Re: [Qemu-devel] [PATCH] use int64_t for return values from rbd instead of int

[Stefan Priebe - Profihost AG]

Am 21.11.2012 07:41, schrieb Stefan Hajnoczi:
> On Tue, Nov 20, 2012 at 8:16 PM, Stefan Priebe <address@hidden> wrote:
> > Hi Stefan,
> >
> > Am 20.11.2012 17:29, schrieb Stefan Hajnoczi:
> >
> > > On Tue, Nov 20, 2012 at 01:44:55PM +0100, Stefan Priebe wrote:
> > > > rbd / rados tends to return pretty often length of writes
> > > > or discarded blocks. These values might be bigger than int.
> > > >
> > > > Signed-off-by: Stefan Priebe <address@hidden>
> > > > ---
> > > >    block/rbd.c |    4 ++--
> > > >    1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > >
> > > Looks good but I want to check whether this fixes an bug you've hit?
> > > Please indicate details of the bug and how to reproduce it in the commit
> > > message.
> >
> >
> > you get various I/O errors in client. As negative return values indicate I/O
> > errors. When now a big positive value is returned by librbd block/rbd tries
> > to store this one in acb->ret which is an int. Then it wraps around and is
> > negative. After that block/rbd thinks this is an I/O error and report this
> > to the guest.
>
> It's still not clear whether this is a bug that you can reproduce.
> After all, the ret value would have to be >2^31 which is a 2+ GB
> request!
Yes and that is the fact.

Look here:
   if (acb->cmd == RBD_AIO_WRITE ||
        acb->cmd == RBD_AIO_DISCARD) {
        if (r < 0) {
            acb->ret = r;
            acb->error = 1;
        } else if (!acb->error) {
            acb->ret = rcb->size;
        }

It sets acb->ret to rcb->size. But the size from a DISCARD if you 
DISCARD a whole device might be 500GB or today even some TB.

Greets,
Stefan