Re: [Xen-devel] [PULL 0/19] xen-2015-09-08-tag

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 10 Sep 2015, Michael S. Tsirkin wrote:
> On Thu, Sep 10, 2015 at 11:29:18AM +0100, Stefano Stabellini wrote:
> > CC Michael
> > 
> > On Thu, 10 Sep 2015, Stefano Stabellini wrote:
> > > On Thu, 10 Sep 2015, Chen, Tiejun wrote:
> > > > > xen-host-pci-device.c is only compiled if CONFIG_XEN_PCI_PASSTHROUGH
> > > > > was set by configure. That won't be the case on OSX or Windows, where
> > > > > the Xen headers don't exist.
> > > > > 
> > > > 
> > > > Okay. This actually shouldn't be enabled on Windows so what about this?
> > > 
> > > I think it would be nicer to replace the pread than introducing ifdefs.
> > 
> > Something like:
> > 
> > ---
> > Replace pread with read to avoid build breakages on Windows
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> 
> I'd prefer a wrapper that does the right thing.
> No sense in doubling the # of system calls for everyone.

If this was done on an hot path I would agree with you, but it is just
one call at initialization time (igd_pt_i440fx_initfn).


> > diff --git a/hw/pci-host/piix.c b/hw/pci-host/piix.c
> > index 58a33fb..9a40429 100644
> > --- a/hw/pci-host/piix.c
> > +++ b/hw/pci-host/piix.c
> > @@ -774,8 +774,11 @@ static int host_pci_config_read(int pos, int len, 
> > uint32_t val)
> >          return -ENODEV;
> >      }
> >  
> > +    if (lseek(config_fd, pos, SEEK_SET) != pos) {
> > +        return -errno;
> > +    }
> >      do {
> > -        rc = pread(config_fd, (uint8_t *)&val, len, pos);
> > +        rc = read(config_fd, (uint8_t *)&val, len);
> >      } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
> >      if (rc != len) {
> >          return -errno;
> 

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