Re: [Qemu-devel] [PATCH] qcow2: Fix segfault in qcow2_invalidate_cache

[Kevin Wolf <kwolf@redhat.com>]

Am 18.03.2013 um 13:40 hat Paolo Bonzini geschrieben:
> Il 18/03/2013 13:10, Kevin Wolf ha scritto:
> > Need to pass an options QDict to qcow2_open() now. This fixes a segfault
> > on the migration target with qcow2.
> > 
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> >  block/qcow2.c | 12 ++++++++++--
> >  block/qcow2.h |  3 +++
> >  2 files changed, 13 insertions(+), 2 deletions(-)
> > 
> > diff --git a/block/qcow2.c b/block/qcow2.c
> > index b90dd9e..7fcdc62 100644
> > --- a/block/qcow2.c
> > +++ b/block/qcow2.c
> > @@ -29,6 +29,7 @@
> >  #include "block/qcow2.h"
> >  #include "qemu/error-report.h"
> >  #include "qapi/qmp/qerror.h"
> > +#include "qapi/qmp/qbool.h"
> >  #include "trace.h"
> >  
> >  /*
> > @@ -520,7 +521,7 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags)
> >          goto fail;
> >      }
> >  
> > -    s->use_lazy_refcounts = qemu_opt_get_bool(opts, "lazy_refcounts",
> > +    s->use_lazy_refcounts = qemu_opt_get_bool(opts, QCOW2_OPT_LAZY_REFCOUNTS,
> >          (s->compatible_features & QCOW2_COMPAT_LAZY_REFCOUNTS));
> 
> Why not add
> 
>    s->use_lazy_refcounts ||
> 
> to the default, and just use an empty QDict in qcow2_invalidate_cache?

I think it's better not to depend on any previous state in qcow2_open(),
but start from scratch with all options directly passed. Otherwise it
would become easy to lose the overview over the data flow.

Also, qcow2_invalidate_cache clears the state so that all other
information in s is properly reset:

    memset(s, 0, sizeof(BDRVQcowState));

So s->use_lazy_refcounts doesn't even have it's old value any more.

Kevin