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;;                                                              ;;

;; Copyright (C) KolibriOS team 2011. All rights reserved.      ;;

;; Distributed under terms of the GNU General Public License    ;;

;;                                                              ;;

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

; =============================================================================

; ================================= Constants =================================

; =============================================================================

; Error codes for callback functions.

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

; Driver flags. Represent bits in DISK.DriverFlags.

DISK_NO_INSERT_NOTIFICATION = 1

; Media flags. Represent bits in DISKMEDIAINFO.Flags.

DISK_MEDIA_READONLY = 1

; If we see too many partitions, probably there is some error on the disk.

; 256 partitions should be enough for any reasonable use.

; Also, the same number is limiting the number of MBRs to process; if we see

; too many MBRs, probably there is a loop in the MBR structure.

MAX_NUM_PARTITIONS = 256

; =============================================================================

; ================================ Structures =================================

; =============================================================================

; This structure defines all callback functions for working with the physical

; device. They are implemented by a driver. Objects with this structure reside

; in a driver.

struct DISKFUNC

.strucsize      dd      ?

; Size of the structure. This field is intended for possible extensions of

; this structure. If a new function is added to this structure and a driver

; implements an old version, the caller can detect this by checking .strucsize,

; so the driver remains compatible.

.close          dd      ?

; The pointer to the function which frees all driver-specific resources for

; the disk.

; Optional, may be NULL.

; void close(void* userdata);

.closemedia     dd      ?

; The pointer to the function which informs the driver that the kernel has

; finished all processing with the current media. If media is removed, the

; driver should decline all requests to that media with DISK_STATUS_NO_MEDIA,

; even if new media is inserted, until this function is called. If media is

; removed, a new call to 'disk_media_changed' is not allowed until this

; function is called.

; Optional, may be NULL (if media is not removable).

; void closemedia(void* userdata);

.querymedia     dd      ?

; The pointer to the function which determines capabilities of the media.

; int querymedia(void* userdata, DISKMEDIAINFO* info);

; Return value: one of DISK_STATUS_*

.read           dd      ?

; The pointer to the function which reads data from the device.

; int read(void* userdata, void* buffer, __int64 startsector, int* numsectors);

; input: *numsectors = number of sectors to read

; output: *numsectors = number of sectors which were successfully read

; Return value: one of DISK_STATUS_*

.write          dd      ?

; The pointer to the function which writes data to the device.

; Optional, may be NULL.

; int write(void* userdata, void* buffer, __int64 startsector, int* numsectors);

; input: *numsectors = number of sectors to write

; output: *numsectors = number of sectors which were successfully written

; Return value: one of DISK_STATUS_*

.flush          dd      ?

; The pointer to the function which flushes the internal device cache.

; Optional, may be NULL.

; int flush(void* userdata);

; Return value: one of DISK_STATUS_*

; Note that read/write are called by the cache manager, so a driver should not

; create a software cache. This function is implemented for flushing a hardware

; cache, if it exists.

ends

; This structure holds an information about a media.

; Objects with this structure are allocated by the kernel as a part of DISK

; structure and filled by a driver in the 'querymedia' callback.

struct DISKMEDIAINFO

.Flags          dd      ?

; Combination of DISK_MEDIA_* bits.

.SectorSize     dd      ?

; Size of the sector.

.Capacity       dq      ?

; Size of the media in sectors.

ends

; This structure represents a disk device and its media for the kernel.

; This structure is allocated by the kernel in the 'disk_add' function,

; freed in the 'disk_dereference' function.

struct DISK

; Fields of disk object

.Next           dd      ?

.Prev           dd      ?

; All disk devices are linked in one list with these two fields.

; Head of the list is the 'disk_list' variable.

.Functions      dd      ?

; Pointer to the 'DISKFUNC' structure with driver functions.

.Name           dd      ?

; Pointer to the string used for accesses through the global filesystem.

.UserData       dd      ?

; This field is passed to all callback functions so a driver can decide which

; physical device is addressed.

.DriverFlags    dd      ?

; Bitfield. Currently only DISK_NO_INSERT_NOTIFICATION bit is defined.

; If it is set, the driver will never issue 'disk_media_changed' notification

; with argument set to true, so the kernel must try to detect media during

; requests from the file system.

.RefCount       dd      ?

; Count of active references to this structure. One reference is kept during

; the lifetime of the structure between 'disk_add' and 'disk_del'.

; Another reference is taken during any filesystem operation for this disk.

; One reference is added if media is inserted.

; The structure is destroyed when the reference count decrements to zero:

; this usually occurs in 'disk_del', but can be delayed to the end of last

; filesystem operation, if one is active.

.MediaLock              MUTEX

; Lock to protect the MEDIA structure. See the description after

; 'disk_list_mutex' for the locking strategy.

; Fields of media object

.MediaInserted          db      ?

; 0 if media is not inserted, nonzero otherwise.

.MediaUsed              db      ?

; 0 if media fields are not used, nonzero otherwise. If .MediaRefCount is

; nonzero, this field is nonzero too; however, when .MediaRefCount goes

; to zero, there is some time interval during which media object is still used.

                align 4

; The following fields are not valid unless either .MediaInserted is nonzero

; or they are accessed from a code which has obtained the reference when

; .MediaInserted was nonzero.

.MediaRefCount          dd      ?

; Count of active references to the media object. One reference is kept during

; the lifetime of the media between two calls to 'disk_media_changed'.

; Another reference is taken during any filesystem operation for this media.

