PDP7-Unix/sys/s2.s
"** 01-s1.pdf page 7
" s2
" file status (stat) system call
" AC/ pointer to status (inode) buffer + i-num (13 words)
" sys status; dir_name_ptr; file_name_ptr
" NO_DD version: sys status; file_name_ptr
.status:
jms arg " fetch directory name pointer
dac .+5
jms arg " fetch file name pointer
dac .+6
lac u.cdir " get current working directory
jms namei; .. " look up source directory
jms error " not found: return error to user
jms namei; .. " look up file
jms error " not found: return error
jms iget " read file inode
lac u.ac " get user buffer pointer
and o17777 " truncate to 13 bits
jms betwen; o10000; o17762 " is user memory (but not last 14 wds)?
jms error " no: error
dac .+3 " save as copy destination
jms copy; inode; ..; 12 " copy inode to user buffer
lac d.i " copy i-num from last dnode read ??
dac 9 i " save thru index 9 (pre-increment) ??
jmp okexit
" capture display?
.capt:
lac u.ac " get user AC
dac u.dspbuf " save as user display buffer
jms movdsp " switch to user display buffer
jmp sysexit
" release display?
.rele:
dzm u.dspbuf " clear user display buffer pointer
law dspbuf " get default display buffer
jms movdsp " change to it
jmp sysexit
.chmod:
jms isown " check if user owns file arg
lac u.ac " get new permissions
and o17 " mask to read/write bits
lmq " save in MQ
lac i.flags " get file flags
and o777760 " clear permissions
omq " or in new permissions from MQ
dac i.flags " save in inode
jms iput " write inode back
jmp okexit
.chown:
jms isown " check if user owns file arg
lac u.ac " get new owner
dac i.uid " save in inode
jms iput " write inode back
jmp okexit
.getuid: " getuid system call
lac u.uid
dac u.ac " return u.uid in user AC
jmp sysexit
.seek:
jms seektell " fetch offset & whence (return seek base)
tad u.base " add offset
"** 01-s1.pdf page 8
spa " positive?
jms error " no: error
lmq " save position in MQ
lac f.flags " get file flags
and d1 " get write bit
sna " open for write?
jmp 1f " no
lacq " yes: get position
jms betwen; d0; i.size " between zero and size?
jms dacisize " no: store new size
jmp 2f
1:
lacq " reading: get position
jms betwen; d0; i.size " between zero and size?
lac i.size " no: get current size
2:
dac f.badd " save as offset
dac u.ac " return in AC
jms fput " copy fnode back to user area
jmp sysexit " return to user
.tell:
jms seektell " fetch offset & whence (return seek base)
cma
tad d1 " negate base
tad u.base " add to user offset
dac u.ac " return in user AC
jmp sysexit
.link:
jms arg " Save the argument pointers in
dac 0f "0f, 1f and 2f
jms arg
dac 1f
jms arg
dac 2f
lac d4 " Search the directory at i-num 4
jms namei; 0:0 " for the first argument
jms error " Didn't find it
jms namei; 1:0 " In the i-num found by 1st namei,
jms error " search for 2nd argument, err not found
dac u.base " save in user data
jms copy; 2:0; name; 4
lac u.cdir " Search the process' current directory
jms namei; name " for the third argument
skp
jms error " Error if it already exists
lac d1
dac mode " Save mode bits for access
jms access " check access (or return error to user)
jms dslot " allocate directory slot
lac u.base " get source file i-number
jms iget " read inode in
lac ii " get the i-num
dac d.i " Save the i-num in the directory entry
jms copy; name; d.name; 4 " Copy the new link name into the directory entry
lac i.uniq " Copy the i-node unique number into
dac d.uniq " the directory entry
-1
tad i.nlks " Decrement link count, i.e. one more link
dac i.nlks
"** 01-s1.pdf page 9
jms iput " Save the i-node and directory entry for
jms dput " the new link
jmp okexit " and return OK
.unlink:
jms argname " fetch filename, inode
dac u.base " save i-number
lac d1 " write mode bit
dac mode " save for access call
jms access " check access or return error (reads inode)
dzm d.i " clear directory i-num
jms dput " write directory entry back
lac u.base " get i-number back
jms iget " read inode back
isz i.nlks " increment link count (kept as negative count)
jmp 1f " not zero
jms itrunc " zero links: free blocks
dzm i.flags " clear status (free inode)
1:
jms iput " write inode back to disk
jmp sysexit
.setuid: " setuid system call
lac u.uid " load current user id
sma " negative (super user)
jms error " no: error!!
lac u.ac " load user AC
dac u.uid " save as new uid
jmp sysexit
" rename system call:
" sys rename; old_name_ptr; new_name_ptr
" Questions:
" when is directory entry read??
" is access check on directory or src file??
" check for existing file with new name??
" when is directory entry written back??
