From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [PATCH v2] ceph/iov_iter: fix bad iov_iter handling in ceph
 splice codepaths
Date: Thu, 12 Jan 2017 11:37:43 +0000
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To: Ilya Dryomov <idryomov@gmail.com>
Cc: Jeff Layton <jlayton@redhat.com>, "Yan, Zheng" <zyan@redhat.com>, Sage Weil <sage@redhat.com>, Ceph Development <ceph-devel@vger.kernel.org>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "Zhu, Caifeng" <zhucaifeng@unissoft-nj.com>
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On Thu, Jan 12, 2017 at 12:13:31PM +0100, Ilya Dryomov wrote:

> It would be a significant and wide-reaching change, but I've been
> meaning to look into switching to iov_iter for a couple of releases
> now.  There is a lot of ugly code in net/ceph/messenger.c to hangle
> iteration over "page vectors", "page lists" and "bio lists".  All of it
> predates iov_iter proliferation and is mostly incomplete anyway: IIRC
> you can send out of a pagelist but can't recv into a pagelist, etc.

Wait a sec...  Is it done from the same thread that has issued a syscall?
If so, we certainly could just pass iov_iter without bothering with any
form of ..._get_pages(); if not, we'll need at least to get from iovec
to bio_vec, since userland addresses make sense only in the caller's
context...