From 0e5eaa95a6e0f7ebfe13b5faffe792ed8124e01e Mon Sep 17 00:00:00 2001
From: Phil Budne <phil@ultimate.com>
Date: Wed, 2 Mar 2016 19:11:42 -0500
Subject: [PATCH] kernel comments

---
 src/sys/s4.s | 14 +++++++----
 src/sys/s6.s | 68 ++++++++++++++++++++++++++--------------------------
 src/sys/s8.s | 43 ++++++++++++++++++---------------
 3 files changed, 68 insertions(+), 57 deletions(-)

diff --git a/src/sys/s4.s b/src/sys/s4.s
index 1d8b983..51c2db3 100644
--- a/src/sys/s4.s
+++ b/src/sys/s4.s
@@ -1,6 +1,7 @@
 "** 01-s1.pdf page 21
 " s4
 
+	" allocate a free disk block
 alloc: 0
    -1
    tad s.nfblks
@@ -29,6 +30,7 @@ alloc: 0
    dac s.nfblks
    jmp alloc+1
 
+	" free a disk block
 free: 0
    lmq
    lac s.nfblks
@@ -54,12 +56,16 @@ free: 0
    jmp free i
 t = t+1
 
+	" load AC indirect (without using indirect!)
+	" AC/ address
+	"   jms laci
+	" AC/ contents of address
 laci: 0
-   and o17777
-   tad o200000
+   and o17777				" clear everything but addr
+   tad o200000				" make into "lac addr"
    dac .+1
-   lac ..
-   jmp laci i
+   lac ..				" fetch
+   jmp laci i				" return
 
 "** 01-s1.pdf page 22
 
diff --git a/src/sys/s6.s b/src/sys/s6.s
index 7af2c27..faaa13f 100644
--- a/src/sys/s6.s
+++ b/src/sys/s6.s
@@ -2,41 +2,41 @@
 " s6
 
 itrunc: 0
-   -7
-   dac 9f+t
-   lac idskpp
-   dac 9f+t+1
-1:
-   lac 9f+t+1 i
-   sna
-   jmp 4f
+   -7					" loop 7 times
+   dac 9f+t				" in t0
+   lac idskpp				" pointer to inode block numbers
+   dac 9f+t+1				" save in t1
+1:			" top of loop for inode blocks
+   lac 9f+t+1 i				" fetch next block number
+   sna					" allocated?
+   jmp 4f				"  no
+   lac i.flags				" check flags
+   and o200000				
+   sna					" large file?
+   jmp 3f				"  no
+   -64					" loop 64 times
+   dac 9f+t+2				" save count in t2
+   lac dskbufp				" get pointer to dskbuf
+   dac 9f+t+3				" in t3
+2:			" inner loop for indirect blocks
+   lac 9f+t+1 i				" get indirect block number
+   jms dskrd				" read it
+   lac 9f+t+3 i				" read block number from indirect
+   sza					" free?
+   jms free				"  no: free it
+   isz 9f+t+3				" increment pointer into indirect block
+   isz 9f+t+2				" increment loop counter, skip if done
+   jmp 2b				"  not done: loop
+3:			" here with small file
+   lac 9f+t+1 i				" load block number
+   jms free				" free it
+   dzm 9f+t+1 i				" clear block number
+4:			" bottom of loop for inode block ptrs
+   isz 9f+t+1				" increment block pointer
+   isz 9f+t				" increment count, skip if done
+   jmp 1b				"  not done
    lac i.flags
-   and o200000
-   sna
-   jmp 3f
-   -64
-   dac 9f+t+2
-   lac dskbufp
-   dac 9f+t+3
-2:
-   lac 9f+t+1 i
-   jms dskrd
-   lac 9f+t+3 i
-   sza
-   jms free
-   isz 9f+t+3
-   isz 9f+t+2
-   jmp 2b
-3:
-   lac 9f+t+1 i
-   jms free
-   dzm 9f+t+1 i
-4:
-   isz 9f+t+1
-   isz 9f+t
-   jmp 1b
-   lac i.flags
-   and o577777
+   and o577777				" clear large file flag
    dac i.flags
    jmp itrunc i
 t = t+4
diff --git a/src/sys/s8.s b/src/sys/s8.s
index 7a60623..20d13f9 100644
--- a/src/sys/s8.s
+++ b/src/sys/s8.s
@@ -160,10 +160,10 @@ crdata:
    crchar: .=.+1
 sysdata:
    s.nxfblk: .=.+1
-   s.nfblks: .=.+1
-   s.fblks: .=.+10
-   s.uniq: .=.+1
-   s.tim: .=.+2
+   s.nfblks: .=.+1			" number of free blocks
+   s.fblks: .=.+10			" free block numbers
+   s.uniq: .=.+1			" next unique value
+   s.tim: .=.+2				" (up)time(?) in 60Hz ticks (low, high)
 ulist:
    0131000;1;0;0
    0031040;0;0;0
@@ -176,12 +176,12 @@ ulist:
    0031400;0;0;0
    0031440;0;0;0
 userdata:
-   u.ac: 0
-   u.mq: 0
-   u.rq: .=.+9
-   u.uid: -1
-   u.pid: 1
-   u.cdir: 3
+   u.ac: 0			" user AC
+   u.mq: 0			" user MQ
+   u.rq: .=.+9			" user 010-017
+   u.uid: -1			" user id
+   u.pid: 1			" process id
+   u.cdir: 3			" connected directory (inode number?)
    u.ulistp: ulist
    u.swapret: 0
    u.base: 0
@@ -194,18 +194,23 @@ userdata:
       .=userdata+64
 ii: .=.+1
 inode:
-   i.flags: .=.+1
-   i.dskps: .=.+7
-   i.uid: .=.+1
-   i.nlks: .=.+1
+   i.flags: .=.+1		" inode flags
+				" 400000 free?? (checked/toggled by icreat)
+				" 200000 large file
+				" 000040 special? (checked by read/write)
+				" 000020  directory
+				" 000017 can be changed by chmod.
+   i.dskps: .=.+7		" disk block pointers (indirect if "large file")
+   i.uid: .=.+1			" owner
+   i.nlks: .=.+1		" link count
    i.size: .=.+1
-   i.uniq: .=.+1
+   i.uniq: .=.+1		" unique number
       .= inode+12
 di: .=.+1
-dnode:
-   d.i: .=.+1
-   d.name: .=.+4
-   d.uniq: .=.+1
+dnode:				" directory entry:
+   d.i: .=.+1			" inode number
+   d.name: .=.+4		" name (space padded)
+   d.uniq: .=.+1		" unique number from directory inode
       . = dnode+8
 fnode:
    f.flags: .=.+1