; The callback 'closemedia' is called when the reference count decrements to

; zero: this usually occurs in 'disk_media_changed', but can be delayed to the

; end of last filesystem operation, if one is active.

.MediaInfo              DISKMEDIAINFO

; This field keeps an information about the current media.

.NumPartitions  dd      ?

; Number of partitions on this media.

.Partitions     dd      ?

; Pointer to array of .NumPartitions pointers to PARTITION structures.

ends

; This structure represents one partition for the kernel. This is a base

; template, the actual contents after common fields is determined by the

; file system code for this partition.

struct PARTITION

.FirstSector    dq      ?

; First sector of the partition.

.Length         dq      ?

; Length of the partition in sectors.

.FSUserFunctions        dd      ?

; Handlers for the sysfunction 70h. This field is a pointer to the following

; array. The first dword is a number of supported subfunctions, other dwords

; point to handlers of corresponding subfunctions.

; This field is 0 if file system is not recognized.

; ...fs-specific data may follow...

ends

; This is an external structure, it represents an entry in the partition table.

struct PARTITION_TABLE_ENTRY

.Bootable       db      ?

; 80h = bootable partition, 0 = non-bootable partition, other values = invalid

.FirstHead      db      ?

.FirstSector    db      ?

.FirstTrack     db      ?

; Coordinates of first sector in CHS.

.Type           db      ?

; Partition type, one of predefined constants. 0 = empty, several types denote

; extended partition (see process_partition_table_entry), we are not interested

; in other values.

.LastHead       db      ?

.LastSector     db      ?

.LastTrack      db      ?

; Coordinates of last sector in CHS.

.FirstAbsSector dd      ?

; Coordinate of first sector in LBA.

.Length         dd      ?

; Length of the partition in sectors.

ends

; =============================================================================

; ================================ Global data ================================

; =============================================================================

iglobal

; The pseudo-item for the list of all DISK structures.

; Initialized to the empty list.

disk_list:

        dd      disk_list

        dd      disk_list

endg

uglobal

; This mutex guards all operations with the global list of DISK structures.

disk_list_mutex MUTEX

; * There are two dependent objects, a disk and a media. In the simplest case

;   disk and media are both non-removable. However, in the general case both

;   can be removed at any time, simultaneously or only media, this makes things

;   complicated.

; * For efficiency, both disk and media objects are located in the one

;   structure named DISK. However, logically they are different.

; * The following operations use data of disk object: adding (disk_add);

;   deleting (disk_del); filesystem (fs_lfn which eventually calls

;   dyndisk_handler or dyndisk_enum_root).

; * The following operations use data of media object: adding/removing

;   (disk_media_changed); filesystem (fs_lfn which eventually calls

;   dyndisk_handler; dyndisk_enum_root doesn't work with media).

; * Notifications disk_add, disk_media_changed, disk_del are synchronized

;   between themselves, this is a requirement for the driver. However, file

;   system operations are asynchronous, can be issued at any time by any

;   thread.

; * We must prevent a situation when a filesystem operation thinks that the

;   object is still valid but in fact the notification has destroyed the

;   object. So we keep a reference counter for both disk and media and destroy

;   the object when this counter goes to zero.

; * The driver must know when it is safe to free driver-allocated resources.

;   The object can be alive even after death notification has completed.

;   We use special callbacks to satisfy both assertions: 'close' for the disk

;   and 'closemedia' for the media. The destruction of the object includes

;   calling the corresponding callback.

; * Each filesystem operation keeps one reference for the disk and one

;   reference for the media. Notification disk_del forces notification on the

;   media death, so the reference counter for the disk is always not less than

;   the reference counter for the media.

; * Two operations "get the object" and "increment the reference counter" can

;   not be done simultaneously. We use a mutex to guard the consistency here.

;   It must be a part of the container for the object, so that this mutex can

;   be acquired as a part of getting the object from the container. The

;   container for disk object is the global list, and this list is guarded by

;   'disk_list_mutex'. The container for media object is the disk object, and

;   the corresponding mutex is DISK.MediaLock.

; * Notifications do not change the data of objects, they can only remove

;   objects. Thus we don't need another synchronization at this level. If two

;   filesystem operations are referencing the same filesystem data, this is

;   better resolved at the level of the filesystem.

endg

iglobal

; The function 'disk_scan_partitions' needs two 512-byte buffers for

; MBR and bootsectors data. It can not use the static buffers always,

; since it can be called for two or more disks in parallel. However, this

; case is not typical. We reserve two static 512-byte buffers and a flag

; that these buffers are currently used. If 'disk_scan_partitions' detects that

; the buffers are currently used, it allocates buffers from the heap.

; The flag is implemented as a global dword variable. When the static buffers

; are not used, the value is -1. When the static buffers are used, the value

; is normally 0 and temporarily can become greater. The function increments

; this value. If the resulting value is zero, it uses the buffers and

; decrements the value when the job is done. Otherwise, it immediately

; decrements the value and uses buffers from the heap, allocated in the

; beginning and freed in the end.

partition_buffer_users  dd      -1

endg

uglobal

; The static buffers for MBR and bootsectors data.

align 16

mbr_buffer      rb      512

bootsect_buffer rb      512

endg

iglobal

; This is the array of default implementations of driver callbacks.

; Same as DRIVERFUNC structure except for the first field; all functions must

; have the default implementations.

align 4

disk_default_callbacks:

        dd      disk_default_close

        dd      disk_default_closemedia

        dd      disk_default_querymedia

        dd      disk_default_read

        dd      disk_default_write

        dd      disk_default_flush

endg

; =============================================================================

; ================================= Functions =================================

; =============================================================================

; This function registers a disk device.

