[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 General Public License as published by the Free
 * Software Foundation; either version 3 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 General Public License for more
 * details.
 *
 * You should have received a copy of the GNU 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>
#include <utime.h>

#ifdef ENABLE_XATTR
#include <attr/xattr.h>
#endif

/* File descriptor to a file open on the WIM filesystem. */
struct wimlib_fd {
        struct inode *f_inode;
        struct lookup_table_entry *lte;
        int staging_fd;
        u16 idx;
        u32 stream_id;
};

/* 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;

/* Next inode number to be assigned. */
static u64 next_ino;

/* List of lookup table entries in the staging directory */
static LIST_HEAD(staging_list);

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

/* Returns nonzero if write permission is requested on the file open flags */
static inline int flags_writable(int open_flags)
{
        return open_flags & (O_RDWR | O_WRONLY);
}

/*
 * Allocate a file descriptor for a stream.
 *
 * @inode:      inode containing the stream we're opening
 * @stream_id:  ID of the stream we're opening
 * @lte:        Lookup table entry for the stream (may be NULL)
 * @fd_ret:     Return the allocated file descriptor if successful.
 *
 * Return 0 iff successful or error code if unsuccessful.
 */
static int alloc_wimlib_fd(struct inode *inode,
                           u32 stream_id,
                           struct lookup_table_entry *lte,
                           struct wimlib_fd **fd_ret)
{
        static const u16 fds_per_alloc = 8;
        static const u16 max_fds = 0xffff;

        DEBUG("Allocating fd for stream ID %u from inode %lx (open = %u, allocated = %u)",
              stream_id, inode->ino, inode->num_opened_fds,
              inode->num_allocated_fds);

        if (inode->num_opened_fds == inode->num_allocated_fds) {
                struct wimlib_fd **fds;
                u16 num_new_fds;

                if (inode->num_allocated_fds == max_fds)
                        return -EMFILE;
                num_new_fds = min(fds_per_alloc,
                                  max_fds - inode->num_allocated_fds);
                
                fds = REALLOC(inode->fds,
                              (inode->num_allocated_fds + num_new_fds) *
                                sizeof(inode->fds[0]));
                if (!fds)
                        return -ENOMEM;
                memset(&fds[inode->num_allocated_fds], 0,
                       num_new_fds * sizeof(fds[0]));
                inode->fds = fds;
                inode->num_allocated_fds += num_new_fds;
        }
        for (u16 i = 0; ; i++) {
                if (!inode->fds[i]) {
                        struct wimlib_fd *fd = CALLOC(1, sizeof(*fd));
                        if (!fd)
                                return -ENOMEM;
                        fd->f_inode    = inode;
                        fd->lte        = lte;
                        fd->staging_fd = -1;
                        fd->idx        = i;
                        fd->stream_id  = stream_id;
                        *fd_ret        = fd;
                        inode->fds[i]  = fd;
                        inode->num_opened_fds++;
                        if (lte)
                                lte->num_opened_fds++;
                        DEBUG("Allocated fd");
                        return 0;
                }
        }
}

static void inode_put_fd(struct inode *inode, struct wimlib_fd *fd)
{
        wimlib_assert(fd);
        wimlib_assert(inode);
        wimlib_assert(fd->f_inode == inode);
        wimlib_assert(inode->num_opened_fds);
        wimlib_assert(fd->idx < inode->num_opened_fds);
        wimlib_assert(inode->fds[fd->idx] == fd);

        inode->fds[fd->idx] = NULL;
        FREE(fd);
        if (--inode->num_opened_fds == 0 && inode->link_count == 0)
                free_inode(inode);
}

static int lte_put_fd(struct lookup_table_entry *lte, struct wimlib_fd *fd)
{
        wimlib_assert(fd);
        wimlib_assert(fd->lte == lte);

        if (!lte) /* Empty stream with no lookup table entry */
                return 0;

        /* Close staging file descriptor if needed. */
        wimlib_assert(lte->num_opened_fds);

        if (lte->resource_location == RESOURCE_IN_STAGING_FILE) {
                wimlib_assert(lte->staging_file_name);
                wimlib_assert(fd->staging_fd != -1);
                if (close(fd->staging_fd) != 0) {
                        ERROR_WITH_ERRNO("Failed to close staging file");
                        return -errno;
                }
        }
        lte_decrement_num_opened_fds(lte, w->lookup_table);
        return 0;
}

