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

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Date:	Fri, 18 Jun 2010 00:35:46 +0100
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"ddutile@...hat.com" <ddutile@...hat.com>,
	"sheng@...ux.intel.com" <sheng@...ux.intel.com>
Subject: Re: [Xen-devel] [PATCH 12/12] Unplug emulated disks and nics

On 06/17/2010 04:42 PM, 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.
>   

What about using Kconfig to define an appropriate symbol and just #ifdef
on that?

>>> +	}
>>> +	/* 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?
>   

strncmp would avoid having to modify the string in place.

    J
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