry_hash);
        if (ret != 0)
                return ret;

        if (!lte) {
                /* Empty file with no lookup-table entry.  This is fine if it's
                 * a read-only filesystem.  Otherwise we need to create a lookup
                 * table entry so that we can keep track of the file descriptors
                 * (this is important in case someone opens the file for
                 * writing) */
                if (!(mount_flags & WIMLIB_MOUNT_FLAG_READWRITE)) {
                        fi->fh = 0;
                        return 0;
                }

                ret = extract_resource_to_staging_dir(dentry, &lte,
                                                      lte->resource_entry.original_size);
                if (ret != 0)
                        return ret;
        }

        ret = alloc_wimlib_fd(lte, &fd);
        if (ret != 0)
                return ret;

        fd->dentry = dentry;

        /* The file resource may be in the staging directory (read-write
         * mounts only) or in the WIM.  If it's in the staging
         * directory, we need to open a native file descriptor for the
         * corresponding file.  Otherwise, we can read the file resource
         * directly from the WIM file if we are opening it read-only,
         * but we need to extract the resource to the staging directory
         * if we are opening it writable. */
        if (flags_writable(fi->flags) && !lte->staging_file_name) {
                ret = extract_resource_to_staging_dir(dentry, &lte,
                                                      lte->resource_entry.original_size);
                if (ret != 0)
                        return ret;
        }
        if (lte->staging_file_name) {
                fd->staging_fd = open(lte->staging_file_name, fi->flags);
                if (fd->staging_fd == -1) {
                        close_wimlib_fd(fd);
                        return -errno;
                }
        }
        fi->fh = (uint64_t)fd;
        return 0;
}

/* Opens a directory. */
static int wimfs_opendir(const char *path, struct fuse_file_info *fi)
{
        struct dentry *dentry;
        
        dentry = get_dentry(w, path);
        if (!dentry || !dentry_is_directory(dentry))
                return -ENOTDIR;
        fi->fh = (uint64_t)dentry;
        return 0;
}


/*
 * Read data from a file in the WIM or in the staging directory. 
 */
static int wimfs_read(const char *path, char *buf, size_t size, 
                      off_t offset, struct fuse_file_info *fi)
{
        struct wimlib_fd *fd = (struct wimlib_fd*)fi->fh;

        if (!fd) {
                /* Empty file with no lookup table entry on read-only mounted
                 * WIM */
                wimlib_assert(!(mount_flags & WIMLIB_MOUNT_FLAG_READWRITE));
                return 0;
        }

        if (fd->lte->staging_file_name) {
                /* Read from staging file */

                wimlib_assert(fd->staging_fd != -1);

                ssize_t ret;

                if (lseek(fd->staging_fd, offset, SEEK_SET) == -1)
                        return -errno;
                ret = read(fd->staging_fd, buf, size);
                if (ret == -1)
                        return -errno;
                return ret;
        } else {

                /* Read from WIM */

                struct resource_entry *res_entry;
                int ctype;
                
                res_entry = &fd->lte->resource_entry;

                ctype = wim_resource_compression_type(w, res_entry);

                if (offset > res_entry->original_size)
                        return -EOVERFLOW;

                size = min(size, res_entry->original_size - offset);

                if (read_resource(w->fp, res_entry->size, 
                                  res_entry->original_size,
                                  res_entry->offset, ctype, size, 
                                  offset, buf) != 0)
                        return -EIO;
                return size;
        }
}

/* Fills in the entries of the directory specified by @path using the
 * FUSE-provided function @filler.  */
static int wimfs_readdir(const char *path, void *buf, fuse_fill_dir_t filler, 
                                off_t offset, struct fuse_file_info *fi)
{
        struct dentry *parent, *child;
        
        parent = (struct dentry*)fi->fh;
        child = parent->children;

        filler(buf, ".", NULL, 0);
        filler(buf, "..", NULL, 0);

        if (!child)
                return 0;

        do {
                if (filler(buf, child->file_name_utf8, NULL, 0))
                        return 0;
                child = child->next;
        } while (child != parent->children);
        return 0;
}


static int wimfs_readlink(const char *path, char *buf, size_t buf_len)
{
        struct dentry *dentry = get_dentry(w, path);
        int ret;
        if (!dentry)
                return -ENOENT;
        if (!dentry_is_symlink(dentry))
                return -EINVAL;

        ret = dentry_readlink(dentry, buf, buf_len, w);
        if (ret > 0)
                ret = 0;
        return ret;
}