; This includes:

; - allocating an internal structure describing this device;

; - registering this structure in the global filesystem.

; The function initializes the disk as if there is no media. If a media is

; present, the function 'disk_media_changed' should be called after this

; function succeeds.

; Parameters:

; [esp+4] = pointer to DISKFUNC structure with the callbacks

; [esp+8] = pointer to name (ASCIIZ string)

; [esp+12] = userdata to be passed to the callbacks as is.

; [esp+16] = flags, bitfield. Currently only DISK_NO_INSERT_NOTIFICATION bit

;            is defined.

; Return value:

; NULL = operation has failed

; non-NULL = handle of the disk. This handle can be used

; in the operations with other Disk* functions.

; The handle is the pointer to the internal structure DISK.

disk_add:

        push    ebx esi         ; save used registers to be stdcall

; 1. Allocate the DISK structure.

; 1a. Call the heap manager.

        push    sizeof.DISK

        pop     eax

        call    malloc

; 1b. Check the result. If allocation failed, return (go to 9) with eax = 0.

        test    eax, eax

        jz      .nothing

; 2. Copy disk name to the DISK structure.

; 2a. Get length of the name, including the terminating zero.

        mov     esi, [esp+8+8]  ; esi = pointer to name

        push    eax             ; save allocated pointer to DISK

        xor     eax, eax        ; the argument of malloc() is in eax

@@:

        inc     eax

        cmp     byte [esi+eax-1], 0

        jnz     @b

; 2b. Call the heap manager.

        call    malloc

; 2c. Check the result. If allocation failed, go to 7.

        pop     ebx             ; restore allocated pointer to DISK

        test    eax, eax

        jz      .free

; 2d. Store the allocated pointer to the DISK structure.

        mov     [ebx+DISK.Name], eax

; 2e. Copy the name.

@@:

        mov     dl, [esi]

        mov     [eax], dl

        inc     esi

        inc     eax

        test    dl, dl

        jnz     @b

; 3. Copy other arguments of the function to the DISK structure.

        mov     eax, [esp+4+8]

        mov     [ebx+DISK.Functions], eax

        mov     eax, [esp+12+8]

        mov     [ebx+DISK.UserData], eax

        mov     eax, [esp+16+8]

        mov     [ebx+DISK.DriverFlags], eax

; 4. Initialize other fields of the DISK structure.

; Media is not inserted, initialized state of mutex is zero,

; reference counter is 1.

        lea     ecx, [ebx+DISK.MediaLock]

        call    mutex_init

        xor     eax, eax

        mov     dword [ebx+DISK.MediaInserted], eax

        inc     eax

        mov     [ebx+DISK.RefCount], eax

; The DISK structure is initialized.

; 5. Insert the new structure to the global list.

; 5a. Acquire the mutex.

        mov     ecx, disk_list_mutex

        call    mutex_lock

; 5b. Insert item to the tail of double-linked list.

        mov     edx, disk_list

        list_add_tail ebx, edx     ;ebx= new edx= list head

; 5c. Release the mutex.

        call mutex_unlock

; 6. Return with eax = pointer to DISK.

        xchg    eax, ebx

        jmp     .nothing

.free:

; Memory allocation for DISK structure succeeded, but for disk name failed.

; 7. Free the DISK structure.

        xchg    eax, ebx

        call    free

; 8. Return with eax = 0.

        xor     eax, eax

.nothing:

; 9. Return.

        pop     esi ebx         ; restore used registers to be stdcall

        ret     16              ; purge 4 dword arguments to be stdcall

; This function deletes a disk device from the global filesystem.

; This includes:

; - removing a media including all partitions;

; - deleting this structure from the global filesystem;

; - dereferencing the DISK structure and possibly destroying it.

; Parameters:

; [esp+4] = handle of the disk, i.e. the pointer to the DISK structure.

; Return value: none.

disk_del:

        push    esi         ; save used registers to be stdcall

; 1. Force media to be removed. If the media is already removed, the

; call does nothing.

        mov     esi, [esp+4+8]  ; esi = handle of the disk

        stdcall disk_media_changed, esi, 0

; 2. Delete the structure from the global list.

; 2a. Acquire the mutex.

        mov     ecx, disk_list_mutex

        call    mutex_lock

; 2b. Delete item from double-linked list.

        mov     eax, [esi+DISK.Next]

        mov     edx, [esi+DISK.Prev]

        mov     [eax+DISK.Prev], edx

        mov     [edx+DISK.Next], eax

; 2c. Release the mutex.

        call    mutex_unlock

; 3. The structure still has one reference created in disk_add. Remove this

; reference. If there are no other references, disk_dereference will free the

; structure.

        call    disk_dereference

; 4. Return.

        pop     esi             ; restore used registers to be stdcall

        ret     4               ; purge 1 dword argument to be stdcall

; This is an internal function which removes a previously obtained reference

; to the disk. If this is the last reference, this function lets the driver

; finalize all associated data, and afterwards frees the DISK structure.

; esi = pointer to DISK structure

disk_dereference:

; 1. Decrement reference counter. Use atomic operation to correctly handle

; possible simultaneous calls.

lock    dec     [esi+DISK.RefCount]

; 2. If the result is nonzero, there are other references, so nothing to do.