.rename:
jms arg " fetch first arg (old name pointer)
dac 0f " save for namei
jms arg " fetch second arg (new name pointer)
dac 1f " save for copy
lac u.cdir " get CWD
jms namei; 0:0 " search for (old) name
jms error " not found: return error
lac d1 " get write mode bit
dac mode " save for access call
jms access " access OK? (or return error to user)
jms copy; 1:0; d.name; 4 " copy new name into directory entry
jms dput " and write it to disk
jmp okexit
" time system call returns line (mains) frequency ticks
" high order bits returned in AC, low order in MQ
" s.tim is located in "system" block (written to disk)
" so this is a running count of uptime since first boot!
" at 60Hz, 36 bits would last 36+ years!
.time:
lac s.tim " load high order bits
dac u.ac " return in AC
lac s.tim+1 " load low order bits
dac u.mq " return in MQ
jmp sysexit
.chdir:
jms argname " fetch argument as filename
jms iget " (re)read inode(???)
lac i.flags " get flags
and o20 " get directory bit
sna " is a directory?
jms error " no: return error to user
lac ii " yes: get i-number
dac u.cdir " save as current working directory
"** 01-s1.pdf page 10
jmp okexit
" open system call
" sys open; filename_ptr; flags (0 for read, 1 for write)
" returns w/ "fd" in AC (or -1 if not found)
.open:
jms arg " get filename
dac 0f " save for namei
jms arg " get flags
sza " zero (read)
lac d1 " no: get write mode bit
sna " non-zero (write)?
lac d2 " no: get read mode bot
dac mode " save for access call
lac u.cdir " get current working directory
jms namei; 0:0 " search for file
jms error " error: return -1
jms iget " load inode
jms access " check access (may return w/ error to user)
lac i.flags " get file flags
and o20 " get directory bit
sna " is directory?
jmp open1 " no, join common code
lac mode " get access mode
and d1 " get write bit
sna " write access?
jmp open1 " no, continue
lac u.uid " yes: get uid?
sma " negative? (-1 is superuser)
jms error " no: return error
jmp open1 " yes: join common code
.creat:
lac d1 " mode bit 1 (write)
dac mode " save for access call
jms arg " get name pointer
dac .+2 " save for copy
jms copy; ..; name; 4 " copy filename to "name"
lac u.cdir
jms namei; name " look up in current working directory
jmp 1f " not found
jms iget " file exists: read inode
jms access " check access (or return error to user)
lac i.flags " get flags
and o20 " get directory bit
sna " is a directory?
jmp .+4 " no: skip to truncate
lac u.uid " get user
sma " is super user?
jms error " no: error
jms itrunc " yes: truncate
cla
jms dacisize " clear i.size
jmp open1
1:
jms access " here if not found
lac u.ac " get access bits from user AC (zero for lock!)
and o17 " mask to permissions
jms icreat
open1: " common exit for open/creat
jms fassign " assign fd slot
jms error " none free, return -1
jmp sysexit
"** 01-s1.pdf page 11
.close:
jms finac " get fnode (open file) for fd in user AC
dzm f.flags " clear flags
jms fput " write fnode back to u.ofiles
jmp sysexit
.read:
jms arg " get argument
and o17777 " mask to address
dac u.base " save as I/O base
jms arg " get second argument
dac u.count " save as count
lac u.base " get base
jms betwen; o10000; o17777 " end inside user memory?
jms error " no: error
tad u.count " get end of buffer
jms betwen; u.base; o17777 " inside buffer/user memory?
jms error " no: error
dac u.limit " yes: save as I/O limit
1:
jms finac " get fnode for fd in user AC
lac f.flags " get open file flags
and d1 " get write bit
sza " open for write?
jms error " yes: error
lac i.flags " get inode flags
and o40 " get special file bit
sna " special?
jmp 1f " no
iof " yes: disable interrupts
lac ii " get i number
tad swr " add to base instruction
dac .+1
jmp .. i " dispatch to read routine
1:
lac u.base " get user base
dac 1f+1 " save as iread base
lac u.count " get user count
dac 1f+2 " save as iread count
lac f.badd " get file offset
1:
jms iread; ..; ..
jmp exitrw
" write system call:
" AC/ fd
" sys write; buffer; count
" AC/ count or -1 on error
.write:
jms arg " pick up buffer
and o17777 " mask to addr
dac u.base " save as I/O base
jms arg " pick up count
dac u.count " save as count
tad u.base " add base (get limit)
jms betwen; u.base; o17777 " check between base and end of memory
jms error " no: error
dac u.limit " yes: save as limit
jms finac " get fnode with fd from user AC
lac f.flags " get open file table flags
and d1 " open for write?
sna " if yes, skip
jms error " no: error
lac i.flags " get inode flags
and o40 " get device bit
"** 01-s1.pdf page 12
sna " special?
jmp 1f " no
iof " yes, special: turn interrupts off
lac ii " get i number
tad sww " get write routine entry addr
dac .+1
jmp .. i " dispatch to write routine
1: " here with regular file
lac u.base " get base
dac 1f+1 " save as iwrite arg 1
lac u.count " get count
dac 1f+2 " save as iwrite 2
lac f.badd " get fd offset
1:
jms iwrite; ..; .. " write to file
exitrw: " common exit for read/write system calls
dac u.ac " save return in user AC
tad f.badd
dac f.badd " update file offset
jms iput " release inode
jms fput " release fnode
jmp sysexit " return to user