/* Close a file descriptor. */
static int close_wimlib_fd(struct wimlib_fd *fd)
{
        int ret;
        wimlib_assert(fd);
        DEBUG("Closing fd (inode = %lu, opened = %u, allocated = %u)",
              fd->f_inode->ino, fd->f_inode->num_opened_fds,
              fd->f_inode->num_allocated_fds);
        ret = lte_put_fd(fd->lte, fd);
        if (ret != 0)
                return ret;

        inode_put_fd(fd->f_inode, fd);
        return 0;
}

/* Remove a dentry; i.e. remove a reference to the corresponding inode.
 *
 * If there are no remaining references to the inode either through dentries or
 * open file descriptors, the inode is freed.  Otherwise, the inode is not
 * removed, but the dentry is unlinked and freed.
 *
 * Either way, all lookup table entries referenced by the inode have their
 * reference count decremented.  If a lookup table entry has no open file
 * descriptors and no references remaining, it is freed, and the staging file is
 * unlinked.
 */
static void remove_dentry(struct dentry *dentry,
                          struct lookup_table *lookup_table)
{
        struct inode *inode = dentry->d_inode;
        struct lookup_table_entry *lte;
        unsigned i;

        for (i = 0; i <= inode->num_ads; i++) {
                lte = inode_stream_lte_resolved(inode, i);
                if (lte)
                        lte_decrement_refcnt(lte, lookup_table);
        }
        unlink_dentry(dentry);
        put_dentry(dentry);
}

/* 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 + SHA1_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,
                                                SHA1_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.
 *
 * @inode:  Inode that contains the stream we are extracting
 *
 * @stream_id: Identifier for the stream (it stays constant even if the indices
 * of the stream entries are changed)
 *
 * @lte: Pointer to pointer to the lookup table entry for the stream we need to
 * extract, or NULL if there was no lookup table entry present for the stream
 *
 * @size:  Number of bytes of the stream we want to extract (this supports the
 * wimfs_truncate() function).
 */
static int extract_resource_to_staging_dir(struct inode *inode,
                                           u32 stream_id,
                                           struct lookup_table_entry **lte,
                                           off_t size)
{
        char *staging_file_name;
        int ret;
        int fd;
        struct lookup_table_entry *old_lte, *new_lte;

        old_lte = *lte;
        fd = create_staging_file(&staging_file_name, O_WRONLY);
        if (fd == -1)
                return -errno;

        if (old_lte)
                ret = extract_wim_resource_to_fd(old_lte, fd, size);
        else
                ret = 0;
        if (ret != 0 || close(fd) != 0) {
                if (errno != 0)
                        ret = -errno;
                else
                        ret = -EIO;
                close(fd);
                goto out_delete_staging_file;
        }

        if (old_lte && inode->link_count == old_lte->refcnt) {
                /* The reference count of the existing lookup table
                 * entry is the same as the link count of the inode that
                 * contains the stream we're opening.  Therefore, ALL
                 * the references to the lookup table entry correspond
                 * to the stream we're trying to extract, so the lookup
                 * table entry can be re-used.  */
                DEBUG("Re-using lookup table entry");
                lookup_table_unlink(w->lookup_table, old_lte);
                new_lte = old_lte;
        } else {
                if (old_lte) {
                        /* There's an existing lookup table entry, but its
                         * reference count is creater than the link count for
                         * the inode containing a stream we're opening.
                         * Therefore, we need to split the lookup table entry.
                         * */
                        wimlib_assert(old_lte->refcnt > inode->link_count);
                        DEBUG("Splitting lookup table entry "
                              "(inode->link_count = %zu, old_lte->refcnt = %u)",
                              inode->link_count, old_lte->refcnt);

                }

                new_lte = new_lookup_table_entry();
                if (!new_lte) {
                        ret = -ENOMEM;
                        goto out_delete_staging_file;
                }

                /* There may already be open file descriptors to this stream if
                 * it's previously been opened read-only, but just now we're
                 * opening it read-write.  Identify those file descriptors and
                 * change their lookup table entry pointers to point to the new
                 * lookup table entry, and open staging file descriptors for
                 * them. 
                 *
                 * At the same time, we need to count the number of these opened
                 * file descriptors to the new lookup table entry.  If there's
                 * an old lookup table entry, this number needs to be subtracted
                 * from the fd's opened to the old entry. */
                for (u16 i = 0, j = 0; j < inode->num_opened_fds; i++) {
                        struct wimlib_fd *fd = inode->fds[i];
                        if (fd) {
                                if (fd->stream_id == stream_id) {
                                        wimlib_assert(fd->lte == old_lte);
                                        fd->lte = new_lte;
                                        new_lte->num_opened_fds++;
                                        fd->staging_fd = open(staging_file_name, O_RDONLY);
                                        if (fd->staging_fd == -1) {
                                                ret = -errno;
                                                goto out_revert_fd_changes;
                                        }
                                }
                                j++;
                        }
                }
                DEBUG("%zu fd's were already opened to the file we extracted",
                      new_lte->num_opened_fds);
                if (old_lte) {
                        old_lte->num_opened_fds -= new_lte->num_opened_fds;
                        old_lte->refcnt -= inode->link_count;
                }
        }

