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driver for managing temporary memory-based disks

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git-svn-id: svn://kolibrios.org@2644 a494cfbc-eb01-0410-851d-a64ba20cac60
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CleverMouse 2012-04-23 09:23:53 +00:00
parent 46ebef439c
commit ccb3bac301
3 changed files with 766 additions and 0 deletions
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295
kernel/trunk/drivers/tmpdisk.asm Normal file
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; Disk driver to create FAT16/FAT32 memory-based temporary disk aka RAM disk.
; (c) CleverMouse
; Note: in the ideal world, a disk driver should not care about a file system
; on it. In the current world, however, there is no way to format a disk in
; FAT, so this part of file-system-specific operations is included in the
; driver.
; When this driver is loading, it registers itself in the system and does
; nothing more. When loaded, this driver controls pseudo-disk devices
; named /tmp#/, where # is a digit from 0 to 9. The driver does not create
; any device by itself, waiting for instructions from an application.
; The driver responds to the following IOCTLs from a control application:
SRV_GETVERSION equ 0 ; input ignored,
; output = dword API_VERSION
DEV_ADD_DISK equ 1 ; input = structure add_disk_struc,
; no output
DEV_DEL_DISK equ 2 ; input = structure del_disk_struc,
; no output
; For all IOCTLs the driver returns one of the following error codes:
NO_ERROR equ 0
ERROR_INVALID_IOCTL equ 1 ; unknown IOCTL code, wrong input/output size...
ERROR_INVALID_ID equ 2 ; .DiskId must be from 0 to 9
ERROR_SIZE_TOO_LARGE equ 3 ; .DiskSize is too large
ERROR_SIZE_TOO_SMALL equ 4 ; .DiskSize is too small
ERROR_NO_MEMORY equ 5 ; memory allocation failed
API_VERSION equ 1
; Input structures:
struc add_disk_struc
{
.DiskSize dd ? ; disk size in sectors, 1 sector = 512 bytes
; Note: .DiskSize is the full size, including FAT service data.
; Size for useful data is slightly less than this number.
.DiskId db ? ; from 0 to 9
.sizeof:
}
virtual at 0
add_disk_struc add_disk_struc
end virtual
struc del_disk_struc
{
.DiskId db ? ; from 0 to 9
.sizeof:
}
virtual at 0
del_disk_struc del_disk_struc
end virtual
max_num_disks equ 10
; standard driver stuff
format MS COFF
DEBUG equ 0
include 'proc32.inc'
include 'imports.inc'
public START
public version
struc IOCTL
{
.handle dd ?
.io_code dd ?
.input dd ?
.inp_size dd ?
.output dd ?
.out_size dd ?
}
virtual at 0
IOCTL IOCTL
end virtual
section '.flat' code readable align 16
; the start procedure (see the description above)
proc START
; This procedure is called in two situations:
; when the driver is loading and when the system is shutting down.
; 1. Check that the driver is loading; do nothing unless so.
xor eax, eax ; set return value in case we will do nothing
cmp dword [esp+4], 1
jne .nothing
; 2. Register the driver in the system.
stdcall RegService, my_service, service_proc
; 3. Return the value returned by RegService back to the system.
.nothing:
retn 4
endp
; Service procedure for the driver - handle all IOCTL requests for the driver.
; The description of handled IOCTLs is located in the start of this file.
proc service_proc
; 1. Save used registers to be stdcall.
; Note: this shifts esp, so the first parameter [esp+4] becomes [esp+16].
; Note: edi is used not by this procedure itself, but by worker procedures.
push ebx esi edi
; 2. Get parameter from the stack: [esp+16] is the first parameter,
; pointer to IOCTL structure.
mov edx, [esp+16] ; edx -> IOCTL
; 3. Set the return value to 'invalid IOCTL'.
