Re: grub-probe for nested BSD partition on Linux

[Andrei Borzenkov]

01.03.2017 01:05, Lennart Sorensen пишет:
> On Tue, Feb 28, 2017 at 09:50:27PM +0300, Andrei Borzenkov wrote:
>> 28.02.2017 21:31, Lennart Sorensen пишет:
>>> On Tue, Feb 28, 2017 at 08:13:53PM +0300, Andrei Borzenkov wrote:
>>>> Sorry? vda7 is 256M, how can you suddenly pretend it is 2G?
>>>>
>>>> 10:~ # fdisk -l /dev/vda
>>>> Disk /dev/vda: 5 GiB, 5368709120 bytes, 10485760 sectors
>>>> Units: sectors of 1 * 512 = 512 bytes
>>>> Sector size (logical/physical): 512 bytes / 512 bytes
>>>> I/O size (minimum/optimal): 512 bytes / 512 bytes
>>>> Disklabel type: dos
>>>> Disk identifier: 0x882b18da
>>>>
>>>> Device     Boot   Start      End Sectors  Size Id Type
>>>> /dev/vda1          2048  2099199 2097152    1G 83 Linux
>>>> /dev/vda2       2099200  6293503 4194304    2G a6 OpenBSD
>>>> /dev/vda3       6293504 10485759 4192256    2G  5 Extended
>>>> /dev/vda5       6295552  6819839  524288  256M 83 Linux
>>>> /dev/vda6       6821888  7346175  524288  256M 83 Linux
>>>> 10:~ # fdisk -l /dev/vda2
>>>> Disk /dev/vda2: 2 GiB, 2147483648 bytes, 4194304 sectors
>>>> Geometry: 16 heads, 63 sectors/track, 10402 cylinders
>>>> Units: sectors of 1 * 512 = 512 bytes
>>>> Sector size (logical/physical): 512 bytes / 512 bytes
>>>> I/O size (minimum/optimal): 512 bytes / 512 bytes
>>>> Disklabel type: bsd
>>>>
>>>> Slice   Start      End  Sectors  Size Type     Fsize Bsize Cpg
>>>> a     2099200  2623488   524289  256M boot         0     0   0
>>>> b     2099200  2623488   524289  256M unused       0     0   0
>>>> c     2099200  6293503  4194304    2G unused       0     0   0
>>>> d           0 10485215 10485216    5G unused       0     0   0
>>>>
>>>> Partition table entries are not in disk order.
>>>
>>> Well that does look mostly sane for an ancient BSD version.
>>>
>>
>> In case I was not clear.
>>
>> BSD partition a is represented in Linux as /dev/vda7. grub-probe -t
>> compatibility_hints -d /dev/vda7 returns hd0,msdos2 which is obviously
>> wrong, because it refers to 2GB area on disk while partition /dev/vda7
>> is just 256M. I would expect either hd0,msdos2,openbsd1 or nothing
>> depending on whether such nested partition is supported.
> 
> Oh now I see what you mean.  Hmm, that is an interesting problem.
> 
> It seems FFS and UFS reserve either 1 or 8KB at the start for bootblock,
> which I suppose would save the disklabel from being overwritten if using
> one of those filesystems. 

Solaris usually does not have issues with slice containing label as the
first block. Native tools (UFS, ZFS, SVM) and non-native (Veritas) all
preserve it. So I never considered it something unusual.