[dm-devel] [Question] Is there any mean to know a bio split is the last one in the original bio?

[Akira Hayakawa]

Hi, I am Akira.
Nice to meet you.
I will post a question for your help.

I have been developing a caching module now
https://github.com/akiradeveloper/dm-lc

and facing a big design problem related to handling REQ_FUA flag.

Suppose we have 4KB split_io and
the original bio is 8KB with REQ_FUA flag.

The device-mapper dm_request function now
splits the original one into two 4KB sized bios with REQ_FUA and
then passes them to map function one by one.
This eventually leads to inefficient code in my case.

All I want to do is flushing the preceding split bios at last but
I know that is not always the most efficient implementation in any dm
modules and
that's why device-mapper is what it is like now.

My question is
Is there any mean to know the second bio split is the last one in the split
sequence?

I need your help.
Thanks.

Akira Hayakawa
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