grub-probe: unknown filesystem (label checksum failed) when not using whole-disk setup

[cyphar]

If you create a grub2-compliant pool on a partition (rather than using the whole disk), grub2-probe fails to recognise it as a ZFS pool because of an internal checksum validation error.

Using a whole-disk pool:

% wipefs -a /dev/sdX*
% sgdisk --zap-all /dev/sdX
% zpool create -o compatibility=grub2 -O mountpoint=/boot -R /mnt bpool /dev/sdX
% grub2-probe /mnt/boot
zfs

Using a partition:

% wipefs -a /dev/sdX*
% sgdisk --zap-all /dev/sdX
% sgdisk -n 1:0:0 -t 1:be00 /dev/sdX
% zpool create -o compatibility=grub2 -O mountpoint=/boot -R /mnt bpool /dev/sdX1
% grub2-probe /mnt/boot
grub2-probe: error: ../grub-core/kern/fs.c:123:unknown filesystem.

grub2-probe -vv /mnt/boot

grub2-probe: info: cannot open `/boot/grub2/device.map': No such file or directory.
grub2-probe: info: /dev/sda1 is not present.
grub2-probe: info: Looking for /dev/sda1.
grub2-probe: info: /dev/sda is a parent of /dev/sda1.
grub2-probe: info: /dev/sda1 starts from 2048.
grub2-probe: info: opening the device hostdisk//dev/sda.
grub-core/kern/disk.c:196:disk: Opening `hostdisk//dev/sda'...
grub2-probe: info: drive = 0.
grub2-probe: info: the size of hostdisk//dev/sda is 976773168.
grub-core/kern/disk.c:196:disk: Opening `hostdisk//dev/sda'...
grub2-probe: info: drive = 0.
grub2-probe: info: the size of hostdisk//dev/sda is 976773168.
grub-core/disk/diskfilter.c:149:diskfilter: Scanning for DISKFILTER devices on disk hostdisk//dev/sda
grub2-probe: info: Scanning for DISKFILTER devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for mdraid1x devices on disk hostdisk//dev/sda.
grub-core/osdep/hostdisk.c:379:hostdisk: opening the device `/dev/sda' in open_device()
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda'
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda'
grub2-probe: info: Scanning for mdraid09 devices on disk hostdisk//dev/sda.
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda'
grub2-probe: info: Scanning for mdraid09_be devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for dmraid_nv devices on disk hostdisk//dev/sda.
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda'
grub2-probe: info: Scanning for ldm devices on disk hostdisk//dev/sda.
grub2-probe: info: scanning hostdisk//dev/sda for LDM.
grub-core/partmap/gpt.c:93:gpt: Read a valid GPT header
grub-core/partmap/gpt.c:115:gpt: GPT entry 0: start=2048, length=976771087
grub2-probe: info: no LDM signature found.
grub2-probe: info: Scanning for lvm devices on disk hostdisk//dev/sda.
grub2-probe: info: no LVM signature found.
grub-core/partmap/gpt.c:93:gpt: Read a valid GPT header
grub-core/partmap/gpt.c:115:gpt: GPT entry 0: start=2048, length=976771087
grub-core/disk/diskfilter.c:149:diskfilter: Scanning for DISKFILTER devices on disk hostdisk//dev/sda
grub2-probe: info: Scanning for DISKFILTER devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for mdraid1x devices on disk hostdisk//dev/sda.
grub-core/osdep/hostdisk.c:379:hostdisk: opening the device `/dev/sda1' in open_device()
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub2-probe: info: Scanning for mdraid09 devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for mdraid09_be devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for dmraid_nv devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for ldm devices on disk hostdisk//dev/sda.
