Re: [PATCH RFC 1/4] block: Make bdev_can_atomic_write() robust against mis-aligned bdev size

[John Garry]

On 12/09/2024 16:07, Christoph Hellwig wrote:
> > We should do be able to, but with this patch we cannot. However, a
> > misaligned partition would be very much unexpected.
> Yes, misaligned partitions is very unexpected, but with large and
> potentially unlimited atomic boundaries I would not expect the size
> to always be aligned.  But then again at least in NVMe atomic writes
> don't need to match the max size anyway, so I'm not entirely sure
> what the problem actually is.

Actually it's not an alignment issue, but a size issue.

Consider a 3.5MB partition and atomic write max is 1MB. If we tried to 
atomic write 1MB at offset 3MB, then it would be truncated to a 0.5MB write.

So maybe it is an application bug.

> > I could also just reject any truncation on the atomic write in fops. Maybe
> > that is better.