; Now, if one of conditions for IOCTL does not met, the code
; can simply return the value already loaded.
mov al, ERROR_INVALID_IOCTL
; 4. Get request code and select a handler for the code.
mov ecx, [edx+IOCTL.io_code]
test ecx, ecx ; check for SRV_GETVERSION
jnz .no.srv_getversion
; 4. This is SRV_GETVERSION request, no input, 4 bytes output, API_VERSION.
; 4a. Output size must be at least 4 bytes.
cmp [edx+IOCTL.out_size], 4
jl .return
; 4b. Write result to the output buffer.
mov eax, [edx+IOCTL.output]
mov dword [eax], API_VERSION
; 4c. Return success.
xor eax, eax
jmp .return
.no.srv_getversion:
dec ecx ; check for DEV_ADD_DISK
jnz .no.dev_add_disk
; 5. This is DEV_ADD_DISK request, input is add_disk_struc, output is 1 byte
; 5a. Input size must be exactly add_disk_struc.sizeof bytes.
cmp [edx+IOCTL.inp_size], add_disk_struc.sizeof
jnz .return
; 5b. Load input parameters and call the worker procedure.
mov eax, [edx+IOCTL.input]
movzx ebx, [eax+add_disk_struc.DiskId]
mov esi, [eax+add_disk_struc.DiskSize]
call add_disk
; 5c. Return back to the caller the value from the worker procedure.
jmp .return
.no.dev_add_disk:
dec ecx ; check for DEV_DEL_DISK
jnz .return
; 6. This is DEV_DEL_DISK request, input is del_disk_struc
; 6a. Input size must be exactly del_disk_struc.sizeof bytes.
cmp [edx+IOCTL.inp_size], del_disk_struc.sizeof
jnz .return
; 6b. Load input parameters and call the worker procedure.
mov eax, [edx+IOCTL.input]
movzx ebx, [eax+del_disk_struc.DiskId]
call del_disk
; 6c. Return back to the caller the value from the worker procedure.
.return:
; 7. Exit.
; 7a. The code above returns a value in al for efficiency,
; propagate it to eax.
movzx eax, al
; 7b. Restore used registers to be stdcall.
pop edi esi ebx
; 7c. Return, popping one argument.
retn 4
endp
; The worker procedure for DEV_ADD_DISK request.
; Creates a memory-based disk of given size and formats it in FAT16/32.
; Called with ebx = disk id, esi = disk size,
; returns error code in al.
proc add_disk
; 1. Check that disk id is correct and free.
; Otherwise, return the corresponding error code.
mov al, ERROR_INVALID_ID
cmp ebx, max_num_disks
jae .return
cmp [disk_pointers+ebx*4], 0
jnz .return
; 2. Check that the size is reasonable.
; Otherwise, return the corresponding error code.
mov al, ERROR_SIZE_TOO_LARGE
cmp esi, MAX_SIZE
ja .return
mov al, ERROR_SIZE_TOO_SMALL
cmp esi, MIN_FAT16_SIZE
jb .return
; 3. Allocate memory for the disk, store the pointer in edi.
; If failed, return the corresponding error code.
mov eax, esi
shl eax, 9
stdcall KernelAlloc, eax
mov edi, eax
test eax, eax
mov al, ERROR_NO_MEMORY
jz .return
; 4. Store the pointer and the size in the global variables.
; It is possible, though very unlikely, that two threads
; have called this function in parallel with the same id,
; so [disk_pointers+ebx*4] could be filled by another thread.
; Play extra safe and store new value only if old value is zero.
xor eax, eax
lock cmpxchg [disk_pointers+ebx*4], edi
jz @f
; Otherwise, free the allocated memory and return the corresponding error code.
stdcall KernelFree, edi
mov al, ERROR_INVALID_ID
jmp .return
@@:
mov [disk_sizes+ebx*4], esi
; 5. Call the worker procedure for formatting this disk.
; It should not fail.
call format_disk
; 6. Register the disk in the system.
