Rewrite filesystem code (WIP)

This patch redoes the filesystem code from the FAT driver up to the
clipboard code in onplay.c.

Not every aspect of this is finished therefore it is still "WIP". I
don't wish to do too much at once (haha!). What is left to do is get
dircache back in the sim and find an implementation for the dircache
indicies in the tagcache and playlist code or do something else that
has the same benefit. Leaving these out for now does not make anything
unusable. All the basics are done.

Phone app code should probably get vetted (and app path handling
just plain rewritten as environment expansions); the SDL app and
Android run well.

Main things addressed:
1) Thread safety: There is none right now in the trunk code. Most of
what currently works is luck when multiple threads are involved or
multiple descriptors to the same file are open.

2) POSIX compliance: Many of the functions behave nothing like their
counterparts on a host system. This leads to inconsistent code or very
different behavior from native to hosted. One huge offender was
rename(). Going point by point would fill a book.

3) Actual running RAM usage: Many targets will use less RAM and less
stack space (some more RAM because I upped the number of cache buffers
for large memory). There's very little memory lying fallow in rarely-used
areas (see 'Key core changes' below). Also, all targets may open the same
number of directory streams whereas before those with less than 8MB RAM
were limited to 8, not 12 implying those targets will save slightly
less.

4) Performance: The test_disk plugin shows markedly improved performance,
particularly in the area of (uncached) directory scanning, due partly to
more optimal directory reading and to a better sector cache algorithm.
Uncached times tend to be better while there is a bit of a slowdown in
dircache due to it being a bit heavier of an implementation. It's not
noticeable by a human as far as I can say.

Key core changes:
1) Files and directories share core code and data structures.

2) The filesystem code knows which descriptors refer to same file.
This ensures that changes from one stream are appropriately reflected
in every open descriptor for that file (fileobj_mgr.c).

3) File and directory cache buffers are borrowed from the main sector
cache. This means that when they are not in use by a file, they are not
wasted, but used for the cache. Most of the time, only a few of them
are needed. It also means that adding more file and directory handles
is less expensive. All one must do in ensure a large enough cache to
borrow from.

4) Relative path components are supported and the namespace is unified.
It does not support full relative paths to an implied current directory;
what is does support is use of "." and "..". Adding the former would
not be very difficult. The namespace is unified in the sense that
volumes may be specified several times along with relative parts, e.g.:
"/<0>/foo/../../<1>/bar" :<=> "/<1>/bar".

5) Stack usage is down due to sharing of data, static allocation and
less duplication of strings on the stack. This requires more
serialization than I would like but since the number of threads is
limited to a low number, the tradoff in favor of the stack seems
reasonable.

6) Separates and heirarchicalizes (sic) the SIM and APP filesystem
code. SIM path and volume handling is just like the target. Some
aspects of the APP file code get more straightforward (e.g. no path
hashing is needed).

Dircache:
Deserves its own section. Dircache is new but pays homage to the old.
The old one was not compatible and so it, since it got redone, does
all the stuff it always should have done such as:

1) It may be update and used at any time during the build process.
No longer has one to wait for it to finish building to do basic file
management (create, remove, rename, etc.).

2) It does not need to be either fully scanned or completely disabled;
it can be incomplete (i.e. overfilled, missing paths), still be
of benefit and be correct.

3) Handles mounting and dismounting of individual volumes which means
a full rebuild is not needed just because you pop a new SD card in the
slot. Now, because it reuses its freed entry data, may rebuild only
that volume.

4) Much more fundamental to the file code. When it is built, it is
the keeper of the master file list whether enabled or not ("disabled"
is just a state of the cache). Its must always to ready to be started
and bind all streams opened prior to being enabled.

5) Maintains any short filenames in OEM format which means that it does
not need to be rebuilt when changing the default codepage.

Miscellaneous Compatibility:
1) Update any other code that would otherwise not work such as the
hotswap mounting code in various card drivers.

2) File management: Clipboard needed updating because of the behavioral
changes. Still needs a little more work on some finer points.

3) Remove now-obsolete functionality such as the mutex's "no preempt"
flag (which was only for the prior FAT driver).

4) struct dirinfo uses time_t rather than raw FAT directory entry
time fields. I plan to follow up on genericizing everything there
(i.e. no FAT attributes).

