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,
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