PDDREF:Physical Device Driver Strategy Commands
The physical device driver strategy routine is called with ES:BX pointing to the request packet.
Request Packets
The operating system does not guarantee that the order of API requests issued by multiple threads will be preserved in the order that the corresponding request packets arrive at the physical device driver. Multiple application threads, or threads created due to DosReadAsync and DosWriteAsync, can get blocked in the operating system. This allows a physical device driver request packet (for an API request by a subsequent thread that does not get blocked) to arrive out of order. If a device driver supports multiple outstanding requests, it is responsible for providing a synchronization mechanism between itself and application processes. Also, request packet ordering must be preserved.
A request packet consists of two parts, the request header and the command-specific data field. The structure of the request packet is detailed below:
| Field | Length |
|---|---|
| Length of Request Packet | BYTE |
| Block Device Unit Code | BYTE |
| Command Code | BYTE |
| Request Packet Status | WORD |
| Reserved | DWORD |
| Queue Linkage | DWORD |
| Command-Specific Data | BYTES |
- Length of Request Packet
- Set to the total length, in bytes, of the request packet (the length of the request header, plus the length of the command-specific data).
- Block Device Unit Code
- Identifies the unit for which the request is intended. This field has no meaning for character devices.
- Command Code
- Indicates the requested device driver function. The physical device driver command codes are summarized in Summary of Strategy Commands.
- Request Packet Status
- Defined only for OPEN and CLOSE request packets on entry to the strategy routine. For all other request packets, the Status field is undefined on entry. For an OPEN request packet, bit 3 (08h) of the Status field is set if the packet was generated from a DosMonOpen; otherwise, it is a DosOpen.
- For a CLOSE request packet, bit 3 (08h) of the Status field is set if the packet was generated by a DosMonClose, or by a DosClose of a handle that was generated by a DosMonOpen. In this way, monitor handles generated and left open when a process exits are closed properly. Otherwise, it was generated by a DosClose on a nonmonitor handle.
- On exit from the strategy routine, the Status field describes the resulting state of the request, as shown in the following table.
| Bits | Description |
|---|---|
| 15 | Error |
| 14 | Driver Defined Error |
| 13-10 | Reserved |
| 9 | Busy |
| 8 | Done |
| 7-0 | ERROR CODE (bit 15 on) |
- Bit 15
- The error bit. If this bit is set, the low 8 bits of the status WORD (7-0) indicate the error code, which is processed by the operating system in one of the following ways:
- If the IOCtl category is User Defined (refer to the Category Code under Generic IOCtl Commands), FF00H is ORed with the byte-wide error code.
- If not User Defined and bit 14 (device driver defined error code) is set, FE00H is ORed with the byte-wide error code.
- Otherwise, the error code must be one of those shown in the Status Field Error Code table, and is mapped into one of the standard OS/2 API return codes.
- Bit 14
- A device driver-defined error, if set in conjunction with bit 15.
- Bits 13-10
- Reserved.
- Bit 9
- The busy bit. It is set only by Status and Removable Media. See 6h, Ah and Fh for more information.
- Bit 8
- The done bit. MUST be set, even when bit 15 (the error bit) is set. That is, whenever you return with the error bit set, you must also set the done bit. The physical device driver sets the done bit to 1 when exiting or calls DevHlp_DevDone when the request is complete.
- Bits 7-0
- The low 8 bits of the status WORD. If bit 15 is set, bits 7-0 contain the error code.
| Error Codes | Description |
|---|---|
| 00h | Write Protect Violation |
| 01h | Unknown Unit |
| 02h | Device Not Ready |
| 03h | Unknown Command |
| 04h | CRC Error |
| 05h | Bad Drive Request Structure Length |
| 06h | Seek Error |
| 07h | Unknown Media |
| 08h | Sector Not Found |
| 09h | Printer Out of Paper |
| 0Ah | Write Fault |
| 0Bh | Read Fault |
| 0Ch | General Failure |
| 0Dh | Change Disk (logical switch) |
| 0Eh | Reserved |
| 0Fh | Reserved |
| 10h | Uncertain Media |
| 11h | Character I/O Call Interrupted |
| 12h | Monitors Not Supported |
| 13h | Invalid Parameter |
| 14h | Device Already in Use |
| 15h | Initialization Failed (non-critical) |
- Uncertain Media (10h)
- Returned when the state of the media in the drive is uncertain. This response should not be returned to the INIT command. For hard disks, the physical device driver must begin in a media-uncertain state in order to have the media correctly labelled. In general, the following guidelines can be used to determine when to respond with uncertain media:
- When a drive-not-ready condition is detected. In this case, return uncertain media to all subsequent commands until a reset media command is received.
