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

[Ben Hutchings]

On Tue, 2012-07-03 at 15:24 +0000, KY Srinivasan wrote:
> 
> > -----Original Message-----
> > From: Ben Hutchings [mailto:ben@xxxxxxxxxxxxxxx]
> > Sent: Monday, July 02, 2012 3:57 PM
> > To: KY Srinivasan
> > Cc: Olaf Hering; Greg KH; apw@xxxxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx;
> > virtualization@xxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > netdev@xxxxxxxxxxxxxxx
> > 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@xxxxxxxxx]
> > > > Sent: Thursday, June 28, 2012 10:24 AM
> > > > To: KY Srinivasan
> > > > Cc: Greg KH; apw@xxxxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx;
> > > > virtualization@xxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > > > Subject: Re: [PATCH 00/13] drivers: hv: kvp
> > > >
> > > > On Tue, Jun 26, KY Srinivasan wrote:
> > > >
> > > > > > From: Greg KH [mailto:gregkh@xxxxxxxxxxxxxxxxxxx]
> > > > > > 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
73.46% of all statistics are made up.

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