5) unicode.c needed some redoing so that the file code does not try
try to load codepages during a scan, which is actually a problem with
the current code. The default codepage, if any is required, is now
kept in RAM separarately (bufalloced) from codepages specified to
iso_decode() (which must not be bufalloced because the conversion
may be done by playback threads).

Brings with it some additional reusable core code:
1) Revised file functions: Reusable code that does things such as
safe path concatenation and parsing without buffer limitations or
data duplication. Variants that copy or alter the input path may be
based off these.

To do:
1) Put dircache functionality back in the sim. Treating it internally
as a different kind of file system seems the best approach at this
time.

2) Restore use of dircache indexes in the playlist and database or
something effectively the same. Since the cache doesn't have to be
complete in order to be used, not getting a hit on the cache doesn't
unambiguously say if the path exists or not.

Change-Id: Ia30f3082a136253e3a0eae0784e3091d138915c8
Reviewed-on: http://gerrit.rockbox.org/566
Reviewed-by: Michael Sevakis <jethead71@rockbox.org>
Tested: Michael Sevakis <jethead71@rockbox.org>

1 files changed, 562 insertions, 0 deletions

diff --git a/firmware/target/hosted/filesystem-app.c b/firmware/target/hosted/filesystem-app.c
new file mode 100644
index 0000000000..7ef8d3109b
--- /dev/null
+++ b/firmware/target/hosted/filesystem-app.c
@@ -0,0 +1,562 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2010 Thomas Martitz
+ *
+ * This program 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 2
+ * of the License, or (at your option) any later version.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+#define RB_FILESYSTEM_OS
+#include <stdio.h> /* snprintf */
+#include <stdlib.h>
+#include <stdarg.h>
+#include <time.h>
+#include <errno.h>
+#include <string.h>
+#include <limits.h>
+#include "config.h"
+#include "system.h"
+#include "file.h"
+#include "dir.h"
+#include "file_internal.h"
+#include "pathfuncs.h"
+#include "string-extra.h"
+#include "rbpaths.h"
+#include "logf.h"
+
+
+#if (CONFIG_PLATFORM & PLATFORM_ANDROID)
+static const char rbhome[] = "/sdcard";
+#elif (CONFIG_PLATFORM & (PLATFORM_SDL|PLATFORM_MAEMO|PLATFORM_PANDORA)) \
+        && !defined(__PCTOOL__)
+const char *rbhome;
+#else
+/* YPR0, YPR1 */
+static const char rbhome[] = HOME_DIR;
+#endif
+
+#if !(defined(SAMSUNG_YPR0) || defined(SAMSUNG_YPR1)) && !defined(__PCTOOL__)
+/* Special dirs are user-accessible (and user-writable) dirs which take priority
+ * over the ones where Rockbox is installed to. Classic example would be
+ * $HOME/.config/rockbox.org vs /usr/share/rockbox */
+#define HAVE_SPECIAL_DIRS
+#endif
+
+#ifdef HAVE_MULTIDRIVE
+/* This is to compare any opened directories with the home directory so that
+   the special drive links may be returned for it only */
+static int rbhome_fildes = -1;
+
+/* A special link is created under e.g. HOME_DIR/<microSD1>, e.g. to access
+ * external storage in a convenient location, much similar to the mount
+ * point on our native targets. Here they are treated as symlink (one which
+ * doesn't actually exist in the filesystem and therefore we have to override
+ * readlink() */
+static const char *handle_special_links(const char* link, unsigned flags,
+                                char *buf, const size_t bufsize)
+{
+    (void) flags;
+    char vol_string[VOL_MAX_LEN + 1];