; 6a. Generate name as /tmp#, where # = ebx + '0'. Use two dwords in the stack.
push 0
push 'tmp'
mov eax, esp ; eax points to 'tmp' + zero byte + zero dword
lea ecx, [ebx+'0'] ; ecx = digit
mov [eax+3], cl ; eax points to 'tmp#' + zero dword
; 6b. Call the kernel API. Use disk id as 'userdata' parameter for callbacks.
stdcall DiskAdd, disk_functions, eax, ebx, 0
; 6c. Restore the stack after 6a.
pop ecx ecx
; 6c. Check the result. If DiskAdd has failed, cleanup and return
; ERROR_NO_MEMORY, this is the most probable or even the only reason to fail.
test eax, eax
jnz @f
mov [disk_sizes+ebx*4], 0
mov [disk_pointers+ebx*4], 0
stdcall KernelFree, edi
mov al, ERROR_NO_MEMORY
jmp .return
@@:
push eax
; 6d. Notify the kernel that media is inserted.
stdcall DiskMediaChanged, eax, 1
; 6e. Disk is fully configured; store its handle in the global variable
; and return success.
pop [disk_handles+ebx*4]
xor eax, eax
; 7. Return.
.return:
retn
endp
; The worker procedure for DEV_DEL_DISK request.
; Deletes a previously created memory-based disk.
; Called with ebx = disk id,
; returns error code in al.
proc del_disk
; 1. Check that disk id is correct.
; Otherwise, return the corresponding error code.
mov al, ERROR_INVALID_ID
cmp ebx, max_num_disks
jae .return
; 2. Get the disk handle, simultaneously clearing the global variable.
xor edx, edx
xchg edx, [disk_handles+ebx*4]
; 3. Check that the handle is non-zero.
; Otherwise, return the corresponding error code.
test edx, edx
jz .return
; 4. Delete the disk from the system.
stdcall DiskDel, edx
; 5. Return success.
; Note that we can't free memory yet; it will be done in tmpdisk_close.
xor eax, eax
.return:
retn
endp
; Include implementation of tmpdisk_* callbacks.
include 'tmpdisk_work.inc'
; Include FAT-specific code.
include 'tmpdisk_fat.inc'
; initialized data
align 4
disk_functions:
dd disk_functions_end - disk_functions
dd tmpdisk_close
dd 0 ; no need in .closemedia
dd tmpdisk_querymedia
dd tmpdisk_read
dd tmpdisk_write
dd 0 ; no need in .flush
dd tmpdisk_adjust_cache_size
disk_functions_end:
; disk_handles = array of values for Disk* kernel functions
label disk_handles dword
times max_num_disks dd 0
; disk_pointers = array of pointers to disk data
label disk_pointers dword
times max_num_disks dd 0
; disk_sizes = array of disk sizes
label disk_sizes dword
times max_num_disks dd 0
version dd 0x00060006
my_service db 'tmpdisk',0
; uninitialized data
; actually, not used here
;section '.data' data readable writable align 16 ; standard driver stuff

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kernel/trunk/drivers/tmpdisk_fat.inc Normal file
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; FAT-specific code for tmpdisk.asm.
; Formats a disk to FAT16 or FAT32, depending on size.
; Note: formatting is adjusted for memory-based disks. Although the resulting
; image is a valid FAT32 volume, it has no "spare" sectors, e.g. second copy
; of FAT or place for second sector of MS FAT32 bootloader.
; Some constants
FAT16_ROOTDIR_SECTORS = 16 ; can be changed, but why not?
; FAT16:
; 1 bootsector,
; min 0xFF5 sectors for data,
; min (0xFF5*2/512) = 16 sectors per FAT, we use only one copy,
; FAT16_ROOTDIR_SECTORS for root directory
MIN_FAT16_SIZE = 1 + 16 + FAT16_ROOTDIR_SECTORS + 0xFF5
; FAT32:
; 1 bootsector,
; 1 sector for fsinfo,
; min 0xFFF5 sectors for data,
; min (0xFFF5*4/512) = 512 sectors per FAT, we use only one copy
MIN_FAT32_SIZE = 1 + 1 + 512 + 0xFFF5
MAX_SIZE = 1 shl (30 - 9) ; 1G in 512-byte sectors
; Initializes FATxx structures on the disk.
