[RFC] Remove requirement of alignment to track from MBR scheme
Andrey V. Elsukov
bu7cher at yandex.ru
Tue May 24 05:29:01 UTC 2011
On 23.05.2011 21:39, Warner Losh wrote:
>>> In any event, I'd be tempted to use a #define for 4096 like
>>> MBR_MAX_SECTOR_SIZE.
>>>
>>> -msize = MIN(pp->mediasize / pp->sectorsize, UINT32_MAX);
>>> +msize = MIN(pp->mediasize / pp->sectorsize, 2 * UINT32_MAX);
>>>
>>> Why this change? I think that it is in two places.
>>
>> Currently we have limit to msize = UINT32_MAX, but partition in MBR has
>> start offset and size (not end offset). Theoretically it can have size
>> that is up to UINT32_MAX sectors, also start offset can be UINT32_MAX.
>> And for example, for 4T disk we can have 2 partitions with 2TB size.
>
> Are there any extant examples of this? The CW is that the maximum size for an MBR device is 2TB.
I tried with 6T md(4) device and it is possible to create 2 partitions
with 2T size, but it is inconvenient to do:
# gpart show md0
=> 1 8589934589 md0 MBR (5.5T)
1 8589934589 - free - (4T)
# gpart add -t freebsd -s 2T md0
gpart: Invalid argument
# gpart add -t freebsd -s `printf %d 0xFFFFFFFE` md0
md0s1 added
# gpart add -t freebsd md0
md0s2 added
# gpart show md0
=> 1 8589934589 md0 MBR (5.5T)
1 4294967294 1 freebsd (2T)
4294967295 4294967295 2 freebsd (2T)
So, i updated the patch and removed this support. Also i removed some
checks that scheme independent code does.
--
WBR, Andrey V. Elsukov
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