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:
³Code ³Function ³Block ³Char ³ ³ 0h ³INIT (See 0h.) ³ X ³ X ³ ³ 1h ³MEDIA CHECK (See 1h.) ³ X ³ ³ ³ 2h ³BUILD BPB (See 2h.) ³ X ³ ³ ³ 3h ³Reserved ³ ³ ³ ³ 4h ³READ (input) (See 4h, 8h, 9h.) ³ X ³ X ³ ³ 5h ³NONDESTRUCTIVE READ NO WAIT (See 5h.) ³ ³ X ³ ³ 6h ³INPUT STATUS (See 6h, Ah.) ³ ³ X ³ ³ 7h ³INPUT FLUSH (See 7h, Bh.) ³ ³ X ³ ³ 8h ³WRITE (output) (See 4h, 8h, 9h.) ³ X ³ X ³ ³ 9h ³WRITE WITH VERIFY (See 4h, 8h, 9h.) ³ X ³ X ³ ³ Ah ³OUTPUT STATUS (See 6h, Ah.) ³ ³ X ³ ³ Bh ³OUTPUT FLUSH (See 7h, Bh.) ³ ³ X ³ ³ Ch ³Reserved ³ ³ ³ ³ Dh ³OPEN DEVICE (See Dh, Eh.) ³ X ³ X ³ ³ Eh ³CLOSE DEVICE (See Dh, Eh.) ³ X ³ X ³ ³ Fh ³REMOVABLE MEDIA (See Fh.) ³ X ³ ³ ³10h ³GENERIC IOCtl (See 10h.) ³ X ³ X ³ ³11h ³RESET MEDIA (See 11h.) ³ X ³ ³ ³12h ³GET LOGICAL DRIVE MAP (See 12h, 13h.) ³ X ³ ³ ³13h ³SET LOGICAL DRIVE MAP (See 12h, 13h.) ³ X ³ ³ ³14h ³DEINSTALL (See 14h.) ³ ³ X ³ ³15h ³Reserved ³ ³ ³ ³16h ³PARTITIONABLE HARD DISKS (See 16h.) ³ X ³ ³ ³17h ³GET HARD DISK/LOGICAL UNIT MAP ³ X ³ ³ ³ ³(See 17h.) ³ ³ ³ ³18h ³Reserved ³ ³ ³ ³19h ³Reserved ³ ³ ³ ³1Ah ³Reserved ³ ³ ³ ³1Bh ³Reserved ³ ³ ³ ³1Ch ³SHUTDOWN (See 1Ch.) ³ X ³ X ³ ³1Dh ³GET DRIVER CAPABILITIES (See 1Dh.) ³ X ³ ³ ³1Eh ³Reserved ³ ³ ³ ³1Fh ³INITIALIZATION COMPLETE (See 1Fh.) ³ ³ X ³
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