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Old 01-26-2010, 05:41 PM   #1
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kernel modules vs built-in

HEre's the thread that confused me:

Originally Posted by MrChilly0 View Post
Is ext4 built as a module? THat'd be the has to be built into the kernel...

What? No it doesn't.

My question is pretty simple...if you are booting to your root partition which is ext4, the ext4 filesystem should be built in and not compiled as a module, or your bootup will fail. Am I wrong?
Old 01-26-2010, 05:53 PM   #2
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I'm not sure what you're asking about and what text and you're quoting.

ext4 support does not need to be in the kernel, providing that you have
an initrd file that supports it.
Old 01-26-2010, 05:56 PM   #3
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Yes and no, actually.

Back in the old days, you *did* need your root's filesystem support bundled into the kernel. That was because if you compiled it as a module, you needed to mount the root filesystem first... But how can you mount, if your kernel didn't have the support for it? It was kind of a chicken-and-egg problem.

Now, some distros use the module approach, and solve that problem by making heavy use of initrd/initramfs techniques. Basically, that involves creating a small "memory hard disk" which can be mounted as root filesystem, load from there all needed modules (like ext4 fs support), and *then and only then*, mount your real root filesystem.
Old 01-26-2010, 05:56 PM   #4
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You could use an initrd (initial ramdisk) to load the module for ext4. A "generic" slackware kernel does this, whereas a slackware "huge" kernel has support for the filesystems (and almost everything else) built into the kernel.

For instance
PHP Code:
mkinitrd --k -f ext4 -/dev/sda1 -/boot/initrd.gz 
would create a file /boot/initrd.gz to load ext4 support for a kernel that doesn't have it built in on my slackware box.
Old 01-26-2010, 06:03 PM   #5
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you answered it...I didn't have ext4 built into the initrd...
my setup was /boot ext3 / ext4 /swap ext4 was built as a kernel module. Upon boot, I would get the "unable to mount vfs blah blah blah" error. Once I built ext4 into the kernel I booted fine. But the problem was when I built the thanks for the answer


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