        new_lte->resource_entry.original_size = size;
        new_lte->refcnt                       = inode->link_count;
        new_lte->staging_file_name            = staging_file_name;
        new_lte->resource_location            = RESOURCE_IN_STAGING_FILE;
        new_lte->lte_inode                        = inode;
        random_hash(new_lte->hash);

        if (stream_id == 0)
                inode->lte = new_lte;
        else
                for (u16 i = 0; i < inode->num_ads; i++)
                        if (inode->ads_entries[i].stream_id == stream_id)
                                inode->ads_entries[i].lte = new_lte;

        lookup_table_insert(w->lookup_table, new_lte);
        list_add(&new_lte->staging_list, &staging_list);
        *lte = new_lte;
        return 0;
out_revert_fd_changes:
        for (u16 i = 0, j = 0; j < new_lte->num_opened_fds; i++) {
                struct wimlib_fd *fd = inode->fds[i];
                if (fd && fd->stream_id == stream_id && fd->lte == new_lte) {
                        fd->lte = old_lte;
                        if (fd->staging_fd != -1) {
                                close(fd->staging_fd);
                                fd->staging_fd = -1;
                        }
                        j++;
                }
        }
out_free_new_lte:
        free_lookup_table_entry(new_lte);
out_delete_staging_file:
        unlink(staging_file_name);
        FREE(staging_file_name);
        return ret;
}

/* 
 * 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 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 mqd_t unmount_to_daemon_mq;
static mqd_t 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 = strcpy(p, s1);
        p = strcat(p, s2);
        p = strcat(p, s3);
        return strcat(p, s4);
}

/* 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 == (mqd_t)-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 == (mqd_t)-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)
{
        /* Permissions not implemented */
        return 0;
}

static int update_lte_of_staging_file(struct lookup_table_entry *lte,
                                      struct lookup_table *table)
{
        struct lookup_table_entry *duplicate_lte;
        int ret;
        u8 hash[SHA1_HASH_SIZE];
        struct stat stbuf;

        wimlib_assert(lte->resource_location == RESOURCE_IN_STAGING_FILE);
        wimlib_assert(lte->staging_file_name);

        ret = sha1sum(lte->staging_file_name, hash);
        if (ret != 0)
                return ret;

        lookup_table_unlink(table, lte);

        duplicate_lte = __lookup_resource(table, hash);

        if (duplicate_lte) {
                /* Merge duplicate lookup table entries */
                duplicate_lte->refcnt += lte->refcnt;
                list_del(&lte->staging_list);
                free_lookup_table_entry(lte);
        } else {
                if (stat(lte->staging_file_name, &stbuf) != 0) {
                        ERROR_WITH_ERRNO("Failed to stat `%s'", lte->staging_file_name);
                        return WIMLIB_ERR_STAT;
                }
                wimlib_assert(&lte->file_on_disk == &lte->staging_file_name);
                lte->resource_location = RESOURCE_IN_FILE_ON_DISK;
                copy_hash(lte->hash, hash);
                lte->resource_entry.original_size = stbuf.st_size;
                lte->resource_entry.size = stbuf.st_size;
                lte->lte_inode = NULL;
                lookup_table_insert(table, lte);
        }

        return 0;
}

static int inode_close_fds(struct inode *inode)
{
        for (u16 i = 0, j = 0; j < inode->num_opened_fds; i++) {
                struct wimlib_fd *fd = inode->fds[i];
                if (fd) {
                        wimlib_assert(fd->f_inode == inode);
                        int ret = close_wimlib_fd(fd);
                        if (ret != 0)
                                return ret;
                        j++;
                }
        }
        return 0;
}

/*static int dentry_close_fds(struct dentry *dentry, void *ignore)*/
/*{*/
        /*return inode_close_fds(dentry->d_inode);*/
/*}*/

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


        DEBUG("Closing all staging file descriptors.");
        list_for_each_entry(lte, &staging_list, staging_list) {
                ret = inode_close_fds(lte->lte_inode);
                if (ret != 0)
                        return ret;
        }
        /*ret = for_dentry_in_tree(wim_root_dentry(w), dentry_close_fds, NULL);*/
        /*if (ret != 0)*/
                /*return ret;*/