grub2-probe: info: scanning hostdisk//dev/sda for LDM.
grub2-probe: info: no LDM signature found.
grub2-probe: info: Scanning for lvm devices on disk hostdisk//dev/sda.
grub2-probe: info: no LVM signature found.
grub-core/partmap/dfly.c:69:partition: bad magic (found 0x0; wanted 0xc4464c59)
grub-core/partmap/apple.c:120:partition: bad magic (found 0x0; wanted 0x4552)
grub-core/partmap/dfly.c:69:partition: bad magic (found 0x20494645; wanted 0xc4464c59)
grub-core/partmap/apple.c:120:partition: bad magic (found 0x0; wanted 0x4552)
grub-core/kern/disk.c:299:disk: Closing `hostdisk//dev/sda'.
grub-core/partmap/gpt.c:93:gpt: Read a valid GPT header
grub-core/partmap/gpt.c:115:gpt: GPT entry 0: start=2048, length=976771087
grub2-probe: info: Partition 0 starts from 2048.
grub-core/kern/disk.c:299:disk: Closing `hostdisk//dev/sda'.
grub2-probe: info: /dev/sda1 is present.
grub2-probe: info: Looking for /dev/sda1.
grub2-probe: info: /dev/sda is a parent of /dev/sda1.
grub2-probe: info: /dev/sda1 starts from 2048.
grub2-probe: info: opening the device hostdisk//dev/sda.
grub-core/kern/disk.c:196:disk: Opening `hostdisk//dev/sda'...
grub2-probe: info: drive = 0.
grub2-probe: info: the size of hostdisk//dev/sda is 976773168.
grub-core/kern/disk.c:196:disk: Opening `hostdisk//dev/sda'...
grub2-probe: info: drive = 0.
grub2-probe: info: the size of hostdisk//dev/sda is 976773168.
grub-core/disk/diskfilter.c:149:diskfilter: Scanning for DISKFILTER devices on disk hostdisk//dev/sda
grub2-probe: info: Scanning for DISKFILTER devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for mdraid1x devices on disk hostdisk//dev/sda.
grub-core/osdep/hostdisk.c:379:hostdisk: opening the device `/dev/sda' in open_device()
grub2-probe: info: Scanning for mdraid09 devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for mdraid09_be devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for dmraid_nv devices on disk hostdisk//dev/sda.
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda'
grub2-probe: info: Scanning for ldm devices on disk hostdisk//dev/sda.
grub2-probe: info: scanning hostdisk//dev/sda for LDM.
grub-core/partmap/gpt.c:93:gpt: Read a valid GPT header
grub-core/partmap/gpt.c:115:gpt: GPT entry 0: start=2048, length=976771087
grub2-probe: info: no LDM signature found.
grub2-probe: info: Scanning for lvm devices on disk hostdisk//dev/sda.
grub2-probe: info: no LVM signature found.
grub-core/partmap/gpt.c:93:gpt: Read a valid GPT header
grub-core/partmap/gpt.c:115:gpt: GPT entry 0: start=2048, length=976771087
grub-core/disk/diskfilter.c:149:diskfilter: Scanning for DISKFILTER devices on disk hostdisk//dev/sda
grub2-probe: info: Scanning for DISKFILTER devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for mdraid1x devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for mdraid09 devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for mdraid09_be devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for dmraid_nv devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for ldm devices on disk hostdisk//dev/sda.
grub2-probe: info: scanning hostdisk//dev/sda for LDM.
grub2-probe: info: no LDM signature found.
grub2-probe: info: Scanning for lvm devices on disk hostdisk//dev/sda.
grub2-probe: info: no LVM signature found.
grub-core/partmap/dfly.c:69:partition: bad magic (found 0x0; wanted 0xc4464c59)
