Re: [Xen-devel] [patch]Make xend to take care of dead qemu-dm process

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

shawn writes ("Re: [Xen-devel] [patch]Make xend to take care of dead qemu-dm 
process"):
> Could I ask if there is any methodology mistakes to solve this problem?
> or need I keep improving this patch?

I made some suggestions in a recent pair of messages in the thread
`c/s 17731 portability issues'.  Did you not receive those messages ?
>From over here they appear to have been copied to you as the author of
the errant patch.

Anyway, let me repeat myself:

Certainly running ps in this way is not the right way to do it.

Since qemu-dm is started by xend, it is quite possible for xend to
have a better and more reliable arrangement for detecting termination
of the qemu-dm process.  No polling is needed (and thus failure
detection can be immediate).

I suggested a design involving a named pipe.  qemu-dm would be passed
the writing end across exec but just keep it, and not write anything
to it.  xend would keep the reading end, and when it becomes readable
would collect the qemu-dm exit status with waitpid (with W_NOHANG).
xend would then kill the domain and report the fact of termination and
also qemu-dm's exit status if available.

On restart, xend would attempt to open the fifo again with
O_RDONLY|O_NONBLOCK which would fail EWOUDLBLOCK if qemu-dm was no
longer running; if it was still running then termination can be
detected as above, although the exit status won't be recoverable.

Does this all make sense ?  I'd be happy to expand on it if you'd like
to ask questions.  We'll make sure to review your next submission
thoroughly.

Ian.

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