        DEBUG("Calculating SHA1 checksums for all new staging files.");
        list_for_each_entry_safe(lte, tmp, &staging_list, staging_list) {
                ret = update_lte_of_staging_file(lte, w->lookup_table);
                if (ret != 0)
                        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;
                }
        } else {
                DEBUG("Read-only mount");
        }
done:
        DEBUG("Sending status %u", status);
        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();
}

#if 0
static int wimfs_fallocate(const char *path, int mode,
                           off_t offset, off_t len, struct fuse_file_info *fi)
{
        struct wimlib_fd *fd = (struct wimlib_fd*)(uintptr_t)fi->fh;
        wimlib_assert(fd->staging_fd != -1);
        return fallocate(fd->staging_fd, mode, offset, len);
}

#endif

static int wimfs_fgetattr(const char *path, struct stat *stbuf,
                          struct fuse_file_info *fi)
{
        struct wimlib_fd *fd = (struct wimlib_fd*)(uintptr_t)fi->fh;
        return inode_to_stbuf(fd->f_inode, fd->lte, stbuf);
}

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

        ret = lookup_resource(w, path,
                              get_lookup_flags() | LOOKUP_FLAG_DIRECTORY_OK,
                              &dentry, &lte, NULL);
        if (ret != 0)
                return ret;
        return inode_to_stbuf(dentry->d_inode, lte, stbuf);
}

#ifdef ENABLE_XATTR
/* Read an alternate data stream through the XATTR interface, or get its size */
static int wimfs_getxattr(const char *path, const char *name, char *value,
                          size_t size)
{
        int ret;
        struct dentry *dentry;
        struct ads_entry *ads_entry;
        size_t res_size;
        struct lookup_table_entry *lte;

        if (!(mount_flags & WIMLIB_MOUNT_FLAG_STREAM_INTERFACE_XATTR))
                return -ENOTSUP;

        if (strlen(name) < 5 || memcmp(name, "user.", 5) != 0)
                return -ENOATTR;
        name += 5;

        dentry = get_dentry(w, path);
        if (!dentry)
                return -ENOENT;
        ads_entry = inode_get_ads_entry(dentry->d_inode, name, NULL);
        if (!ads_entry)
                return -ENOATTR;

        lte = ads_entry->lte;
        res_size = wim_resource_size(lte);

        if (size == 0)
                return res_size;
        if (res_size > size)
                return -ERANGE;
        ret = read_full_wim_resource(lte, (u8*)value);
        if (ret != 0)
                return -EIO;
        return res_size;
}
#endif

/* Create a hard link */
static int wimfs_link(const char *to, const char *from)
{
        struct dentry *from_dentry, *from_dentry_parent;
        const char *link_name;
        struct inode *inode;
        struct lookup_table_entry *lte;

        inode = wim_pathname_to_inode(w, to);
        if (!inode)
                return -ENOENT;

        if (!inode_is_regular_file(inode))
                return -EPERM;

        from_dentry_parent = get_parent_dentry(w, from);
        if (!from_dentry_parent)
                return -ENOENT;
        if (!dentry_is_directory(from_dentry_parent))
                return -ENOTDIR;

        link_name = path_basename(from);
        if (get_dentry_child_with_name(from_dentry_parent, link_name))
                return -EEXIST;
        from_dentry = new_dentry(link_name);
        if (!from_dentry)
                return -ENOMEM;


        inode_add_dentry(from_dentry, inode);
        from_dentry->d_inode = inode;
        inode->link_count++;

        for (unsigned i = 0; i <= inode->num_ads; i++) {
                lte = inode_stream_lte_resolved(inode, i);
                if (lte)
                        lte->refcnt++;
        }

        link_dentry(from_dentry, from_dentry_parent);
        return 0;
}

#ifdef ENABLE_XATTR
static int wimfs_listxattr(const char *path, char *list, size_t size)
{
        struct dentry *dentry;
        int ret;
        char *p = list;
        size_t needed_size;
        unsigned i;
        struct inode *inode;
        if (!(mount_flags & WIMLIB_MOUNT_FLAG_STREAM_INTERFACE_XATTR))
                return -ENOTSUP;

        /* List alternate data streams, or get the list size */

        ret = lookup_resource(w, path, get_lookup_flags(), &dentry, NULL, NULL);
        if (ret != 0)
                return ret;
        inode = dentry->d_inode;

        if (size == 0) {
                needed_size = 0;
                for (i = 0; i < inode->num_ads; i++)
                        needed_size += inode->ads_entries[i].stream_name_utf8_len + 6;
                return needed_size;
        } else {
                for (i = 0; i < inode->num_ads; i++) {
                        needed_size = inode->ads_entries[i].stream_name_utf8_len + 6;
                        if (needed_size > size)
                                return -ERANGE;
                        p += sprintf(p, "user.%s",
                                     inode->ads_entries[i].stream_name_utf8) + 1;
                        size -= needed_size;
                }
                return p - list;
        }
}
#endif

