On 03/05/2010 04:44 PM, Sven-Hendrik Haase wrote:

On 03.03.2010 18:12, Sven-Hendrik Haase wrote:

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On 03.03.2010 02:08, Gerardo Exequiel Pozzi wrote:

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Hi, just to leave in some visible place this experiment if some is interested.

My idea: remove archiso_early hook, and take the advantage of symlink /dev/disk/by-label/XYZ created by 60-persistent-storage.rules installed via udev hook, without doing other tricks.

Result: * OK: when booting in cdrom mode. * FAIL: when booting in disk mode.

The reason is because hybrid mode (via isohybrid). * The LABEL is defined at first sector of iso "sda" (simulate a MBR) also there is a fake partition "sda1" (with offset 1 [+512 bytes ahead of sda]) so you can create another partitions on the destination media. * When mount the UDF filesystem, sda is mounted and not sda1 (sda1 is just a fake part to avoid overwriting data). * There is a udev rule at 60-persistent-storage.rules that make all parent (sda in this case) ID_* env data available to childrens (sda1 in this case), so sda1 inherits the LABEL, and this data is not overwrited because blkid fail (remember sda1 is not a real partition)

Consequence: * /dev/disk/by-label/XYZ points to /dev/sda1 instead of /dev/sda. (when isohybrid offset> 0)

What works: * if offset = 0 will works, but doing this we lost the capability of create another partitions in the medium that .iso is copied (USB media) * Also works on real partition scheme (usb drive with the real MBR, and real partiton with label) * As said before if boot as cdrom.

Conclusion: * Keep with archiso_early, that is pretty simple and does not require other tools [#1]

If some is interested in changes for your personal usage, the patch is here [#2]

[#1] http://bugs.archlinux.org/task/18523 [mkinitcpio] usb_id, ata_id, scsi_id, path_id: should be added to udev install hook? [#2] https://gist.github.com/1f6f5a67008bf3b927ee

The problem with the recursive stuff might actually be in parted while other tools may be able to modify the resulting partition. Follow the syslinux mailing list for more infos on this. I'm currently trying to get some help as to how I would be able to add more partitions with offset = 0.

-- Sven-Hendrik

I just did some empiric tests here with surprising results.

Thanks for the feedback :)

Using offset 1 and off-the-shelf archiso-git official master, I dd'd my netinstall medium (x86_64) onto my USB key (sdb) and used gparted to make a second partition (sdb2) at the end of type ext2. I was able to mount it, put some crap onto it and rebooted into my live system. I did not expect this to work, however it booted just fine. In the live system, I was able to mount -o loop sdb2 fine and found my crap on there. I looked up what /dev/disk/by-label/ looked like and to my surprise found that ARCH_201003 pointed to sdb2! How did it even boot?

Because without this patch, "by-label" is not used at all. Just /dev/archiso is used that points to /dev/sdb in your case.

Astonished by this work of magic I moved on to retry the same test using offset 0. I repeated the same procedure and found myself in a happily booted Arch live system that still pointed its /dev/disk/by-label/ARCH_201003 at /dev/sdb2 (still the extra ext2 part).

Yes, offset does not change in how symlink is created. The magic rule is (this make all sdbN, inherits parent ID_* data from sdb. ENV{DEVTYPE}=="partition", IMPORT{parent}="ID_*" and rule that create symlink is: ENV{ID_FS_USAGE}=="filesystem|other", ENV{ID_FS_LABEL_ENC}=="?*", SYMLINK+="disk/by-label/$env{ID_FS_LABEL_ENC}" and this is the rule that export ID_* KERNEL!="sr*", IMPORT{program}="/sbin/blkid -o udev -p $tempnode"

This time however it reported both partitions correctly in blkid.

Yes, this is because as I explained before sdb points to sector 0, and sdb1 also points to sector 0, so only and only in this case, is a valid filesystem.

Earlier it only showed the ext2 partition while the udf one it was booted from was hidden. This time I got the udf one as well.

Set an e2fslabel on your ext2 partition and see how another by-label/ entry is created that points to correct partition.

Anyhow, turns out you *are*able to create partitions on the offset 0 device just fine using fdisk and mkfs friends. H. Peter Anvin, the syslinux guy, also advises to not rely on parted for more exotic layouts (which a recursive partition certainly is). I therefore conclude my tests and suggest trying to move forward on the course to remove archiso_early. This could be done by improving the 60-persistent-storage.rules hook to make it find the stuff we need it to find more properly.

60-persistent-storage.rules is ""untoucheable"", rules are OK. There is a dirty hack, that I didn't commented before, this is how udev uevents are triggered. The dirty hack is just before looking at "by-label" trigger udev events for disks, this is done with udevadm trigger --property-match=DEVTYPE=disk In this way only disk are retriggered, not partitions, so again by-label/xyz will point to sdb and not sdb1 or sdb2 ;)

At its current state, it appears we cannot rely on it to create correct LABELs for us using isohybrid.

I guess this is not possible, since the partition created is not a real partition (is just a fake, to avoid overwriting the data), so can not contain a boot sector with a LABEL. I guess that at that offset (512-1023) there are important data that can not be overwrited like bettween 0-512 at some portions. Good Luck! -- Gerardo Exequiel Pozzi ( djgera ) http://www.djgera.com.ar KeyID: 0x1B8C330D Key fingerprint = 0CAA D5D4 CD85 4434 A219 76ED 39AB 221B 1B8C 330D