Re: [Xen-devel] [PATCH 12/12] Unplug emulated disks and nics

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Thu, Jun 17, 2010 at 04:42:14PM +0100, Stefano Stabellini wrote:
> On Mon, 14 Jun 2010, Konrad Rzeszutek Wilk wrote:
> > > +#if (defined(CONFIG_XEN_NETDEV_FRONTEND) || \
> > > +         defined(CONFIG_XEN_NETDEV_FRONTEND_MODULE)) && \
> > > +         (defined(CONFIG_XEN_PLATFORM_PCI) || \
> > > +          defined(CONFIG_XEN_PLATFORM_PCI_MODULE))
> > > +         printk(KERN_INFO "Netfront and the Xen platform PCI driver have 
> > > "
> > > +                         "been compiled for this kernel: unplug emulated 
> > > NICs.\n");
> > > +         xen_emul_unplug |= XEN_UNPLUG_ALL_NICS;
> > > +#endif
> > > +#if (defined(CONFIG_XEN_BLKDEV_FRONTEND) || \
> > > +         defined(CONFIG_XEN_BLKDEV_FRONTEND_MODULE)) && \
> > > +         (defined(CONFIG_XEN_PLATFORM_PCI) || \
> > > +          defined(CONFIG_XEN_PLATFORM_PCI_MODULE))
> > > +         printk(KERN_INFO "Blkfront and the Xen platform PCI driver have 
> > > "
> > > +                         "been compiled for this kernel: unplug emulated 
> > > disks.\n"
> > > +                         "You might have to change the root device\n"
> > > +                         "from /dev/hd[a-d] to /dev/xvd[a-d]\n"
> > > +                         "in your root= kernel command line option\n");
> > > +         xen_emul_unplug |= XEN_UNPLUG_ALL_IDE_DISKS;
> > > +#endif
> > 
> > Wow. Can you move those checks to the header file and make it deal with
> > the #ifdef and setting of xen_emul_unplug?
> > 
> 
> I tried, but it didn't improve the elegance of the code, mainly because I
> want to keep the printk in place, so the code would look very much like
> this, but instead of being in platform-pci-unplug.c would be in
> platform_pci.h.

If was thinking of something like this in the header file:


int xen_must_unplug_nics() {
#if (defined(CONFIG_XEN_NETDEV_FRONTEND) || \
                defined(CONFIG_XEN_NETDEV_FRONTEND_MODULE)) && \
                (defined(CONFIG_XEN_PLATFORM_PCI) || \
                 defined(CONFIG_XEN_PLATFORM_PCI_MODULE))
        return 1;
#else
        return 0;
}

and then your code would be:

        if (xen_must_unplug_nics()) {
                printk(".. blah blah ");
                xen_emul_unplug |- XEN_unPLIG_ALL_NICS;
        }

and similar for the IDE disks.

> 
> 
> > > + }
> > > + /* Now unplug the emulated devices */
> > > + if (xen_platform_pci_enabled && !(xen_emul_unplug & XEN_UNPLUG_IGNORE))
> > > +         outw(xen_emul_unplug, XEN_IOPORT_UNPLUG);
> > > +}
> > > +
> > > +static int __init parse_xen_emul_unplug(char *arg)
> > > +{
> > > + char *p, *q;
> > > +
> > > + for (p = arg; p; p = q) {
> > > +         q = strchr(arg, ',');
> > > +         if (q)
> > > +                 *q++ = '\0';
> > > +         if (!strcmp(p, "all"))
> > > +                 xen_emul_unplug |= XEN_UNPLUG_ALL;
> > 
> > strncmp..
> > 
> 
> is it really needed considering that we know that both strings are NULL
> terminated and one of them is a constant?

Please do.

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