How to understand 'make oldconfig'?

[Leonid V. Fedorenchik]

On Fri, 26 Aug 2011 10:33:40 +0800
Parmenides <mobile.parmenides at gmail.com> wrote:

> >> 2. When there is a .config in /usr/src/linux indeed, make do nothing
> >> but generate a copy of .config, namely .config.old.
> >
> > I don't understand.....
> 
> Other 'make XXXconfig' such as:
> 
>                make config
>                make menuconfig
>                make xconfig
>                make defconfig
> 
> do some modification to the .config more or less. If 'make oldconfig'
> have not ask some questions, then the .config does not changed. So, I
> think the 'make oldconfig' does nothing.  I wonder what 'make
> oldconfig' does.

AFAIK, 'make oldconfig' is used to update your old .config file to the newer
kernel. For exapmle, you have .config file of your current kernel and you
downloaded new kernel and want to build your new kernel. Since very likely new
kernel will have some new configuration options, you will need to update your
config. Easiest way to do this is to run 'make oldconfig' which will ask you
questions about new configuration options. (that is the ones your current
.config file doesn't have)

> 
> 
> 2011/8/26 Mulyadi Santosa <mulyadi.santosa at gmail.com>:
> > hi....
> >
> > On Thu, Aug 25, 2011 at 23:32, Parmenides <mobile.parmenides at gmail.com> wrote:
> >> Hi,
> >>
> >>    I have tried to understand 'make oldconfig' command while
> >> configurating kernel. I do some experiments and get the following
> >> ideas:
> >>
> >> 1. When there is no a .config in /usr/src/linux,
> >>    (1)  If there is no a /boot/config-x.y.z, make will ask some
> >> questions and then produce a .config.
> >>    (2)  Otherwise, make will copy the /boot/config-x.y.z to
> >> /usr/src/linux/.config.
> >>
> >> My question: According to the messages generated by make, I get that
> >> both 'make defconfig' and 'make oldconfig' will gerenate .config based
> >> on 'i386_defconfig'. Why does 'make oldconfig' ask some questions,
> >> while 'make defconfig' does not?
> >
> > because "make defconfig" is simply generating a default pre configured
> > config file (it's based on i386_defconfig as you said).
> >
> > make oldconfig asks something? quite likely because you tried to fetch
> > that config into newer kernel version. Thus, it asks your decision on
> > what to do on those new introduced options.
> >
> >> 2. When there is a .config in /usr/src/linux indeed, make do nothing
> >> but generate a copy of .config, namely .config.old.
> >
> > I don't understand.....
> >
> >
> > --
> > regards,
> >
> > Mulyadi Santosa
> > Freelance Linux trainer and consultant
> >
> > blog: the-hydra.blogspot.com
> > training: mulyaditraining.blogspot.com
> >
> 
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Leonid V. Fedorenchik