/* Close a file. */
static int wimfs_release(const char *path, struct fuse_file_info *fi)
{
        int ret;
        struct wimlib_fd *fd = (struct wimlib_fd*)fi->fh;

        if (!fd) {
                /* Empty file with no lookup table entry on read-only mounted
                 * WIM */
                wimlib_assert(!(mount_flags & WIMLIB_MOUNT_FLAG_READWRITE));
                return 0;
        }
        return close_wimlib_fd(fd);
}

/* Renames a file or directory.  See rename (3) */
static int wimfs_rename(const char *from, const char *to)
{
        struct dentry *src;
        struct dentry *dst;
        struct dentry *parent_of_dst;
        
        src = get_dentry(w, from);
        if (!src)
                return -ENOENT;

        dst = get_dentry(w, to);

        if (dst) {
                if (!dentry_is_directory(src)) {
                        /* Cannot rename non-directory to directory. */
                        if (dentry_is_directory(dst))
                                return -EISDIR;
                } else {
                        /* Cannot rename directory to a non-directory or a non-empty
                         * directory */
                        if (!dentry_is_directory(dst))
                                return -ENOTDIR;
                        if (dst->children != NULL)
                                return -ENOTEMPTY;
                }
                parent_of_dst = dst->parent;
                unlink_dentry(dst);
                lookup_table_decrement_refcnt(w->lookup_table, dst->hash);
                free_dentry(dst);
        } else {
                parent_of_dst = get_parent_dentry(w, to);
                if (!parent_of_dst)
                        return -ENOENT;
        }

        unlink_dentry(src);
        change_dentry_name(src, path_basename(to));
        link_dentry(src, parent_of_dst);
        /*calculate_dentry_full_path(src);*/
        return 0;
}

/* Remove a directory */
static int wimfs_rmdir(const char *path)
{
        struct dentry *dentry;
        
        dentry = get_dentry(w, path);
        if (!dentry)
                return -ENOENT;

        if (!dentry_is_empty_directory(dentry))
                return -ENOTEMPTY;

        unlink_dentry(dentry);
        free_dentry(dentry);
        return 0;
}


/* Reduce the size of a file */
static int wimfs_truncate(const char *path, off_t size)
{
        struct dentry *dentry;
        struct lookup_table_entry *lte;
        int ret;
        u8 *dentry_hash;
        
        ret = lookup_resource(w, path, get_lookup_flags(), &dentry,
                              &lte, &dentry_hash);

        if (ret != 0)
                return ret;

        if (!lte) /* Already a zero-length file */
                return 0;

        if (lte->staging_file_name) {
                ret = truncate(lte->staging_file_name, size);
                if (ret != 0)
                        return -errno;
                lte->resource_entry.original_size = size;
        } else {
                /* File in WIM.  Extract it to the staging directory, but only
                 * the first @size bytes of it. */
                ret = extract_resource_to_staging_dir(dentry, &lte, size);
        }
        dentry_update_all_timestamps(dentry);
        return ret;
}

/* Remove a regular file */
static int wimfs_unlink(const char *path)
{
        struct dentry *dentry;
        struct lookup_table_entry *lte;
        int ret;
        u8 *dentry_hash;
        
        ret = lookup_resource(w, path, get_lookup_flags(), &dentry,
                              &lte, &dentry_hash);

        if (ret != 0)
                return ret;

        if (lte && lte->staging_file_name)
                if (unlink(lte->staging_file_name) != 0)
                        return -errno;

        if (dentry_hash == dentry->hash) {
                /* We are removing the full dentry including all alternate data
                 * streams. */
                const u8 *hash = dentry->hash;
                u16 i = 0;
                while (1) {
                        lookup_table_decrement_refcnt(w->lookup_table, hash);
                        if (i == dentry->num_ads)
                                break;
                        hash = dentry->ads_entries[i].hash;
                        i++;
                }

                unlink_dentry(dentry);
                free_dentry(dentry);
        } else {
                /* We are removing an alternate data stream. */
                struct ads_entry *cur_entry = dentry->ads_entries;
                while (cur_entry->hash != dentry_hash)
                        cur_entry++;
                lookup_table_decrement_refcnt(w->lookup_table, cur_entry->hash);
                
                dentry_remove_ads(dentry, cur_entry);
        }
        /* Beware: The lookup table entry(s) may still be referenced by users
         * that have opened the corresponding streams.  They are freed later in
         * wimfs_release() when the last file user has closed the stream. */
        return 0;
}

