fatfs.c: fix earlier fix, update dir_size in map_cluster loop

Earlier fix was #242 (this got the
cluster value to use wrong).

Original problem recorded in #241

Reset disk scriptlet:

nasm -I ~/proj/lmacros/ ~/proj/bootimg/bootimg.asm \
  -D_PAYLOADFILE=::empty -o diskempt.img
cp -a ~/proj/kernel/bin/kernel.sys fdkernel.sys

Run dosemu2 with -I "floppy { device diskempt.img }"

After a test, run /sbin/dosfsck -n diskempt.img

The following Script for lDebug files are test cases:

=== testshrt.sld
e 200 "A:\test.dat" 0
f 300 l 100 26
a
 mov ah, 3C
 mov cx, 0
 mov dx, 200
 int 21
 xchg bx, ax
 mov ax, 4200
 mov cx, 1000
 mov dx, cx
 int 21
 mov dx, 300
 mov cx, 10
 mov ah, 3F
 int 21
 .
r v0 := aao
a
 mov ah, 40
 int 21
 int3
 int3
 jmp (v0)
 .

=== testfull.sld
e 200 "A:\test.dat" 0
f 400 l 400 38
a
 mov ah, 3C
 mov cx, 0
 mov dx, 200
 int 21
 xchg bx, ax
 mov ax, 4200
 mov cx, ((#1424 * #1024 - 1) >> 10)
 mov dx, ((#1424 * #1024 - 1) & FFFF)
 int 21
 mov ah, 40
 mov dx, 400
 mov cx, 1
 int 21
 mov ah, 68
 int 21
 mov ax, 4202
 mov cx, -1
 mov dx, -10
 int 21
 mov ah, 40
 mov dx, 400
 mov cx, 10
 int 21
 int3
 mov ah, 68
 int 21
 nop
 int3
 nop
 jmp 100
 .

=== testful2.sld
e 200 "A:\test.dat" 0
f 400 l 400 38
a
 mov ah, 3C
 mov cx, 0
 mov dx, 200
 int 21
 xchg bx, ax
 mov ax, 4200
 mov cx, ((#1424 * #1024 - #512 - 1) >> 10)
 mov dx, ((#1424 * #1024 - #512 - 1) & FFFF)
 int 21
 mov ah, 40
 mov dx, 400
 mov cx, 1
 int 21
 mov ah, 68
 int 21
 mov ax, 4202
 mov cx, -1
 mov dx, -10
 int 21
 mov ah, 40
 mov dx, 400
 mov cx, 10
 int 21
 int3
 mov ah, 68
 int 21
 nop
 int3
 nop
 jmp 100
 .

=== testful3.sld
e 200 "A:\test.dat" 0
f 400 l 400 38
a
 mov ah, 3C
 mov cx, 0
 mov dx, 200
 int 21
 xchg bx, ax
 mov ax, 4200
 mov cx, ((#1424 * #1024 - #512) >> 10)
 mov dx, ((#1424 * #1024 - #512) & FFFF)
 int 21
 mov ah, 40
 mov dx, 400
 mov cx, 0
 int 21
 mov ah, 68
 int 21
 mov ax, 4202
 mov cx, -1
 mov dx, -10
 int 21
 mov ah, 40
 mov dx, 400
 mov cx, 10
 int 21
 int3
 mov ah, 68
 int 21
 nop
 int3
 nop
 jmp 100
 .

===

Author: ecm-pushbx

kernel/fatfs.c

@@ -1029,7 +1029,7 @@ COUNT map_cluster(REG f_node_ptr fnp, COUNT mode)
     fnp->f_cluster = cluster;
     fnp->f_cluster_offset++;
     fnp->f_dir.dir_size =
-      ((ULONG)fnp->f_cluster
+      (((ULONG)fnp->f_cluster_offset + 1)
       * (ULONG)fnp->f_dpb->dpb_secsize)
       <<
       fnp->f_dpb->dpb_shftcnt;