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Re: [Xen-devel] [PATCH 0 of 4] libxl: improve error handling when device

To: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 0 of 4] libxl: improve error handling when device model fails to start early on
From: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
Date: Fri, 20 May 2011 08:08:30 +0100
Cc: Blank <waldi@xxxxxxxxxx>, Bastian, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On Thu, 2011-05-19 at 17:04 +0100, Ian Jackson wrote:
> Ian Campbell writes ("[Xen-devel] [PATCH 0 of 4] libxl: improve error 
> handling when device model fails to start early on"):
> > Currently when the device model fails to start there is a delay until
> > we timeout and report error, some users have misinterpretted this
> > delay as a hang.
> This is disappointing.  I fixed exactly this problem about 6 months
> ago.

Hmm, now you mention it that does sound familiar. And indeed:

        changeset:   20468:2f7cb671ef38
        user:        Keir Fraser <keir.fraser@xxxxxxxxxx>
        date:        Mon Nov 23 07:01:51 2009 +0000
        libxenlight: check for early failures of qemu-dm
        This patch makes xl create check whether qemu-dm has started
        correctly, and causes it to fail immediately with appropriate errors
        if not.  There are other bugfixes too.
        Signed-off-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>

So more like 18 months ago? (or I found another different attempt ;-))

> > Secondly we can propagate child failures to the parent much quicker by
> > adding a pipe between the intermediate process (which blocks in
> > waitpid() on the child until libxl__spawn_detach is called or the
> > child exits) to allow failure to be reported immediately and with a
> > slightly more specific error message.
> And this is what I thought I'd done.

Either way, it appears to be broken now.

You can confirm by removing one of the libraries that qemu-dm needs, or
by chmod -x.


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