Hey Rich,
> I've written about 1000 lines of D code (using lots of cpp),
> in order to generate parsable logs of system activity. The
> output format looks like:
>
> syscall={
> func=13'open_nocancel'
> pid=9171
> ppid=8738
> time=63505036663689
> av={
> path=40'/dev/dtracehelper'
> oflag=0
> mode=438
> }
> rv=3
> }
>
> For the curious, the format is Boulder IO with counted
> strings. I came up with this format in order to keep D
> from needing to escape oddball characters, etc.
>
>
> The problem is, sometimes the code acts in peculiar ways.
> Most of the time, it prints (correctly):
>
> path=17'/dev/dtracehelper'
>
> But sometimes (as in the output format example), it prints:
>
> path=40'/dev/dtracehelper'
>
>
> I suspect that someone here can help me find the bug (and
> most likely, in the process, teach me some D lore :-). I
> certainly hope so...
>
>
> FYI, the code below was generated by some macros. I then
> edited the white space a bit for this posting. Consequently,
> it may look a bit odd in spots. Try to ignore that detail...
>
> -r
>
>
> syscall::open*:entry {
> self->arg2 = arg2;
> self->arg1 = arg1;
> self->arg0 = arg0;
> self->follow = 1;
> }
>
> syscall::open*:return /self->follow != 0/ {
> printf("\n");
> printf("syscall={\n");
> func_l = strlen(probefunc);
> printf(" func=%d'%s'\n", func_l, probefunc);
> printf(" pid=%d\n", pid);
> printf(" ppid=%d\n", curpsinfo->pr_ppid);
> printf(" time=%d\n", timestamp);
> printf(" av={\n");
>
> path = copyinstr(self->arg0);
> path_l = strlen(path);
> printf(" path=%d'%s'\n", path_l, path);
>
> printf(" oflag=%d\n", self->arg1);
> printf(" mode=%d\n", self->arg2);
> printf(" }\n");
> printf(" rv=%d\n", arg0);
> printf("}\n");
> }
You're using globals to hold the path and path length -- so you're
occasionally getting the wrong answer when you're racing with another
thread executing open on another CPU. To rectify this, use clause-local
variables:
this->func_l = strlen(probefunc);
...
this->path = copyinstr(self->arg0);
this->path_l = strlen(path);
...
See the DTrace documentation on clause-local variables for details:
http://wikis.sun.com/display/DTrace/Variables#Variables-ClauseLocalVariables
(It's so nice to be able to send out URLs to chapter and verse in the docs!
Thank you, wiki!)
- Bryan
--------------------------------------------------------------------------
Bryan Cantrill, Sun Microsystems FishWorks. http://blogs.sun.com/bmc
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