+    get_volume_name(-1, vol_string);
+
+    /* link might be passed with or without HOME_DIR expanded. To handle
+     * both perform substring matching (VOL_NAMES is unique enough) */
+    const char *begin = strstr(link, vol_string);
+    if (begin)
+    {
+        /* begin now points to the start of vol_string within link,
+         * we want to copy the remainder of the paths, prefixed by
+         * the actual mount point (the remainder might be "") */
+        snprintf(buf, bufsize, MULTIDRIVE_DIR"%s", begin + len);
+        return buf;
+    }
+
+    return link;
+}
+#endif
+
+#ifdef HAVE_MULTIDRIVE
+/* we keep an open descriptor of the home directory to detect when it has been
+   opened by opendir() so that its "symlinks" may be enumerated */
+static void cleanup_rbhome(void)
+{
+    os_close(rbhome_fildes);
+    rbhome_fildes = -1;
+}
+#endif /* HAVE_MULTIDRIVE */
+
+void paths_init(void)
+{
+#ifdef HAVE_SPECIAL_DIRS
+    /* make sure $HOME/.config/rockbox.org exists, it's needed for config.cfg */
+#if (CONFIG_PLATFORM & PLATFORM_ANDROID)
+    os_mkdir("/sdcard/rockbox" __MKDIR_MODE_ARG);
+    os_mkdir("/sdcard/rockbox/rocks.data" __MKDIR_MODE_ARG);
+#else
+    char config_dir[MAX_PATH];
+
+    const char *home = getenv("RBROOT");
+    if (!home)
+    {
+        home = getenv("HOME");
+    }
+
+    if (!home)
+    {
+        logf("HOME environment var not set. Can't write config");
+        return;
+    }
+
+    rbhome = home;
+    snprintf(config_dir, sizeof(config_dir), "%s/.config", home);
+    os_mkdir(config_dir __MKDIR_MODE_ARG);
+    snprintf(config_dir, sizeof(config_dir), "%s/.config/rockbox.org", home);
+    os_mkdir(config_dir __MKDIR_MODE_ARG);
+    /* Plugin data directory */
+    snprintf(config_dir, sizeof(config_dir), "%s/.config/rockbox.org/rocks.data", home);
+    os_mkdir(config_dir __MKDIR_MODE_ARG);
+#endif
+#endif /* HAVE_SPECIAL_DIRS */
+
+#ifdef HAVE_MULTIDRIVE
+    /* if this fails then alternate volumes will not work, but this function
+       cannot return that fact */
+    rbhome_fildes = os_opendirfd(rbhome);
+    if (rbhome_fildes >= 0)
+        atexit(cleanup_rbhome);
+#endif /* HAVE_MULTIDRIVE */
+}
+
+#ifdef HAVE_SPECIAL_DIRS
+static const char* _get_user_file_path(const char *path,
+                                       unsigned flags,
+                                       char* buf,
+                                       const size_t bufsize)
+{
+    const char *ret = path;
+    const char *pos = path;
+    /* replace ROCKBOX_DIR in path with $HOME/.config/rockbox.org */
+    pos += ROCKBOX_DIR_LEN;
+    if (*pos == '/') pos += 1;
+
+#if (CONFIG_PLATFORM & PLATFORM_ANDROID)
+    if (path_append(buf, "/sdcard/rockbox", pos, bufsize) >= bufsize)
+        return NULL;
+#else
+    if (path_append(buf, rbhome, ".config/rockbox.org", bufsize) >= bufsize ||
+        path_append(buf, PA_SEP_SOFT, pos, bufsize) >= bufsize)
+        return NULL;
+#endif
+
+    /* always return the replacement buffer (pointing to $HOME) if
+     * write access is needed */
+    if (flags & NEED_WRITE)
+        ret = buf;
+    else if (os_file_exists(buf))
+        ret = buf;
+
+    if (ret != buf) /* not found in $HOME, try ROCKBOX_BASE_DIR, !NEED_WRITE only */
+    {
+        if (path_append(buf, ROCKBOX_SHARE_PATH, pos, bufsize) >= bufsize)
+            return NULL;
+
+        if (os_file_exists(buf))
+            ret = buf;
+    }
+
+    return ret;
+}
+
+#endif
+