grub-core/partmap/apple.c:120:partition: bad magic (found 0x0; wanted 0x4552)
grub-core/partmap/dfly.c:69:partition: bad magic (found 0x20494645; wanted 0xc4464c59)
grub-core/partmap/apple.c:120:partition: bad magic (found 0x0; wanted 0x4552)
grub-core/kern/disk.c:299:disk: Closing `hostdisk//dev/sda'.
grub-core/partmap/gpt.c:93:gpt: Read a valid GPT header
grub-core/partmap/gpt.c:115:gpt: GPT entry 0: start=2048, length=976771087
grub2-probe: info: Partition 0 starts from 2048.
grub-core/kern/disk.c:299:disk: Closing `hostdisk//dev/sda'.
grub2-probe: info: /dev/sda1 is present.
grub2-probe: info: Looking for /dev/sda1.
grub2-probe: info: /dev/sda is a parent of /dev/sda1.
grub2-probe: info: /dev/sda1 starts from 2048.
grub2-probe: info: opening the device hostdisk//dev/sda.
grub-core/kern/disk.c:196:disk: Opening `hostdisk//dev/sda'...
grub2-probe: info: drive = 0.
grub2-probe: info: the size of hostdisk//dev/sda is 976773168.
grub-core/kern/disk.c:196:disk: Opening `hostdisk//dev/sda'...
grub2-probe: info: drive = 0.
grub2-probe: info: the size of hostdisk//dev/sda is 976773168.
grub-core/disk/diskfilter.c:149:diskfilter: Scanning for DISKFILTER devices on disk hostdisk//dev/sda
grub2-probe: info: Scanning for DISKFILTER devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for mdraid1x devices on disk hostdisk//dev/sda.
grub-core/osdep/hostdisk.c:379:hostdisk: opening the device `/dev/sda' in open_device()
grub2-probe: info: Scanning for mdraid09 devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for mdraid09_be devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for dmraid_nv devices on disk hostdisk//dev/sda.
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda'
grub2-probe: info: Scanning for ldm devices on disk hostdisk//dev/sda.
grub2-probe: info: scanning hostdisk//dev/sda for LDM.
grub-core/partmap/gpt.c:93:gpt: Read a valid GPT header
grub-core/partmap/gpt.c:115:gpt: GPT entry 0: start=2048, length=976771087
grub2-probe: info: no LDM signature found.
grub2-probe: info: Scanning for lvm devices on disk hostdisk//dev/sda.
grub2-probe: info: no LVM signature found.
grub-core/partmap/gpt.c:93:gpt: Read a valid GPT header
grub-core/partmap/gpt.c:115:gpt: GPT entry 0: start=2048, length=976771087
grub-core/disk/diskfilter.c:149:diskfilter: Scanning for DISKFILTER devices on disk hostdisk//dev/sda
grub2-probe: info: Scanning for DISKFILTER devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for mdraid1x devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for mdraid09 devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for mdraid09_be devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for dmraid_nv devices on disk hostdisk//dev/sda.
grub2-probe: info: Scanning for ldm devices on disk hostdisk//dev/sda.
grub2-probe: info: scanning hostdisk//dev/sda for LDM.
grub2-probe: info: no LDM signature found.
grub2-probe: info: Scanning for lvm devices on disk hostdisk//dev/sda.
grub2-probe: info: no LVM signature found.
grub-core/partmap/dfly.c:69:partition: bad magic (found 0x0; wanted 0xc4464c59)
grub-core/partmap/apple.c:120:partition: bad magic (found 0x0; wanted 0x4552)
grub-core/partmap/dfly.c:69:partition: bad magic (found 0x20494645; wanted 0xc4464c59)
grub-core/partmap/apple.c:120:partition: bad magic (found 0x0; wanted 0x4552)
grub-core/kern/disk.c:299:disk: Closing `hostdisk//dev/sda'.