; Called with edi = pointer to disk data, esi = size of disk.
proc format_disk
; Determine FAT type and jump to the corresponding handler.
cmp esi, MIN_FAT32_SIZE
jae format_disk_fat32
; Fall through to format_disk_fat16.
endp
; Structure of FAT16 bootsector. Field names are from MS spec.
struc FAT16BOOT
{
.BS_jmpBoot rb 3
.BS_OEMName rb 8
.BPB_BytsPerSec dw ?
.BPB_SecsPerClus db ?
.BPB_RsvdSecCnt dw ?
.BPB_NumFATs db ?
.BPB_RootEntCnt dw ?
.BPB_TotSec16 dw ?
.BPB_Media db ?
.BPB_FATSz16 dw ?
.BPB_SecPerTrk dw ?
.BPB_NumHeads dw ?
.BPB_HiddSec dd ?
.BPB_TotSec32 dd ?
.BS_DrvNum db ?
.BS_Reserved1 db ?
.BS_BootSig db ?
.BS_VolID dd ?
.BS_VolLab rb 11
.BS_FilSysType rb 8
}
virtual at 0
FAT16BOOT FAT16BOOT
end virtual
; Initializes FAT16 structures on the disk.
; Called with edi = pointer to disk data, esi = size of disk.
format_disk_fat16:
; 1. Calculate number of clusters.
; 1a. There are fixed-sized areas and there are data+FAT;
; every cluster uses 512 bytes in data area and 2 bytes in FAT area.
lea eax, [esi-1-FAT16_ROOTDIR_SECTORS]
; two following lines are equivalent to edx = floor(eax*512/514)
mov ecx, 0xFF00FF01
mul ecx ; edx = number of clusters
; 1b. Force the number be less than 0xfff5.
mov eax, 0xFFF4
cmp edx, eax
jb @f
mov edx, eax
@@:
; 2. Zero all system areas on the disk.
lea ecx, [256*(1+FAT16_ROOTDIR_SECTORS)/2+edx+255]
and ecx, not 255
shr ecx, 1
xor eax, eax
push edi
rep stosd
pop edi
; 3. Generate the bootsector.
; 3a. Copy static stub.
push esi edi
mov esi, fat16bootsector_stub
mov ecx, fat16bootsector_stub_size
rep movsb
pop edi esi
mov word [edi+510], 0xAA55
; 3b. Set fields which depend on size.
cmp esi, 0x10000
jae .size_is_32bit
mov [edi+FAT16BOOT.BPB_TotSec16], si
jmp .size_written
.size_is_32bit:
mov [edi+FAT16BOOT.BPB_TotSec32], esi
.size_written:
lea eax, [edx+255]
shr eax, 8
mov [edi+FAT16BOOT.BPB_FATSz16], ax
; 3c. Generate volume ID.
call generate_volume_id
mov [edi+FAT16BOOT.BS_VolID], eax
; 4. Initialize FAT.
mov dword [edi+512], 0xFFFFFFF8
; 5. Return.
ret
; Structure of FAT32 bootsector. Field names are from MS spec.
struc FAT32BOOT
{
.BS_jmpBoot rb 3
.BS_OEMName rb 8
.BPB_BytsPerSec dw ?
.BPB_SecsPerClus db ?
.BPB_RsvdSecCnt dw ?
.BPB_NumFATs db ?
.BPB_RootEntCnt dw ?
.BPB_TotSec16 dw ?
.BPB_Media db ?
.BPB_FATSz16 dw ?
.BPB_SecPerTrk dw ?
.BPB_NumHeads dw ?
.BPB_HiddSec dd ?
.BPB_TotSec32 dd ?
.BPB_FATSz32 dd ?
.BPB_ExtFlags dw ?
.BPB_FSVer dw ?
.BPB_RootClus dd ?
.BPB_FSInfo dw ?
.BPB_BkBootSec dw ?
.BPB_Reserved rb 12
.BS_DrvNum db ?
