Hi, Andrei Borzenkov wrote: > as long as generated GUID has reasonable chance to be different from > any other GUID on the system where ISO was booted, it should be good. > For GRUB itself it does not matter anyway - it does not use GUID, so FS > UUID collision is worse problem.
That's the decisive point i gnaw on. Vladimir decided to use the low-entropy Volume Modification Date as --fs-uuid for grub-mkrescue ISOs. I understand it uses it for finding the device from where it booted. But other than with this GRUB specific interpretation, the GPT GUIDs have a meaning after GRUB completed its work of booting. Meanwhile i found a strong reason not to rely on the low-entropy ids by default. xorriso lists the --modification-date among the -as mkisofs options which it reports about existing bootable ISOs by: xorriso -indev some_bootable.iso -report_system_area as_mkisofs These options are meant for helping to produce modified ISOs with the same boot equipment as the input ISO. So this is a use case where an ISO is not identical to its predecessor but needs to get the same --modification-date, in case GRUB is in the ISO. This leads me to the decision not to base the GPT GUIDs on --modification-date by default. So those who are not in the business of reproducible ISOs will not experience a change. For those users for whom it matters i will offer a constant option to use the modification timestamp: --gpt_disk_guid modification-date but also the option to provide an externally generated GUID which gets generated once in good quality: $ uuidgen >guid_of_iso and then re-used as often as needed and appropriate $ xorriso -as mkisofs ... --gpt_disk_guid $(cat guid_of_iso) ... -------------------------------------------------------------------------- In order to be able to create reproducible ISOs, grub-mkrescue would need an option to set a user defined modification date which overrides /* obtain date-based UUID. */ at http://git.savannah.gnu.org/cgit/grub.git/tree/util/grub-mkrescue.c#n541 If EFI boot equipment is generated, the user would have to additionaly give one of above --gpt_disk_guid options as extra xorrisofs arguments. Have a nice day :) Thomas _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel
