Re: [PATCH v7 01/31] iov_iter: Add ITER_XARRAY

David Howells
2021-04-25T13:58:20Z

Al Viro <viro@zeniv.linux.org.uk> wrote:

> > +struct address_space;
> > struct pipe_inode_info;
> >
> > struct kvec {
>
> What is that chunk for?

Ah, that can go. It used to be ITER_MAPPING.

> > + }),
> > + ({
> > + rem = copy_mc_to_page(v.bv_page, v.bv_offset,
> > + (from += v.bv_len) - v.bv_len, v.bv_len);
> > + if (rem) {
> > + curr_addr = (unsigned long) from;
> > + bytes = curr_addr - s_addr - rem;
> > + rcu_read_unlock();
> > + return bytes;
> > + }
>
> That's broken, same way as kvec and bvec cases are in the same primitive.
> Iterator not advanced on failure halfway through.

Okay. I just copied what ITER_BVEC does. Should this be handled in
iterate_and_advance() rather than in the code snippets it takes as parameters?

But for the moment, I guess I should just add:

i->iov_offset += bytes;

to all three (kvec, bvec and xarray)?

> > @@ -1246,7 +1349,8 @@ unsigned long iov_iter_alignment(const struct iov_iter *i)
> > iterate_all_kinds(i, size, v,
> > (res |= (unsigned long)v.iov_base | v.iov_len, 0),
> > res |= v.bv_offset | v.bv_len,
> > - res |= (unsigned long)v.iov_base | v.iov_len
> > + res |= (unsigned long)v.iov_base | v.iov_len,
> > + res |= v.bv_offset | v.bv_len
> > )
> > return res;
> > }
>
> Hmm... That looks like a really bad overkill - do you need anything beyond
> count and iov_offset in that case + perhaps "do we have the very last page"?
> IOW, do you need to iterate anything at all here? What am I missing here?

Good point. I wonder, even, if the alignment could just be set to 1. There's
no kdoc description on the function that says what the result is meant to
represent.

> > @@ -1268,7 +1372,9 @@ unsigned long iov_iter_gap_alignment(const struct iov_iter *i)
> > ...
> Very limited use; it shouldn't be called for anything other than IOV_ITER case.
Should that just be cut down, then?

> > @@ -1849,7 +2111,12 @@ int iov_iter_for_each_range(struct iov_iter *i, size_t bytes,
> > ...
>
> Would be easier to have that sucker removed first...

I could do that. I'd rather not do that here since it hasn't sat in
linux-next, but since nothing uses it, but Linus might permit it.

David