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<b>DOS_OPT_CHANGENOWARN</b> must be set in the <b>dosvc_options</b> field of the
<b>DOS_VOL_CONFIG</b> structure, if the driver and/or
application is unable to issue a <b><i><a href="./dosFsLib.html#dosFsVolUnmount">dosFsVolUnmount</a></i>(&nbsp;)</b> call or assert a
ready-change when a disk is changed.
<p>
This configuration option results in a significant performance disadvantage,
because the disk configuration data must be regularly read in from the
physical disk, in case the disk has been changed.  In addition, setting
<b>DOS_OPT_CHANGENOWARN</b> also enables auto-sync mode (see below).
<p>
Note that for disk change notification, all that is required is that
<b><i><a href="./dosFsLib.html#dosFsVolUnmount">dosFsVolUnmount</a></i>(&nbsp;)</b> or <b><i><a href="./dosFsLib.html#dosFsReadyChange">dosFsReadyChange</a></i>(&nbsp;)</b> be called each time the disk is
changed.  It is not necessary that either routine be called from the
device driver or an interrupt handler.  For example, if your application
provided a user interface through which an operator could enter a command
which would result in a <b><i><a href="./dosFsLib.html#dosFsVolUnmount">dosFsVolUnmount</a></i>(&nbsp;)</b> call before removing the disk,
that would be sufficient, and <b>DOS_OPT_CHANGENOWARN</b> should not be set.
It is important, however, that such a procedure be followed strictly.
</blockQuote><h4>Synchronizing Volumes</h4><blockQuote>
A disk should be "synchronized" before is is unmounted.  To synchronize a
disk means to write out all buffered data (files, directories, and the FAT
table) that have been modified, so that the disk is "up-to-date."  It may
or may not be necessary to explicitly synchronize a disk, depending on
when (or if) the <b><i><a href="./dosFsLib.html#dosFsVolUnmount">dosFsVolUnmount</a></i>(&nbsp;)</b> call is issued.
<p>
When <b><i><a href="./dosFsLib.html#dosFsVolUnmount">dosFsVolUnmount</a></i>(&nbsp;)</b> is called, an attempt will be made to synchronize the
device before unmounting.  If the disk is still present and writable at the
time <b><i><a href="./dosFsLib.html#dosFsVolUnmount">dosFsVolUnmount</a></i>(&nbsp;)</b> is called, the synchronization will take place; there
is no need to independently synchronize the disk.
<p>
However, if <b><i><a href="./dosFsLib.html#dosFsVolUnmount">dosFsVolUnmount</a></i>(&nbsp;)</b> is called after a disk has been removed,
it is obviously too late to synchronize.  (In this situation, <b><i><a href="./dosFsLib.html#dosFsVolUnmount">dosFsVolUnmount</a></i>(&nbsp;)</b>
discards the buffered data.)  Therefore, a separate <b><i><a href="./ioLib.html#ioctl">ioctl</a></i>(&nbsp;)</b> call with
the FIOFLUSH or FIOSYNC function should be made before the disk is removed.  
(This could be done in response to an operator command.)
</blockQuote><h4>Auto-Sync Mode</h4><blockQuote>
The dosFs file system provides a modified mode of behavior called "auto-sync."
This mode is enabled by setting <b>DOS_OPT_AUTOSYNC</b> in the <b>dosvc_options</b> field of
the <b>DOS_VOL_CONFIG</b> structure when calling <b><i><a href="./dosFsLib.html#dosFsDevInit">dosFsDevInit</a></i>(&nbsp;)</b>.  When this
option is enabled, modified directory and FAT data is written to
the physical device as soon as these structures are altered.  (Normally,
such changes may not be written out until the involved file is closed.)
This results in a performance penalty, but it provides the highest level
of data security, since it minimizes the amount of time when directory
and FAT data on the disk are not up-to-date.
<p>
Auto-sync mode is automatically enabled if the volume does not have disk
change notification, i.e., if <b>DOS_OPT_CHANGENOWARN</b> is set in the <b>dosvc_options</b>
field of the <b>DOS_VOL_CONFIG</b> structure when <b><i><a href="./dosFsLib.html#dosFsDevInit">dosFsDevInit</a></i>(&nbsp;)</b> is
called.  It may also be desirable for applications where data integrity--
in case of a system crash--is a larger concern than simple disk I/O 
performance.
<p>
</blockquote><h4>CHANGES IN VOLUME CONFIGURATION</h4><blockquote><p>
Various disk configuration parameters are specified
when the dosFs device is first initialized using <b><i><a href="./dosFsLib.html#dosFsDevInit">dosFsDevInit</a></i>(&nbsp;)</b>.  This
data is kept in the volume descriptor (<b>DOS_VOL_DESC</b>) for the device.
However, it is possible for a disk with different parameters than those
defined to be placed in a drive after the device has already been
initialized.  For such a disk to be usable, the configuration data
in the volume descriptor must be modified when a new disk is present.
<p>
When a disk is mounted, the boot sector information is read from the disk.
This data is used to update the configuration data in the volume descriptor.
Note that this will happen the first time the disk is accessed after the
volume has been unmounted (using <b><i><a href="./dosFsLib.html#dosFsVolUnmount">dosFsVolUnmount</a></i>(&nbsp;)</b>).
<p>
This automatic re-initialization of the configuration data has two
important implications:
<dl>
<dt>
(1)
<dd>

