Re: [PATCH RFC 4/4] btrfs-progs: convert: support ext2 unwritten file data extents

Qu Wenruo
2024-05-03T22:23:32Z

在 2024/5/3 21:55, Anand Jain 写道:
[...]
>>> +int find_prealloc(struct blk_iterate_data *data, int index, bool
>>> *prealloc)
>>
>> This function is called for every file extent we're going to create.
>> I'm not a big fan of doing so many lookup.
>>
>> My question is, is this the only way to determine the flag of the data
>> extent?
>>
>> My instinct says there should be a straight forward way to determine
>> if a file extent is preallocated or not, just like what we do in our
>> file extent items.
>
>
>> Thus during the ext2fs_block_iterate2(), there should be some way to
>> tell if a block is preallocated or not.
>
> Unfortunately, the callback doesn't provide the extent flags. Unless,  I
> miss something?

You're right, the iterator interface does not provide any extra info.

And I also checked the kernel implementation, they have extra
ext4_map_blocks() to do the resolve, and then ext4_es_lookup_extent() to
determine if it's unwritten.

So I'm afraid we have to go this solution.

Meanwhile related to the implementation, can we put the prealloc flat
into blk_iterate_data?
So that we can handle different fses' preallocated extents in a more
common way.

Thanks,
Qu