/* 
 * 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_with_inode(basename);
        newdir->d_inode->attributes |= FILE_ATTRIBUTE_DIRECTORY;
        newdir->d_inode->resolved = true;
        newdir->d_inode->ino = next_ino++;
        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))) {
                /* Make an alternate data stream */
                struct ads_entry *new_entry;
                struct dentry *dentry;

                char *p = (char*)stream_name - 1;
                wimlib_assert(*p == ':');
                *p = '\0';

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

                /* Make a normal file (not an alternate data stream) */

                /* 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_with_inode(basename);
                if (!dentry)
                        return -ENOMEM;
                dentry->d_inode->resolved = true;
                dentry->d_inode->ino = next_ino++;
                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;
        int ret;
        struct wimlib_fd *fd;
        struct inode *inode;
        u16 stream_idx;
        u32 stream_id;

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

        inode = dentry->d_inode;

        if (stream_idx == 0)
                stream_id = 0;
        else
                stream_id = inode->ads_entries[stream_idx - 1].stream_id;

        /* 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 || lte->resource_location != RESOURCE_IN_STAGING_FILE)) {
                u64 size = (lte) ? wim_resource_size(lte) : 0;
                ret = extract_resource_to_staging_dir(inode, stream_id,
                                                      &lte, size);
                if (ret != 0)
                        return ret;
        }

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

        if (lte && lte->resource_location == RESOURCE_IN_STAGING_FILE) {
                fd->staging_fd = open(lte->staging_file_name, fi->flags);
                if (fd->staging_fd == -1) {
                        close_wimlib_fd(fd);
                        return -errno;
                }
        }
        fi->fh = (uintptr_t)fd;
        return 0;
}

/* Opens a directory. */
static int wimfs_opendir(const char *path, struct fuse_file_info *fi)
{
        struct inode *inode;
        int ret;
        struct wimlib_fd *fd = NULL;
        
        inode = wim_pathname_to_inode(w, path);
        if (!inode)
                return -ENOENT;
        if (!inode_is_directory(inode))
                return -ENOTDIR;
        ret = alloc_wimlib_fd(inode, 0, NULL, &fd);
        fi->fh = (uintptr_t)fd;
        return ret;
}


/*
 * 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*)(uintptr_t)fi->fh;

        if (!fd)
                return -EBADF;

        if (!fd->lte) /* Empty stream with no lookup table entry */
                return 0;

        if (fd->lte->resource_location == RESOURCE_IN_STAGING_FILE) {
                /* Read from staging file */

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

                ssize_t ret;
                DEBUG("Seek to offset %zu", offset);

                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 */

                u64 res_size = wim_resource_size(fd->lte);
                
                if (offset > res_size)
                        return -EOVERFLOW;

                size = min(size, res_size - offset);

                if (read_wim_resource(fd->lte, (u8*)buf,
                                      size, offset, false) != 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 wimlib_fd *fd = (struct wimlib_fd*)(uintptr_t)fi->fh;
        struct inode *inode;
        struct dentry *child;

        if (!fd)
                return -EBADF;

        inode = fd->f_inode;

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

        child = inode->children;

        if (!child)
                return 0;

        do {
                if (filler(buf, child->file_name_utf8, NULL, 0))
                        return 0;
                child = child->next;
        } while (child != inode->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 = inode_readlink(dentry->d_inode, 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)
{
        struct wimlib_fd *fd = (struct wimlib_fd*)(uintptr_t)fi->fh;
        return close_wimlib_fd(fd);
}

/* Close a directory */
static int wimfs_releasedir(const char *path, struct fuse_file_info *fi)
{
        struct wimlib_fd *fd = (struct wimlib_fd*)(uintptr_t)fi->fh;
        return close_wimlib_fd(fd);
}

#ifdef ENABLE_XATTR
/* Remove an alternate data stream through the XATTR interface */
static int wimfs_removexattr(const char *path, const char *name)
{
        struct dentry *dentry;
        struct ads_entry *ads_entry;
        u16 ads_idx;
        if (!(mount_flags & WIMLIB_MOUNT_FLAG_STREAM_INTERFACE_XATTR))
                return -ENOTSUP;

        if (strlen(name) < 5 || memcmp(name, "user.", 5) != 0)
                return -ENOATTR;
        name += 5;

        dentry = get_dentry(w, path);
        if (!dentry)
                return -ENOENT;

        ads_entry = inode_get_ads_entry(dentry->d_inode, name, &ads_idx);
        if (!ads_entry)
                return -ENOATTR;
        inode_remove_ads(dentry->d_inode, ads_idx, w->lookup_table);
        return 0;
}
#endif