; In this case, return (go to 4).

        jnz     .nothing

; 3. If we are here, we just removed the last reference and must destroy the

; disk object.

; 3a. Call the driver.

        mov     al, DISKFUNC.close

        stdcall disk_call_driver

; 3b. Free the structure.

        xchg    eax, esi

        call    free

; 4. Return.

.nothing:

        ret

; This is an internal function which removes a previously obtained reference

; to the media. If this is the last reference, this function calls 'closemedia'

; callback to signal the driver that the processing has finished and it is safe

; to inform about a new media.

; esi = pointer to DISK structure

disk_media_dereference:

; 1. Decrement reference counter. Use atomic operation to correctly handle

; possible simultaneous calls.

lock    dec     [esi+DISK.MediaRefCount]

; 2. If the result is nonzero, there are other references, so nothing to do.

; In this case, return (go to 4).

        jnz     .nothing

; 3. If we are here, we just removed the last reference and must destroy the

; media object.

; Note that the same place inside the DISK structure is reused for all media

; objects, so we must guarantee that reusing does not happen while freeing.

; Reusing is only possible when someone processes a new media. There are two

; mutually exclusive variants:

; * driver issues media insert notifications (DISK_NO_INSERT_NOTIFICATION bit

;   in DISK.DriverFlags is not set). In this case, we require from the driver

;   that such notification (except for the first one) can occur only after a

;   call to 'closemedia' callback.

; * driver does not issue media insert notifications. In this case, the kernel

;   itself must sometimes check whether media is inserted. We have the flag

;   DISK.MediaUsed, visible to the kernel. This flag signals to the other parts

;   of kernel that the way is free.

; In the first case other parts of the kernel do not use DISK.MediaUsed, so it

; does not matter when this flag is cleared. In the second case this flag must

; be cleared after all other actions, including call to 'closemedia'.

; 3a. Free all partitions.

        push    esi edi

        mov     edi, [esi+DISK.NumPartitions]

        mov     esi, [esi+DISK.Partitions]

        test    edi, edi

        jz      .nofree

.freeloop:

        lodsd

        call    free

        dec     edi

        jnz     .freeloop

.nofree:

        pop     edi esi

; 3b. Call the driver.

        mov     al, DISKFUNC.closemedia

        stdcall disk_call_driver

; 3c. Clear the flag.

        mov     [esi+DISK.MediaUsed], 0

.nothing:

        ret

; This function is called by the driver and informs the kernel that the media

; has changed. If the media is non-removable, it is called exactly once

; immediately after 'disk_add' and once from 'disk_del'.

; Parameters:

; [esp+4] = handle of the disk, i.e. the pointer to the DISK structure.

; [esp+8] = new status of the media: zero = no media, nonzero = media inserted.

disk_media_changed:

        push    ebx esi edi             ; save used registers to be stdcall

; 1. Remove the existing media, if it is present.

        mov     esi, [esp+4+12]         ; esi = pointer to DISK

; 1a. Check whether it is present. Since DISK.MediaInserted is changed only

; in this function and calls to this function are synchronized, no lock is

; required for checking.

        cmp     [esi+DISK.MediaInserted], 0

        jz      .noremove

; We really need to remove the media.

; 1b. Acquire mutex.

        lea     ecx, [esi+DISK.MediaLock]

        call    mutex_lock

; 1c. Clear the flag.

        mov     [esi+DISK.MediaInserted], 0

; 1d. Release mutex.

        call    mutex_unlock

; 1e. Remove the "lifetime" reference and possibly destroy the structure.

        call    disk_media_dereference

.noremove:

; 2. Test whether there is new media.

        cmp     dword [esp+8+12], 0

        jz      .noinsert

; Yep, there is.

; 3. Process the new media. We assume that all media fields are available to

; use, see comments in 'disk_media_dereference' (this covers using by previous

; media referencers) and note that calls to this function are synchronized

; (this covers using by new media referencers).

; 3a. Call the 'querymedia' callback.

; .Flags are set to zero for possible future extensions.

        lea     edx, [esi+DISK.MediaInfo]

        and     [edx+DISKMEDIAINFO.Flags], 0

        mov     al, DISKFUNC.querymedia

        stdcall disk_call_driver, edx

; 3b. Check the result of the callback. Abort if it failed.

        test    eax, eax

        jnz     .noinsert

; 3c. Acquire the lifetime reference for the media object.

        inc     [esi+DISK.MediaRefCount]

; 3d. Scan for partitions. Ignore result; the list of partitions is valid even

; on errors.

        call    disk_scan_partitions

; 3e. Media is inserted and available for use.

        inc     [esi+DISK.MediaInserted]

.noinsert:

; 4. Return.

        pop     edi esi ebx             ; restore used registers to be stdcall

        ret     8                       ; purge 2 dword arguments to be stdcall

; This function is a thunk for all functions of a disk driver.

; It checks whether the referenced function is implemented in the driver.

; If so, this function jumps to the function in the driver.

; Otherwise, it jumps to the default implementation.

