Re: [Qemu-devel] [PATCH 1/2] qemu-file: fix flaws of qemu_put_compression_data

[Li, Liang Z]

> > There are some flaws in qemu_put_compression_data, this patch tries to
> > fix it. Now it can be used by other code.
> >
> > Signed-off-by: Liang Li <address@hidden>
> > ---
> >  migration/qemu-file.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/migration/qemu-file.c b/migration/qemu-file.c index
> > 0bbd257..ef9cd4a 100644
> > --- a/migration/qemu-file.c
> > +++ b/migration/qemu-file.c
> > @@ -616,7 +616,9 @@ ssize_t qemu_put_compression_data(QEMUFile *f,
> const uint8_t *p, size_t size,
> >      ssize_t blen = IO_BUF_SIZE - f->buf_index - sizeof(int32_t);
> >
> >      if (blen < compressBound(size)) {
> > -        return 0;
> > +        if (f->ops->writev_buffer || f->ops->put_buffer) {
> > +            qemu_fflush(f);
> > +        }
> >      }
> 
> With your change, when we arrive here:
> 
> - blen could still be smaller that compressBound(size), you need to
>   recheck
> - blen could have changed, but you don't take that in account for the
>   following caller.
> 
> So, I think code has a bug?

Yes, there is a bug, I should consider the case QEMUFile with empty ops.
The right code should be like:

if (blen < compressBound(size)) {
        if (f->ops->writev_buffer || f->ops->put_buffer) {
            qemu_fflush(f);
        } else {
            return 0;
        }
}
....

It is enough?

Liang



> 
> Later, Juan.