Re: [PATCH v5 3/9] iov_iter: Use IOCB/IOMAP_WRITE if available rather than iterator direction

[Christoph Hellwig]

On Thu, Jan 12, 2023 at 01:49:14PM -0800, Bart Van Assche wrote:
> I'm not sure that we still need the double copy in the sg driver. It seems
> obscure to me that there is user space software that relies on finding
> "0xec" in bytes not originating from a SCSI device. Additionally, SCSI
> drivers that do not support residuals should be something from the past.
> 
> Others may be better qualified to comment on this topic.

Yeah.  And that weird (ab)use of blk_rq_map_user_iov into preallocated
pages in sg has been a constant source of pain.  I'd be very happy to
make it match the generic SG_IO implementation and either do
get_user_pages or the normal bounce buffering implemented in the
common code.