grub-core/partmap/gpt.c:93:gpt: Read a valid GPT header
grub-core/partmap/gpt.c:115:gpt: GPT entry 0: start=2048, length=976771087
grub2-probe: info: Partition 0 starts from 2048.
grub-core/kern/disk.c:299:disk: Closing `hostdisk//dev/sda'.
grub2-probe: info: opening hostdisk//dev/sda,gpt1.
grub-core/kern/disk.c:196:disk: Opening `hostdisk//dev/sda,gpt1'...
grub2-probe: info: drive = 0.
grub2-probe: info: the size of hostdisk//dev/sda is 976773168.
grub-core/partmap/gpt.c:93:gpt: Read a valid GPT header
grub-core/partmap/gpt.c:115:gpt: GPT entry 0: start=2048, length=976771087
grub-core/kern/fs.c:57:fs: Detecting zfs...
grub-core/osdep/hostdisk.c:379:hostdisk: opening the device `/dev/sda1' in open_device()
grub-core/fs/zfs/zfs.c:1201:zfs: label ok 0
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/fs/zfs/zfs.c:1016:zfs: check 2 passed
grub-core/fs/zfs/zfs.c:1027:zfs: check 3 passed
grub-core/fs/zfs/zfs.c:1034:zfs: check 4 passed
grub-core/fs/zfs/zfs.c:1044:zfs: check 6 passed
grub-core/fs/zfs/zfs.c:1052:zfs: check 7 passed
grub-core/fs/zfs/zfs.c:1063:zfs: check 8 passed
grub-core/fs/zfs/zfs.c:1073:zfs: check 9 passed
grub-core/fs/zfs/zfs.c:1095:zfs: check 11 passed
grub-core/fs/zfs/zfs.c:1121:zfs: check 10 passed
grub-core/fs/zfs/zfs.c:1137:zfs: str=com.delphix:hole_birth
grub-core/fs/zfs/zfs.c:1137:zfs: str=com.delphix:embedded_data
grub-core/fs/zfs/zfs.c:1146:zfs: check 12 passed (feature flags)
grub-core/fs/zfs/zfs.c:448:zfs: checksum label verification failed
grub-core/fs/zfs/zfs.c:449:zfs: actual checksum a6c1dcddf6578713 400c5e24f09f7a77 5ee7ed3bd9fb859a e318d1ad525e3ec8
grub-core/fs/zfs/zfs.c:454:zfs: expected checksum f88b8053263128a6 419f972d30233a0d 2ab648c07d4da961 039debc2f86473ce
grub-core/fs/zfs/zfs.c:448:zfs: checksum label verification failed
grub-core/fs/zfs/zfs.c:449:zfs: actual checksum 6b4d18b98d4d1f9f e3096cacac771612 82938c4109083f96 587a6c4ec237fd1f
grub-core/fs/zfs/zfs.c:454:zfs: expected checksum b306d82dc1196a77 09337ef2034812ac 8d8bf30ccd3ff280 b28197f2dd92950f
grub-core/fs/zfs/zfs.c:1213:zfs: No uberblock found
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/fs/zfs/zfs.c:1201:zfs: label ok 1
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/fs/zfs/zfs.c:1016:zfs: check 2 passed
grub-core/fs/zfs/zfs.c:1027:zfs: check 3 passed
grub-core/fs/zfs/zfs.c:1034:zfs: check 4 passed
grub-core/fs/zfs/zfs.c:1044:zfs: check 6 passed
grub-core/fs/zfs/zfs.c:1052:zfs: check 7 passed
grub-core/fs/zfs/zfs.c:1063:zfs: check 8 passed
grub-core/fs/zfs/zfs.c:1073:zfs: check 9 passed
grub-core/fs/zfs/zfs.c:1095:zfs: check 11 passed
grub-core/fs/zfs/zfs.c:1121:zfs: check 10 passed
grub-core/fs/zfs/zfs.c:1137:zfs: str=com.delphix:hole_birth
grub-core/fs/zfs/zfs.c:1137:zfs: str=com.delphix:embedded_data
grub-core/fs/zfs/zfs.c:1146:zfs: check 12 passed (feature flags)
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/fs/zfs/zfs.c:1201:zfs: label ok 2
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/fs/zfs/zfs.c:1201:zfs: label ok 3
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/zfs/zfs.c:1238:couldn't find a valid label.
grub-core/kern/fs.c:81:fs: zfs detection failed.
grub-core/kern/fs.c:57:fs: Detecting xfs...
grub-core/fs/xfs.c:1032:xfs: Reading sb
grub-core/fs/xfs.c:303:xfs: Validating superblock
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/xfs.c:309:not a XFS filesystem.
grub-core/kern/fs.c:81:fs: xfs detection failed.
