Device node major comes out wrong on HFS+ under linux

Hi.

Executive summary:

/dev/null:
osx: crw-rw-rw- 1 root wheel 1, 3 Oct 13 04:12 null
linux: crw-rw-rw- 1 root root 16, 3 Oct 13 02:12 /dev/null

/dev/console:
osx: crw------- 1 root wheel 5, 1 Oct 13 04:12 console
linux: crw------- 1 root root 80, 1 Oct 13 02:12 /dev/console

/dev/sda4:
osx: brw-r----- 1 root wheel 8, 4 Oct 13 04:12 sda4
linux: brw-r----- 1 root root 128, 4 Oct 13 02:12 /dev/sda4

Details:

I am slowly figuring out how to boot linux on my shiny new macbook air.

The actual *booting* bit turns out to be incredibly easy with rEFIt, keithp's macbook air tree, and mfleming's efi stub tree. (3.1.0-ish) Just pop a suitable kernel somewhere rEFIt can see it, and off you go. No mucking with bootloaders or repartitioning with esoteric tools and options. Slick. Got to use a built-in kernel command line, though.

Shrinking the existing OSX HFS+ partition and adding another for a linux root fs from within OSX also turned out to be a breeze.

I decided to give HFS+ a go for the root fs, just for a POC. (I'll make an initramfs for making a sane fs. Would be cooler to do everything from within OSX, and just reboot straight into Linux.)

Untarring a root fs on a my new HFS+ filesystem was straightforward. I *do* get a warning from OSX' tar when creating the devicenodes, but the nodes are created with the correct perms and major/minor.

tar: qtn_file_apply_to_path(./dev/console): Operation not permitted results in (when viewed from OSX):

crw------- 1 root wheel 5, 1 Oct 13 04:12 dev/console
which nicely reflects what the source filesystem has.

Booting a linux kernel (with init=/bin/sh) results in:
crw------- 1 root wheel 80, 1 Oct 13 02:12 /dev/console

Clearly a Major bug. ("ka-pisch".....)

Looks like an endianness issue at hand here:
1 p
1
16 p
10000

5 p
101
80 p
1010000

8 p
1000
128 p
10000000

Good thing I didn't end up trying to dial out through my HDD....

Anyone care to squash this bug, please?

Dag B

Am Samstag, den 15.10.2011, 20:04 +0200 schrieb DagB:

This is not a bug. Linux uses a 12/20 split for major and minor device ids and the xnu kernel uses a 8/24 split:

8, 4
00001000 000000000000000000000100
= 128, 4
000010000000 00000000000000000100

with kind regards
thomas