Re: [PATCH v3 01/22] btrfs-progs: convert: Introduce functions to read used space

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

David Sterba wrote on 2016/04/04 15:35 +0200:
> On Fri, Jan 29, 2016 at 01:03:11PM +0800, Qu Wenruo wrote:
>> Before we do real convert, we need to read and build up used space cache
>> tree for later data/meta separate chunk layout.
>>
>> This patch will iterate all used blocks in ext2 filesystem and record it
>> into cctx->used cache tree, for later use.
>>
>> This provides the very basic of later btrfs-convert rework.
>>
>> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
>> Signed-off-by: David Sterba <dsterba@suse.com>
>> ---
>>   btrfs-convert.c | 80 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 80 insertions(+)
>>
>> diff --git a/btrfs-convert.c b/btrfs-convert.c
>> index 4baa68e..65841bd 100644
>> --- a/btrfs-convert.c
>> +++ b/btrfs-convert.c
>> @@ -81,6 +81,7 @@ struct btrfs_convert_context;
>>   struct btrfs_convert_operations {
>>   	const char *name;
>>   	int (*open_fs)(struct btrfs_convert_context *cctx, const char *devname);
>> +	int (*read_used_space)(struct btrfs_convert_context *cctx);
>>   	int (*alloc_block)(struct btrfs_convert_context *cctx, u64 goal,
>>   			   u64 *block_ret);
>>   	int (*alloc_block_range)(struct btrfs_convert_context *cctx, u64 goal,
>> @@ -230,6 +231,73 @@ fail:
>>   	return -1;
>>   }
>>
>> +static int __ext2_add_one_block(ext2_filsys fs, char *bitmap,
>> +				unsigned long group_nr, struct cache_tree *used)
>> +{
>> +	unsigned long offset;
>> +	unsigned i;
>> +	int ret = 0;
>> +
>> +	offset = fs->super->s_first_data_block;
>> +	offset /= EXT2FS_CLUSTER_RATIO(fs);
>
> This macro does not exist on my reference host for old distros. The
> e2fsprogs version is 1.41.14 and I'd like to keep the compatibility at
> least at that level.
>
> The clustering has been added in 1.42 but can we add some compatibility
> layer that will work on both version?
>
No problem.

It's a simple macro. For older version which doesn't provide it, we can 
just define it in btrfs-covert.c.

Thanks,
Qu