grub-core/kern/fs.c:57:fs: Detecting ufs2...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/ufs.c:633:not an ufs2 filesystem.
grub-core/kern/fs.c:81:fs: ufs2 detection failed.
grub-core/kern/fs.c:57:fs: Detecting ufs1_be...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/ufs.c:635:not an ufs1 filesystem.
grub-core/kern/fs.c:81:fs: ufs1_be detection failed.
grub-core/kern/fs.c:57:fs: Detecting ufs1...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/ufs.c:635:not an ufs1 filesystem.
grub-core/kern/fs.c:81:fs: ufs1 detection failed.
grub-core/kern/fs.c:57:fs: Detecting udf...
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/udf.c:743:not an UDF filesystem.
grub-core/kern/fs.c:81:fs: udf detection failed.
grub-core/kern/fs.c:57:fs: Detecting tarfs...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/tar.c:261:not a tarfs filesystem.
grub-core/kern/fs.c:81:fs: tarfs detection failed.
grub-core/kern/fs.c:57:fs: Detecting squash4...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/squash4.c:398:not squash4.
grub-core/kern/fs.c:81:fs: squash4 detection failed.
grub-core/kern/fs.c:57:fs: Detecting sfs...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/sfs.c:395:not a SFS filesystem.
grub-core/kern/fs.c:81:fs: sfs detection failed.
grub-core/kern/fs.c:57:fs: Detecting romfs...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/romfs.c:108:too short filesystem.
grub-core/kern/fs.c:81:fs: romfs detection failed.
grub-core/kern/fs.c:57:fs: Detecting reiserfs...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/reiserfs.c:703:not a ReiserFS filesystem.
grub-core/kern/fs.c:81:fs: reiserfs detection failed.
grub-core/kern/fs.c:57:fs: Detecting procfs...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/proc.c:145:not a procfs.
grub-core/kern/fs.c:81:fs: procfs detection failed.
grub-core/kern/fs.c:57:fs: Detecting odc...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/cpio_common.c:169:not a odc filesystem.
grub-core/kern/fs.c:81:fs: odc detection failed.
grub-core/kern/fs.c:57:fs: Detecting ntfs...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/ntfs.c:1044:not an ntfs filesystem.
grub-core/kern/fs.c:81:fs: ntfs detection failed.
grub-core/kern/fs.c:57:fs: Detecting nilfs2...
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/nilfs2.c:795:not a nilfs2 filesystem.
grub-core/kern/fs.c:81:fs: nilfs2 detection failed.
grub-core/kern/fs.c:57:fs: Detecting newc...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/cpio_common.c:169:not a newc filesystem.
grub-core/kern/fs.c:81:fs: newc detection failed.
grub-core/kern/fs.c:57:fs: Detecting jfs...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/jfs.c:387:not a JFS filesystem.
grub-core/kern/fs.c:81:fs: jfs detection failed.
grub-core/kern/fs.c:57:fs: Detecting iso9660...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/iso9660.c:522:not a ISO9660 filesystem.
grub-core/kern/fs.c:81:fs: iso9660 detection failed.
grub-core/kern/fs.c:57:fs: Detecting hfsplus...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/hfsplus.c:306:not a HFS+ filesystem.
grub-core/kern/fs.c:81:fs: hfsplus detection failed.
grub-core/kern/fs.c:57:fs: Detecting hfs...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/hfs.c:338:not an HFS filesystem.
grub-core/kern/fs.c:81:fs: hfs detection failed.
