Re: [Gptfdisk-general] misreads NetBSD as FreeBSD
Brought to you by:
srs5694
Menu
▾
▴
Re: [Gptfdisk-general] misreads NetBSD as FreeBSD
|
From: Rod S. <rod...@ro...> - 2023-08-03 15:16:57
|
On 8/3/23 04:31, dch...@gm... wrote:
> Lately I also use gdisk, etc. Unlike fdisk, gdisk misreads my NetBSD
> partition as a FreeBSD one.
There's a lot you haven't stated that's likely relevant. For instance,
is the disk currently MBR or GPT? If the latter, was it once MBR, but
was converted to GPT; and if so, by what program? Is the fdisk you're
using from util-linux or based on libparted? What column(s) of output
are you reading in both fdisk and gdisk? Because I don't know the
answers to these questions, I can't give you an answer about what's
going on; however, I can say this....
On an MBR disk, FreeBSD and NetBSD can use the same partition type code
(0xA5), although NetBSD also has its own code (0xA9)[1]; however, on a
GPT disk, the two OSes each have their own set of unique GUIDs[2]. That
said, the MBR 0xA5 and 0xA9 codes are both most often used for a BSD
"disklabel," which holds sub-partitions, similar to an MBR extended
partition. Among the GPT type codes, AFAIK only FreeBSD's set includes
an explicit "disklabel" partition
(516E7CB4-6ECF-11D6-8FF8-00022D09712B); AFAIK, there is no NetBSD
equivalent to this in GPT. Because GPT fdisk does an automatic
conversion from MBR to GPT, when you read an MBR disk with a NetBSD 0xA5
partition with GPT fdisk, that partition will show up as a FreeBSD
partition, since 0xA5 is more strongly associated with FreeBSD than with
NetBSD. Also, in GPT fdisk, most a9xx codes get converted to unique
NetBSD codes; however, a900 (or 0xA9, when reading an MBR disk) gets
converted to 516E7CB4-6ECF-11D6-8FF8-00022D09712B, the FreeBSD disklabel
code, since the GPT type code list on Wikipedia[2] doesn't specify a
unique NetBSD disklabel type code, and I don't see anything labeled as a
"disklabel" code in the relevant NetBSD source code file[3], either.
It's possible that what you're seeing is a result of this, either on an
MBR disk or a disk converted to GPT from MBR. An fdisk that's based on
libparted, by contrast, would read the contents of the partition and
present a filesystem type rather than present the type code itself; and
util-linux fdisk would present the type code for an MBR partition,
rather than try to convert it to GPT, as GPT fdisk does.
If the disk was partitioned initially as a GPT disk, then I'd expect
that NetBSD's partitions should use native NetBSD type codes, which GPT
fdisk presents as a901 through a906. If one of the partitions hold an
old-style BSD "disklabel," then AFAIK there's no NetBSD-specific GPT
type code for that, so the best choice for the GPT partition type code
would be 516E7CB4-6ECF-11D6-8FF8-00022D09712B, which is officially a
FreeBSD type code, and is presented as such by both GPT fdisk and
util-linux fdisk. (I don't know offhand how a libparted-based fdisk
presents such a partition, if it's created in NetBSD.)
One more factor: The GPT fdisk output includes the partition name. If
the partition is created in gdisk, then gdisk sets this name to a
description that's tied to the type code, by default. For instance:
Number Start (sector) End (sector) Size Code Name
1 2048 30296063 14.4 GiB A500 FreeBSD disklabel
(That's two lines; the second one will likely wrap in this e-mail.)
If the type code is changed outside of GPT fdisk, the name may not be
updated. For instance, taking the above disk and changing the type code
in util-linux's fdisk to fdisk's 79 ("NetBSD FFS") results in it looking
like this in GPT fdisk:
Number Start (sector) End (sector) Size Code Name
1 2048 30296063 14.4 GiB A902 FreeBSD disklabel
Note that the type code has changed from A500 to A902, but the
partition's name remains "FreeBSD disklabel," although that's no longer
accurate. This is another strong possibility for what you're seeing. If
so, the solution is simply to update the partition's name in GPT fdisk
to something appropriate. This can be done with the "c" main-menu option
in gdisk. Note that util-linux fdisk does not present the partition name
in its main summary, although the information is available via the "i"
main-menu option.
[1] https://www.win.tue.nl/~aeb/partitions/partition_types-1.html
[2] https://en.wikipedia.org/wiki/GUID_Partition_Table
[3]
http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/sys/disklabel_gpt.h?rev=1.15&content-type=text/x-cvsweb-markup&f=h&only_with_tag=MAIN
--
Rod Smith
rod...@ro...
http://www.rodsbooks.com
|
