Re: Formalizing the use of Boot Area B

[Chris Mason <clm@fb.com>]

On 05/20/2014 07:29 PM, H. Peter Anvin wrote:
> On 05/14/2014 05:01 PM, H. Peter Anvin wrote:
>> It turns out that the primary 64K "Boot Area A" is too small for some
>> applications and/or some architectures.
>>
>> When I discussed this with Chris Mason, he pointed out that the area
>> beyond the superblock is also unused, up until at least the megabyte
>> point (from my reading of the mkfs code, it is actually slightly more
>> than a megabyte.)
>>
>> This is present in all versions of mkfs.btrfs that has the superblock at
>> 64K (some very early ones had the superblock at 16K, but that format is
>> no longer supported), so all that is needed is formalizing the specs as
>> to the use of this area.
>>
>> My suggestion is that 64-128K is reserved for extension of the
>> superblock and/or any other filesystem uses, and 128-1024K is defined as
>> Boot Area B.  However, if there may be reason to reserve more, then we
>> should do that.  Hence requesting a formal decision as to the extent and
>> ownership of this area.
>>
>> 	-hpa
>>
> 
> Ping on this?  If I don't hear back on this I will probably just go
> ahead and use 128K-1024K.

Hi Peter,

We do leave the first 1MB of each device alone.  Can we do 256K-1024K
for the boot loader?  We don't have an immediate need for the extra
space, but I'd like to reserve a little more than the extra 64KB.

-chris