grub-core/kern/fs.c:57:fs: Detecting fat...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/fat.c:448:not a FAT filesystem.
grub-core/kern/fs.c:81:fs: fat detection failed.
grub-core/kern/fs.c:57:fs: Detecting f2fs...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/f2fs.c:839:not a F2FS filesystem (no superblock).
grub-core/kern/fs.c:81:fs: f2fs detection failed.
grub-core/kern/fs.c:57:fs: Detecting ext2...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/ext2.c:677:not an ext2 filesystem.
grub-core/kern/fs.c:81:fs: ext2 detection failed.
grub-core/kern/fs.c:57:fs: Detecting exfat...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/fat.c:448:not a FAT filesystem.
grub-core/kern/fs.c:81:fs: exfat detection failed.
grub-core/kern/fs.c:57:fs: Detecting cpiofs_be...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/cpio_common.c:169:not a cpiofs_be filesystem.
grub-core/kern/fs.c:81:fs: cpiofs_be detection failed.
grub-core/kern/fs.c:57:fs: Detecting cpiofs...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/cpio_common.c:169:not a cpiofs filesystem.
grub-core/kern/fs.c:81:fs: cpiofs detection failed.
grub-core/kern/fs.c:57:fs: Detecting cbfs...
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/kern/disk.c:424:disk: Read out of range: sector 0x3a38580f (../grub-core/kern/disk_common.c:26:attempt to read or write outside of partition).
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/cbfs.c:200:not a cbfs filesystem.
grub-core/kern/fs.c:81:fs: cbfs detection failed.
grub-core/kern/fs.c:57:fs: Detecting btrfs...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/btrfs.c:303:not a Btrfs filesystem.
grub-core/kern/fs.c:81:fs: btrfs detection failed.
grub-core/kern/fs.c:57:fs: Detecting bfs...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/bfs.c:849:not a BFS filesystem.
grub-core/kern/fs.c:81:fs: bfs detection failed.
grub-core/kern/fs.c:57:fs: Detecting afs...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/bfs.c:849:not an AFS filesystem.
grub-core/kern/fs.c:81:fs: afs detection failed.
grub-core/kern/fs.c:57:fs: Detecting affs...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/affs.c:275:not an AFFS filesystem.
grub-core/kern/fs.c:81:fs: affs detection failed.
grub-core/kern/fs.c:57:fs: Detecting minix_be...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/minix.c:555:not a minix filesystem.
grub-core/kern/fs.c:81:fs: minix_be detection failed.
grub-core/kern/fs.c:57:fs: Detecting minix3_be...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/minix.c:551:not a minix3 filesystem.
grub-core/kern/fs.c:81:fs: minix3_be detection failed.
grub-core/kern/fs.c:57:fs: Detecting minix3...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/minix.c:551:not a minix3 filesystem.
grub-core/kern/fs.c:81:fs: minix3 detection failed.
grub-core/kern/fs.c:57:fs: Detecting minix2_be...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/minix.c:553:not a minix2 filesystem.
grub-core/kern/fs.c:81:fs: minix2_be detection failed.
grub-core/kern/fs.c:57:fs: Detecting minix2...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/minix.c:553:not a minix2 filesystem.
grub-core/kern/fs.c:81:fs: minix2 detection failed.
grub-core/kern/fs.c:57:fs: Detecting minix...
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/minix.c:555:not a minix filesystem.
grub-core/kern/fs.c:81:fs: minix detection failed.
grub2-probe: error: ../grub-core/kern/fs.c:123:unknown filesystem.

