s6.s: add comments
This commit is contained in:
Phil Budne
+63
-61
@@ -99,6 +99,8 @@ namei: 0
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jmp 1b " yes: keep going
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jmp namei i " Didn't find it, return zero in AC (without skip)
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t = t+2
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" NOTE: iget/iput share "temp" vars!!!
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" Given an i-number in AC, fetch that i-node
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" from disk and store it in the inode buffer
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iget: 0
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@@ -113,49 +115,50 @@ iget: 0
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cll; mul; 12 " Multiply the i-num within the block by 12
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lacq " to get the offset into the block
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tad dskbufp " Add on the base of the disk buffer
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dac 9f+t
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dac 9f+t " save pointer into dskbuf in "t0"
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dac .+2
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jms copy; ..; inode; 12 " Copy 12 words from buffer to inode
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jmp iget i " and return
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iput: 0
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lac 9f+t+1
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jms dskrd
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law inode-1
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dac 8
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lac 9f+t+1 " get block number saved by iget
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jms dskrd " read the block
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law inode-1 " pointer to "in core" inode
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dac 8 " in index 8
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-1
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tad 9f+t
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dac 9
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-12
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dac 9f+t+2
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tad 9f+t " get saved pointer into buffer
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dac 9 " in index 9
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-12 " 12 word loop count
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dac 9f+t+2 " in t2
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1:
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lac 8 i
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lac 8 i " fetch source word
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"** 01-s1.pdf page 36
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sad 9 i
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skp
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jmp 2f
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isz 9f+t+2
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jmp 1b
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jmp iput i
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2:
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-1
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sad 9 i " differs from disk?
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skp " no:
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jmp 2f " yes:
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isz 9f+t+2 " no difference: done?
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jmp 1b " no: keep going
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jmp iput i " yes: return w/o writing to disk
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2: " here with in-core inode changed
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-1 " back up both pointers
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tad 8
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dac 8
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-1
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tad 9
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dac 9
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1:
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lac 8 i
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dac 9 i
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isz 9f+t+2
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jmp 1b
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lac 9f+t+1
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jms dskwr
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jmp iput i
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lac 8 i " fetch word
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dac 9 i " copy to dskbuf
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isz 9f+t+2 " done?
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jmp 1b " no: keep going
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lac 9f+t+1 " get block number
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jms dskwr " write back to disk
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jmp iput i " return
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t = t+3
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" NOTE! dget/dput share "temp" vars
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" allocate directory entry
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" AC/ entry number
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dget: 0
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@@ -164,30 +167,31 @@ dget: 0
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dac 9f+t " save in t0
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jms pget " get free disk block
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dac 9f+t+1 " save in t1
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jms dskrd
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lac 9f+t
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and o77
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tad dskbufp
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dac 9f+t+2
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dac .+2
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jms copy; ..; dnode; 8
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lac 9f+t
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tad d8
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jms betwen; d0; i.size
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skp
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jmp dget i
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jms dacisize
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dzm d.i
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jmp dget i
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jms dskrd " read block
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lac 9f+t " get word number
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and o77 " get word within block
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tad dskbufp " make pointer into dskbuf
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dac 9f+t+2 " save in t2
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dac .+2 " save as copy source
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jms copy; ..; dnode; 8 " copy entry into dnode
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lac 9f+t " get word number
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tad d8 " of end of new node
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jms betwen; d0; i.size " already allocated?
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skp " no
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jmp dget i " yes: return
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jms dacisize " store new file size
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dzm d.i " mark new entry as free
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jmp dget i " return
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" write directory entry (back) to disk
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dput: 0
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lac 9f+t+1
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jms dskrd
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lac 9f+t+2
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dac .+3
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jms copy; dnode; ..; 8
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lac 9f+t+1
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jms dskwr
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lac 9f+t+1 " get disk block number back
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jms dskrd " read into dskbuf
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lac 9f+t+2 " get pointer into dskbuf
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dac .+3 " save as copy dest
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jms copy; dnode; ..; 8 " copy into dskbuf
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lac 9f+t+1 " get disk block number
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jms dskwr " write back to disk
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jmp dput i
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t = t+3
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@@ -262,6 +266,10 @@ pget: 0
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jmp pget i " return it
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t = t+3
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" write to file referenced by loaded inode
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" AC/ file offset
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" jms iwrite; addr; count
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iwrite: 0
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dac 9f+t " save arg in t0
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lac iwrite " load return address
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@@ -273,14 +281,14 @@ iwrite: 0
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dac iwrite " save as iwrite instruction
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jmp 1f
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" iread from file referenced by loaded inode
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" read from file referenced by loaded inode
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" AC/ file offset
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" jms iread; addr; count
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iread: 0
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dac 9f+t " save offset in t0
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lac cnop " get nop
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dac iwrite " save as iwrite instruction
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1:
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1: " common code for iread/iwrite
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-1
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tad iread i " get word before return addr
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dac 10 " store in index 10 & 11
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@@ -289,20 +297,14 @@ iread: 0
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lac iread i " load addr
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dac 9f+t+1 " save in t1
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isz iread " increment return addr
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lac o70000
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lac o70000 " get max file size
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xct iwrite " skip if write
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lac i.size " read: get file size
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cma
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tad 9f+t " add offset
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cma
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jms betwen; d0; 9f+t+1
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lac 9f+t+1
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dac 9f+t+2
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cma
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tad d1
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sna
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jmp iread i
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dac 9f+t+1
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tad 9f+t " subtract offset
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sna " offset == size?
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jmp iread i " yes, return
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dac 9f+t+1 " save size-offset in t1
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1:
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lac 9f+t
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jms pget
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@@ -312,7 +314,7 @@ iread: 0
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and o77
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tad dskbufp
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tad dm1
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xct iwrite
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xct iwrite " skip if write
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jmp .+3
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dac 10
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cskp:
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