Why must I modprobe? [was: LVM snapshot doesn't seem to work]

[David Abrahams]

Alexander Skwar <listen at alexander.skwar.name> writes:

> Gabriel Dragffy <dragffy at yandex.ru>:
>
>> I'm trying the following command:
>> $ sudo lvcreate --size 100m --snapshot --name snap /dev/bouncyball/root
>> 
>> and getting the error:
>>   snapshot: Required device-mapper target(s) not detected in your kernel
>>   lvcreate: Create a logical volume
>> 
>> I have tried many other combinations including the -s and -n switches
>> but still no joy, what am I overlooking?
>
> You're overlooking the message that lvcreate is telling you:
>         
>         Required device-mapper target(s) not detected in your kernel
>
> Solution: Enable the kernel to support snapshots.
>
>         modprobe dm-snapshots   (or something like this)

Alright, this has been bugging me for a while, and this gives me
occasion to ask.  Why does Linux require me to do this, rather than
simply auto-loading modules when an attempt is made to use their
functionality?

It's a serious usability blocker: I often find instructions that fail
to work (with much less helpful error messages) unless I'm sharp
enough to remember that a module load might be required, and then
clever enough to figure out what that module might be called.  

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com