; al = offset of function in the DISKFUNC structure;

; esi = pointer to the DISK structure;

; stack is the same as for the corresponding function except that the

; first parameter (void* userdata) is prepended automatically.

disk_call_driver:

        movzx   eax, al ; eax = offset of function in the DISKFUNC structure

; 1. Prepend the first argument to the stack.

        pop     ecx     ; ecx = return address

        push    [esi+DISK.UserData]     ; add argument

        push    ecx     ; save return address

; 2. Check that the required function is inside the table. If not, go to 5.

        mov     ecx, [esi+DISK.Functions]

        cmp     eax, [ecx+DISKFUNC.strucsize]

        jae     .default

; 3. Check that the required function is implemented. If not, go to 5.

        mov     ecx, [ecx+eax]

        test    ecx, ecx

        jz      .default

; 4. Jump to the required function.

        jmp     ecx

.default:

; 5. Driver does not implement the required function; use default implementation.

        jmp     dword [disk_default_callbacks+eax-4]

; The default implementation of DISKFUNC.querymedia.

disk_default_querymedia:

        push    DISK_STATUS_INVALID_CALL

        pop     eax

        ret     8

; The default implementation of DISKFUNC.read and DISKFUNC.write.

disk_default_read:

disk_default_write:

        push    DISK_STATUS_INVALID_CALL

        pop     eax

        ret     20

; The default implementation of DISKFUNC.close, DISKFUNC.closemedia and

; DISKFUNC.flush.

disk_default_close:

disk_default_closemedia:

disk_default_flush:

        xor     eax, eax

        ret     4

; This is an internal function called from 'disk_media_changed' when new media

; is detected. It creates the list of partitions for the media.

; If media is not partitioned, then the list consists of one partition which

; covers all the media.

; esi = pointer to the DISK structure.

disk_scan_partitions:

; 1. Initialize .NumPartitions and .Partitions fields as zeros: empty list.

        and     [esi+DISK.NumPartitions], 0

        and     [esi+DISK.Partitions], 0

; 2. Currently we can work only with 512-bytes sectors. Check this restriction.

; The only exception is 2048-bytes CD/DVD, but they are not supported yet by

; this code.

        cmp     [esi+DISK.MediaInfo.SectorSize], 512

        jz      .doscan

        DEBUGF 1,'K : sector size is %d, only 512 is supported\n',[esi+DISK.MediaInfo.SectorSize]

        ret

.doscan:

; 3. Acquire the buffer for MBR and bootsector tests. See the comment before

; the 'partition_buffer_users' variable.

        mov     ebx, mbr_buffer         ; assume the global buffer is free

lock    inc     [partition_buffer_users]

        jz      .buffer_acquired        ; yes, it is free

lock    dec     [partition_buffer_users]        ; no, we must allocate

        stdcall kernel_alloc, 1024

        test    eax, eax

        jz      .nothing

        xchg    eax, ebx

.buffer_acquired:

; MBR/EBRs are organized in the chain. We use a loop over MBR/EBRs, but no

; more than MAX_NUM_PARTITION times.

; 4. Prepare things for the loop.

; ebp will hold the sector number for current MBR/EBR.

; [esp] will hold the sector number for current extended partition, if there

; is one.

; [esp+4] will hold the counter that prevents long loops.

        push    ebp             ; save ebp

        push    MAX_NUM_PARTITIONS      ; the counter of max MBRs to process

        xor     ebp, ebp        ; start from sector zero

        push    ebp             ; no extended partition yet

.new_mbr:

; 5. Read the current sector.

; Note that 'read' callback operates with 64-bit sector numbers, so we must

; push additional zero as a high dword of sector number.

        mov     al, DISKFUNC.read

        push    1

        stdcall disk_call_driver, ebx, ebp, 0, esp

        pop     ecx

; 6. If the read has failed, abort the loop.

        dec     ecx

        jnz     .mbr_failed

; 7. Check the MBR/EBR signature. If it is wrong, abort the loop.

; Soon we will access the partition table which starts at ebx+0x1BE,

; so we can fill its address right now. If we do it now, then the addressing

; [ecx+0x40] is shorter than [ebx+0x1fe]: one-byte offset vs 4-bytes offset.

        lea     ecx, [ebx+0x1be]        ; ecx -> partition table

        cmp     word [ecx+0x40], 0xaa55

        jnz     .mbr_failed

; 8. The MBR is treated differently from EBRs. For MBR we additionally need to

; execute step 9 and possibly step 10.

        test    ebp, ebp

        jnz     .mbr

; Partition table can be present or not present. In the first case, we just

; read the MBR. In the second case, we just read the bootsector for some

; filesystem.

; We use the following algorithm to distinguish between these cases.

; A. If at least one entry of the partition table is invalid, this is

;    a bootsector. See the description of 'is_partition_table_entry' for

;    definition of validity.

; B. If all entries are empty (filesystem type field is zero) and the first

;    byte is jmp opcode (0EBh or 0E9h), this is a bootsector which happens to

;    have zeros in the place of partition table.

; C. Otherwise, this is a MBR.

; 9. Test for MBR vs bootsector.

; 9a. Check entries. If any is invalid, go to 10 (rule A).

        call    is_partition_table_entry

        jc      .notmbr

        add     ecx, 10h

        call    is_partition_table_entry

        jc      .notmbr

        add     ecx, 10h

        call    is_partition_table_entry

        jc      .notmbr

        add     ecx, 10h

        call    is_partition_table_entry

        jc      .notmbr

; 9b. Check types of the entries. If at least one is nonzero, go to 11 (rule C).

        mov     al, [ecx-30h+PARTITION_TABLE_ENTRY.Type]

        or      al, [ecx-20h+PARTITION_TABLE_ENTRY.Type]

        or      al, [ecx-10h+PARTITION_TABLE_ENTRY.Type]

        or      al, [ecx+PARTITION_TABLE_ENTRY.Type]

        jnz     .mbr

; 9c. Empty partition table or bootsector with many zeroes? (rule B)

        cmp     byte [ebx], 0EBh

        jz      .notmbr

        cmp     byte [ebx], 0E9h

        jnz     .mbr

.notmbr:

