REQUESTHEADER STRUC
rhLength db ? ;length of record, in bytes
rhUnit db ? ;unit number (block device only)
rhFunction db ? ;function number
rhStatus dw ? ;status
rhReserved db 8 dup(?) ;reserved
REQUESTHEADER ENDS
The REQUESTHEADER structure contains information about a device-driver function.
rhLength
Specifies the length of the record, in bytes.
rhUnit
Identifies the device-driver function the request is for. For example, if the driver defines three functions, this field will contain 0, 1, or 2.
rhFunction
Specifies the action to be performed by the device driver. This field can be one of the following:
| Value | Function |
| 00h | Init |
| 01h | Media Check |
| 02h | Build BPB |
| 03h | IOCTL Read |
| 04h | Read |
| 05h | Nondestructive Read |
| 06h | Input Status |
| 07h | Input Flush |
| 08h | Write |
| 09h | Write with Verify |
| 0Ah | Output Status |
| 0Bh | Output Flush |
| 0Ch | IOCTL Write |
| 0Dh | Open Device |
| 0Eh | Close Device |
| 0Fh | Removable Media |
| 10h | Output Until Busy |
| 13h | Generic IOCTL |
| 17h | Get Logical Device |
| 18h | Set Logical Device |
| 19h | IOCTL Query |
rhStatus
Specifies the status of the request when the device-driver interrupt routine returns control to MS-DOS. This field must be zero before MS-DOS calls the interrupt routine, which must set one or more bits in the field before returning to MS-DOS. The bits in this field have the following meanings:
| Bit | Meaning |
| 0–7 | Specify an error value, but only if bit 15 is set. If an error occurs, the interrupt routine must set bit 15 and copy an error value to these bits. The error value can be one of the following: |
| Error | Meaning |
| 00h | Write-protect violation |
| 01h | Unknown unit |
| 02h | Drive not ready |
| 03h | Unknown command |
| 04h | CRC error |
| 05h | Incorrect length for drive-request structure |
| 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 | Reserved |
| 0Eh | Reserved |
| 0Fh | Invalid disk change |
| 8 | Specifies whether the operation has completed. If this bit is set, the operation is done. |
| 9 | Specifies whether the device is busy. If this bit is set, the device is busy. This bit is set only by Input Status, Output Status, and Removable Media (Device-Driver Functions 06h, 0Ah, and 0Fh). |
| 15 | Specifies whether an error occurred. If this bit is 1, bits 0 through 7 of the rhStatus field contain an error value. |
rhReserved
Reserved; do not use.
All other bits are reserved and must be zero.