netdev - Re: [PATCH 00/13] drivers: hv: kvp

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Date:	Sun, 22 Jul 2012 03:50:58 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	KY Srinivasan <kys@...rosoft.com>
Cc:	Olaf Hering <olaf@...fle.de>, Greg KH <gregkh@...uxfoundation.org>,
	"apw@...onical.com" <apw@...onical.com>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"virtualization@...ts.osdl.org" <virtualization@...ts.osdl.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 00/13] drivers: hv: kvp

On Tue, 2012-07-03 at 15:24 +0000, KY Srinivasan wrote:
> 
> > -----Original Message-----
> > From: Ben Hutchings [mailto:ben@...adent.org.uk]
> > Sent: Monday, July 02, 2012 3:57 PM
> > To: KY Srinivasan
> > Cc: Olaf Hering; Greg KH; apw@...onical.com; devel@...uxdriverproject.org;
> > virtualization@...ts.osdl.org; linux-kernel@...r.kernel.org;
> > netdev@...r.kernel.org
> > Subject: Re: [PATCH 00/13] drivers: hv: kvp
> > 
> > On Mon, Jul 02, 2012 at 03:22:25PM +0000, KY Srinivasan wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: Olaf Hering [mailto:olaf@...fle.de]
> > > > Sent: Thursday, June 28, 2012 10:24 AM
> > > > To: KY Srinivasan
> > > > Cc: Greg KH; apw@...onical.com; devel@...uxdriverproject.org;
> > > > virtualization@...ts.osdl.org; linux-kernel@...r.kernel.org
> > > > Subject: Re: [PATCH 00/13] drivers: hv: kvp
> > > >
> > > > On Tue, Jun 26, KY Srinivasan wrote:
> > > >
> > > > > > From: Greg KH [mailto:gregkh@...uxfoundation.org]
> > > > > > The fact that it was Red Hat specific was the main part, this should be
> > > > > > done in a standard way, with standard tools, right?
> > > > >
> > > > > The reason I asked this question was to make sure I address these
> > > > > issues in addition to whatever I am debugging now. I use the standard
> > > > > tools and calls to retrieve all the IP configuration. As I look at
> > > > > each distribution the files they keep persistent IP configuration
> > > > > Information is different and that is the reason I chose to start with
> > > > > RedHat. If there is a standard way to store the configuration, I will
> > > > > do that.
> > > >
> > > >
> > > > KY,
> > > >
> > > > instead of using system() in kvp_get_ipconfig_info and kvp_set_ip_info,
> > > > wouldnt it be easier to call an external helper script which does all
> > > > the distribution specific work? Just define some API to pass values to
> > > > the script, and something to read values collected by the script back
> > > > into the daemon.
> > >
> > > On the "Get" side I mostly use standard commands/APIs to get all the
> > information:
> > >
> > > 1) IP address information and subnet mask: getifaddrs()
> > > 2) DNS information:  Parsing /etc/resolv.conf
> > > 3) /sbin/ip command for all the routing information
> > 
> > If you're interested in the *current* configuration then (1) and (3)
> > are OK but you should really use the rtnetlink API.
> > 
> > However, I suspect that Hyper-V assumes that current and persistent
> > configuration are the same thing, which is obviously not true in
> > general on Linux.  But if NetworkManager is running then you can
> > assume they are.
> 
> I am only interested in the currently active information. Why do you
> recommend the use of rtnetlink API over the "ip" command. If I am not
> mistaken, the ip command uses netlink to get the information. 
[...]

'Screen-scraping' the output of administrative tools is not good
practice.  It may be the best you can do when writing a shell script,
but for a C program it's generaly less reliable and often more difficult
than using the underlying C API.

Ben.

-- 
Ben Hutchings
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