; 10. This is not MBR. The media is not partitioned. Create one partition

; which covers all the media and abort the loop.

        stdcall disk_add_partition, 0, 0, \

                dword [esi+DISK.MediaInfo.Capacity], dword [esi+DISK.MediaInfo.Capacity+4]

        jmp     .done

.mbr:

; 11. Process all entries of the new MBR/EBR

        lea     ecx, [ebx+0x1be]        ; ecx -> partition table

        push    0       ; assume no extended partition

        call    process_partition_table_entry

        add     ecx, 10h

        call    process_partition_table_entry

        add     ecx, 10h

        call    process_partition_table_entry

        add     ecx, 10h

        call    process_partition_table_entry

        pop     ebp

; 12. Test whether we found a new EBR and should continue the loop.

; 12a. If there was no next EBR, return.

        test    ebp, ebp

        jz      .done

; Ok, we have EBR.

; 12b. EBRs addresses are relative to the start of extended partition.

; For simplicity, just abort if an 32-bit overflow occurs; large disks

; are most likely partitioned with GPT, not MBR scheme, since the precise

; calculation here would increase limit just twice at the price of big

; compatibility problems.

        pop     eax     ; load extended partition

        add     ebp, eax

; 12c. If extended partition has not yet started, start it.

        test    eax, eax

        jnz     @f

        mov     eax, ebp

@@:

; 12c. If the limit is not exceeded, continue the loop.

        dec     dword [esp]

        push    eax     ; store extended partition

        jnz     .new_mbr

.mbr_failed:

.done:

; 13. Cleanup after the loop.

        pop     eax     ; not important anymore

        pop     eax     ; not important anymore

        pop     ebp     ; restore ebp

; 14. Release the buffer.

; 14a. Test whether it is the global buffer or we have allocated it.

        cmp     ebx, mbr_buffer

        jz      .release_partition_buffer

; 14b. If we have allocated it, free it.

        xchg    eax, ebx

        call    free

        jmp     .nothing

; 14c. Otherwise, release reference.

.release_partition_buffer:

lock    dec     [partition_buffer_users]

.nothing:

; 15. Return.

        ret

; This is an internal function called from disk_scan_partitions. It checks

; whether the entry pointed to by ecx is a valid entry of partition table.

; The entry is valid if the first byte is 0 or 80h, the first sector plus the

; length is less than twice the size of media. Multiplication by two is

; required since the size mentioned in the partition table can be slightly

; greater than the real size.

is_partition_table_entry:

; 1. Check .Bootable field.

        mov     al, [ecx+PARTITION_TABLE_ENTRY.Bootable]

        and     al, 7Fh

        jnz     .invalid

; 3. Calculate first sector + length. Note that .FirstAbsSector is relative

; to the MBR/EBR, so the real sum is ebp + .FirstAbsSector + .Length.

        mov     eax, ebp

        xor     edx, edx

        add     eax, [ecx+PARTITION_TABLE_ENTRY.FirstAbsSector]

        adc     edx, 0

        add     eax, [ecx+PARTITION_TABLE_ENTRY.Length]

        adc     edx, 0

; 4. Divide by two.

        shr     edx, 1

        rcr     eax, 1

; 5. Compare with capacity. If the subtraction (edx:eax) - .Capacity does not

; overflow, this is bad.

        sub     eax, dword [esi+DISK.MediaInfo.Capacity]

        sbb     edx, dword [esi+DISK.MediaInfo.Capacity+4]

        jnc     .invalid

.valid:

; 5. Return success: CF is cleared.

        clc

        ret

.invalid:

; 6. Return fail: CF is set.

        stc

        ret

; This is an internal function called from disk_scan_partitions. It processes

; the entry pointed to by ecx.

; * If the entry is invalid, just ignore this entry.

; * If the type is zero, just ignore this entry.

; * If the type is one of types for extended partition, store the address

;   of this partition as the new MBR in [esp+4].

; * Otherwise, add the partition to the list of partitions for this disk.

;   We don't use the type from the entry to identify the file system;

;   fs-specific checks do this more reliably.

process_partition_table_entry:

; 1. Check for valid entry. If invalid, return (go to 5).

        call    is_partition_table_entry

        jc      .nothing

; 2. Check for empty entry. If invalid, return (go to 5).

        mov     al, [ecx+PARTITION_TABLE_ENTRY.Type]

        test    al, al

        jz      .nothing

; 3. Check for extended partition. If extended, go to 6.

irp type,\

    0x05,\                 ; DOS: extended partition

    0x0f,\                 ; WIN95: extended partition, LBA-mapped

    0xc5,\                 ; DRDOS/secured: extended partition

    0xd5                   ; Old Multiuser DOS secured: extended partition

{

        cmp     al, type

        jz      .extended

}

; 4. If we are here, that is a normal partition. Add it to the list.