/* 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;
        char *file_name_utf16 = NULL, *file_name_utf8 = NULL;
        u16 file_name_utf16_len, file_name_utf8_len;
        int ret;

        /* This rename() implementation currently only supports actual files
         * (not alternate data streams) */
        
        src = get_dentry(w, from);
        if (!src)
                return -ENOENT;

        dst = get_dentry(w, to);


        ret = get_names(&file_name_utf16, &file_name_utf8,
                        &file_name_utf16_len, &file_name_utf8_len,
                        path_basename(to));
        if (ret != 0)
                return -ENOMEM;

        if (dst) {
                /* Destination file exists */

                if (src == dst) /* Same file */
                        return 0;

                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->d_inode->children != NULL)
                                return -ENOTEMPTY;
                }
                parent_of_dst = dst->parent;
                remove_dentry(dst, w->lookup_table);
        } else {
                /* Destination does not exist */
                parent_of_dst = get_parent_dentry(w, to);
                if (!parent_of_dst)
                        return -ENOENT;

                if (!dentry_is_directory(parent_of_dst))
                        return -ENOTDIR;
        }

        FREE(src->file_name);
        FREE(src->file_name_utf8);
        src->file_name          = file_name_utf16;
        src->file_name_utf8     = file_name_utf8;
        src->file_name_len      = file_name_utf16_len;
        src->file_name_utf8_len = file_name_utf8_len;

        unlink_dentry(src);
        link_dentry(src, parent_of_dst);
        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;

        remove_dentry(dentry, w->lookup_table);
        return 0;
}

#ifdef ENABLE_XATTR
/* Write an alternate data stream through the XATTR interface */
static int wimfs_setxattr(const char *path, const char *name,
                          const char *value, size_t size, int flags)
{
        struct ads_entry *existing_ads_entry;
        struct ads_entry *new_ads_entry;
        struct lookup_table_entry *existing_lte;
        struct lookup_table_entry *lte;
        struct inode *inode;
        u8 value_hash[SHA1_HASH_SIZE];
        u16 ads_idx;

        if (!(mount_flags & WIMLIB_MOUNT_FLAG_STREAM_INTERFACE_XATTR))
                return -ENOTSUP;

        if (strlen(name) < 5 || memcmp(name, "user.", 5) != 0)
                return -ENOATTR;
        name += 5;

        inode = wim_pathname_to_inode(w, path);
        if (!inode)
                return -ENOENT;

        existing_ads_entry = inode_get_ads_entry(inode, name, &ads_idx);
        if (existing_ads_entry) {
                if (flags & XATTR_CREATE)
                        return -EEXIST;
                inode_remove_ads(inode, ads_idx, w->lookup_table);
        } else {
                if (flags & XATTR_REPLACE)
                        return -ENOATTR;
        }
        new_ads_entry = inode_add_ads(inode, name);
        if (!new_ads_entry)
                return -ENOMEM;

        sha1_buffer((const u8*)value, size, value_hash);

        existing_lte = __lookup_resource(w->lookup_table, value_hash);

        if (existing_lte) {
                lte = existing_lte;
                lte->refcnt++;
        } else {
                u8 *value_copy;
                lte = new_lookup_table_entry();
                if (!lte)
                        return -ENOMEM;
                value_copy = MALLOC(size);
                if (!value_copy) {
                        FREE(lte);
                        return -ENOMEM;
                }
                memcpy(value_copy, value, size);
                lte->resource_location            = RESOURCE_IN_ATTACHED_BUFFER;
                lte->attached_buffer              = value_copy;
                lte->resource_entry.original_size = size;
                lte->resource_entry.size          = size;
                lte->resource_entry.flags         = 0;
                copy_hash(lte->hash, value_hash);
                lookup_table_insert(w->lookup_table, lte);
        }
        new_ads_entry->lte = lte;
        return 0;
}
#endif

static int wimfs_symlink(const char *to, const char *from)
{
        struct dentry *dentry_parent, *dentry;
        const char *link_name;
        struct inode *inode;
        
        dentry_parent = get_parent_dentry(w, from);
        if (!dentry_parent)
                return -ENOENT;
        if (!dentry_is_directory(dentry_parent))
                return -ENOTDIR;

        link_name = path_basename(from);

        if (get_dentry_child_with_name(dentry_parent, link_name))
                return -EEXIST;
        dentry = new_dentry_with_inode(link_name);
        if (!dentry)
                return -ENOMEM;
        inode = dentry->d_inode;

        inode->attributes  = FILE_ATTRIBUTE_REPARSE_POINT;
        inode->reparse_tag = WIM_IO_REPARSE_TAG_SYMLINK;
        inode->ino         = next_ino++;
        inode->resolved    = true;

        if (inode_set_symlink(inode, to, w->lookup_table, NULL) != 0)
                goto out_free_dentry;

        link_dentry(dentry, dentry_parent);
        return 0;
out_free_dentry:
        free_dentry(dentry);
        return -ENOMEM;
}


