[libvirt] [PATCH v5] Add functions for handling exponential backoff loops.

[Peter Krempa]

On Fri, Apr 15, 2016 at 16:45:07 +0200, Michal Privoznik wrote:
> On 15.04.2016 13:53, Richard W.M. Jones wrote:
> > In a few places in libvirt we busy-wait for events, for example qemu
> > creating a monitor socket.  This is problematic because:
> > 
> >  - We need to choose a sufficiently small polling period so that
> >    libvirt doesn't add unnecessary delays.
> > 
> >  - We need to choose a sufficiently large polling period so that
> >    the effect of busy-waiting doesn't affect the system.
> > 
> > The solution to this conflict is to use an exponential backoff.
> > 
> > This patch adds two functions to hide the details, and modifies a few
> > places where we currently busy-wait.
> > ---
> >  src/fdstream.c           | 10 +++---
> >  src/libvirt_private.syms |  2 ++
> >  src/qemu/qemu_agent.c    |  9 +++---
> >  src/qemu/qemu_monitor.c  | 10 +++---
> >  src/util/virtime.c       | 81 ++++++++++++++++++++++++++++++++++++++++++++++++
> >  src/util/virtime.h       | 11 +++++++
> >  6 files changed, 111 insertions(+), 12 deletions(-)
> 
> ACK. Sorry for making you send v5 to such simple patch.

GCC 5.3.0 doesn't like this very much:

qemu/qemu_agent.c:238:8: error: 'ret' may be used uninitialized in this function [-Werror=maybe-uninitialized]
     if (ret != 0) {

qemu/qemu_monitor.c:369:8: error: 'ret' may be used uninitialized in this function [-Werror=maybe-uninitialized]
     if (ret != 0) {

The static analyzer considers the possibility that the while loop will
never execute, which would be possible in a very strange lockup of the
host.

Please initialize ret to -1 before pushing in those two functions.

Peter

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