Could it be made possible to offer "supplementary" data to a DIO write ?

[David Howells]

Hi,

I'm working on network filesystem write helpers to go with the read helpers,
and I see situations where I want to write a few bytes to the cache, but have
more available that could be written also if it would allow the
filesystem/blockdev to optimise its layout.

Say, for example, I need to write a 3-byte change from a page, where that page
is part of a 256K sequence in the pagecache.  Currently, I have to round the
3-bytes out to DIO size/alignment, but I could say to the API, for example,
"here's a 256K iterator - I need bytes 225-227 written, but you can write more
if you want to"?

Would it be useful/feasible to have some sort of interface that allows the
offer to be made?

David