Re: [RFC ONLY 5/8] btrfs: add code to delete raid extent

[Johannes Thumshirn <Johannes.Thumshirn@wdc.com>]

On 17/05/2022 10:06, Qu Wenruo wrote:
>> +	ret = btrfs_search_slot(trans, stripe_root, &stripe_key, path, -1, 1);
>> +	if (ret < 0)
>> +		goto out;
>> +	if (ret == 0)
>> +		goto delete;
>> +
>> +	leaf = path->nodes[0];
>> +	slot = path->slots[0];
>> +	btrfs_item_key_to_cpu(leaf, &found_key, slot);
>> +	found_start = found_key.objectid;
>> +	found_end = found_start + found_key.offset;
>> +
>> +	/*
>> +	 * | -- range to drop --|
>> +	 * | ---------- extent ---------- |
>> +	 */
> Thus I believe we don't need those complex checking.
> 
> The call site has make sure we're the last one owning the file extent,
> and since raid stripe is 1:1 mapped to the full extent (not just part of
> a data extent, like btrfs_file_extent_item can do), we should be safe to
> just do an ASSERT() without the complex split.
> 
> 
> Thus, I guess to be extra accurate, the 1:1 mapping is between an (data)
> EXTENT_ITEM and a raid stripe?

Unfortunately not, as we can split extents. I've found out the hard way that
we need this. See btrfs_drop_extents() for details.