[RFC] unifying write variants for filesystems

[Zach Brown]

> So what exactly does generic_segments_check() give us?  Is it just that
> everybody went "well, maybe there's some weird path where we don't do
> validation; let's leave it there"?  Linus?

Sounds likely.  I'd bet that the btrfs call was just copied from
__generic_file_aio_write() when btrfs grew its own .aio_write method:

11c65dccf70be9ace5dbd3906778e1a099b1fee1
Author: Josef Bacik <josef at redhat.com>
Date:   Sun May 23 11:07:21 2010 -0400

    Btrfs: do aio_write instead of write

It probably amounts to no more than ocount = iov_length().

- z