mirror of
https://github.com/DoctorWkt/unix-jun72.git
synced 2026-05-05 07:33:34 +00:00
f7108bb0eb
according to what seemed right by reading the code. Documented all of the changes in notes.txt. Mostly accepting the hand written corrections in the pdf file.
57 lines
1.8 KiB
Plaintext
57 lines
1.8 KiB
Plaintext
mov r1,i.dskp(r2) / put block number of new block in i-node
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jsr r0,setimod / set i-node modified byte
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jsr r0,clear / clear new block
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2:
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jsr r0,dskrd / read in indirect block
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mov (sp)+,r2 / get offset
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mov r1,-(sp) / save block number of indirect block on stack
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add r5,r2 / r5 points to first word in indirect block, r2
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/ points to location of inter
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mov (r2),r1 / put physical block no of block in file
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/ sought in r1
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bne 2f / if no block exists
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jsr r0,alloc / allocate a new block
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mov r1,(r2) / put new block number into proper location in
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/ indirect block
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mov (sp)+,r1 / get block number of indirect block
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mov (r2),-(sp) / save block number of new block
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jsr r0,wslot
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jsr r0,dskwr / write newly modified indirect block back out
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/ on disk
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mov (sp),r1 / restore block number of new block
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jsr r0,clear / clear new block
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2:
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tst (sp)+ / bump stack pointer
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rts r0
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alloc:
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mov r2,-(sp) / save r2, r3 on stack
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mov r3,-(sp)
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mov $systm,r2 / start of inode and free storage map for drum
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tst cdev
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beq 1f / drum ls device
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mov $mount,r2 / disk or tape is device, start of inode and free
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/ storage map
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1:
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mov (r2)+,r1 / first word contains number of bytes in free
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/ storage map
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asl r1 / multiply r1 by eight gives, number of blocks in device
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asl r1
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asl r1
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mov r1,-(sp) / save # of blocks in device on stack
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clr r1 / r1 contains bit count of free storage map
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1:
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mov (r2)+,r3 / word of free storage map in r3
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bne 1f / branch if any free blocks in this word
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add $16.,r1
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cmp r1 ,(sp) / have we examined all free storage bytes
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blo 1b
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jmp panic / found no free storage
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1:
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asr r3 / find a free block
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bcs 1f / branch when free block found; bit for block k is in
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/ byte k/8 / in bit k (mod 8)
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inc r1 / increment bit count in bit k (mod8)
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br 1b
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1:
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