during fedora boot, what picks up the initrd.img from /boot?

[Robert P. J. Day]

On Fri, 30 Nov 2007, Mikkel L. Ellertson wrote:

> Robert P. J. Day wrote:
> >   i'm sure i'm going to regret asking this only seconds after i
> > hit ENTER, but at what point during the boot process does the
> > kernel's corresponding /boot/initrd.img file kick in and get used?
> >
> >   i'm following along reading the logic of initramfs and early
> > userspace, and can see where a compressed cpio archive can be
> > incorporated into the kernel image itself.  fair enough.
> >
> >   but how does the /boot/initrd.img (which is itself a compressed
> > cpio image) get processed during boot?  it's certainly not passed
> > as an argument to the kernel as i can see via /proc/cmdline.  so
> > how does it affect the boot sequence?  thanks.

> I believe that Grub loads the image, and then passes the location to
> the kernel at boot. Support for the file system of initrd.img has to
> be built into the kernel.

but *how* does grub pass that info?  that's the question here.  on my
f8 system, the contents of /proc/cmdline is simply:

ro root=/dev/f8/root rhgb quiet

so how exactly is the kernel notified about the location of that
external initrd.img file?  i'm guessing i might just start reading
through the early kernel code to see where it figures that out.

rday

p.s.  is my question making any sense?  maybe i'm just phrasing it
badly.

========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry
Waterloo, Ontario, CANADA

http://crashcourse.ca
========================================================================