[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH] trace: teach lttng backend to use format string
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH] trace: teach lttng backend to use format strings |
Date: |
Wed, 26 Mar 2014 09:27:07 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Tue, Mar 25, 2014 at 02:49:42PM +0000, Alex Bennée wrote:
>
> Stefan Hajnoczi <address@hidden> writes:
>
> > On Mon, Mar 24, 2014 at 05:04:54PM +0000, address@hidden wrote:
> >> From: Alex Bennée <address@hidden>
> >>
> >> This makes the UST backend pay attention to the format string arguments
> >> that are defined when defining payload data. With this you can now
> >> ensure integers are reported in hex mode if you want.
> >>
> >> Signed-off-by: Alex Bennée <address@hidden>
> >> ---
> >> scripts/tracetool/__init__.py | 13 +++++++++++--
> >> scripts/tracetool/backend/ust.py | 16 ++++++++++++----
> >> 2 files changed, 23 insertions(+), 6 deletions(-)
> >
> > How are strings handled, can LTTng copy them from the QEMU process'
> > memory space?
>
> lttng provides ctf_string for passing strings to the payload. But I
> wouldn't expect to use them for the result of format string calculations
> as that would defeat the point of the low impact tracing.
>
> There are a number of trace-events that pass strings for various things.
> I've not actually experimented with the output of any of them though.
Sounds like it should work but can you test it? Try enabling the
bdrv_open_common() trace event when booting a guest. You should see the
filename of the disk image file.
Stefan