linux-kernel - Re: [PATCH 03/24] iov_iter: Add I/O discard iterator

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Message-ID: <17220.1540225080@warthog.procyon.org.uk>
Date:   Mon, 22 Oct 2018 17:18:00 +0100
From:   David Howells <dhowells@...hat.com>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     dhowells@...hat.com, linux-afs@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/24] iov_iter: Add I/O discard iterator

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

> > @@ -1060,6 +1074,9 @@ void iov_iter_revert(struct iov_iter *i, size_t unroll)
> >  	}
> >  	unroll -= i->iov_offset;
> >  	switch (iov_iter_type(i)) {
> > +	case ITER_DISCARD:
> > +		i->iov_offset = 0;
> > +		return;
> 
> ... the hell?  That makes no sense whatsoever; what, besides this and immediately
> preceding part of iov_iter_revert() so much as looks at ->iov_offset for those?
> Just have it bugger off before the
>         if (unroll <= i->iov_offset) {
>                 i->iov_offset -= unroll;
>                 return;
>         }
> bit...

I didn't want to add another case before that if I could avoid it.  If
iov_offset > unroll, the discard iterator really doesn't care.  Maybe I should
just ignore iov_offset for the discard iterator.

David