.BS_Reserved1 db ?
.BS_BootSig db ?
.BS_VolID dd ?
.BS_VolLab rb 11
.BS_FilSysType rb 8
}
virtual at 0
FAT32BOOT FAT32BOOT
end virtual
; Initializes FAT32 structures on the disk.
; Called with edi = pointer to disk data, esi = size of disk.
format_disk_fat32:
; 1. Calculate number of clusters.
; 1a. There is fixed-sized area and there are data+FAT;
; every cluster uses 512 bytes in data area and 4 bytes in FAT area.
lea eax, [esi-1-1]
; two following lines are equivalent to edx=floor(eax*512/516) if eax<10000000h
mov ecx, 0xFE03F810
mul ecx ; edx = number of clusters
; 2. Zero all system areas on the disk and first cluster of data,
; used for root directory.
lea ecx, [128*(1+1+1)+edx+127]
and ecx, not 127
xor eax, eax
push edi
rep stosd
pop edi
; 3. Generate the bootsector.
; 3a. Copy static stub.
push esi edi
mov esi, fat32bootsector_stub
mov ecx, fat32bootsector_stub_size
rep movsb
pop edi esi
mov word [edi+510], 0xAA55
; 3b. Set fields which depend on size.
mov [edi+FAT32BOOT.BPB_TotSec32], esi
lea eax, [edx+127]
shr eax, 7
mov [edi+FAT32BOOT.BPB_FATSz32], eax
; 3c. Generate volume ID.
call generate_volume_id
mov [edi+FAT32BOOT.BS_VolID], eax
; 4. Initialize fsinfo sector.
mov dword [edi+512], 'RRaA'
mov dword [edi+512+484], 'rrAa'
dec edx ; one cluster is occupied by root dir
mov dword [edi+512+488], edx ; free count
mov byte [edi+512+492], 3 ; first free cluster
mov word [edi+512+510], 0xAA55
; 5. Initialize FAT.
mov dword [edi+512*2], 0x0FFFFFF8
mov dword [edi+512*2+4], 0x0FFFFFFF
mov dword [edi+512*2+8], 0x0FFFFFFF
; 6. Return.
ret
; Generate volume serial number, which should try to be unique for each volume.
; Use CMOS date+time, copy-pasted from fat32.inc.
generate_volume_id:
call get_time_for_file
mov cx, ax
call get_date_for_file
shl eax, 16
mov ax, cx
ret
; Three following procedures are copy-pasted from fat32.inc.
bcd2bin:
;----------------------------------
; input : AL=BCD number (eg. 0x11)
; output : AH=0
; AL=decimal number (eg. 11)
;----------------------------------
xor ah, ah
shl ax, 4
shr al, 4
aad
ret
get_date_for_file:
;-----------------------------------------------------
; Get date from CMOS and pack day,month,year in AX
; DATE bits 0..4 : day of month 0..31
; 5..8 : month of year 1..12
; 9..15 : count of years from 1980
;-----------------------------------------------------
mov al, 0x7 ;day
out 0x70, al
in al, 0x71
call bcd2bin
ror eax, 5
mov al, 0x8 ;month
out 0x70, al
in al, 0x71
call bcd2bin
ror eax, 4
mov al, 0x9 ;year
out 0x70, al
in al, 0x71
call bcd2bin
add ax, 20 ;because CMOS return only the two last
;digit (eg. 2000 -> 00 , 2001 -> 01) and we
rol eax, 9 ;need the difference with 1980 (eg. 2001-1980)
ret
get_time_for_file:
;-----------------------------------------------------
; Get time from CMOS and pack hour,minute,second in AX
; TIME bits 0..4 : second (the low bit is lost)
; 5..10 : minute 0..59
; 11..15 : hour 0..23
;-----------------------------------------------------