The key part of the log is this bit, which shows that grub thinks there is a checksum error (checksum label verification failed):

grub-core/partmap/gpt.c:93:gpt: Read a valid GPT header
grub-core/partmap/gpt.c:115:gpt: GPT entry 0: start=2048, length=976771087
grub2-probe: info: Partition 0 starts from 2048.
grub-core/kern/disk.c:299:disk: Closing `hostdisk//dev/sda'.
grub2-probe: info: opening hostdisk//dev/sda,gpt1.
grub-core/kern/disk.c:196:disk: Opening `hostdisk//dev/sda,gpt1'...
grub2-probe: info: drive = 0.
grub2-probe: info: the size of hostdisk//dev/sda is 976773168.
grub-core/partmap/gpt.c:93:gpt: Read a valid GPT header
grub-core/partmap/gpt.c:115:gpt: GPT entry 0: start=2048, length=976771087
grub-core/kern/fs.c:57:fs: Detecting zfs...
grub-core/osdep/hostdisk.c:379:hostdisk: opening the device `/dev/sda1' in open_device()
grub-core/fs/zfs/zfs.c:1201:zfs: label ok 0
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/fs/zfs/zfs.c:1016:zfs: check 2 passed
grub-core/fs/zfs/zfs.c:1027:zfs: check 3 passed
grub-core/fs/zfs/zfs.c:1034:zfs: check 4 passed
grub-core/fs/zfs/zfs.c:1044:zfs: check 6 passed
grub-core/fs/zfs/zfs.c:1052:zfs: check 7 passed
grub-core/fs/zfs/zfs.c:1063:zfs: check 8 passed
grub-core/fs/zfs/zfs.c:1073:zfs: check 9 passed
grub-core/fs/zfs/zfs.c:1095:zfs: check 11 passed
grub-core/fs/zfs/zfs.c:1121:zfs: check 10 passed
grub-core/fs/zfs/zfs.c:1137:zfs: str=com.delphix:hole_birth
grub-core/fs/zfs/zfs.c:1137:zfs: str=com.delphix:embedded_data
grub-core/fs/zfs/zfs.c:1146:zfs: check 12 passed (feature flags)
grub-core/fs/zfs/zfs.c:448:zfs: checksum label verification failed
grub-core/fs/zfs/zfs.c:449:zfs: actual checksum a6c1dcddf6578713 400c5e24f09f7a77 5ee7ed3bd9fb859a e318d1ad525e3ec8
grub-core/fs/zfs/zfs.c:454:zfs: expected checksum f88b8053263128a6 419f972d30233a0d 2ab648c07d4da961 039debc2f86473ce
grub-core/fs/zfs/zfs.c:448:zfs: checksum label verification failed
grub-core/fs/zfs/zfs.c:449:zfs: actual checksum 6b4d18b98d4d1f9f e3096cacac771612 82938c4109083f96 587a6c4ec237fd1f
grub-core/fs/zfs/zfs.c:454:zfs: expected checksum b306d82dc1196a77 09337ef2034812ac 8d8bf30ccd3ff280 b28197f2dd92950f
grub-core/fs/zfs/zfs.c:1213:zfs: No uberblock found
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/fs/zfs/zfs.c:1201:zfs: label ok 1
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/fs/zfs/zfs.c:1016:zfs: check 2 passed
grub-core/fs/zfs/zfs.c:1027:zfs: check 3 passed
grub-core/fs/zfs/zfs.c:1034:zfs: check 4 passed
grub-core/fs/zfs/zfs.c:1044:zfs: check 6 passed
grub-core/fs/zfs/zfs.c:1052:zfs: check 7 passed
grub-core/fs/zfs/zfs.c:1063:zfs: check 8 passed
grub-core/fs/zfs/zfs.c:1073:zfs: check 9 passed
grub-core/fs/zfs/zfs.c:1095:zfs: check 11 passed
grub-core/fs/zfs/zfs.c:1121:zfs: check 10 passed
grub-core/fs/zfs/zfs.c:1137:zfs: str=com.delphix:hole_birth
grub-core/fs/zfs/zfs.c:1137:zfs: str=com.delphix:embedded_data
grub-core/fs/zfs/zfs.c:1146:zfs: check 12 passed (feature flags)
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/fs/zfs/zfs.c:1201:zfs: label ok 2
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/fs/zfs/zfs.c:1201:zfs: label ok 3
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/osdep/hostdisk.c:358:hostdisk: reusing open device `/dev/sda1'
grub-core/kern/fs.c:80:fs: error: ../grub-core/fs/zfs/zfs.c:1238:couldn't find a valid label.
grub-core/kern/fs.c:81:fs: zfs detection failed.

This happens with the latest grub2, but also if you download the latest HEAD (i.e. upstream grub) you get the same results.

% grub2-probe --version
grub2-probe (GRUB2) 2.12

This also happens if you do the whole complicated procedure for a bpool pool as outlined in the documentation, but this is a minimal reproducer. I'm guessing that grub2-probe failing is not an issue for a bpool setup in general, because other people appear to have working setups despite the fact that the documentation says to run grub2-probe and it seems this has never worked for the setup described in the documentation.

My main questions are:

1. Does it seem like this is a fairly "obvious" issue (maybe with partitions the offsets calculated by grub are wrong and it's just a matter of adjusting the offset calculation)?
2. This also causes grub2-install to fail with the same error. Is there a workaround (--skip-fs-probe doesn't do anything) / should I just skip using a /boot pool and go to mdraid for /boot? Should the docs reflect the fact that the current recommended setup doesn't work?