- When accessing removable media without change-line support, and a time delay of two or more seconds has occurred.
- When the state of the change-line indicates that the media might have changed.
- Character I/O Call Interrupted (11h)
- Returned when the thread performing the I/O was interrupted out of a DevHlp_Block, before completing the requested operation.
- Monitors Not Supported (12h)
- Returned for monitor commands (monitor open/close, register IOCtl), if monitors are not supported by the physical device driver.
- Invalid Parameter (13h)
- Returned when one or more fields of the request packet contain invalid values.
Initialization Failed (noncritical) (15h) Returned when the device driver initialization fails, but a message does not appear indicating a failure.
- Queue Linkage
- Provided to maintain a linked list of request packets. The device driver can use the request queue management DevHlp services, or it can use its own queue management.
- Command-Specific Data
- The parameters required for the physical device driver command. The commands and actual formats of the corresponding request packets are discussed in the following sections.
Summary of Strategy Commands
The following table lists the physical device driver strategy commands:
| Code | Function | Block | Char |
| 0h | INIT (See 0h.) | X | X |
| 1h | MEDIA CHECK (See 1h.) | X | |
| 2h | BUILD BPB (See 2h.) | X | |
| 3h | Reserved | ||
| 4h | READ (input) (See 4h, 8h, 9h.) | X | X |
| 5h | NONDESTRUCTIVE READ NO WAIT (See 5h.) | X | |
| 6h | INPUT STATUS (See 6h, Ah.) | X | |
| 7h | INPUT FLUSH (See 7h, Bh.) | X | |
| 8h | WRITE (output) (See 4h, 8h, 9h.) | X | X |
| 9h | WRITE WITH VERIFY (See 4h, 8h, 9h.) | X | X |
| Ah | OUTPUT STATUS (See 6h, Ah.) | X | |
| Bh | OUTPUT FLUSH (See 7h, Bh.) | X | |
| Ch | Reserved | ||
| Dh | OPEN DEVICE (See Dh, Eh.) | X | X |
| Eh | CLOSE DEVICE (See Dh, Eh.) | X | X |
| Fh | REMOVABLE MEDIA (See Fh.) | X | |
| 10h | GENERIC IOCtl (See 10h.) | X | X |
| 11h | RESET MEDIA (See 11h.) | X | |
| 12h | GET LOGICAL DRIVE MAP (See 12h, 13h.) | X | |
| 13h | SET LOGICAL DRIVE MAP (See 12h, 13h.) | X | |
| 14h | DEINSTALL (See 14h.) | X | |
| 15h | Reserved | ||
| 16h | PARTITIONABLE HARD DISKS (See 16h.) | X | |
| 17h | GET HARD DISK/LOGICAL UNIT MAP (See 17h.) | X | |
| 18h | Reserved | ||
| 19h | Reserved | ||
| 1Ah | Reserved | ||
| 1Bh | Reserved | ||
| 1Ch | SHUTDOWN (See 1Ch.) | X | X |
| 1Dh | GET DRIVER CAPABILITIES (See 1Dh.) | X | |
| 1Eh | Reserved | ||
| 1Fh | INITIALIZATION COMPLETE (See 1Fh.) | X |
- Note
- All DWORD pointers are stored with offset first, then segment.
INIT - 0h MEDIA CHECK - 1h BUILD BIOS PARAMETER BLOCK (BPB) - 2h READ/WRITE/WRITE WITH VERIFY - 4h, 8h, 9h NONDESTRUCTIVE READ NO WAIT - 5h INPUT OR OUTPUT STATUS - 6h, Ah FLUSH INPUT OR OUTPUT - 7h, Bh OPEN OR CLOSE DEVICE - Dh, Eh REMOVABLE MEDIA - Fh GENERIC IOCtl - 10h RESET MEDIA - 11h GET OR SET LOGICAL DRIVE MAP - 12h, 13h DEINSTALL - 14h PARTITIONABLE HARD DISKS - 16h GET HARD DISK/LOGICAL UNIT MAP - 17h BASEDEVINIT - 1bh SHUTDOWN - 1Ch GET DRIVER CAPABILITIES - 1Dh INITIALIZATION COMPLETE - 1Fh