linux-ext4 - Re: [PATCH RFC 4/4] btrfs-progs: convert: support ext2 unwritten file data extents

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Message-ID: <459ec128-eddd-4575-ab28-788f340a6a7c@suse.com>
Date: Sat, 4 May 2024 07:53:26 +0930
From: Qu Wenruo <wqu@...e.com>
To: Anand Jain <anand.jain@...cle.com>, linux-btrfs@...r.kernel.org,
 linux-ext4@...r.kernel.org
Subject: Re: [PATCH RFC 4/4] btrfs-progs: convert: support ext2 unwritten file
 data extents



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