mov al, 0x0 ;second
out 0x70, al
in al, 0x71
call bcd2bin
ror eax, 6
mov al, 0x2 ;minute
out 0x70, al
in al, 0x71
call bcd2bin
ror eax, 6
mov al, 0x4 ;hour
out 0x70, al
in al, 0x71
call bcd2bin
rol eax, 11
ret
; some data
fat16bootsector_stub:
db 0EBh, 3Ch, 90h ; BS_jmpBoot
db 'KOLIBRI ' ; BS_OEMName
dw 512 ; BPB_BytsPerSec
db 1 ; BPB_SecsPerClus
dw 1 ; BPB_RsvdSecCnt
db 1 ; BPB_NumFATs
dw FAT16_ROOTDIR_SECTORS*16 ; BPB_RootEntCnt
dw 0 ; BPB_TotSec16, filled in format_disk_fat16
db 0F8h ; BPB_Media
dw 0 ; BPB_FATSz16, filled in format_disk_fat16
dw 32 ; BPB_SecPerTrk
dw 128 ; BPB_NumHeads
dd 0 ; BPB_HiddSec
dd 0 ; BPB_TotSec32, filled in format_disk_fat16
db 80h ; BS_DrvNum
db 0 ; BS_Reserved1
db 29h ; BS_BootSig
dd 0 ; BS_VolID, filled in format_disk_fat16
db 'NO NAME ' ; BS_VolLab
db 'FAT16 ' ; BS_FilSysType
; just in case add some meaningful bytes if someone tries to boot
db 0CDh, 19h, 0EBh, 0FEh ; int 19h, jmp $
fat16bootsector_stub_size = $ - fat16bootsector_stub
fat32bootsector_stub:
db 0EBh, 58h, 90h ; BS_jmpBoot
db 'KOLIBRI ' ; BS_OEMName
dw 512 ; BPB_BytsPerSec
db 1 ; BPB_SecsPerClus
dw 1 ; BPB_RsvdSecCnt
db 1 ; BPB_NumFATs
dw 0 ; BPB_RootEntCnt
dw 0 ; BPB_TotSec16
db 0F8h ; BPB_Media
dw 0 ; BPB_FATSz16
dw 32 ; BPB_SecPerTrk
dw 128 ; BPB_NumHeads
dd 0 ; BPB_HiddSec
dd 0 ; BPB_TotSec32, filled in format_disk_fat32
dd 0 ; BPB_FATSz32, filled in format_disk_fat32
dw 0 ; BPB_ExtFlags
dw 0 ; BPB_FSVer
dd 2 ; BPB_RootClus
dw 1 ; BPB_FSInfo
dw 0 ; BPB_BkBootSec
rb 12 ; BPB_Reserved
db 80h ; BS_DrvNum
db 0 ; BS_Reserved1
db 29h ; BS_BootSig
dd 0 ; BS_VolID, filled in format_disk_fat32
db 'NO NAME ' ; BS_VolLab
db 'FAT32 ' ; BS_FilSysType
; same bytes as in fat16bootsector_stub
db 0CDh, 19h, 0EBh, 0FEh ; int 19h, jmp $
fat32bootsector_stub_size = $ - fat32bootsector_stub

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kernel/trunk/drivers/tmpdisk_work.inc Normal file
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; Callbacks which implement tmpdisk-specific disk functions for tmpdisk.asm.
; The first argument of every callback is .userdata = userdata arg of AddDisk.
; For tmpdisk, .userdata is the disk id, one of 0,...,max_num_disks-1.
DISK_STATUS_OK = 0 ; success
DISK_STATUS_GENERAL_ERROR = -1; if no other code is suitable
DISK_STATUS_INVALID_CALL = 1 ; invalid input parameters
DISK_STATUS_NO_MEDIA = 2 ; no media present
DISK_STATUS_END_OF_MEDIA = 3 ; end of media while reading/writing data
; The last function that is called for the given disk. The kernel calls it when
; the kernel has finished all operations with the disk and it is safe to free
; all driver-specific data identified by 'userdata'.
proc tmpdisk_close
virtual at esp+4
.userdata dd ?
end virtual
; Free the memory for disk and zero global variables.
mov edx, [.userdata]
mov [disk_sizes+edx*4], 0
xor eax, eax
xchg eax, [disk_pointers+edx*4]
stdcall KernelFree, eax
retn 4
endp
struc DISKMEDIAINFO
{
.flags dd ?
