Re: [Qemu-devel] [PATCH v3] bugfix: passing reference instead of value

["Michael S. Tsirkin" <mst@redhat.com>]

On Sat, Jan 02, 2016 at 10:06:10AM +0100, Stefan Weil wrote:
> Am 02.01.2016 um 09:02 schrieb Cao jin:
> > Fix the bug introduced by 595a4f07: function host_pci_config_read() should be
> > pass-by-reference, not value.
> >
> > Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
> > ---
> > v3 changelog:
> > 1. Remove cpu_to_le32() since the code only runs on X86.
> >
> >  hw/pci-host/piix.c | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/hw/pci-host/piix.c b/hw/pci-host/piix.c
> > index 715208b..924f0fa 100644
> > --- a/hw/pci-host/piix.c
> > +++ b/hw/pci-host/piix.c
> > @@ -761,7 +761,7 @@ static const IGDHostInfo igd_host_bridge_infos[] = {
> >      {0xa8, 4},  /* SNB: base of GTT stolen memory */
> >  };
> >  
> > -static int host_pci_config_read(int pos, int len, uint32_t val)
> > +static int host_pci_config_read(int pos, int len, uint32_t *val)
> >  {
> >      char path[PATH_MAX];
> >      int config_fd;
> > @@ -784,12 +784,14 @@ static int host_pci_config_read(int pos, int len, uint32_t val)
> >          ret = -errno;
> >          goto out;
> >      }
> > +
> >      do {
> > -        rc = read(config_fd, (uint8_t *)&val, len);
> > +        rc = read(config_fd, (uint8_t *)val, len);
> 
> The type cast is not needed here, because read accepts any pointer
> type for the buffer argument.
> 
> While looking at that code, I noticed more potential issues:
> 
> * The open statement needs O_RDWR | O_BINARY, otherwise the code won't
> work on Windows.

I pokes at sysfs, it has no chance to work on windows anyway.

> * The len argument can obviously be 2 or 4. Will endianness handling
> work for both cases?
> 
> Regards,
> Stefan
> 
>