+const char * handle_special_dirs(const char *dir, unsigned flags,
+                                 char *buf, const size_t bufsize)
+{
+    (void) flags; (void) buf; (void) bufsize;
+#ifdef HAVE_SPECIAL_DIRS
+    if (!strncmp(HOME_DIR, dir, HOME_DIR_LEN))
+    {
+        const char *p = dir + HOME_DIR_LEN;
+        while (*p == '/') p++;
+        snprintf(buf, bufsize, "%s/%s", rbhome, p);
+        dir = buf;
+    }
+    else if (!strncmp(ROCKBOX_DIR, dir, ROCKBOX_DIR_LEN))
+        dir = _get_user_file_path(dir, flags, buf, bufsize);
+#endif
+#ifdef HAVE_MULTIDRIVE
+    dir = handle_special_links(dir, flags, buf, bufsize);
+#endif
+    return dir;
+}
+
+int app_open(const char *path, int oflag, ...)
+{
+    int flags = IS_FILE;
+    if (oflag & O_ACCMODE)
+        flags |= NEED_WRITE;
+
+    char realpath[MAX_PATH];
+    const char *fpath = handle_special_dirs(path, flags, realpath,
+                                            sizeof (realpath));
+    if (!fpath)
+        FILE_ERROR_RETURN(ENAMETOOLONG, -1);
+
+    return os_open(fpath, oflag __OPEN_MODE_ARG);
+}
+
+int app_creat(const char *path, mode_t mode)
+{
+    return app_open(path, O_CREAT|O_WRONLY|O_TRUNC, mode);
+}
+
+int app_remove(const char *path)
+{
+    char realpath[MAX_PATH];
+    const char *fpath = handle_special_dirs(path, NEED_WRITE, realpath,
+                                            sizeof (realpath));
+    if (!fpath)
+        FILE_ERROR_RETURN(ENAMETOOLONG, -1);
+
+    return os_remove(fpath);
+}
+
+int app_rename(const char *old, const char *new)
+{
+    char realpath_old[MAX_PATH], realpath_new[MAX_PATH];
+    const char *fold = handle_special_dirs(old, NEED_WRITE, realpath_old,
+                                           sizeof (realpath_old));
+    const char *fnew = handle_special_dirs(new, NEED_WRITE, realpath_new,
+                                           sizeof (realpath_new));
+    if (!fold || !fnew)
+        FILE_ERROR_RETURN(ENAMETOOLONG, -1);
+
+    return os_rename(fold, fnew);
+}
+
+#ifdef HAVE_SDL_THREADS
+ssize_t app_read(int fd, void *buf, size_t nbyte)
+{
+    return os_read(fd, buf, nbyte);
+}
+
+ssize_t app_write(int fd, const void *buf, size_t nbyte)
+{
+    return os_write(fd, buf, nbyte);
+}
+#endif /* HAVE_SDL_THREADS */
+
+int app_relate(const char *path1, const char *path2)
+{
+    char realpath_1[MAX_PATH], realpath_2[MAX_PATH];
+    const char *fpath1 = handle_special_dirs(path1, 0, realpath_1,
+                                             sizeof (realpath_1));
+    const char *fpath2 = handle_special_dirs(path2, 0, realpath_2,
+                                             sizeof (realpath_2));
+
+    if (!fpath1 || !fpath2)
+        FILE_ERROR_RETURN(ENAMETOOLONG, -1);
+
+    return os_relate(fpath1, fpath2);
+}
+
+bool app_file_exists(const char *path)
+{
+    char realpath[MAX_PATH];
+    const char *fpath = handle_special_dirs(path, NEED_WRITE, realpath,
+                                            sizeof (realpath));
+    if (!fpath)
+        FILE_ERROR_RETURN(ENAMETOOLONG, false);
+
+    return os_file_exists(fpath);
+}
+
+/* need to wrap around DIR* because we need to save the parent's directory
+ * path in order to determine dirinfo for volumes or convert the path to UTF-8;
+ * also is required to implement get_dir_info() */
+struct __dir
+{
+    OS_DIR_T *osdirp;
+#ifdef HAVE_MULTIDRIVE
+    int volumes_returned;
+#endif
+    int osfd;
+    bool osfd_is_opened;
+#if defined(OS_DIRENT_CONVERT) || defined (HAVE_MULTIDRIVE)
