Messages in this thread | | | From | Linus Torvalds <> | Date | Fri, 13 Jan 2017 17:46:34 -0800 | Subject | Re: 4.9.0 regression in pipe-backed iov_iter with systemd-nspawn |
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On Fri, Jan 13, 2017 at 5:24 PM, Al Viro <viro@zeniv.linux.org.uk> wrote: > > Why would advance by 0 change ->iov_offset here?
That's not my worry. Advancing by zero obviously doesn't change the position.
But the _truncation_ of the rest requires iov_offset to be zero in order to actually truncate everything.
So I was worrying about something updating it, and then wanting to truncate things on error.
But you bring up the kinds of cases I worried about:
> On error it does use iov_iter_advance(), pretty much as a way to > trigger pipe_truncate(). There we directly reset ->iov_offset to 0 > and ->idx to its original value.
Ok, this was the part I worried about. And this
> However, theoretically it is possible that ->read_iter() instance does > successful copy_to_iter() and then decides to return an error. This > } else if (ret < 0) { > to.idx = idx; > to.iov_offset = 0; > iov_iter_advance(&to, 0); /* to free what was emitted */ > in generic_file_splice_read() catches any such cases.
So I'm happy with that last patch then, and my worries are laid to rest.
Linus
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