/* Change the timestamp on a file dentry. 
 *
 * There is no distinction between a file and its alternate data streams here.  */
static int wimfs_utimens(const char *path, const struct timespec tv[2])
{
        struct dentry *dentry = get_dentry(w, path);
        if (!dentry)
                return -ENOENT;
        time_t last_access_t = (tv[0].tv_nsec == UTIME_NOW) ? 
                                time(NULL) : tv[0].tv_sec;
        dentry->last_access_time = unix_timestamp_to_ms(last_access_t);
        time_t last_mod_t = (tv[1].tv_nsec == UTIME_NOW) ?  
                                time(NULL) : tv[1].tv_sec;
        dentry->last_write_time = unix_timestamp_to_ms(last_mod_t);
        return 0;
}

/* Writes to a file in the WIM filesystem. 
 * It may be an alternate data stream, but here we don't even notice because we
 * just get a lookup table entry. */
static int wimfs_write(const char *path, const char *buf, size_t size, 
                       off_t offset, struct fuse_file_info *fi)
{
        struct wimlib_fd *fd = (struct wimlib_fd*)fi->fh;
        int ret;

        wimlib_assert(fd->lte);
        wimlib_assert(fd->lte->staging_file_name);
        wimlib_assert(fd->staging_fd != -1);

        /* Write the data. */
        ret = write(fd->staging_fd, buf, size);
        if (ret == -1)
                return -errno;

        /* The file has been modified, so all its timestamps must be
         * updated. */
        dentry_update_all_timestamps(fd->dentry);

        return ret;
}


static struct fuse_operations wimfs_oper = {
        .access    = wimfs_access,
        .destroy   = wimfs_destroy,
        .ftruncate = wimfs_ftruncate,
        .getattr   = wimfs_getattr,
        .mkdir     = wimfs_mkdir,
        .mknod     = wimfs_mknod,
        .open      = wimfs_open,
        .opendir   = wimfs_opendir,
        .read      = wimfs_read,
        .readdir   = wimfs_readdir,
        .readlink  = wimfs_readlink,
        .release   = wimfs_release,
        .rename    = wimfs_rename,
        .rmdir     = wimfs_rmdir,
        .truncate  = wimfs_truncate,
        .unlink    = wimfs_unlink,
        .utimens   = wimfs_utimens,
        .write     = wimfs_write,
};


/* Mounts a WIM file. */
WIMLIBAPI int wimlib_mount(WIMStruct *wim, int image, const char *dir, 
                           int flags)
{
        int argc = 0;
        char *argv[6];
        int ret;
        char *p;

        DEBUG("Mount: wim = %p, image = %d, dir = %s, flags = %d, ",
                        wim, image, dir, flags);

        if (!dir)
                return WIMLIB_ERR_INVALID_PARAM;

        ret = wimlib_select_image(wim, image);

        if (ret != 0)
                return ret;

        if (flags & WIMLIB_MOUNT_FLAG_READWRITE)
                wim_get_current_image_metadata(wim)->modified = true;

        if (!(flags & (WIMLIB_MOUNT_FLAG_STREAM_INTERFACE_NONE |
                       WIMLIB_MOUNT_FLAG_STREAM_INTERFACE_XATTR |
                       WIMLIB_MOUNT_FLAG_STREAM_INTERFACE_WINDOWS)))
                flags |= WIMLIB_MOUNT_FLAG_STREAM_INTERFACE_XATTR;

        mount_dir = dir;
        working_directory = getcwd(NULL, 0);
        if (!working_directory) {
                ERROR_WITH_ERRNO("Could not determine current directory");
                return WIMLIB_ERR_NOTDIR;
        }

        p = STRDUP(dir);
        if (!p)
                return WIMLIB_ERR_NOMEM;

        argv[argc++] = "mount";
        argv[argc++] = p;
        argv[argc++] = "-s"; /* disable multi-threaded operation */

        if (flags & WIMLIB_MOUNT_FLAG_DEBUG) {
                argv[argc++] = "-d";
        }
        if (!(flags & WIMLIB_MOUNT_FLAG_READWRITE)) {
                argv[argc++] = "-o";
                argv[argc++] = "ro";
        } else {
                make_staging_dir();
                if (!staging_dir_name) {
                        FREE(p);
                        return WIMLIB_ERR_MKDIR;
                }
        }

#ifdef ENABLE_DEBUG
        {
                int i;
                DEBUG("FUSE command line (argc = %d): ", argc);
                for (i = 0; i < argc; i++) {
                        fputs(argv[i], stdout);
                        putchar(' ');
                }
                putchar('\n');
                fflush(stdout);
        }
#endif

        /* Set static variables. */
        w = wim;
        mount_flags = flags;

        ret = fuse_main(argc, argv, &wimfs_oper, NULL);

        return (ret == 0) ? 0 : WIMLIB_ERR_FUSE;
}


/* 
 * Unmounts the WIM file that was previously mounted on @dir by using
 * wimlib_mount().
 */
WIMLIBAPI int wimlib_unmount(const char *dir, int flags)
{
        pid_t pid;
        int status;
        int ret;
        char msg[2];
        struct timeval now;
        struct timespec timeout;
        int msgsize;
        int errno_save;