+    #define USE_DIRENTP
+    struct dirent *direntp;
+    size_t d_name_size;
+#endif
+    char path[];
+};
+
+static void __dir_free(struct __dir *this)
+{
+    if (!this)
+        return;
+
+#ifdef USE_DIRENTP
+    free(this->direntp);
+#endif
+
+    if (this->osfd_is_opened)
+        os_close(this->osfd);
+
+    free(this);
+}
+
+DIR * app_opendir(const char *dirname)
+{
+    int rc;
+    char realpath[MAX_PATH];
+    const char *fname = handle_special_dirs(dirname, 0, realpath,
+                                            sizeof (realpath));
+    if (!fname)
+        FILE_ERROR_RETURN(ENAMETOOLONG, NULL);
+
+    size_t name_len = path_strip_trailing_separators(fname, &fname);
+    struct __dir *this = calloc(1, sizeof (*this) + name_len + 1);
+    if (!this)
+        FILE_ERROR(ENOMEM, RC);
+
+#ifdef USE_DIRENTP
+    /* allocate what we're really going to return to callers, making certain
+       it has at least the d_name size we want */
+    this->d_name_size = MAX(MAX_PATH, sizeof (this->direntp->d_name));
+    this->direntp = calloc(1, offsetof(typeof (*this->direntp), d_name) +
+                                 this->d_name_size);
+    if (!this->direntp)
+        FILE_ERROR(ENOMEM, RC);
+
+    /* only the d_name field will be valid but that is all that anyone may
+       truely count on portably existing */
+#endif /* USE_DIRENTP */
+
+    strmemcpy(this->path, fname, name_len);
+
+    rc = os_opendir_and_fd(this->path, &this->osdirp, &this->osfd);
+    if (rc < 0)
+        FILE_ERROR(ERRNO, RC);
+
+    this->osfd_is_opened = rc > 0;
+
+#ifdef HAVE_MULTIDRIVE
+    this->volumes_returned = INT_MAX; /* assume NOT $HOME */
+    if (rbhome_fildes >= 0 && os_samefile(rbhome_fildes, fd) > 0)
+        this->volumes_returned = 0; /* there's no place like $HOME */
+#endif /* HAVE_MULTIDRIVE */
+
+    return (DIR *)this;
+file_error:
+    __dir_free(this);
+    return NULL;
+}
+
+int app_closedir(DIR *dirp)
+{
+    struct __dir *this = (struct __dir *)dirp;
+    if (!this)
+        FILE_ERROR_RETURN(EBADF, -1);
+
+    OS_DIR_T *osdirp = this->osdirp;
+    __dir_free(this);
+
+    return os_closedir(osdirp);
+}
+
+struct dirent * app_readdir(DIR *dirp)
+{
+    struct __dir *this = (struct __dir *)dirp;
+    if (!this)
+        FILE_ERROR_RETURN(EBADF, NULL);
+
+#ifdef HAVE_MULTIDRIVE
+    if (this->volumes_returned < NUM_VOLUMES)
+    {
+        while (++this->volumes_returned < NUM_VOLUMES)
+        {
+            if (!volume_present(this->volumes_returned))
+                continue;
+
+            get_volume_name(this->volumes_returned, this->direntp->d_name);
+            return this->direntp;
+        }
+    }
+    /* do normal directory reads */
+#endif /* HAVE_MULTIDRIVE */
+
+    OS_DIRENT_T *osdirent = os_readdir(this->osdirp);
+
+#ifdef OS_DIRENT_CONVERT
+    if (strlcpy_from_os(this->direntp->d_name, osdirent->d_name,
+                        this->d_name_size) >= this->d_name_size)
+    {
+        this->direntp->d_name[0] = '\0';
+        errno = EOVERFLOW;
+        return NULL;
+    }
+
+    osdirent = (OS_DIRENT_T *)this->direntp;
+#endif /* OS_DIRENT_CONVERT */
+
+    return (struct dirent *)osdirent;
+}
+
+int app_mkdir(const char *path)
+{
+    char realpath[MAX_PATH];
+    const char *fname = handle_special_dirs(path, NEED_WRITE, realpath,
+                                            sizeof (realpath));
+    if (!fname)
+        FILE_ERROR_RETURN(ENAMETOOLONG, -1);
+
+    return os_mkdir(fname __MKDIR_MODE_ARG);
