296 lines
10 KiB
NASM
296 lines
10 KiB
NASM
; Disk driver to create FAT16/FAT32 memory-based temporary disk aka RAM disk.
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; (c) CleverMouse
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; Note: in the ideal world, a disk driver should not care about a file system
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; on it. In the current world, however, there is no way to format a disk in
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; FAT, so this part of file-system-specific operations is included in the
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; driver.
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; When this driver is loading, it registers itself in the system and does
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; nothing more. When loaded, this driver controls pseudo-disk devices
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; named /tmp#/, where # is a digit from 0 to 9. The driver does not create
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; any device by itself, waiting for instructions from an application.
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; The driver responds to the following IOCTLs from a control application:
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SRV_GETVERSION equ 0 ; input ignored,
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; output = dword API_VERSION
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DEV_ADD_DISK equ 1 ; input = structure add_disk_struc,
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; no output
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DEV_DEL_DISK equ 2 ; input = structure del_disk_struc,
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; no output
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; For all IOCTLs the driver returns one of the following error codes:
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NO_ERROR equ 0
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ERROR_INVALID_IOCTL equ 1 ; unknown IOCTL code, wrong input/output size...
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ERROR_INVALID_ID equ 2 ; .DiskId must be from 0 to 9
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ERROR_SIZE_TOO_LARGE equ 3 ; .DiskSize is too large
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ERROR_SIZE_TOO_SMALL equ 4 ; .DiskSize is too small
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ERROR_NO_MEMORY equ 5 ; memory allocation failed
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API_VERSION equ 1
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; Input structures:
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struc add_disk_struc
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{
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.DiskSize dd ? ; disk size in sectors, 1 sector = 512 bytes
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; Note: .DiskSize is the full size, including FAT service data.
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; Size for useful data is slightly less than this number.
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.DiskId db ? ; from 0 to 9
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.sizeof:
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}
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virtual at 0
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add_disk_struc add_disk_struc
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end virtual
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struc del_disk_struc
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{
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.DiskId db ? ; from 0 to 9
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.sizeof:
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}
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virtual at 0
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del_disk_struc del_disk_struc
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end virtual
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max_num_disks equ 10
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; standard driver stuff
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format MS COFF
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DEBUG equ 0
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include 'proc32.inc'
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include 'imports.inc'
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public START
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public version
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struc IOCTL
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{
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.handle dd ?
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.io_code dd ?
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.input dd ?
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.inp_size dd ?
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.output dd ?
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.out_size dd ?
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}
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virtual at 0
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IOCTL IOCTL
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end virtual
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section '.flat' code readable align 16
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; the start procedure (see the description above)
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proc START
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; This procedure is called in two situations:
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; when the driver is loading and when the system is shutting down.
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; 1. Check that the driver is loading; do nothing unless so.
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xor eax, eax ; set return value in case we will do nothing
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cmp dword [esp+4], 1
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jne .nothing
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; 2. Register the driver in the system.
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stdcall RegService, my_service, service_proc
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; 3. Return the value returned by RegService back to the system.
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.nothing:
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retn 4
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endp
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; Service procedure for the driver - handle all IOCTL requests for the driver.
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; The description of handled IOCTLs is located in the start of this file.
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proc service_proc
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; 1. Save used registers to be stdcall.
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; Note: this shifts esp, so the first parameter [esp+4] becomes [esp+16].
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; Note: edi is used not by this procedure itself, but by worker procedures.
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push ebx esi edi
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; 2. Get parameter from the stack: [esp+16] is the first parameter,
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; pointer to IOCTL structure.
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mov edx, [esp+16] ; edx -> IOCTL
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; 3. Set the return value to 'invalid IOCTL'.
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; Now, if one of conditions for IOCTL does not met, the code
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; can simply return the value already loaded.
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mov al, ERROR_INVALID_IOCTL
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; 4. Get request code and select a handler for the code.
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mov ecx, [edx+IOCTL.io_code]
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test ecx, ecx ; check for SRV_GETVERSION
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jnz .no.srv_getversion
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; 4. This is SRV_GETVERSION request, no input, 4 bytes output, API_VERSION.
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; 4a. Output size must be at least 4 bytes.
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cmp [edx+IOCTL.out_size], 4
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jl .return
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; 4b. Write result to the output buffer.
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mov eax, [edx+IOCTL.output]
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mov dword [eax], API_VERSION
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; 4c. Return success.
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xor eax, eax
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jmp .return
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.no.srv_getversion:
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dec ecx ; check for DEV_ADD_DISK
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jnz .no.dev_add_disk
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; 5. This is DEV_ADD_DISK request, input is add_disk_struc, output is 1 byte
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; 5a. Input size must be exactly add_disk_struc.sizeof bytes.
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cmp [edx+IOCTL.inp_size], add_disk_struc.sizeof
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jnz .return
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; 5b. Load input parameters and call the worker procedure.
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mov eax, [edx+IOCTL.input]
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movzx ebx, [eax+add_disk_struc.DiskId]
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mov esi, [eax+add_disk_struc.DiskSize]
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call add_disk
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; 5c. Return back to the caller the value from the worker procedure.
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jmp .return
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.no.dev_add_disk:
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dec ecx ; check for DEV_DEL_DISK
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jnz .return
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; 6. This is DEV_DEL_DISK request, input is del_disk_struc
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; 6a. Input size must be exactly del_disk_struc.sizeof bytes.
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cmp [edx+IOCTL.inp_size], del_disk_struc.sizeof
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jnz .return
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; 6b. Load input parameters and call the worker procedure.
