From: Matthew Wilcox > Sent: Friday, August 18, 2023 1:27 PM > > On Fri, Aug 18, 2023 at 12:16:23PM +0000, David Laight wrote: > > > > + ITER_IOVEC = 1, > > > > + ITER_UBUF = 2, > > > > + ITER_KVEC = 4, > > > > + ITER_BVEC = 8, > > > > + ITER_XARRAY = 16, > > > > + ITER_DISCARD = 32, > > > > IIRC Linus had type:6 - that doesn't leave any headroom > > for additional types (even though they shouldn't proliferate). > > I have proposed an ITER_KBUF in the past (it is to KVEC as UBUF is > to IOVEC). I didn't care enough to keep pushing it, but it's clearly > a common idiom. Indeed, I didn't spot UBUF going in - I spot a lot of stuff. I did wonder if you could optimise for a vector length of 1 (inside the KVEC conditional). That would also pick up the cases where there only happens to be a single buffer. I also remember writing a patch that simplified import_iovec() by combining the iov_iter with a struct iovec iovec[UIO_FASTIOV]. All got bogged down in io_uring which would need changing first. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
