saute procfs lyonnais
procfs supports two levels of directory. the filesystem root
directory contains a representation of the system process table.
this consists of an entry for each active and zombie process, and
an additional entry "curproc" which always represents the process
making the lookup request.
each of the sub-directories contains several files. these files
are used to control and interrogate processes. the files implemented
are:
file - xxx. the exec'ed file.
status - r/o. returns process status.
ctl - w/o. sends a control message to the process.
for example:
echo hup > /proc/curproc/note
will send a SIGHUP to the shell.
whereas
echo attach > /proc/1293/ctl
would set up process 1293 for debugging.
see below for more details.
mem - r/w. virtual memory image of the process.
parts of the address space are readable
only if they exist in the target process.
a more reasonable alternative might be
to return zero pages instead of an error.
comments?
note - w/o. writing a string here sends the
equivalent note to the process.
[ not implemented. ]
notepg - w/o. the same as note, but sends to all
members of the process group.
[ not implemented. ]
regs - r/w. process register set. this can be read
or written any time even if the process
is not stopped. since the bsd kernel
is single-processor, this implementation
will get the "right" register values.
a multi-proc kernel would need to do some
synchronisation.
this then looks like:
% ls -li /proc
total 0
9 dr-xr-xr-x 2 root wheel 0 Sep 21 15:06 0
17 dr-xr-xr-x 2 root wheel 0 Sep 21 15:06 1
89 dr-xr-xr-x 2 root wheel 0 Sep 21 15:06 10
25 dr-xr-xr-x 2 root wheel 0 Sep 21 15:06 2
2065 dr-xr-xr-x 2 root wheel 0 Sep 21 15:06 257
2481 dr-xr-xr-x 2 jsp staff 0 Sep 21 15:06 309
265 dr-xr-xr-x 2 root wheel 0 Sep 21 15:06 32
3129 dr-xr-xr-x 2 jsp staff 0 Sep 21 15:06 390
3209 dr-xr-xr-x 2 jsp staff 0 Sep 21 15:06 400
3217 dr-xr-xr-x 2 jsp staff 0 Sep 21 15:06 401
3273 dr-xr-xr-x 2 jsp staff 0 Sep 21 15:06 408
393 dr-xr-xr-x 2 root wheel 0 Sep 21 15:06 48
409 dr-xr-xr-x 2 root wheel 0 Sep 21 15:06 50
465 dr-xr-xr-x 2 root wheel 0 Sep 21 15:06 57
481 dr-xr-xr-x 2 root wheel 0 Sep 21 15:06 59
537 dr-xr-xr-x 2 root kmem 0 Sep 21 15:06 66
545 dr-xr-xr-x 2 root wheel 0 Sep 21 15:06 67
657 dr-xr-xr-x 2 jsp staff 0 Sep 21 15:06 81
665 dr-xr-xr-x 2 jsp staff 0 Sep 21 15:06 82
673 dr-xr-xr-x 2 jsp staff 0 Sep 21 15:06 83
681 dr-xr-xr-x 2 root wheel 0 Sep 21 15:06 84
3273 dr-xr-xr-x 2 jsp staff 0 Sep 21 15:06 curproc
% ls -li /proc/curproc
total 408
3341 --w------- 1 jsp staff 0 Sep 21 15:06 ctl
1554 -r-xr-xr-x 1 bin bin 90112 Mar 29 04:52 file
3339 -rw------- 1 jsp staff 118784 Sep 21 15:06 mem
3343 --w------- 1 jsp staff 0 Sep 21 15:06 note
3344 --w------- 1 jsp staff 0 Sep 21 15:06 notepg
3340 -rw------- 1 jsp staff 0 Sep 21 15:06 regs
3342 -r--r--r-- 1 jsp staff 0 Sep 21 15:06 status
% df /proc/curproc /proc/curproc/file
Filesystem 512-blocks Used Avail Capacity Mounted on
proc 2 2 0 100% /proc
/dev/wd0a 16186 13548 1018 93% /
% cat /proc/curproc/status
cat 446 439 400 81 12,0 ctty 748620684 270000 0 0 0 20000 nochan 11 20 20 20 0 21 117
the basic sequence of commands written to "ctl" would be
attach - this stops the target process and
arranges for the sending process
to become the debug control process
wait - wait for the target process to come to
a steady state ready for debugging.
step - single step, with no signal delivery.
run - continue running, with no signal delivery,
until next trap or breakpoint.
<signame> - deliver signal <signame> and continue running.
detach - continue execution of the target process
and remove it from control by the debug process
in a normal debugging environment, where the target is fork/exec'd by
the debugger, the debugger should fork and the child should stop itself
(with a self-inflicted SIGSTOP). the parent should do a "wait" then an
"attach". as before, the child will hit a breakpoint on the first
instruction in any newly exec'd image.
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