Re: How can we identify an ISO file is an EFI bootable ISO image?

[Heyi Guo <heyi.guo@linaro.org>]

Thank you so much. I will try that :)

Regards,

Gary (Heyi Guo)


在 6/21/2017 12:47 AM, Laszlo Ersek 写道:
> On 06/20/17 14:34, Heyi Guo wrote:
>> Is there any simple tool to parse ISO images (El Torito partition) and
>> identify whether it is EFI bootable?
> $ dumpet --iso Fedora-Server-dvd-aarch64-25-20161015.n.0.iso
>
>    Validation Entry:
>            Header Indicator: 0x01 (Validation Entry)
>            PlatformId: 0xef (EFI)                      <---------- [1]
>            ID: ""
>            Checksum: 0x66aa
>            Key bytes: 0x55aa
>    Boot Catalog Default Entry:
>            Entry is bootable
>            Boot Media emulation type: no emulation     <---------- [2]
>            Media load address: 0 (0x0000)
>            System type: 0 (0x00)
>            Load Sectors: 9208 (0x23f8)
>            Load LBA: 2456 (0x00000998)
>
> The source for dumpet is at <https://github.com/rhboot/dumpet>.
>
>> I think EFI bootable image should contain a FAT volume so that EFI can
>> load bootxx.efi file from the file system.
> For a large Wiki page on this, I can recommend:
> <https://fedoraproject.org/wiki/User:Pjones/BootableCDsForBIOSAndUEFI>.
>
> For a short summary, these are the commands you need, to format an
> EFI-bootable (and EFI-only) CD-ROM:
>
> (1) Create a non-partitioned FAT image in a file, with "mkdosfs -C", and
>      populate it with the "mtools" utilities.
>
>      For a heavier-weight (but also a lot more feature-ful) toolset, you
>      can also use libguestfs / guestfish.
>
> (2) Generate the ISO image like this:
>
>      genisoimage -input-charset ASCII -J -rational-rock \
>        -efi-boot "$FAT_IMAGE_FILE" -no-emul-boot \
>        -o "$ISO_IMAGE" -- "$FAT_IMAGE_FILE"
>
>      So what you do is, create an ISO9660 filesystem with the FAT image
>      file copied into it as a normal file (simply to the root directory).
>      You can enable Joliet and/or RockRidge extensions if you want to,
>      but those aren't necessary. Then, you set the EFI boot image name
>      with "-efi-boot" [1], and also specify that the boot image is a "no
>      emulation" [2] image
>      <https://en.wikipedia.org/wiki/El_Torito_(CD-ROM_standard)#Boot_modes>.
>
>> Several tools like mount in Linux will show all files together
>> including EFI/BOOT directory,
> That directory, displayed as part of the ISO9660 filesystem that was
> written to the ISO image / CD-ROM, is entirely irrelevant when it comes
> to UEFI-bootability. I doesn't even need to exist, and if it does, it's
> likely there only for convenience reasons (so that people don't have to
> run "dumpet" or similar tools to extract the FAT image first, and then
> the EFI binaries second, if they want to investigate the EFI binaries).
>
> For UEFI boot, only the ElTorito image matters.
>
>> so if an ISO image contains such files but not organizes the data in a
>> FAT sub-volume as EFI requires, I can't see any difference.
> In order to extract the ElTorito image(s), use "dumpet --dumpdisks", and
> then work on the extracted files with guestfish or mtools. For example:
>
> $ MTOOLS_SKIP_CHECK=1 mdir -i extracted.iso.0  -/ ::
>
> Thanks
> Laszlo