ID Number: Q39534
3.x 4.00 4.01
MS-DOS
Summary:
When writing a block device driver that supports the Open, Close, and
Removable Media abilities new to MS-DOS Versions 3.x and later, the
driver should set bit 11 of the Attribute Field word to 1.
For block devices that enable this bit 11, MS-DOS will be able to use
the following command codes in the device-driver request packet:
Code Function
13 Device Open
14 Device Close
15 Removable Media
When these device-driver calls are requested by MS-DOS, the driver
will be able to maintain a reference count of opens and closes for the
media.
Note, however, that the installation of the MS-DOS utility SHARE.EXE
is REQUIRED in order for MS-DOS to call the removable-media device
driver calls.
More Information:
Correct semantics of file handle opens and closes are not guaranteed
to be enforced without SHARE.EXE installed. There are many early
applications that perform ill-behaved FCB file I/O, such as the
following:
400 opens with no closes
200 opens with 100 closes
100 opens with 400 closes
delete an open file
rename an open file
With SHARE.EXE installed, such strange I/O behavior is not tolerated.
Thus, since proper file I/O semantics are being enforced, MS-DOS will
then be able to call the device-driver command codes listed above.
Since such semantics are not being enforced, MS-DOS does NOT make the
calls to these command codes to prevent the device driver from being
confused.