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Re: Accessing probe info synchronously
- From: fche at redhat dot com (Frank Ch. Eigler)
- To: Lasse Bigum <zenith at zenith dot dk>
- Cc: systemtap at sources dot redhat dot com
- Date: 07 Feb 2007 07:59:48 -0500
- Subject: Re: Accessing probe info synchronously
- References: <20070207101140.GA18524@meridian.zenith.dk>
Lasse Bigum <zenith@zenith.dk> writes:
> So my question is this: Is there any way to access the information
> that SystemTap probes directly from kernel space, without using
> relayfs?
In a sense, sure: the systemtap script "knows" the instant the
application is invoking a system call, and could take some action.
But because normal systemtap scripts are normally non-intrusive, they
will let the calling thread resume pretty soon (a couple of
microseconds probably). This means that they likely won't be able to
communicate that knowledge to a slow/faraway (user-space) tool in time
for that tool to take control.
There have been experiments with systemtap scripts actively blocking
threads (by enqueuing a SIGSTOP signal), and this might be part of a
solution for your problem, but this area hasn't been thoroughly
explored. (Hmm, maybe there is a way of supporting this generally via
prologue code in the syscall tapset...)
- FChE