On 08/10/20 05:04, Gao, Zhichao wrote: > Andrew, > > Thanks for your info. I didn’t aware the partition driver is part of the UEFI > spec. And the order is mismatch between the code implementation and spec > description. > The order now is GPT > MBR > UDF( ISO 9660). I would send a patch to correct > it as it would both follow the spec and fix our issue.
Sounds good, thanks. Laszlo > > Thanks, > Zhichao > > From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Andrew Fish > via groups.io > Sent: Monday, August 10, 2020 5:15 AM > To: devel@edk2.groups.io; Gao, Zhichao <zhichao....@intel.com> > Cc: Ni, Ray <ray...@intel.com>; Laszlo Ersek <ler...@redhat.com>; Gary Lin > <g...@suse.com>; Wu, Hao A <hao.a...@intel.com> > Subject: Re: [edk2-devel] Partition issue with Linux Distribution iso image > > Zhichao, > > The discovery algorithm for partitions is defined in the UEFI Spec. > > 13.3.2 Partition Discovery > ... > > The following is the order in which a block device must be scanned to > determine if it contains partitions. > When a check for a valid partitioning scheme succeeds, the search terminates. > > 1) Check for GUID Partition Table Headers. > 2) Follow ISO-9660 specification to search for ISO-9660 volume structures on > the magic LBA. > 3) Check for an “El Torito” volume extension and follow the “El Torito” > CD-ROM specification. > 4) If none of the above, check LBA 0 for a legacy MBR partition table. > 5) No partition found on device. > > If a disk contains a recognized RAID structure (e.g. DDF structure as defined > in The Storage Networking Industry Association Common RAID Disk Data Format > Specification--see Glossary), the data on the disk must be ignored, unless > the driver is using the RAID structure to produce a logical RAID volume. > EFI supports the nesting of legacy MBR partitions, by allowing any legacy MBR > partition to contain more legacy MBR partitions. This is accomplished by > supporting the same partition discovery algorithm on every logical block > device. It should be noted that the GUID Partition Table does not allow > nesting of GUID Partition Table Headers. Nesting is not needed since a GUID > Partition Table Header can support an arbitrary number of partitions (the > addressability limits of a 64-bit LBA are the limiting factor). > > 13.3.2.1 ISO-9660 and El Torito > IS0-9660 is the industry standard low level format used on CD-ROM and > DVD-ROM. The CD-ROM format is completely described by the “El Torito” > Bootable CD-ROM Format Specification Version 1.0. To boot from a CD-ROM or > DVD-ROM in the boot services environment, an EFI System partition is stored > in a “no emulation” mode as defined by the “El Torito” specification. A > Platform ID of 0xEF indicates an EFI System Partition. The Platform ID is in > either the Section Header Entry or the Validation Entry of the Booting > Catalog as defined by the “El Torito” specification. EFI differs from “El > Torito” “no emulation” mode in that it does not load the “no emulation” image > into memory and jump to it. EFI interprets the “no emulation” image as an EFI > system partition. EFI interprets the Sector Count in the Initial/Default > Entry or the Section Header Entry to be the size of the EFI system partition. > If the value of Sector Count is set to 0 or 1, EFI will assume the system > partition consumes the space from the beginning of the “no emulation” image > to the end of the CD-ROM. > A DVD-ROM image formatted as required by the UDF 2.0 specification (OSTA > Universal Disk Format Specification, Revision 2.0) shall be booted by UEFI if: > • the DVD-ROM image conforms to the "UDF Bridge" format defined in the UDF > 2.0 specification, and > • the DVD-ROM image contains exactly one ISO-9660 file system, and > • the ISO-9660 file system conforms to the "El Torito" Bootable CD-ROM Format > Specification. > Booting from a DVD-ROM that satisfies the above requirements is accomplished > using the same methods as booting from a CD-ROM: the ISO-9660 file system > shall be booted. > Since the EFI file system definition does not use the same Initial/Default > entry as a legacy CD-ROM it is possible to boot personal computers using an > EFI CD-ROM or DVD-ROM. The inclusion of boot code for personal computers is > optional and not required by EFI. > > Thanks, > > Andrew Fish > > > On Aug 9, 2020, at 6:51 AM, Gao, Zhichao > <zhichao....@intel.com<mailto:zhichao....@intel.com>> wrote: > > Hi All, > > Some Linux Distribution ISO image would contain both Eltorito(iso 9660) > volume info and MBR table at the same time. That would cause the partition > check pass the MBR and ignore the UDF (Eltorito compatible) check. > There is a bug in the partition child handler: > https://bugzilla.tianocore.org/show_bug.cgi?id=2843. It would make the MBR > transfer the wrong device size. That cause the FAT driver fail to install the > FAT protocol onto the device. > But when I solve the issue, the EFI partition can be found as MBR FAT device. > That would cause another issue. Boot from the MBR FAT from ISO image is > different with boot from CD FAT. > Here is the difference: > Boot from MBR FAT: go to the grub terminal window. > Boot from CD FAT: go to the installation window. > I don’t know why the same grub image act different behaviors. But I believe > “Boot from CD FAT” is the right behavior. That means the ISO 9660 should not > be treated as MBR device in UEFI BIOS. > > So I would like to add a logic: the ISO image that contain both ISO 9660 > volume info and MBR partition, the partition driver would skip the MBR check > and continue to do the ISO 9660 check. There is a easy way to do this, i.e. > put the UDF (ISO 9660 compatible) before the MBR check. It means the > partition routine child handle would have a priority and the UDF (ISO 9660) > has high priority than the MBR. That would solve all the Linux Distribution > ISO image issue in my thought. > > I want to get some suggestion from the community before I sent the patch. > > Thanks, > Zhichao > > > > > -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#63910): https://edk2.groups.io/g/devel/message/63910 Mute This Topic: https://groups.io/mt/76084526/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