; Note that the first sector is relative to MBR/EBR.

        mov     eax, ebp

        xor     edx, edx

        add     eax, [ecx+PARTITION_TABLE_ENTRY.FirstAbsSector]

        adc     edx, 0

        push    ecx

        stdcall disk_add_partition, eax, edx, \

                [ecx+PARTITION_TABLE_ENTRY.Length], 0

        pop     ecx

.nothing:

; 5. Return.

        ret

.extended:

; 6. If we are here, that is an extended partition. Store the address.

        mov     eax, [ecx+PARTITION_TABLE_ENTRY.FirstAbsSector]

        mov     [esp+4], eax

        ret

; This is an internal function called from disk_scan_partitions and

; process_partition_table_entry. It adds one partition to the list of

; partitions for the media.

proc disk_add_partition stdcall uses ebx edi, start:qword, length:qword

; 1. Check that this partition will not exceed the limit on total number.

        cmp     [esi+DISK.NumPartitions], MAX_NUM_PARTITIONS

        jae     .nothing

; 2. Check that this partition does not overlap with any already registered

; partition. Since any file system assumes that the disk data will not change

; outside of its control, such overlap could be destructive.

; Since the number of partitions is usually very small and is guaranteed not

; to be large, the simple linear search is sufficient.

; 2a. Prepare the loop: edi will point to the current item of .Partitions

; array, ecx will be the current item, ebx will hold number of items left.

        mov     edi, [esi+DISK.Partitions]

        mov     ebx, [esi+DISK.NumPartitions]

        test    ebx, ebx

        jz      .partitionok

.scan_existing:

; 2b. Get the next partition.

        mov     ecx, [edi]

        add     edi, 4

; The range [.FirstSector, .FirstSector+.Length) must be either entirely to

; the left of [start, start+length) or entirely to the right.

; 2c. Subtract .FirstSector - start. The possible overflow distinguish between

; cases "to the left" (2?) and "to the right" (2d).

        mov     eax, dword [ecx+PARTITION.FirstSector]

        mov     edx, dword [ecx+PARTITION.FirstSector+4]

        sub     eax, dword [start]

        sbb     edx, dword [start+4]

        jb      .less

; 2d. .FirstSector is greater than or equal to start. Check that .FirstSector

; is greater than or equal to start+length; the subtraction

; (.FirstSector-start) - length must not cause overflow. Go to 2g if life is

; good or to 2f in the other case.

        sub     eax, dword [length]

        sbb     edx, dword [length+4]

        jb      .overlap

        jmp     .next_existing

.less:

; 2e. .FirstSector is less than start. Check that .FirstSector+.Length is less

; than or equal to start. If the addition (.FirstSector-start) + .Length does

; not cause overflow, then .FirstSector + .Length is strictly less than start;

; since the equality is also valid, use decrement preliminarily. Go to 2g or

; 2f depending on the overflow.

        sub     eax, 1

        sbb     edx, 0

        add     eax, dword [ecx+PARTITION.Length]

        adc     edx, dword [ecx+PARTITION.Length+4]

        jnc     .next_existing

.overlap:

; 2f. The partition overlaps with previously registered partition. Say warning

; and return with nothing done.

        dbgstr 'two partitions overlap, ignoring the last one'

        jmp     .nothing

.next_existing:

; 2g. The partition does not overlap with the current partition. Continue the

; loop.

        dec     ebx

        jnz     .scan_existing

.partitionok:

; 3. The partition has passed tests. Reallocate the partitions array for a new

; entry.

; 3a. Call the allocator.

        mov     eax, [esi+DISK.NumPartitions]

        inc     eax     ; one more entry

        shl     eax, 2  ; each entry is dword

        call    malloc

; 3b. Test the result. If failed, return with nothing done.

        test    eax, eax

        jz      .nothing

; 3c. Copy the old array to the new array.

        mov     edi, eax

        push    esi

        mov     ecx, [esi+DISK.NumPartitions]

        mov     esi, [esi+DISK.Partitions]

        rep     movsd

        pop     esi

; 3d. Set the field in the DISK structure to the new array.

        xchg    [esi+DISK.Partitions], eax

; 3e. Free the old array.

        call    free

; 4. Recognize the file system.

; 4a. Call the filesystem recognizer. It will allocate the PARTITION structure

; with possible filesystem-specific fields.

        call    disk_detect_partition

; 4b. Check return value. If zero, return with list not changed; so far only

; the array was reallocated, this is ok for other code.

        test    eax, eax

        jz      .nothing

; 5. Insert the new partition to the list.

        stosd

        inc     [esi+DISK.NumPartitions]

; 6. Return.

.nothing:

        ret

endp

; This is an internal function called from disk_add_partition.

; It tries to recognize the file system on the partition and allocates the

; corresponding PARTITION structure with filesystem-specific fields.

disk_detect_partition:

; This function inherits the stack frame from disk_add_partition. In stdcall

; with ebp-based frame arguments start from ebp+8, since [ebp]=saved ebp

; and [ebp+4]=return address.

virtual at ebp+8

.start  dq      ?

.length dq      ?

end virtual

; Currently no file systems are supported, so just allocate the PARTITION

; structure without extra fields.

; 1. Allocate and check result.

        push    sizeof.PARTITION

        pop     eax

        call    malloc

        test    eax, eax

        jz      .nothing

; 2. Fill the common fields: copy .start and .length.

        mov     edx, dword [.start]

        mov     dword [eax+PARTITION.FirstSector], edx

        mov     edx, dword [.start+4]

        mov     dword [eax+PARTITION.FirstSector+4], edx

        mov     edx, dword [.length]

        mov     dword [eax+PARTITION.Length], edx

        mov     edx, dword [.length+4]

        mov     dword [eax+PARTITION.Length+4], edx

.nothing:

; 3. Return with eax = pointer to PARTITION or NULL.

        ret

; This function is called from file_system_lfn.

; This handler gets the control each time when fn 70 is called

; with unknown item of root subdirectory.

