Thank you for your response Adam!
The example you provided worked with BEGIN, but failed to work on any
other probes. For example:
$ sudo dtrace -l | grep sys_read
32272 fbt kernel sys_read entry
This is the read syscall on FreeBSD, but any example would likely
function the same way.
$ sudo dtrace -s foo.d '"fbt:kernel:sys_read:entry"'
dtrace: failed to compile script foo.d: line 1: probe description
:::"fbt:kernel:sys_read:entry" does not match any probes
$ sudo dtrace -s foo.d "'fbt:kernel:sys_read:entry'"
dtrace: failed to compile script foo.d: line 1: probe description
:::'fbt:kernel:sys_read:entry' does not match any probes
It seems to be adding the ::: string. I am not certain how to resolve
this issue.
On 11/12/2017 09:40 PM, Adam Leventhal wrote:
Hey Farhan,
You can't use variables (e.g. self->func) as a probespec (the string
that specifies the set of probes to enable), but you can use
command-line arguments. The mistake you're making in the second example
is using $$1 (which quotes the first command-line argument); you want to
use $1. For example:
---8<---
# cat foo.d
$1
{
trace("hi");
}
# dtrace -s foo.d BEGIN
dtrace: script 'foo.d' matched 1 probe
CPU ID FUNCTION:NAME
0 1 :BEGIN hi
^C
---8<---
Hopefully that helps.
A couple of notes:
Here's an example that demonstrates where you'd use $$1:
dtrace -n 'BEGIN{ trace($$1) }' foo
If you use just "$1" you'll see an error like this:
dtrace: invalid probe specifier BEGIN{ trace($1) }: in action list:
failed to resolve foo: Unknown variable name
You'll never put the $ before D variables; $variable is exclusively for
macros--replaced before the D language parser executes.
Adam
On Sun, Nov 12, 2017 at 12:19 AM, Farhan Khan <kha...@gmail.com
<mailto:kha...@gmail.com>> wrote:
Hi all,
I am trying to write a generic Dtrace script that will read the
probe function from the console, but can't figure out the syntax. I
am doing this:
# ./myscript.d "variable"
I must use the quotes, otherwise it complains that "variable" was
not found. I want to do:
dtrace:::BEGIN { self->func=$1; }
And then:
fbt::$self->func:entry { ... }
However, $self->func does not seem to work. If I use $$1, it tells
me that the function fbt::"variable":entry does not exist, because
the quotes are present. When I remove the quotes from the command
line, it gives me that initial error.
How do I read in a probefunc name from the console?
Thanks,
Farhan
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