Re: [PATCH v2 00/16] block atomic writes

[Christoph Hellwig]

On Thu, Dec 21, 2023 at 12:48:24PM +0000, John Garry wrote:
>>> - ubuf / iovecs need to be PAGE-aligned
>>> - each iovec needs to be length of multiple of atomic_write_unit_min. If
>>> total length > PAGE_SIZE, each iovec also needs to be a multiple of
>>> PAGE_SIZE.
>>>
>>> I'd rather something simpler. Maybe it's ok.
>> If we decided to not support atomic writes on anything setting a virt
>> boundary we don't have to care about the alignment of each vector,
>
> ok, I think that alignment is not so important, but we still need to 
> consider a minimum length per iovec, such that we will always be able to 
> fit a write of length atomic_write_unit_max in a bio.

I don't think you man a minim length per iovec for that, but a maximum
number of iovecs instead.  For SGL-capable devices that would be
BIO_MAX_VECS, otherwise 1.