Re: [Qemu-devel] [PATCH] oslib: make error handling more reasonable

[Stefan Weil]

Am 13.02.2012 03:37, schrieb Zhi Yong Wu:
> On Fri, Feb 10, 2012 at 11:53 PM, Stefan Weil <address@hidden> wrote:
> > Am 10.02.2012 16:13, schrieb Zhi Yong Wu:
> >
> > > On Fri, Feb 10, 2012 at 10:41 PM, Daniel P. Berrange
> > > <address@hidden> wrote:
> > > > On Fri, Feb 10, 2012 at 10:34:13PM +0800, Zhi Yong Wu wrote:
> > > > > From: Zhi Yong Wu <address@hidden>
> > > > >
> > > > > Signed-off-by: Zhi Yong Wu <address@hidden>
> > > > > ---
> > > > >  oslib-posix.c |    4 ++--
> > > > >  oslib-win32.c |    4 ++--
> > > > >  2 files changed, 4 insertions(+), 4 deletions(-)
> > > > >
> > > > > diff --git a/oslib-posix.c b/oslib-posix.c
> > > > > index b6a3c7f..f978d56 100644
> > > > > --- a/oslib-posix.c
> > > > > +++ b/oslib-posix.c
> > > > > @@ -80,7 +80,7 @@ void *qemu_oom_check(void *ptr)
> > > > >  {
> > > > >     if (ptr == NULL) {
> > > > >         fprintf(stderr, "Failed to allocate memory: %s\n",
> > > > > strerror(errno));
> > > > > -        abort();
> > > > > +        exit(EXIT_FAILURE);
> > > >
> > > >
> > > > exit() will call any atexit()/on_exit() handlers, as well as trying
> > > > to flush I/O streams. Any of these actions may require further
> > > > memory allocations, which will likely fail, or worse cause this
> > > > code to re-enter itself if an atexit() handler calls qemu_malloc
> > >
> > > Nice, very reasonable.
> > > > The only option other than abort(), is to use  _Exit() which
> > > > doesn't try to run cleanup handlers.
> > >
> > > I will try to send out v2
> >
> >
> > Could you please explain why calling exit, _Exit or _exit is more
> > reasonable than calling abort?
> >
> > abort can create core dumps or start a debugger which is
> > useful for me and maybe other developers, too.
> pls refer to 
> http://lists.gnu.org/archive/html/qemu-devel/2012-02/msg01270.html.
> In the scenario, the user should not see core dump, and he perhaps
> think that one bug exists in qemu code.
> So we hope to use _Exit() instead of abort() here.

So you say that you don't want a core dump just because the
user called QEMU with -m 4000 or some other large value.

Allocating RAM for the emulated machine is perhaps the only
scenario where a core dump is indeed not reasonable. In most
other cases, out-of-memory is an indication of a QEMU internal
problem, so a core dump should be written.

I therefore suggest to restrict any modification to the handling
of -m. In that case you could even improve the error message by
telling the user how much memory would be possible.
Simply call the allocating function with decreasing values until
it no longer fails.

Regards,
Stefan Weil