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mov eax, [edx+IOCTL.input]
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movzx ebx, [eax+del_disk_struc.DiskId]
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call del_disk
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; 6c. Return back to the caller the value from the worker procedure.
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.return:
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; 7. Exit.
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; 7a. The code above returns a value in al for efficiency,
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; propagate it to eax.
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movzx eax, al
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; 7b. Restore used registers to be stdcall.
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pop edi esi ebx
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; 7c. Return, popping one argument.
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retn 4
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endp
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; The worker procedure for DEV_ADD_DISK request.
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; Creates a memory-based disk of given size and formats it in FAT16/32.
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; Called with ebx = disk id, esi = disk size,
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; returns error code in al.
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proc add_disk
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; 1. Check that disk id is correct and free.
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; Otherwise, return the corresponding error code.
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mov al, ERROR_INVALID_ID
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cmp ebx, max_num_disks
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jae .return
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cmp [disk_pointers+ebx*4], 0
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jnz .return
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; 2. Check that the size is reasonable.
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; Otherwise, return the corresponding error code.
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mov al, ERROR_SIZE_TOO_LARGE
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cmp esi, MAX_SIZE
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ja .return
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mov al, ERROR_SIZE_TOO_SMALL
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cmp esi, MIN_FAT16_SIZE
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jb .return
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; 3. Allocate memory for the disk, store the pointer in edi.
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; If failed, return the corresponding error code.
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mov eax, esi
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shl eax, 9
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stdcall KernelAlloc, eax
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mov edi, eax
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test eax, eax
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mov al, ERROR_NO_MEMORY
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jz .return
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; 4. Store the pointer and the size in the global variables.
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; It is possible, though very unlikely, that two threads
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; have called this function in parallel with the same id,
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; so [disk_pointers+ebx*4] could be filled by another thread.
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; Play extra safe and store new value only if old value is zero.
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xor eax, eax
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lock cmpxchg [disk_pointers+ebx*4], edi
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jz @f
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; Otherwise, free the allocated memory and return the corresponding error code.
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stdcall KernelFree, edi
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mov al, ERROR_INVALID_ID
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jmp .return
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@@:
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mov [disk_sizes+ebx*4], esi
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; 5. Call the worker procedure for formatting this disk.
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; It should not fail.
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call format_disk
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; 6. Register the disk in the system.
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; 6a. Generate name as /tmp#, where # = ebx + '0'. Use two dwords in the stack.
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push 0
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push 'tmp'
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mov eax, esp ; eax points to 'tmp' + zero byte + zero dword
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lea ecx, [ebx+'0'] ; ecx = digit
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mov [eax+3], cl ; eax points to 'tmp#' + zero dword
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; 6b. Call the kernel API. Use disk id as 'userdata' parameter for callbacks.
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stdcall DiskAdd, disk_functions, eax, ebx, 0
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; 6c. Restore the stack after 6a.
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pop ecx ecx
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; 6c. Check the result. If DiskAdd has failed, cleanup and return
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; ERROR_NO_MEMORY, this is the most probable or even the only reason to fail.
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test eax, eax
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jnz @f
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mov [disk_sizes+ebx*4], 0
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mov [disk_pointers+ebx*4], 0
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stdcall KernelFree, edi
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mov al, ERROR_NO_MEMORY
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jmp .return
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@@:
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push eax
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; 6d. Notify the kernel that media is inserted.
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stdcall DiskMediaChanged, eax, 1
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; 6e. Disk is fully configured; store its handle in the global variable
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; and return success.
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pop [disk_handles+ebx*4]
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xor eax, eax
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; 7. Return.
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.return:
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retn
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endp
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; The worker procedure for DEV_DEL_DISK request.
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; Deletes a previously created memory-based disk.
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; Called with ebx = disk id,
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; returns error code in al.
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proc del_disk
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; 1. Check that disk id is correct.
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; Otherwise, return the corresponding error code.
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mov al, ERROR_INVALID_ID
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cmp ebx, max_num_disks
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jae .return
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; 2. Get the disk handle, simultaneously clearing the global variable.
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xor edx, edx
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xchg edx, [disk_handles+ebx*4]
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; 3. Check that the handle is non-zero.
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; Otherwise, return the corresponding error code.
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test edx, edx
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jz .return
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; 4. Delete the disk from the system.
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stdcall DiskDel, edx
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; 5. Return success.
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; Note that we can't free memory yet; it will be done in tmpdisk_close.
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xor eax, eax
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.return:
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retn
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endp
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; Include implementation of tmpdisk_* callbacks.
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include 'tmpdisk_work.inc'
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; Include FAT-specific code.
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include 'tmpdisk_fat.inc'
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; initialized data
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align 4
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disk_functions:
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dd disk_functions_end - disk_functions
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dd tmpdisk_close
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dd 0 ; no need in .closemedia
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dd tmpdisk_querymedia
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dd tmpdisk_read
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dd tmpdisk_write
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dd 0 ; no need in .flush
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dd tmpdisk_adjust_cache_size
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disk_functions_end:
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; disk_handles = array of values for Disk* kernel functions
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label disk_handles dword
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times max_num_disks dd 0
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; disk_pointers = array of pointers to disk data
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label disk_pointers dword
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times max_num_disks dd 0
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; disk_sizes = array of disk sizes
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label disk_sizes dword
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times max_num_disks dd 0
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version dd 0x00060006
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my_service db 'tmpdisk',0
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; uninitialized data
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; actually, not used here
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;section '.data' data readable writable align 16 ; standard driver stuff
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