[PATCH] fs: remove power of 2 and length boundary atomic write restrictions

[Vitaliy Filippov]

> Note that the alignment rule is not just for atomic HW boundaries. We
> also support atomic writes on stacked devices, where this is relevant -
> specifically striped devices, like raid0. Doing an unaligned atomic
> write on a striped device may result in trying to issue an atomic write
> which straddles 2x separate devices, which would obviously be broken.

Ok, then I'd also add atomic boundary checks and
atomic_write_boundary_bytes = stripe size to /sys/block/**/queue for
md devices. Not 2^N and length-alignment checks, just the boundary.

> It seems that you just want to take advantage of the block layer code to
> handle submission of an atomic write bio, i.e. reject anything which
> cannot be atomically written. In essence, that would be to just set
> REQ_ATOMIC. Maybe that could be done as a passthrough command, I'm not sure.

Of course. I thought it was the whole point of RWF_ATOMIC - REQ_ATOMIC
for userspace.

I don't want passthrough commands, I want to use normal kernel I/O.