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; -*- fundamental -*- ---------------------------------------------------
;
; Copyright 2004-2008 H. Peter Anvin - All Rights Reserved
;
; This program is free software; you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation, Inc., 53 Temple Place Ste 330,
; Boston MA 02111-1307, USA; either version 2 of the License, or
; (at your option) any later version; incorporated herein by reference.
;
; -----------------------------------------------------------------------
section .text
struc cptr
.sector: resd 1 ; Sector number
.prev: resw 1 ; LRU pointer to previous (less recent)
.next: resw 1 ; LRU pointer to next (more recent)
endstruc
cptr_size_lg2 equ 3
NCacheEntries equ 65536/SECTOR_SIZE
;
; initcache: Initialize the cache data structures
;
initcache:
xor eax,eax ; We don't care about sector 0
mov di,CachePtrs
mov cx,NCacheEntries+1
mov bx,CachePtrs+NCacheEntries*cptr_size ; "prev" pointer
.loop:
mov [di+cptr.sector],eax ; Zero sector number
mov [di+cptr.prev],bx ; Previous pointer
mov [bx+cptr.next],di ; Previous entry's next pointer
mov bx,di
add di,cptr_size
loop .loop
ret
;
; getcachesector: Check for a particular sector (EAX) in the sector cache,
; and if it is already there, return a pointer in GS:SI
; otherwise load it and return said pointer.
;
; Assumes CS == DS.
;
getcachesector:
push cx
push bx
push di
mov si,cache_seg
mov gs,si
mov si,CachePtrs+cptr_size ; Real sector cache pointers
mov cx,NCacheEntries
.search:
cmp eax,[si]
jz .hit
add si,cptr_size
loop .search
.miss:
TRACER 'M'
; Need to load it.
push es
push gs
pop es
mov bx,[CachePtrs+cptr.next] ; "Next most recent than head node"
mov [bx+cptr.sector],eax
mov si,bx
sub bx,CachePtrs+cptr_size
shl bx,SECTOR_SHIFT-cptr_size_lg2 ; Buffer address
pushad
%if IS_EXTLINUX
call getonesec_ext
%else
call getonesec
%endif
popad
pop es
.hit:
; Update LRU, then compute buffer address
TRACER 'H'
; Remove from current position in the list
mov bx,[si+cptr.prev]
mov di,[si+cptr.next]
mov [bx+cptr.next],di
mov [di+cptr.prev],bx
; Add to just before head node
mov bx,[CachePtrs+cptr.prev]
mov [si+cptr.prev],bx
mov [bx+cptr.next],si
mov [CachePtrs+cptr.prev],si
mov word [si+cptr.next],CachePtrs
sub si,CachePtrs+cptr_size
shl si,SECTOR_SHIFT-cptr_size_lg2 ; Buffer address
pop di
pop bx
pop cx
ret
section .bss
; Each CachePtr contains:
; - Block pointer
; - LRU previous pointer
; - LRU next pointer
; The first entry is the head node of the list
alignb 4
CachePtrs resb (NCacheEntries+1)*cptr_size