Monday, 16 August 2010

DTrace Progress 20100816 - SDT Probes - at last

At last some progress in the SDT probes area. I had started work
a few weeks ago and hit some issues in trying to align the invoked
probe with the expected user interface arguments (translators).

I have finally got a version of this working (now need to clean it up).
There was some subtley in sdt_subr.c as I tried to isolate how the args
work, along with a lot of time studying the stack tracing mechanism.
I went up various dead-ends, but can now get to a point where I can
communicate an io:::start probe to the outside world.

I hope to clean this up. (I am not convinced my io:::start probe is the
"right" one, e.g. compared to a Mac, I am firing on all reads/writes, but
at least I can get the cosmetics working and then hunt a better place to
plant the probe).

Also found that if a translator mis-references structure offsets, this
will cause problems and/or a kernel segmentation violation - so I need
to ensure this is safe from userland destruction techniques.

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