Messages in this thread | | | Date | Wed, 05 Jul 2006 20:11:02 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [klibc 30/31] Remove in-kernel resume-from-disk invocation code |
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Nigel Cunningham wrote: > Hi again. > > (Excuse me replying to myself, but this might help someone else). > > On Thursday 06 July 2006 11:45, Nigel Cunningham wrote: >> Is there a klibc howto somewhere? I tried googling for 'klibc howto', >> reading the files in Documentation/ and browsing your klibc mailing list >> archive before asking! > >> What I'm wondering specifically is: Say a user needs to run some commands >> to set up access to encrypted storage before they can resume. At the >> moment, we'd tell them to put these commands and the echo > do_resume in >> their linuxrc (or init) script prior to mounting their root filesystem. >> Forgive me if I'm asking a stupid question but it's not immediately obvious >> to me how they would now do that. I'd much rather follow a simple howto >> than spend a good amount of time tracing function calls etc. I still see >> init/initramfs.c, and it mentions both CONFIG_BLK_DEV_INITRD and >> CONFIG_BLK_DEV_RAM. Would I be right in surmising that you can still have >> an initrd or ramfs to do such things as the above, after klibc has done its >> work? If not, is there some other way I'm ignorant of? > > For the record, I've since discovered that what you really want is an > initramfs howto. I think I stuck with those old-fangled initrds for too long. > Better update my desktop from Mandrake 10 too :)... is there a pattern here? >
Okay, let's try to start from the beginning...
initramfs is, indeed, a replacement for initrd, but it's not a 1:1 map. Instead, initramfs contents -- which can come from multiple sources! -- is simply extracted right into rootfs.
kinit is a replacement for the in-kernel root-handling code, as well as other related in-kernel code like resume from disk. It is compiled as a monolithic binary for size reasons.
klibc is a very small C library which *can* be used to produce initramfs binaries; in particular, it's used to produce kinit, and is small enough that it can be realistically included with the kernel distribution.
If you provide your own /init in an initramfs, it will override the default, which is /init -> /kinit. You can then choose to invoke kinit if you want to; for example, you could try to resume from suspend2, and invoke kinit if that fails.
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