FS_HEADR/IOF_RHDR

This trap reads a file header.

Call Parameters		Return Parameters
D0.B	$47	D0.L	Error code.
D1.L		D1.W	Length of header read.
D2.L	Buffer length	D2.L	Preserved.
D3.W	Timeout	D3.L	Preserved.
A0.L	Channel ID	A0.L	Preserved.
A1.L	Pointer to buffer	A1.L	Updated.

ERR_NC	Not complete.
ERR_NO	Channel not found.
ERR_BO	Buffer full.

All registers not shown above are not used on entry and are preserved on exit.
The length of header is 64 bytes for a directory driver and 15 bytes for other device drivers.
After the buffer has been read A1.L points to one after the last character read.
The form of header is shown below.
The file type (byte 5) is 0 for data files, 1 for executable files, 2 for relocatable files and 255 for subdirectories.

File Header

Address	Length	Contents
$00	long	File length
$04	byte	File access set to 0 in QDOS v1.03
$05	byte	File type
$06	long	Size of data space for executable files
$0A	long	Unused

Additionally for Directory Drivers

Address	Length	Contents
$0E	word	Length of filename
$10	36 bytes	Filename
$34	long	Update date
$38	word	Version number
$3A	word	Reserved
$3C	long	Backup date

The example below shows how to read the header of an executable file and put its length into D2.L.

Read_h  lea     -64(a7),a7      ; Space on the stack for the header.
        movea.l a7,a1           ; Point to the space.
        moveq   #64,d2          ; Length of buffer.
        moveq   #-1,d3          ; Timeout.
        moveq   #$47,d0         ; FS_HEADR
        trap    #3              ; Read the header.
        tst.l   d0              ; OK? . .
        bne     error           ; . . no!
        movea.l a7,a1           ; Reset A1
        subq.b  #1,5(a1)        ; Check for executable file
        bne     error           ; OOPS!
        move.l  (a1),d2         ; Set file length in D2
        lea     64(a7),a7       ; Tidy stack

 ; We could now load the file into memory.

FS_HEADR/IOF_RHDR

Errors

Notes

File Header

Additionally for Directory Drivers

Example

QDOS Internals