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Re: command line arguments
- From: "Daniel P. Berrange" <berrange at redhat dot com>
- To: "Frank Ch. Eigler" <fche at redhat dot com>
- Cc: systemtap at sources dot redhat dot com
- Date: Fri, 24 Feb 2006 13:42:22 +0000
- Subject: Re: command line arguments
- References: <20060223224218.GE20902@redhat.com>
- Reply-to: "Daniel P. Berrange" <berrange at redhat dot com>
On Thu, Feb 23, 2006 at 05:42:18PM -0500, Frank Ch. Eigler wrote:
> Hi -
>
> I committed a draft of command line argument support as per bug #1304.
> One part (plain substitution into scripts) is usable now. Another
> part (initializing globals at module init time) is sort of dormant.
>
> The way the first part works is by making any additional arguments
> passed to "stap" available to the script for substitution as string
> or number literals:
>
> # stap -e 'probe kernel.function(@1) { print($2) }' sys_open 4
>
> The @ vs $ distinction encodes whether the numbered argument should be
> pasted as a string or number literal. I considered guessing but
> heuristics don't seem to belong somewhere so critical.
>
> I'm open to suggestions about better notation than $n and @n. (#n is
> out because of comments; % and others because of arithmetic operators.)
The scenarios I'd like to use command line args in, are for tweaking
aspects of the data capture, say, sampling rate of a timer, or if I
was probing 'sys_read', some variable to control how often to log.
So I'd think named arguments would be clearer to use, possibly to set
global variables. So for example
global samplerate = 1000
probe timer.jiffies(samplerate) {
...
}
One could tweak the rate with
# stap --define samplerate=50 stuff.stp
Or another exaple, if one wanted to watch all file opens under a particular
directory
global prefix = "/"
probe kernel.function("sys_open") {
if ( isinstr(prefix, substr(user_string(filename),0,strlen(prefix)) ) {
print("Pid " . pid() . " opens " . user_strin(filename))
}
}
Then one could restrict it to just files under /etc with
# stap -D prefix=/etc watchopen.stp
Dan.
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