Messages in this thread | | | Date | Sat, 14 Jan 2017 01:57:57 +0000 | From | Al Viro <> | Subject | Re: 4.9.0 regression in pipe-backed iov_iter with systemd-nspawn |
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On Fri, Jan 13, 2017 at 05:46:34PM -0800, Linus Torvalds wrote: > 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.
OK. Let's wait for Alan to confirm that the last variant works and I'll send a pull request (with Cc: stable # v4.9).
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