Re: [PATCH v2 2/4] btrfs: Add incompat flags check for btrfs_check_super_valid()

[David Sterba <dsterba@suse.cz>]

On Tue, Apr 24, 2018 at 07:28:27PM +0800, Qu Wenruo wrote:
> > I've read the discussion under previous version again, IMHO the best way
> > to report what's going on is to use 2 functions for mount ant pre-commit
> > time.
> 
> OK, next version will go that direction.
> 
> Although it may still be a little tricky to split what we need in
> btrfs_validate_super() and btrfs_precheck_super().
> 
> What about this idea:
> - btrfs_precheck_super() only checks the very basis:
>   * magic
>   * incompat flags
>   * csum type
>   Any mismatch will do friendly prompt ("no btrfs detected" or
>   "unsupported flags/csum type" respectively)
> 
> - btrfs_validate_super() do the comprehensive check:
>   * Everything we did in this patchset
>   * including magic, incompat flags and csum type
>   Any mismatch will be considered as corruption.
> 
> For mount time, we call btrfs_precheck_super() then btrfs_validate_super().
> 
> For commit time, only btrfs_validate_super().
> 
> How about this solution?

I'd do that the other way around:

* mount checks: btrfs_validate_super - the superblock on disk must be
  valid before we mount it

  btrfs_validate_super()

* pre-commit checks: the superblock must be valid and we can also do
  some additional checks to detect in-memory corruption

  btrfs_super_precommit_check()
	  btrfs_validate_super()
	  if (incompat) {
		  ...
	  }