Re: [Xen-devel] [RFC][PATCH] Use ioemu block drivers through blktap

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Kevin Wolf writes ("Re: [Xen-devel] [RFC][PATCH] Use ioemu block drivers 
through blktap"):
> I needed a shutdown handler to properly close the blktap connection and
> delete the named pipes associated with the qemu-dm instance. When a
> domain is destroyed, qemu-dm receives a SIGHUP. However, with the
> default SIGHUP handler no atexit functions are called, so I had to add
> this handler which performs a clean exit.

Sadly in that case using a signal hanlder is no good, because qemu-dm
might die for some other reason than SIGHUP, skipping the cleanup.
(For example, it might have a bug and segfault, or the kernel's OOM
killer might send it a SIGKILL, or ...)

If this cleanup is really necessary, then that will cause problems for
future runs.  If not then the cleanup isn't really necessary :-).
Leftover named pipes, for example, aren't really a big problem and can
just be garbage collected at some point (provided their names are
sufficiently unique).

I haven't eyeballed all of the new qemu blktap arrangements in detail.
What processes are there and why can't the process at the other end of
the pipe do the cleanup ?

Ian.

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