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Re: [libvirt] PATCH: Fix infinite loop when QEMU quits at startup

"Daniel P. Berrange" <berrange redhat com> wrote:
> The recent refactoring of the QEMU startup process now reads the monitor
> TTY from the logfile. Unfortunately in this refactoring we lost the check
> for the 'ret == 0' scenario in the read() return value. So if QEMU quits
> at startup, eg  due to missing disk image, we loop forever on read() == 0
> because we hit end-of-file and QEMU has quit.
> This patch adds back handling for this scenario, and takes care to
> propagate the contents of the log to the user as an error message
>  # start demo
> libvir: QEMU error : internal error unable to start guest: qemu: could
>   not open disk image /home/berrange/Fedora-9-i686-Live.iso
> error: Failed to start domain demo
> In addition, there were a couple of other bugs
>  - a memory leak where we set the 'monitorpath' variable, even
>    though we'd just set it moments before.
>  - a missing check for whether the driver VNC password was present
>    when initializing passwords at VM startupo
>  - missing initialization of the monitor_watch field, and missing
>    checking for whether the watch was set before removing it.
>  - a gratuitous LOG_INFO when shutting down any VM, which could
>    just be LOG_DEBUG.

FYI, I reproduced the infloop with the following:

cat <<\EOF > d.xml
<domain type='qemu'>
    <type arch='i686' machine='pc'>hvm</type>
    <boot dev='cdrom'/>
    <disk type='file' device='cdrom'>
      <source file='no-such-file'/>
      <target dev='hdc'/>
    <disk type='file' device='disk'>
      <source file='no-such-file'/>
      <target dev='hda'/>
    <graphics type='vnc' port='-1'/>

Before, this use of virsh would hang:

    qemud/libvirtd &
    src/virsh -c qemu:///session "define d.xml; start D"

Now, it fails with a diagnostic, as you'd expect.

Somehow, while testing this, I got numerous segfaults
from libvirtd (due to dereferencing NULL doms->objs[i]->def,
but those should never be NULL), yet when I went to set up a
reproducer, it stopped happening altogether.

So not only does the infloop-fix look like it does the right thing,
I confirmed it with the above.  The rest looks fine, too.

Once we have something like my unix_sock_dir patch or an improved testing
framework, I'll add a test like the above.  Or maybe you know how to
reproduce the infloop using the test driver?


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