; in: esi -> name

;     ebp = 0 or rest of name relative to esi

; out: if the handler processes path, it must not return in file_system_lfn,

;      but instead pop return address and return directly to the caller

;      otherwise simply return

dyndisk_handler:

        push    ebx edi         ; save registers used in file_system_lfn

; 1. Acquire the mutex.

        mov     ecx, disk_list_mutex

        call    mutex_lock

; 2. Loop over the list of DISK structures.

; 2a. Initialize.

        mov     ebx, disk_list

.scan:

; 2b. Get the next item.

        mov     ebx, [ebx+DISK.Next]

; 2c. Check whether the list is done. If so, go to 3.

        cmp     ebx, disk_list

        jz      .notfound

; 2d. Compare names. If names match, go to 5.

        mov     edi, [ebx+DISK.Name]

        push    esi

@@:

; esi points to the name from fs operation; it is terminated by zero or slash.

        lodsb

        test    al, al

        jz      .eoin_dec

        cmp     al, '/'

        jz      .eoin

; edi points to the disk name.

        inc     edi

; edi points to lowercase name, this is a requirement for the driver.

; Characters at esi can have any register. Lowercase the current character.

; This lowercasing works for latin letters and digits; since the disk name

; should not contain other symbols, this is ok.

        or      al, 20h

        cmp     al, [edi-1]

        jz      @b

.wrongname:

; 2f. Names don't match. Continue the loop.

        pop     esi

        jmp     .scan

.notfound:

; The loop is done and no name matches.

; 3. Release the mutex.

        call mutex_unlock

; 4. Return normally.

        pop     edi ebx         ; restore registers used in file_system_lfn

        ret

; part of 2d: the name matches partially, but we must check that this is full

; equality.

.eoin_dec:

        dec     esi

.eoin:

        cmp     byte [edi], 0

        jnz     .wrongname

; We found the addressed DISK structure.

; 5. Reference the disk.

lock    inc     [ebx+DISK.RefCount]

; 6. Now we are sure that the DISK structure is not going to die at least

; while we are working with it, so release the global mutex.

        call    mutex_unlock

; 7. Acquire the mutex for media object.

        pop     edi             ; restore edi

        lea     ecx, [ebx+DISK.MediaLock]

        call    mutex_lock

; 8. Get the media object. If it is not NULL, reference it.

        xor     edx, edx

        cmp     [ebx+DISK.MediaInserted], dl

        jz      @f

        mov     edx, ebx

        inc     [ebx+DISK.MediaRefCount]

@@:

; 9. Now we are sure that the media object, if it exists, is not going to die

; at least while we are working with it, so release the mutex for media object.

        call    mutex_unlock

        mov     ecx, ebx

        pop     ebx eax         ; restore ebx, pop return address

; 10. Check whether the fs operation wants to enumerate partitions (go to 11)

; or work with some concrete partition (go to 12).

        cmp     byte [esi], 0

        jnz     .haspartition

; 11. The fs operation wants to enumerate partitions.

; 11a. Only "list directory" operation is applicable to / path. Check

; the operation code. If wrong, go to 13.

        cmp     dword [ebx], 1

        jnz     .access_denied

; 11b. If the media is inserted, use 'fs_dyndisk_next' as an enumeration

; procedure. Otherwise, use 'fs_dyndisk_next_nomedia'.

        mov     esi, fs_dyndisk_next_nomedia

        test    edx, edx

        jz      @f

        mov     esi, fs_dyndisk_next

@@:

; 11c. Let the procedure from fs_lfn.inc do the job.

        jmp     file_system_lfn.maindir_noesi

.haspartition:

; 12. The fs operation has specified some partition.

; 12a. Store parameters for callback functions.

        push    edx

        push    ecx

; 12b. Store callback functions.

        push    dyndisk_cleanup

        push    fs_dyndisk

        mov     edi, esp

; 12c. Let the procedure from fs_lfn.inc do the job.

        jmp     file_system_lfn.found2

.access_denied:

; 13. Fail the operation with the appropriate code.

        mov     dword [esp+32], ERROR_ACCESS_DENIED

.cleanup:

; 14. Cleanup.

        mov     esi, ecx        ; disk*dereference assume that esi points to DISK

.cleanup_esi:

        test    edx, edx        ; if there are no media, we didn't reference it

        jz      @f

        call    disk_media_dereference

@@:

        call    disk_dereference

; 15. Return.

        ret

; This is a callback for cleaning up things called from file_system_lfn.found2.

dyndisk_cleanup:

        mov     esi, [edi+8]

        mov     edx, [edi+12]

        jmp     dyndisk_handler.cleanup_esi

; This is a callback for enumerating partitions called from

; file_system_lfn.maindir in the case of inserted media.

; It just increments eax until DISK.NumPartitions reached and then

; cleans up.

fs_dyndisk_next:

        cmp     eax, [ecx+DISK.NumPartitions]

        jae     .nomore

        inc     eax

        clc

        ret

.nomore:

        pusha

        mov     esi, ecx

        call    disk_media_dereference

        call    disk_dereference

        popa

        stc

        ret

; This is a callback for enumerating partitions called from

; file_system_lfn.maindir in the case of missing media.

; In this case we create one pseudo-partition.

fs_dyndisk_next_nomedia:

        cmp     eax, 1

        jae     .nomore

        inc     eax

        clc

        ret

.nomore:

        pusha

        mov     esi, ecx

        call    disk_dereference

        popa

        stc