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On Sat, May 4, 2013 at 3:05 PM, Fabio Erculiani <lxnay@g.o> wrote: |
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> |
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> Scenario: |
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> - you have an initramfs with mdev, your pivot_chroot system runs udev. |
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> - you have a LVM volume group, containing the lvm volume for / and |
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> /home, and perhaps you also have swap on another volume. |
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> - you boot using the current genkernel initramfs, which uses mdev and |
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> comes with lvm support |
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> |
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> The initramfs code activates your lvm volumes, lvm itself may or not |
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> may be compiled with udev support. In the former case, nothing gets |
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> written onto /run/udev (and devtmpfs), in the latter case, lvm writes |
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> metadata that are useful to lvm itself to udev. |
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> mdev is not udev, doesn't deal with udev rules so the metadata is |
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> either pristine or completely unavailable. |
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> busybox switches root and the boot starts: you obviously have lvm |
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> compiled with udev there, since you're using udev (or systemd-udevd, |
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> or gudev). The lvm there is either unable to find valid metadata so it |
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> doesn't automatically activate the volumes (note: /home does not get |
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> activated by the initramfs code) or, until some time ago but now |
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> defaulted to off, lvm itself creates the device nodes (which should |
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> have been created by udev + udev rules if lvm is compiled with udev |
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> support). |
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> If it's not enough, our current genkernel initramfs code (I fixed this |
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> as well, it's in the systemd-love overlay) doesn't mount --move /run |
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> to /newroot before switching root, so /run/udev is not ported over, |
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> which means that even if mdev would have been able to do do all the |
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> udev magic, things wouldn't work anyway. |
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> |
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> Long story short, we should: |
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> 1) give up with cross compiler support in genkernel, which has been |
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> anyway in a broken state for ages. Nobody is using it anyway. |
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> 2) make possible to optionally use udev in the initramfs (compiling |
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> just for it is a pita and the trend here [dracut and others do this] |
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> is to copy udevd from the system) |
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> 3) default to udev? |
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> |
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I just forgot the tricky part. |
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If future lvm versions are going to use udev more extensively (for eg: |
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storing more critical metadata in it), the net result will be that |
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mdev won't work anymore. This is why I wrote that lvm is working "by |
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miracle for now". |
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mdev is not future proof wrt lvm support. |
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|
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> |
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> -- |
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> Fabio Erculiani |
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-- |
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Fabio Erculiani |
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