        /* Execute `fusermount -u', which is installed setuid root, to unmount
         * the WIM.
         *
         * FUSE does not yet implement synchronous unmounts.  This means that
         * fusermount -u will return before the filesystem daemon returns from
         * wimfs_destroy().  This is partly what we want, because we need to
         * send a message from this process to the filesystem daemon telling
         * whether --commit was specified or not.  However, after that, the
         * unmount process must wait for the filesystem daemon to finish writing
         * the WIM file. 
         */

        mount_dir = dir;
        pid = fork();
        if (pid == -1) {
                ERROR_WITH_ERRNO("Failed to fork()");
                return WIMLIB_ERR_FORK;
        }
        if (pid == 0) {
                execlp("fusermount", "fusermount", "-u", dir, NULL);
                ERROR_WITH_ERRNO("Failed to execute `fusermount'");
                return WIMLIB_ERR_FUSERMOUNT;
        }

        ret = waitpid(pid, &status, 0);
        if (ret == -1) {
                ERROR_WITH_ERRNO("Failed to wait for fusermount process to "
                                 "terminate");
                return WIMLIB_ERR_FUSERMOUNT;
        }

        if (status != 0) {
                ERROR("fusermount exited with status %d", status);
                return WIMLIB_ERR_FUSERMOUNT;
        }

        /* Open message queues between the unmount process and the
         * filesystem daemon. */
        ret = open_message_queues(false);
        if (ret != 0)
                return ret;

        /* Send a message to the filesystem saying whether to commit or
         * not. */
        msg[0] = (flags & WIMLIB_UNMOUNT_FLAG_COMMIT) ? 1 : 0;
        msg[1] = (flags & WIMLIB_UNMOUNT_FLAG_CHECK_INTEGRITY) ? 1 : 0;

        DEBUG("Sending message: %s, %s", 
                        (msg[0] == 0) ? "don't commit" : "commit",
                        (msg[1] == 0) ? "don't check"  : "check");
        ret = mq_send(unmount_to_daemon_mq, msg, 2, 1);
        if (ret == -1) {
                ERROR("Failed to notify filesystem daemon whether we want to "
                      "commit changes or not");
                close_message_queues();
                return WIMLIB_ERR_MQUEUE;
        }

        /* Wait for a message from the filesytem daemon indicating whether  the
         * filesystem was unmounted successfully (0) or an error occurred (1).
         * This may take a long time if a big WIM file needs to be rewritten. */

        /* Wait at most 600??? seconds before giving up and returning false.
         * Either it's a really big WIM file, or (more likely) the
         * filesystem daemon has crashed or failed for some reason.
         *
         * XXX come up with some method to determine if the filesystem
         * daemon has really crashed or not. */

        gettimeofday(&now, NULL);
        timeout.tv_sec = now.tv_sec + 600;
        timeout.tv_nsec = now.tv_usec * 1000;

        msgsize = mq_get_msgsize(daemon_to_unmount_mq);
        char mailbox[msgsize];

        mailbox[0] = 0;
        DEBUG("Waiting for message telling us whether the unmount was "
                        "successful or not.");
        ret = mq_timedreceive(daemon_to_unmount_mq, mailbox, msgsize,
                              NULL, &timeout);
        errno_save = errno;
        close_message_queues();
        if (ret == -1) {
                if (errno_save == ETIMEDOUT) {
                        ERROR("Timed out- probably the filesystem daemon "
                              "crashed and the WIM was not written "
                              "successfully.");
                        return WIMLIB_ERR_TIMEOUT;
                } else {
                        ERROR("mq_receive(): %s", strerror(errno_save));
                        return WIMLIB_ERR_MQUEUE;
                }

        }
        DEBUG("Received message: %s",
              (mailbox[0] == 0) ?  "Unmount OK" : "Unmount Failed");
        if (mailbox[0] != 0)
                ERROR("Unmount failed");
        return mailbox[0];
}

#else /* WITH_FUSE */


static inline int mount_unsupported_error()
{
        ERROR("WIMLIB was compiled with --without-fuse, which disables support "
              "for mounting WIMs.");
        return WIMLIB_ERR_UNSUPPORTED;
}

WIMLIBAPI int wimlib_unmount(const char *dir, int flags)
{
        return mount_unsupported_error();
}

WIMLIBAPI int wimlib_mount(WIMStruct *wim_p, int image, const char *dir, 
                           int flags)
{
        return mount_unsupported_error();
}

#endif /* WITH_FUSE */