On Wed, Dec 22, 2021 at 05:29:34PM +0100, Tilo Stritzky wrote:
> (With an MBR disk you could force feed a handcrafted disklabel but
> that won't work here because on a GPT disk without OpenBSD partition
> the disklabel and the primary GPT share a physical sector and that
> won't work.)
That is incorrect.
At one time, the disklabel program would try to write it to the second block,
I.E. the sector after the MBR. This would indeed fail if a GPT was already
there.
However, if you test this on OpenBSD 7.0-release, you will see that the
disklabel will happily be written elsewhere:
# dd if=/dev/zero of=/tmp/vd bs=1m count=512
# vnconfig vnd0 /tmp/vd
# fdisk -e vnd0 # Create a non-OpenBSD GPT partition
# disklabel -E vnd0 # Write the disklabel to the media
# hexdump -C /tmp/vd
00000000 ea 05 00 c0 07 8c c8 8e d0 bc fc ff 8e d8 b8 a0 |................|
00000010 07 8e c0 31 f6 31 ff b9 00 02 fc f3 a4 ea 22 00 |...1.1........".|
00000020 a0 07 1e 07 0e 1f b4 02 cd 16 a8 03 74 0d b0 07 |............t...|
00000030 e8 de 00 67 80 0d b4 01 00 00 01 f6 c2 80 75 08 |...g..........u.|
00000040 be 49 01 e8 bf 00 b2 80 be be 01 b9 04 00 8a 04 |.I..............|
00000050 3c 80 74 0f 83 c6 10 e2 f5 be 7d 01 e8 a6 00 fb |<.t.......}.....|
00000060 f4 eb fc 88 d0 24 0f 04 30 a2 3a 01 b0 34 28 c8 |.....$..0.:..4(.|
00000070 a2 47 01 56 be 2d 01 67 f6 05 b4 01 00 00 01 75 |.G.V.-.g.......u|
00000080 01 46 e8 80 00 5e 26 67 c7 05 fe 01 00 00 00 00 |.F...^&g........|
00000090 67 f6 05 b4 01 00 00 01 75 34 88 14 bb aa 55 b4 |g.......u4....U.|
000000a0 41 cd 13 8a 14 72 27 81 fb 55 aa 75 21 f6 c1 01 |A....r'..U.u!...|
000000b0 74 1c b0 2e e8 5a 00 66 8b 4c 08 67 66 89 0d 25 |t....Z.f.L.gf..%|
000000c0 01 00 00 56 b4 42 be 1d 01 cd 13 5e 73 1a b0 3b |...V.B.....^s..;|
000000d0 e8 3e 00 8a 74 01 8b 4c 02 b8 01 02 31 db cd 13 |.>..t..L....1...|
000000e0 73 06 be 65 01 e9 74 ff be 90 01 e8 17 00 26 67 |s..e..t.......&g|
000000f0 81 3d fe 01 00 00 55 aa 75 05 ea 00 7c 00 00 be |.=....U.u...|...|
00000100 74 01 e9 57 ff 50 fc ac 84 c0 74 0f e8 02 00 eb |t..W.P....t.....|
00000110 f6 50 53 b4 0e bb 01 00 cd 10 5b 58 c3 10 00 01 |.PS.......[X....|
00000120 00 00 00 c0 07 00 00 00 00 00 00 00 00 21 55 73 |.............!Us|
00000130 69 6e 67 20 64 72 69 76 65 20 58 2c 20 70 61 72 |ing drive X, par|
00000140 74 69 74 69 6f 6e 20 59 00 4d 42 52 20 6f 6e 20 |tition Y.MBR on |
00000150 66 6c 6f 70 70 79 20 6f 72 20 6f 6c 64 20 42 49 |floppy or old BI|
00000160 4f 53 0d 0a 00 0d 0a 52 65 61 64 20 65 72 72 6f |OS.....Read erro|
00000170 72 0d 0a 00 4e 6f 20 4f 2f 53 0d 0a 00 4e 6f 20 |r...No O/S...No |
00000180 61 63 74 69 76 65 20 70 61 72 74 69 74 69 6f 6e |active partition|
00000190 0d 0a 00 90 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000001a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000001b0 00 00 00 00 00 00 4f 78 00 00 00 00 00 00 00 ff |......Ox........|
000001c0 ff ff ee ff ff ff 01 00 00 00 ff ff ff ff 00 00 |................|
000001d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 aa |..............U.|
