build initramfs: explain modprobe?

build initramfs: explain modprobe?

[John Reiser]

What properties of modprobe are essential for building initramfs?
Modprobe works for only one kernel module at a time, and this is
a cause of slowness.  For instance, computing the transitive
closure of the Requires relationship over a non-small set of modules
can be performed faster by loading modules.dep into a bash associative
array, then processing in bash.  Also, modinfo now is invoked once per
module to find firmware, but this can be sped up by invoking on batches
of modules, using "split -C 32000" to avoid the argsize limit of execve.

Invoking modprobe with --ignore-install seems to remove any effects
due to (possibly host-specific) /etc/modules.d/*.conf.  Is there anything
else that modprobe does for building initramfs, other than transitive
closure of Requires?

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Re: build initramfs: explain modprobe?

[Harald Hoyer]

On 31.08.2011 00:48, John Reiser wrote:
> What properties of modprobe are essential for building initramfs?
> Modprobe works for only one kernel module at a time, and this is
> a cause of slowness.  For instance, computing the transitive
> closure of the Requires relationship over a non-small set of modules
> can be performed faster by loading modules.dep into a bash associative
> array, then processing in bash.  Also, modinfo now is invoked once per
> module to find firmware, but this can be sped up by invoking on batches
> of modules, using "split -C 32000" to avoid the argsize limit of execve.
>
> Invoking modprobe with --ignore-install seems to remove any effects
> due to (possibly host-specific) /etc/modules.d/*.conf.  Is there anything
> else that modprobe does for building initramfs, other than transitive
> closure of Requires?
>

Hmm, you are right. Modules loaded in "/etc/modules.d/*.conf" are not honored.
And yes, "modprobe" is only used to easily get the requirements.

Re: build initramfs: explain modprobe?

[John Reiser]

>> What properties of modprobe are essential for building initramfs?
>> [snip]

> And yes, "modprobe" is only used to easily get the requirements.

Explicitly:
  0) Expand short names: "pcmcia" ==> "kernel/drivers/pcmcia/pcmcia.ko".
  1) Compute transitive closure of Requires from modules.dep.
  2) Ignore modules listed in modules.builtin.
  3) Handle aliasing of underscore and minus:
     "usb_storage" ==> "usb-storage".

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