Re: [PATCH 03/10] btrfs: split btrfs_submit_data_bio

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2022/4/25 17:19, Christoph Hellwig wrote:
> On Mon, Apr 25, 2022 at 05:11:15PM +0800, Qu Wenruo wrote:
>>
>>
>> On 2022/4/25 15:54, Christoph Hellwig wrote:
>>> Split btrfs_submit_data_bio into one helper for reads and one for writes.
>>
>> If we're splitting the bio mapping, wouldn't it be better to split by
>> read/write first, then by data/meta?
>>
>> Especially for all read bios, we use workqueue to defer to a less strict
>> context, which is unrelated to data/metadata.
>
> Splitting the read vs write handling entirely and not allocating a
> btrfs_bio for writes will be the next series after this one.  You're
> getting ahead of me :)

Oh, please don't completely get rid of btrfs_bio, even just for writes.

The btrfs_bio::iter is pretty important for us to grab the original
logical bytenr of a bio.
As bio::bi_iter can be modified by lower level (does dm modifies it
too?), or btrfs itself.

In fact, my incoming updated btrfs repair repair code heavily rely on
btrfs_bio::iter, both read and write, to grab the original logical
bytenr of the bio.

Thanks,
Qu