mirror of
https://github.com/DoctorWkt/unix-jun72.git
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55 lines
1.8 KiB
Plaintext
55 lines
1.8 KiB
Plaintext
/ u5 - unix
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mget:
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mov *u.fofp,mq / file offset ln mq
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clr ac / later to be high sig
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mov $-8,lsh / divide ac/mq by 256.
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mov mq,r2
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blt $10000,i.flgs / lg/sm is this a large or small file
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bne 4f / branch for large file
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blt $!17,r2
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bne 3f / branch if/r2 greater than or equal to 16
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blc $!16,r2 / clear all bits but bits 1,2,3
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mov 1.dskp(r2),r1 / r1 has physical block number
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bne 2f / lf physical block num is zero then need a new block
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/ for file
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jsr rO,alloc / allocate a new block
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mov r1,i.dskp(r2) / physical block number stored in i-node
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jsr r0,setimod / set inode modified byte (imod)
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jsr r0,clear / zero out disk/drum block just allocated
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2:
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rts rO
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3: / adding on block which changes small file to a large file
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jsr rD,alloc / allocate a new block for this file; block number
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/in r1
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jsr r0,wslot / set up I/0 buffer for write, r5 points to first
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/ data word in buffer
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mov $8.,r3 / next 6 instructions transfer old physical block
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/ pointers
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mov $i.dskp,r2 / into new indirect block for the new large file
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1:
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mov (r2),(r5)+
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clr (r2)+
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dec r3
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bgt 1b
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mov $256.-8.,r3 / clear rest of data buffer
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1:
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clr (r5)+
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dec r3
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bgt 1b
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jsr rO,dskwr / write new indirect block on disk
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mov r1,i.dskp / put pointer to indirect block ln i—node
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bis $10000,i.f1gs / set large file blt in i.flgs word of i-node
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jsr rO,setlmod / set i-node modified flag
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br mget
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4: / large file
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mov 9-8,lsh / divide byte number by 256.
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blc $!776,r2 / zero all bits but 1,2,3,4,5,6,7,8; gives offset
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/ in indirect block
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mov r2,-(sp) / save on stack
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mov mq,r2 / calculate offset in i-node for pointer to proper
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/ indirect block
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bic $!16,r2
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mov i.dskp(r2),r1
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bne 2f / if no indirect block exists
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jsr r0,alloc / allocate a new block
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