Since the values in the volume descriptor are reset when a new
volume is mounted, it is possible to omit the dosFs configuration data (by
specifying a NULL pointer instead of the address of a <b>DOS_VOL_CONFIG</b>
structure during <b><i><a href="./dosFsLib.html#dosFsDevInit">dosFsDevInit</a></i>(&nbsp;)</b>).  The first use of the volume must be with
a properly formatted and initialized disk.  (Attempting to initialize a
disk, using FIODISKINIT, before a valid disk has been mounted is 
fruitless.)
<p>
<dt>
(2)
<dd>

The volume descriptor data is used when initializing a disk
(with FIODISKINIT).  The FIODISKINIT function initializes a disk with
the configuration of the most recently mounted disk, regardless of the
original specification during <b><i><a href="./dosFsLib.html#dosFsDevInit">dosFsDevInit</a></i>(&nbsp;)</b>.  Therefore, it is recommended
that FIODISKINIT be used immediately after <b><i><a href="./dosFsLib.html#dosFsDevInit">dosFsDevInit</a></i>(&nbsp;)</b>, before any disk
has been mounted.  (The device should be opened in raw mode; the FIODISKINIT
function is then performed; and the device is then closed.) 
</dl>

<p>

</blockquote><h4>IOCTL FUNCTIONS</h4><blockquote><p>
The dosFs file system supports the following <b><i><a href="./ioLib.html#ioctl">ioctl</a></i>(&nbsp;)</b> functions.  The
functions listed are defined in the header <b>ioLib.h</b>.  Unless stated
otherwise, the file descriptor used for these functions may be any file
descriptor which is opened to a file or directory on the volume or to 
the volume itself.
<p>
<dl>
<dt>
<b>FIODISKFORMAT</b>
<dd>

Formats the entire disk with appropriate hardware track and sector marks.
No file system is initialized on the disk by this request.
Note that this is a driver-provided function:
<pre>    fd = open ("DEV1:", O_WRONLY);
    status = ioctl (fd, FIODISKFORMAT, 0);
</pre>

<dt>
<b>FIODISKINIT</b>
<dd>

Initializes a DOS file system on the disk volume.
This routine does not format the disk; formatting must be done by the driver.
The file descriptor should be obtained by opening the entire volume in raw mode:
<pre>    fd = open ("DEV1:", O_WRONLY);
    status = ioctl (fd, FIODISKINIT, 0);
</pre>