DISK_MEDIA_READONLY = 1
.sectorsize dd ?
.capacity dq ?
}
virtual at 0
DISKMEDIAINFO DISKMEDIAINFO
end virtual
; Returns information about disk media.
proc tmpdisk_querymedia
virtual at esp+4
.userdata dd ?
.info dd ?
end virtual
; Media is always present, sector size is always 512 bytes,
; the size of disk in sectors is stored in a global variable.
mov edx, [.userdata]
mov ecx, [.info]
mov [ecx+DISKMEDIAINFO.flags], 0
mov [ecx+DISKMEDIAINFO.sectorsize], 512
mov eax, [disk_sizes+edx*4]
mov dword [ecx+DISKMEDIAINFO.capacity], eax
mov dword [ecx+DISKMEDIAINFO.capacity+4], 0
; Return zero as an indicator of success.
xor eax, eax
retn 8
endp
; Reads one or more sectors from the device.
tmpdisk_read:
xor edx, edx ; 0 = reading
jmp tmpdisk_readwrite
; Writes one or more sectors to the device.
tmpdisk_write:
mov dl, 1 ; 1 = writing
; Fall through to tmpdisk_readwrite.
; Common procedure for reading and writing.
; dl = 0 for reading, dl = 1 for writing.
; Arguments of tmpdisk_read and tmpdisk_write are the same,
; they continue to be stack arguments of this procedure.
proc tmpdisk_readwrite \
userdata:dword, \
buffer:dword, \
start_sector:qword, \
numsectors_ptr:dword
; 1. Save used registers to be stdcall.
push esi edi
mov esi, [userdata]
mov edi, [numsectors_ptr]
; 1. Determine number of sectors to be transferred.
; This is either the requested number of sectors or number of sectors
; up to the disk boundary, depending of what is less.
xor ecx, ecx
; 1a. Test whether [start_sector] is less than [disk_sizes] for selected disk.
; If so, calculate number of sectors between [start_sector] and [disk_sizes].
; Otherwise, the actual number of sectors is zero.
cmp dword [start_sector+4], ecx
jnz .got_number
mov eax, [disk_sizes+esi*4]
sub eax, dword [start_sector]
jbe .got_number
; 1b. Get the requested number of sectors.
mov ecx, [edi]
; 1c. If it is greater than number of sectors calculated in 1a, use the value
; from 1a.
cmp ecx, eax
jb .got_number
mov ecx, eax
.got_number:
; 2. Compare the actual number of sectors with requested. If they are
; equal, set eax (it will be the returned value) to zero. Otherwise,
; use DISK_STATUS_END_OF_MEDIA.
xor eax, eax
cmp ecx, [edi]
jz @f
mov al, DISK_STATUS_END_OF_MEDIA
@@:
; 3. Store the actual number of sectors.
mov [edi], ecx
; 4. Calculate source and destination addresses.
mov edi, dword [start_sector]
shl edi, 9
add edi, [disk_pointers+esi*4]
mov esi, [buffer]
; 5. Calculate number of dwords to be transferred.
shl ecx, 9-2
; 6. Now esi = [buffer], edi = pointer inside disk.
; This is normal for write operations;
; exchange esi and edi for read operations.
test dl, dl
jnz @f
xchg esi, edi
@@:
; 7. Copy data.
rep movsd
; 8. Restore used registers to be stdcall and return.
; The value in eax was calculated in step 2.
pop edi esi
ret
endp
; The kernel calls this function when initializing cache subsystem for
; the media. This call allows the driver to adjust the cache size.
proc tmpdisk_adjust_cache_size
virtual at esp+4
.userdata dd ?
.suggested_size dd ?
end virtual
; Since tmpdisk does not need cache, just return 0.
xor eax, eax
retn 8
endp