/* 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;
        u16 stream_idx;
        u32 stream_id;
        struct inode *inode;
        
        ret = lookup_resource(w, path, get_lookup_flags(), &dentry,
                              &lte, &stream_idx);

        if (ret != 0)
                return ret;

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

        inode = dentry->d_inode;

        if (stream_idx == 0)
                stream_id = 0;
        else
                stream_id = inode->ads_entries[stream_idx - 1].stream_id;

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

/* Remove a regular file */
static int wimfs_unlink(const char *path)
{
        struct dentry *dentry;
        struct lookup_table_entry *lte;
        struct inode *inode;
        int ret;
        u16 stream_idx;
        unsigned i;
        
        ret = lookup_resource(w, path, get_lookup_flags(), &dentry,
                              &lte, &stream_idx);

        if (ret != 0)
                return ret;

        if (stream_idx == 0)
                remove_dentry(dentry, w->lookup_table);
        else
                inode_remove_ads(dentry->d_inode, stream_idx - 1, w->lookup_table);
        return 0;
}

#ifdef HAVE_UTIMENSAT
/* 
 * Change the timestamp on a file dentry. 
 *
 * Note that alternate data streams do not have their own timestamps.
 */
static int wimfs_utimens(const char *path, const struct timespec tv[2])
{
        struct dentry *dentry;
        struct inode *inode;
        dentry = get_dentry(w, path);
        if (!dentry)
                return -ENOENT;
        inode = dentry->d_inode;

        if (tv[0].tv_nsec != UTIME_OMIT) {
                if (tv[0].tv_nsec == UTIME_NOW)
                        inode->last_access_time = get_wim_timestamp();
                else
                        inode->last_access_time = timespec_to_wim_timestamp(&tv[0]);
        }
        if (tv[1].tv_nsec != UTIME_OMIT) {
                if (tv[1].tv_nsec == UTIME_NOW)
                        inode->last_write_time = get_wim_timestamp();
                else
                        inode->last_write_time = timespec_to_wim_timestamp(&tv[1]);
        }
        return 0;
}
#else
static int wimfs_utime(const char *path, struct utimbuf *times)
{
        struct dentry *dentry;
        struct inode *inode;
        dentry = get_dentry(w, path);
        if (!dentry)
                return -ENOENT;
        inode = dentry->d_inode;

        inode->last_write_time = unix_timestamp_to_wim(times->modtime);
        inode->last_access_time = unix_timestamp_to_wim(times->actime);
        return 0;
}
#endif

/* 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*)(uintptr_t)fi->fh;
        int ret;
        u64 now;

        if (!fd)
                return -EBADF;

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

        /* Seek to the requested position */
        if (lseek(fd->staging_fd, offset, SEEK_SET) == -1)
                return -errno;

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

        now = get_wim_timestamp();
        fd->f_inode->last_write_time = now;
        fd->f_inode->last_access_time = now;
        return ret;
}

static struct fuse_operations wimfs_operations = {
        .access      = wimfs_access,
        .destroy     = wimfs_destroy,
#if 0
        .fallocate   = wimfs_fallocate,
#endif
        .fgetattr    = wimfs_fgetattr,
        .ftruncate   = wimfs_ftruncate,
        .getattr     = wimfs_getattr,
#ifdef ENABLE_XATTR
        .getxattr    = wimfs_getxattr,
#endif
        .link        = wimfs_link,
#ifdef ENABLE_XATTR
        .listxattr   = wimfs_listxattr,
#endif
        .mkdir       = wimfs_mkdir,
        .mknod       = wimfs_mknod,
        .open        = wimfs_open,
        .opendir     = wimfs_opendir,
        .read        = wimfs_read,
        .readdir     = wimfs_readdir,
        .readlink    = wimfs_readlink,
        .release     = wimfs_release,
        .releasedir  = wimfs_releasedir,
#ifdef ENABLE_XATTR
        .removexattr = wimfs_removexattr,
#endif
        .rename      = wimfs_rename,
        .rmdir       = wimfs_rmdir,
#ifdef ENABLE_XATTR
        .setxattr    = wimfs_setxattr,
#endif
        .symlink     = wimfs_symlink,
        .truncate    = wimfs_truncate,
        .unlink      = wimfs_unlink,
#ifdef HAVE_UTIMENSAT
        .utimens     = wimfs_utimens,
#else
        .utime       = wimfs_utime,
#endif
        .write       = wimfs_write,
};