<dt>
<b>FIODISKCHANGE</b>
<dd>

Announces a media change.  It performs the same function as <b><i><a href="./dosFsLib.html#dosFsReadyChange">dosFsReadyChange</a></i>(&nbsp;)</b>.
This function may be called from interrupt level:
<pre>    status = ioctl (fd, FIODISKCHANGE, 0);
</pre>

<dt>
<b>FIOUNMOUNT</b>
<dd>

Unmounts a disk volume.  It performs the same function as <b><i><a href="./dosFsLib.html#dosFsVolUnmount">dosFsVolUnmount</a></i>(&nbsp;)</b>.
This function must not be called from interrupt level:
<pre>    status = ioctl (fd, FIOUNMOUNT, 0);
</pre>

<dt>
<b>FIOGETNAME</b>
<dd>

Gets the file name of the file descriptor and copies it to the buffer <i>nameBuf</i>:
<pre>    status = ioctl (fd, FIOGETNAME, &amp;nameBuf );
</pre>

<dt>
<b>FIORENAME</b>
<dd>

Renames the file or directory to the string <i>newname</i>:
<pre>    status = ioctl (fd, FIORENAME, "newname");
</pre>

<dt>
<b>FIOSEEK</b>
<dd>

Sets the current byte offset in the file to the position specified by
<i>newOffset</i>:
<pre>    status = ioctl (fd, FIOSEEK, newOffset);
</pre>

<dt>
<b>FIOWHERE</b>
<dd>

Returns the current byte position in the file.  This is the byte offset of
the next byte to be read or written.  It takes no additional argument:
<pre>    position = ioctl (fd, FIOWHERE, 0);
</pre>

<dt>
<b>FIOFLUSH</b>
<dd>

Flushes the file output buffer.  It guarantees that any output that has
been requested is actually written to the device.  If the specified file
descriptor was obtained by opening the entire volume (raw mode), this 
function will flush all buffered file buffers, directories, and the FAT 
table to the physical device:
<pre>    status = ioctl (fd, FIOFLUSH, 0);
</pre>

<dt>
<b>FIOSYNC</b>
<dd>

Performs the same function as FIOFLUSH, and additionally re-reads buffered
file data from the disk.  This allows file changes made via a different file
descriptor to be seen.
<p>
<dt>
<b>FIOTRUNC</b>
<dd>

Truncates the specified file's length to <i>newLength</i> bytes.  Any disk
clusters which had been allocated to the file but are now unused are
returned, and the directory entry for the file is updated to reflect
the new length.  Only regular files may be truncated; attempts to use
FIOTRUNC on directories or the entire volume will return an error.
FIOTRUNC may only be used to make files shorter; attempting to specify
a <i>newLength</i> larger than the current size of the file produces an
error (setting errno to S_dosFsLib_INVALID_NUMBER_OF_BYTES).
<pre>    status = ioctl (fd, FIOTRUNC, newLength);
</pre>

<dt>
<b>FIONREAD</b>
<dd>

Copies to <i>unreadCount</i> the number of unread bytes in the file:
<pre>    status = ioctl (fd, FIONREAD, &amp;unreadCount);
</pre>

<dt>
<b>FIONFREE</b>
<dd>

Copies to <i>freeCount</i> the amount of free space, in bytes, on the volume:
<pre>   status = ioctl (fd, FIONFREE, &amp;freeCount);
</pre>

<dt>
<b>FIOMKDIR</b>
<dd>

Creates a new directory with the name specified as <i>dirName</i>:
<pre>    status = ioctl (fd, FIOMKDIR, "dirName");
</pre>

<dt>
<b>FIORMDIR</b>
<dd>

Removes the directory whose name is specified as <i>dirName</i>:
<pre>    status = ioctl (fd, FIORMDIR, "dirName");
</pre>

<dt>
<b>FIOLABELGET</b>
<dd>

Gets the volume label (located in root directory) and copies the string to
<i>labelBuffer</i>:
<pre>    status = ioctl (fd, FIOLABELGET, &amp;labelBuffer);
</pre>