Hi Chip,
Chip Bennett wrote:
> First, the length on tracemem is a constant because the output from one
> clause must be the same length every time it executes. With ASCII
> strings, you can fake it, because you can set the maximum length of
> strings to whatever you want. When the used length of a string varies
> each time the same clause is executed, this isn't a problem because D
> always records the full length of the string in the switch buffer, not
> just the used length. The full length never varies.
>
> However, the problem with this for binary data, is that all of the
> string format items in printf stop when a null character ('\0') is
> reached: not a good thing for binary data.
>
> I have a possible solution, but I don't think you're going to like it.
> I've thought about this before, and considered how I might solve it. If
> you know the buffer you want to trace is between say 1 and 8000 bytes,
> include enough additional probe specs and clauses for the same function
> over and over to display the whole thing, but trace it 100 bytes at a
> time. So for a maximum of 8000 bytes, you'd need 80 clauses. Then use
> a counter in a predicate to limit the number of clauses executed for
> each pass. It's crude, I know.
>
Yes, I thought of that. The problem is that I can not assume
that a given dump has, say 100 bytes in it. I would have to have a separate
probe for each byte (ugh). I think I'll end up dumping the maximum size
using tracemem, and then let an application whittle it down based
on a length I can place into the output.
> I considered a profile probe that fires over and over with a predicate
> that stops the output when the end of the buffer is reached, but the
> buffer would likely be modified before you'd get a chance to get all of
> the data traced.
>
> We need a tracemem that has two parameters: buffer len, a variable, a
> max length, a constant. Tracemem would then always record the full
> length in the switch buffer, but only the actual data would be
> displayed, along with the length.
>
Yes! That would be nice...
Thanks much,
max
> Good luck!
>
> Chip
>
>
>
>> -----Original Message-----
>> From: [EMAIL PROTECTED] [mailto:dtrace-discuss-
>> [EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED]
>> Sent: Friday, November 21, 2008 7:10 AM
>> To: dtrace-discuss@opensolaris.org
>> Subject: [dtrace-discuss] tracemem question
>>
>> Hi All,
>> I am sure this has been asked before (in fact, I think I asked it over
>> 2
>> years ago).
>> I am snooping tcp traffic on the e1000g using dtrace. Almost
>> everything
>> works (I print mac header,
>> ip header, and tcp header). I would like to use something like
>> tracemem() to dump the payload.
>> However, tracemem() won't let me specify anything but a constant as
>>
> the
>
>> length. Has anyone
>> succeeded in dumping an arbitrary number of hex bytes? What I want is
>> something
>> like:
>> tracemem(mp->b_rptr+offset, mp->b_wptr-(mp->b_rptr+offset));
>>
>> Or maybe there is a way to do this with printf???
>>
>> thanks,
>> max
>>
>> _______________________________________________
>> dtrace-discuss mailing list
>> dtrace-discuss@opensolaris.org
>>
>
>
>
>
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