/* Mounts a WIM file. */
WIMLIBAPI int wimlib_mount(WIMStruct *wim, int image, const char *dir, 
                           int flags, WIMStruct **additional_swms,
                           unsigned num_additional_swms)
{
        int argc = 0;
        char *argv[16];
        int ret;
        char *p;
        struct lookup_table *joined_tab, *wim_tab_save;
        struct image_metadata *imd;

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

        if (!wim || !dir)
                return WIMLIB_ERR_INVALID_PARAM;

        ret = verify_swm_set(wim, additional_swms, num_additional_swms);
        if (ret != 0)
                return ret;

        if (num_additional_swms) {
                ret = new_joined_lookup_table(wim, additional_swms,
                                              num_additional_swms,
                                              &joined_tab);
                if (ret != 0)
                        return ret;
                wim_tab_save = wim->lookup_table;
                wim->lookup_table = joined_tab;
        }

        ret = wimlib_select_image(wim, image);

        if (ret != 0)
                goto out;

        imd = &wim->image_metadata[image - 1];

        DEBUG("Selected image %d", image);

        next_ino = assign_inode_numbers(&imd->inode_list);

        DEBUG("(next_ino = %"PRIu64")", next_ino);

        /* Resolve all the lookup table entries of the dentry tree */
        DEBUG("Resolving lookup table entries");
        for_dentry_in_tree(imd->root_dentry, dentry_resolve_ltes,
                           wim->lookup_table);

        if (flags & WIMLIB_MOUNT_FLAG_READWRITE)
                imd->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;

        DEBUG("Getting current directory");

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

        DEBUG("Closing POSIX message queues");
        /* XXX hack to get rid of the message queues if they already exist for
         * some reason (maybe left over from a previous mount that wasn't
         * unmounted correctly) */
        ret = open_message_queues(true);
        if (ret != 0)
                goto out;
        close_message_queues();

        DEBUG("Preparing arguments to fuse_main()");


        p = STRDUP(dir);
        if (!p) {
                ret = WIMLIB_ERR_NOMEM;
                goto out;
        }

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

        if (flags & WIMLIB_MOUNT_FLAG_DEBUG)
                argv[argc++] = "-d";

        /* 
         * We provide the use_ino option because we are going to assign inode
         * numbers oursides.  We've already numbered the inodes with unique
         * numbers in the assign_inode_numbers() function, and the static
         * variable next_ino is set to the next available inode number.
         */
        char optstring[256] = "use_ino,subtype=wimfs,attr_timeout=0";
        argv[argc++] = "-o";
        argv[argc++] = optstring;
        if ((flags & WIMLIB_MOUNT_FLAG_READWRITE)) {
                /* Read-write mount.  Make the staging directory */
                make_staging_dir();
                if (!staging_dir_name) {
                        FREE(p);
                        ret = WIMLIB_ERR_MKDIR;
                        goto out;
                }
        } else {
                /* Read-only mount */
                strcat(optstring, ",ro");
        }
        argv[argc] = NULL;

#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_operations, NULL);
        if (ret)
                ret = WIMLIB_ERR_FUSE;
out:
        if (num_additional_swms) {
                free_lookup_table(wim->lookup_table);
                wim->lookup_table = wim_tab_save;
        }
        return ret;
}


/* 
 * 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;

        mount_dir = dir;

        /* 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;
        }

        /* 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. 
         */


        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'");
                exit(WIMLIB_ERR_FUSERMOUNT);
        }

        ret = wait(&status);
        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);

                /* Try again, but with the `umount' program.  This is required
                 * on other FUSE implementations such as FreeBSD's that do not
                 * have a `fusermount' program. */

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

                ret = wait(&status);
                if (ret == -1) {
                        ERROR_WITH_ERRNO("Failed to wait for `umount' process to "
                                         "terminate");
                        return WIMLIB_ERR_FUSERMOUNT;
                }
                if (status != 0) {
                        ERROR("`umount' exited with failure status");
                        return WIMLIB_ERR_FUSERMOUNT;
                }
        }


        /* 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. 
         *
         * XXX Idea: have mount daemon write its PID into the WIM file header?
         * */

        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, WIMStruct **additional_swms,
                           unsigned num_additional_swms)
{
        return mount_unsupported_error();
}

#endif /* WITH_FUSE */