Re: [patch] reiser4: port for Linux-4.1

[Edward Shishkin <edward.shishkin@gmail.com>]

On 07/05/2015 11:11 PM, Ivan Shapovalov wrote:
> On 2015-07-05 at 21:46 +0800, Edward Shishkin wrote:
>> On 07/05/2015 09:08 PM, Ivan Shapovalov wrote:
>>> On 2015-07-05 at 02:33 +0800, Edward Shishkin wrote:
>>>> On 07/05/2015 01:53 AM, Ivan Shapovalov wrote:
>>>>> On 2015-07-04 at 15:53 +0800, Edward Shishkin wrote:
>>>>>> [...]
>>>>>> And how to test directly at mount time?
>>>>> Something along the lines of
>>>>> - allocate 1 MiB of contiguous space
>>>>> - fill it with non-zeros
>>>>> - for N = 1, 2, 4, ...:
>>>>>      - discard N sectors from the contiguous space
>>>>>      - check if anything in the discarded space became zero
>>>>> -filled
>>>>>      - if it did, infer alignnment from the first zero-filled
>>>>> block,
>>>>>        infer granularity from the zero-filled region size.
>>>> mkfs seems to be more suitable for this funny business
>>> Yeah, sure. So... new superblock format with two extra fields?
>>
>> The change will be forward and backward compatible, so there is no
>> need in a new format. Just add two new fields to the superblock40.
> So there will be zeroes in case we mount a non-aware filesystem,
> correct?


Yup.
We have a "reserved" space of 428 bytes at the end of 
format40_disk_super_block
for such purposes. This space is filled with zeros by mkfs. So 
"non-aware filesystems"
including the ones that were created by old versions of mkfs will have 
zeros there.

Edward.


>
>> Also people will want to "mount -o discard" when discard parameters
>> are not known. In this case I think to provide them
>> discard_extents().
>> which is currently merged. Otherwise use discard_precise_extents().
> Yeah.
> I'll do something with this after I finish porting ->write()
> to ->write_iter() (or if I run into heavy problems with that).
>
> Thanks,