Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH v3 2/2] iov_iter: Don't deal with iter->copy_mc in memcpy_from_iter_mc() | Date | Fri, 18 Aug 2023 12:41:21 +0000 |
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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
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