With the ability to back a memory ring into an mmapped file, it makes
sense to be able to dump these files. That's what this utility does.
The entire ring is dumped to stdout. It's well suited to large dumps,
it converts roughly 6 GB of logs per second.
The utility is really meant for developers at the moment. It might
evolve into a more general tool but at the moment it's still possible
that it might need to be run under gdb to process certain crash dumps.
Also at the moment it must not be used on a ring being actively written
to or it will dump garbage.
The code is made so that we can envision later to attach to a live
ring and dump live contents, but this requires that the utility is
built with the exact same options (threads etc), and that the file
is opened read-write. For now these parts have been commented out,
waiting for a reasonably balanced and non-intrusive solution to be
found (e.g. signals must be intercepted so that the tool cannot
leave the ring with a watcher present).
If it is detected that the memory layout of the ring struct differs,
a warning is emitted. At the end, if an error occurs, a warning is
printed as well (this does happen when the process is not cleanly
stopped, but it indicates the end was reached).
Willy Tarreau