Re: [PATCH] fstests: btrfs: make nospace_cache related test cases to work with latest v2 cache

[Josef Bacik <josef@toxicpanda.com>]

On Thu, Nov 04, 2021 at 08:55:53AM +0800, Qu Wenruo wrote:
> In the coming btrfs-progs v5.15 release, mkfs.btrfs will change to use
> v2 cache by default.
> 
> However nospace_cache mount option will not work with v2 cache, as it
> will make v2 cache out of sync with on-disk used space.
> 
> So mounting a btrfs with v2 cache using "nospace_cache" will make btrfs
> to reject the mount.
> 
> There are quite some test cases relying on nospace_cache to prevent v1
> cache to take up data space.
> 
> For that case, we can append "clear_cache" mount option to it, so that
> btrfs knows we do not only want to prevent cache from being created, but
> also want to clear any existing v2 cache.
> 
> By this, we can keep those existing tests to do the same behavior for
> both v1 and v2 cache.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>

This will re-generate the free space tree needlessly, and in fact won't be
allowed for extent-tree-v2, so we'll just have to mess with it again.  Instead
add a helper to get the options if they're needed, something like

_btrfs_nocache_opt() {
	$BTRFS_UTIL_PROG inspect-internal $SCRATCH_DEV | grep FREE_SPACE_TREE
	if [ $? -eq 0 ]; then
		return "-o nospace_cache"
	fi
	return ""
}

or something like that.  Thanks,

Josef