+}
+
+int app_rmdir(const char *path)
+{
+    char realpath[MAX_PATH];
+    const char *fname = handle_special_dirs(path, NEED_WRITE, realpath,
+                                            sizeof (realpath));
+    if (!fname)
+        FILE_ERROR_RETURN(ENAMETOOLONG, -1);
+
+    return os_rmdir(fname);
+}
+
+int app_samedir(DIR *dirp1, DIR *dirp2)
+{
+    struct __dir *this1 = (struct __dir *)dirp1;
+    struct __dir *this2 = (struct __dir *)dirp2;
+
+    if (!this1 || !this2)
+    {
+        errno = EBADF;
+        return -1;
+    }
+
+    return os_fsamefile(this1->osfd, this2->osfd);
+}
+
+bool app_dir_exists(const char *dirname)
+{
+    char realpath[MAX_PATH];
+    const char *fname = handle_special_dirs(dirname, 0, realpath,
+                                            sizeof (realpath));
+    if (!fname)
+        FILE_ERROR_RETURN(ENAMETOOLONG, false);
+
+    OS_DIR_T *osdirp = os_opendir(fname);
+    if (!osdirp)
+        return false;
+
+    os_closedir(osdirp);
+    return true;
+}
+
+struct dirinfo dir_get_info(DIR *dirp, struct dirent *entry)
+{
+    struct __dir *this = (struct __dir *)dirp;
+    struct dirinfo ret = { .mtime = 0 };
+
+    if (!this)
+        FILE_ERROR_RETURN(EBADF, ret);
+
+    if (!entry || entry->d_name[0] == '\0')
+        FILE_ERROR_RETURN(ENOENT, ret);
+
+    char path[MAX_PATH];
+
+#ifdef HAVE_MULTIDRIVE
+    if (this->volumes_returned < NUM_VOLUMES)
+    {
+        /* last thing read was a "symlink" */
+        ret.attribute = ATTR_LINK;
+        strcpy(path, MULTIDRIVE_DIR);
+    }
+    else
+#endif
+    if (path_append(path, this->path, entry->d_name, sizeof (path))
+            >= sizeof (path))
+    {
+        FILE_ERROR_RETURN(ENAMETOOLONG, ret);
+    }
+
+    struct stat s;
+    if (os_lstat(path, &s) < 0)
+        FILE_ERROR_RETURN(ERRNO, ret);
+
+    int err = 0;
+    if (S_ISLNK(s.st_mode))
+    {
+        ret.attribute |= ATTR_LINK;
+        err = os_stat(path, &s);
+    }
+
+    if (err < 0)
+        FILE_ERROR_RETURN(ERRNO, ret);
+
+    if (S_ISDIR(s.st_mode))
+        ret.attribute |= ATTR_DIRECTORY;
+
+    ret.size = s.st_size;
+
+    struct tm tm;
+    if (!localtime_r(&s.st_mtime, &tm))
+        FILE_ERROR_RETURN(ERRNO, ret);
+
+    ret.mtime = mktime(&tm);
+    return ret;
+}
+
+/* On MD we create a virtual symlink for the external drive,
+ * for this we need to override readlink(). */
+ssize_t app_readlink(const char *path, char *buf, size_t bufsiz)
+{
+    char _buf[MAX_PATH];
+    path = handle_special_dirs(path, 0, _buf, sizeof(_buf));
+#ifdef HAVE_MULTIDRIVE
+    /* if path == _buf then we can be sure handle_special_dir() did something
+     * and path is not an ordinary directory */
+    if (path == _buf && !strncmp(path, MULTIDRIVE_DIR, sizeof(MULTIDRIVE_DIR)-1))
+    {
+        /* copying NUL is not required as per readlink specification */
+        ssize_t len = strlen(path);
+        memcpy(buf, path, len);
+        return len;
+    }
+#endif
+    /* does not append NUL !! */
+    return os_readlink(path, buf, bufsiz);
+    (void) path; (void) buf; (void) bufsiz;
+}
+
+int os_volume_path(IF_MV(int volume, ) char *buffer, size_t bufsize)
+{
+#ifdef HAVE_MULTIVOLUME
+    char volname[VOL_MAX_LEN + 1];
+    get_volume_name(volume, volname);
+#else
+    const char *volname = "/";
+#endif
+
+    if (!handle_special_dirs(volname, NEED_WRITE, buffer, bufsize))
+    {
+        errno = ENAMETOOLONG;
+        return -1;
+    }
+
+    return 0;
+}