00000200 45 46 49 20 50 41 52 54 00 00 01 00 5c 00 00 00 |EFI PART....\...|
00000210 65 43 91 cc 00 00 00 00 01 00 00 00 00 00 00 00 |eC..............|
00000220 ff ff 0f 00 00 00 00 00 22 00 00 00 00 00 00 00 |........".......|
00000230 de ff 0f 00 00 00 00 00 f2 63 79 02 b9 99 39 48 |.........cy...9H|
00000240 99 97 2e 77 79 98 35 f5 02 00 00 00 00 00 00 00 |...wy.5.........|
00000250 80 00 00 00 80 00 00 00 a7 be 55 7f 00 00 00 00 |..........U.....|
00000260 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00000400 a2 a0 d0 eb e5 b9 33 44 87 c0 68 b6 b7 26 99 c7 |......3D..h..&..|
00000410 41 60 b8 b5 2b 54 10 41 ba 44 ee f8 3e 55 7b 50 |A`..+T.A.D..>U{P|
00000420 22 00 00 00 00 00 00 00 de ff 0f 00 00 00 00 00 |"...............|
00000430 00 00 00 00 00 00 00 00 66 00 6f 00 6f 00 00 00 |........f.o.o...|
00000440 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
vvv BSD disklabel here vvv
00004600 57 45 56 82 0c 00 00 00 76 6e 64 20 64 65 76 69 |WEV.....vnd devi|
00004610 63 65 00 00 00 00 00 00 66 69 63 74 69 74 69 6f |ce......fictitio|
00004620 75 73 00 00 00 00 00 00 00 02 00 00 64 00 00 00 |us..........d...|
00004630 01 00 00 00 f5 28 00 00 64 00 00 00 00 00 10 00 |.....(..d.......|
00004640 38 88 61 0e cf 69 90 5f 00 00 00 00 00 00 00 00 |8.a..i._........|
00004650 22 00 00 00 df ff 0f 00 00 00 00 00 00 00 00 00 |"...............|
00004660 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00004670 00 00 01 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00004680 00 00 00 00 57 45 56 82 97 e8 10 00 00 20 00 00 |....WEV...... ..|
00004690 00 00 01 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000046a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000046b0 00 00 00 00 00 00 10 00 00 00 00 00 00 00 00 00 |................|
000046c0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00004710 00 00 00 00 bd ff 0f 00 22 00 00 00 00 00 00 00 |........".......|
00004720 08 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00004730 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
^^^ BSD disklabel here ^^^
*
1fffbe00 a2 a0 d0 eb e5 b9 33 44 87 c0 68 b6 b7 26 99 c7 |......3D..h..&..|
1fffbe10 41 60 b8 b5 2b 54 10 41 ba 44 ee f8 3e 55 7b 50 |A`..+T.A.D..>U{P|
1fffbe20 22 00 00 00 00 00 00 00 de ff 0f 00 00 00 00 00 |"...............|
1fffbe30 00 00 00 00 00 00 00 00 66 00 6f 00 6f 00 00 00 |........f.o.o...|
1fffbe40 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
1ffffe00 45 46 49 20 50 41 52 54 00 00 01 00 5c 00 00 00 |EFI PART....\...|
1ffffe10 61 46 22 48 00 00 00 00 ff ff 0f 00 00 00 00 00 |aF"H............|
1ffffe20 01 00 00 00 00 00 00 00 22 00 00 00 00 00 00 00 |........".......|
1ffffe30 de ff 0f 00 00 00 00 00 f2 63 79 02 b9 99 39 48 |.........cy...9H|
1ffffe40 99 97 2e 77 79 98 35 f5 df ff 0f 00 00 00 00 00 |...wy.5.........|
1ffffe50 80 00 00 00 80 00 00 00 a7 be 55 7f 00 00 00 00 |..........U.....|
1ffffe60 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
20000000
