Hi, Sreyan Chakravarty wrote: > I am kind of confused as to the difference/advantage between keeping the old > boot image versus rebuilding one. My first multi-session proposal was to keep as much of the boot equipment as possible. After all, we began with the riddle why your genisoimage produced ISO boots to an ISOLINUX menu but that menu does not work. So "keep" seemed to be better than "replay". Boot equipment is a manifold topic, even if restricted to x86 machines. Roughly there are "boot images", which are intervals of data blocks. Either they are executable programs, like isolinux.bin, or they are filesystem images like efiboot.img. The firmware, PC-BIOS or EFI, expects easy-to-understand pointers to the boot images. These pointers are stored in the El Torito boot sector and El Torito boot catalog (for DVD), or as MBR boot code (for PC-BIOS and USB stick), or as partition table (for EFI and USB stick). As long as the boot images stay where they are in the original ISO, it is ok to keep the pointers as they are. The only problem you reported so far is that the quite unimportant partition 1 did not grow with the ISO image when you added the new session. The boot pointer in the partition table is partition 2, which is marked as EFI System Partition. Replaying all boot preparations bears more potential points of failure. xorriso could misunderstand the boot equipment of the original ISO or it could make mistakes when trying to re-create it. But if it works correctly, it will re-create partition 1 with the new size of the ISO. So no part of the ISO filesystem lies outside of it and GNOME Disks will be happy when it tries to mount partition 1. > Secondly, > > -compliance no_emul_toc \ > Why aren't you keeping a Table of Contents ? Aren't they required for > compatibility reasons ? It's for getting an ISO image with no extra multi-session history. The original ISO doesn't have that history either. Multi-session is actually a feature of sequential optical media: CD-R, CD-RW, DVD-R, DVD+R, BD-R, unformatted DVD-RW. With these media the Linux convention is to mount the first track of the last session. This track can be found by the medium's Table-Of-Content which tells start addresses of sessions and tracks. Each of the listed sessions can be mounted by Linux mount option sbsector= and will show the disk state from the time when it was the last session. Quite useful for incremental multi-session backups. Overwritable media (DVD-RAM, DVD+RW, BD-RE, formatted DVD-RW) and data files do not have such a table of content. Linux by default mounts what it finds at the usual offset starting from block 0. ISO 9660 multi-session on such media and files thus has to overwrite the old superblock at this standard location by new content which points to the root directory of the newest session. (Invention of Andy Polyakov for his program growisofs with DVD+RW.) By this overwriting of the superblock, the old root directory becomes lost in the woods. It is still there and still could be mounted. But no superblock points to it. So only one session is to see. The newest. That's the reason for my invention of emulated table of content. The first session does not get written to block 0 but rather to block 32. This leaves room for an official superblock at block 0 and thus saves the superblock of the first session from being overwritten by session 2. Now the superblocks of the sessions form a chain, which xorriso command -toc can display. This offset 32 of the new session gets disabled by -compliance no_emul_toc. As said, because mkisofs does not do it and thus xorrisofs doesn't either by default. But xorriso would do it by default. And the new ISO would differ in this way from the old one more than is necessary. For a motivation of xorriso's default see one of my backup BD-REs which i update daily by a xorriso run with -update_r commands: $ xorriso -indev /dev/sr4 -toc ... Media current: BD-RE Media status : is written , is appendable Media summary: 138 sessions, 9405258 data blocks, 17.9g data, 5236m free ... TOC layout : Idx , sbsector , Size , Volume Id ISO session : 1 , 32 , 2112020s , HOME_2019_11_24_152510 ISO session : 2 , 2112064 , 68114s , HOME_2019_11_25_160120 ISO session : 3 , 2180192 , 77406s , HOME_2019_11_26_154114 ... ISO session : 136 , 9255008 , 55002s , HOME_2020_04_07_181157 ISO session : 137 , 9310016 , 47622s , HOME_2020_04_08_150526 ISO session : 138 , 9357664 , 49682s , HOME_2020_04_09_155619 If needed i can mount any of these daily backup states by the number in the "sbsector" column. xorriso offers a helper command to mount by session number or a search text for the volume id. On a BD-R with its hardware table of content, i see without such emulation effort: Media current: BD-R sequential recording Media status : is written , is appendable Media summary: 55 sessions, 4935104 data blocks, 9639m data, 13.9g free ... TOC layout : Idx , sbsector , Size , Volume Id ISO session : 1 , 0 , 2112619s , HOME_2020_02_15_121306 ISO session : 2 , 2112800 , 44925s , HOME_2020_02_16_110515 ... ISO session : 55 , 4885696 , 49252s , HOME_2020_04_09_111237 The only visible difference is that session 1 starts at block 0. On hardware level, BD-RE and BD-R differ much more. Have a nice day :) Thomas _______________________________________________ users mailing list -- users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to users-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/users@xxxxxxxxxxxxxxxxxxxxxxx
