Passing information from initramfs to real rootfs
Hi all,
is it possible to get information out of initramfs to be passed to the real root fs?
Currently initramfs is 'magically' mounted during boot, but vanished equally magically as soon as the root device is mounted. Is there a way planned/provided as to how information gathered/generated during the boot process can be passed to the real root-fs?
I'm thinking especially on udev and friends; udev could handle hotplug-events during boot-up from initramfs, but the devices generated cannot be passed to the real root-device, so essentially we have to re-scan sysfs to find and generate all events which might have been generated during boot and pass them to udev _again_.
Nothing gained there; we can as well let it be handled entirely during init as it is done now.
Easiest solution would be to have it moved initrd-style to /initramfs or somesuch, then we could easily access it und umount it (i.e. free the memory) as soon as we're done with the processing.
Comments? Enlightenments?
Cheers,
Hannes
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Quoted 4 lines · Hannes Reinecke
Hi all,
is it possible to get information out of initramfs to be passed to the real root fs?
mkdir /foo
mkfs.minix /dev/ram42
mount -nt minix /dev/ram42 /foo
echo my content > /foo/backup.txt
umount /foo
...
mount -n /dev/ram42 /oldinitramfscontent
might work.
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Quoted 5 lines · Hannes Reinecke
I'm thinking especially on udev and friends; udev could handle hotplug-events during boot-up from initramfs, but the devices generated cannot be passed to the real root-device, so essentially we have to re-scan sysfs to find and generate all events which might have been generated during boot and pass them to udev _again_.
[...]
Quoted 3 lines
Easiest solution would be to have it moved initrd-style to /initramfs or somesuch, then we could easily access it und umount it (i.e. free the memory) as soon as we're done with the processing.
That's what I was planning to do for my test system. With the current kernel I basically have to eliminate mount_root anyway in order to use initramfs at all, so I was going to do the "real" root mount in userspace and pivot_root to it explicitly.
As far as the initramfs /dev, my plan is to try symlinking or bind mounting it into the new root, and continue to use the same /dev as initramfs. If you want to umount and free the initramfs memory then I guess you'd have to copy the dev contents somehow (unless or until someone has a way to create a dedicated ramfs for /dev during initramfs and then remount that at /dev after a pivot_root).
-Dave Dodge
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Quoted 13 lines · Olaf Hering
Quoted 4 lines · Hannes Reinecke
Hi all,
is it possible to get information out of initramfs to be passed to the real root fs?
mkdir /foo
mkfs.minix/dev/ram42
mount -nt minix/dev/ram42/foo
echo my content > /foo/backup.txt
umount /foo
Quoted 6 lines
...
mount -n
/dev/ram42/oldinitramfscontentmight work.
Doesnt work, the ramdisk content disappears during umount. Does anyone know what it disappears in the initramfs context, but not in the running system?
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Quoted 17 lines · Olaf Hering
Quoted 15 lines · Olaf Hering
Quoted 4 lines · Hannes Reinecke
Hi all,
is it possible to get information out of initramfs to be passed to the real root fs?
mkdir /foo
mkfs.minix/dev/ram42
mount -nt minix/dev/ram42/foo
echo my content > /foo/backup.txt
umount /foo...
Quoted 8 lines
Quoted 4 lines
mount -n
/dev/ram42/oldinitramfscontentmight work.
Doesnt work, the ramdisk content disappears during umount. Does anyone know what it disappears in the initramfs context, but not in the running system?
Why umount it then?
greg k-h
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Quoted 21 lines · Greg KH
Quoted 20 lines · Olaf Hering
Quoted 18 lines · Olaf Hering
Quoted 4 lines · Hannes Reinecke
Hi all,
is it possible to get information out of initramfs to be passed to the real root fs?
mkdir /foo
mkfs.minix/dev/ram42
mount -nt minix/dev/ram42/foo
echo my content > /foo/backup.txt
umount /foo...
mount -n
/dev/ram42/oldinitramfscontent
Quoted 7 lines
Quoted 5 lines
Quoted 1 line
might work.
Doesnt work, the ramdisk content disappears during umount. Does anyone know what it disappears in the initramfs context, but not in the running system?
Why umount it then?
/foo is in initramfs and not accessible after mounting the real root. But there are ways to preserve the content somehow. It should not disappear according to viro.
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