On Thu, Sep 01, 2022 at 05:04:34PM +0800, Qu Wenruo wrote:

But for the verification part, I still don't like the idea of putting
the verification code at endio context at all.

Why?

This is especially true when data and metadata are still doing different
checksum verfication at different timing.

Note that this does not handle the metadata checksum verification at
all.  Both because it actually works very different and I could not
verify that we'd actually always read all data that needs to be verified
together for metadata, but also because there is zero metadata repair
coverage in xfstests, so I don't dare to touch that code.

Can we just let the endio function to do the IO, and let the reader to
do the verification after all needed data is read out?

What would the benefit be?  It will lead to a lot of duplicate (and thus
inconsistent) code that is removed here, and make splitting the bios
under btrfs_submit_bio much more complicated and expensive.