On 12/04/2015 09:12 PM, David Sterba wrote:
On Fri, Dec 04, 2015 at 09:21:59AM +0800, Qu Wenruo wrote:
We do have the alignment check in kernel, but it's in the early phase
where we don't know if nodesize is reliable and print only a warning.
This can be enhanced by the following method:
At minimum, we can promote the 4k alignment checks in
btrfs_check_super_valid from a warning to an error. The blocks must be
4k aligned, regardless of sectorsize or nodesize.
1) Check sectorsize first
Only several sector size is valid for current btrfs:
4K, 8K, 16K, 32K, 64K
Just five numbers, quite easy to check.
The sectorsize must be PAGE_SIZE at the moment. This will change with
Chandan's patchset though.
PAGE_SIZE would be good enough.
Or if anyone is going to extend supported sectorsize, we can change
the check to if the number is power of 2 starting from 4K.
2) Check nodesize/leafsize then
It should be aligned to sectorsize.
This particular check is missing but is implicit because of the
sectorsize == PAGE_SIZE restriction.
But still need to check nodesize/leafsize validation against sectorsize.
Current btrfs is already using large nodesize by default.
For example, 20K nodesize can pass 4K page size check but still wrong.
(And I'm also wrong in previous mail, it's not only aligned to
sectorisze, but also need to be power of 2)
And nodesize must match with leafsize.
Currently, it's done out of check_super_valid(), we can integrate it.
Yeah it's done, then I don't see why we should add it agian.
Just want to move it to check_super_valid(), as it's better to put
validation check codes together, and that's why we have check_super_valid().
3) Check all super root bytenr against *sectorsize*
Yeah, not nodesize.
As some old bad convert will cause metadata extent unaligned to
nodesize(just before my convert rework patch), but only aligned to
sectorsize.
So only check alignment of sectorsize.
While the real check should be against the sectorsize, at the moment I
think it's covered by the 4k checks anyway. I understand why we can't
use the nodesize.
4K is good enough for x86 family but can't find all problem for 64K page
size like PPC64 or AArch64.
So it's still better to change the check at least to page size even we
don't have subpage size support yet.
So, if we do the warning -> error, we're fine for now. Some of the
checks you suggest would be good to merge when the subpage blocksize
patchset is merged.
Right, more accurate check is only needed after subpage patchset.
Thanks,
Qu
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