From: Trond Myklebust <trondmy@hammerspace.com>
To: "viro@ZenIV.linux.org.uk" <viro@ZenIV.linux.org.uk>,
"dhowells@redhat.com" <dhowells@redhat.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-afs@lists.infradead.org" <linux-afs@lists.infradead.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH 04/10] iov_iter: Add mapping and discard iterator types
Date: Fri, 14 Sep 2018 12:57:26 +0000 [thread overview]
Message-ID: <a37220c23479c79239b046e2487cfc95544b8f13.camel@hammerspace.com> (raw)
In-Reply-To: <20180914041831.GY19965@ZenIV.linux.org.uk>
On Fri, 2018-09-14 at 05:18 +0100, Al Viro wrote:
> On Thu, Sep 13, 2018 at 04:52:09PM +0100, David Howells wrote:
> > Add two new iterator types to iov_iter:
> >
> > (1) ITER_MAPPING
> >
> > This walks through a set of pages attached to an address_space
> > that
> > are pinned or locked, starting at a given page and offset and
> > walking
> > for the specified amount of space. A facility to get a
> > callback each
> > time a page is entirely processed is provided.
> >
> > This is useful for copying data from socket buffers to inodes
> > in
> > network filesystems.
>
> Interesting... Questions:
> * what will hold those pages? IOW, where will you
> unlock/drop/whatnot
> those sucker?
> * "callback" sounds dangerous - it appears to imply that you
> won't
> copy to/from the same page twice. Not true for a lot of iov_iter
> users; what
> happens if you pass such a beast to them?
> * why not simply "build and populate ITER_BVEC aliasing a piece
> of mapping",
> possibly in "grab" and "grab+lock" variants? Those ITER_MAPPING do
> seem to be
> related to ITER_BVEC, at the very least. Note, BTW, that
> iov_iter_get_pages...()
> might mutate into something similar - "build and populate ITER_BVEC
> aliasing a piece
> of given iov_iter". Or, perhaps, a nicer-on-memory analogue of
> ITER_BVEC -
> with <offset, bytes, pointer to pages array> instead of <offset,
> bytes, page> as
> elements, with the same "populate from mapping" to get something
> similar to your
> functionality and "populate from iov_iter" for iov_iter_get_pages...
> replacement.
Another question that is relevant for most networked filesystems
(including AFS, I believe), is how will you deal with encryption of the
data you are transmitting? Encrypting and decrypting in-place directly
in the page cache or in a userspace O_DIRECT mapped buffer might not be
the best and most secure option, so won't you find yourself wanting to
copy the data anyway?
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com
next prev parent reply other threads:[~2018-09-14 18:12 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-13 15:51 [PATCH 00/10] iov_iter: Add new iters and use with AFS David Howells
2018-09-13 15:51 ` [PATCH 01/10] iov_iter: Separate type from direction and use accessor functions David Howells
2018-09-13 15:51 ` [PATCH 02/10] iov_iter: Renumber the ITER_* constants in uio.h David Howells
2018-09-13 15:52 ` [PATCH 03/10] iov_iter: Make count and iov_offset loff_t not size_t David Howells
2018-09-13 15:52 ` [PATCH 04/10] iov_iter: Add mapping and discard iterator types David Howells
2018-09-14 4:18 ` Al Viro
2018-09-14 12:57 ` Trond Myklebust [this message]
2018-09-17 21:32 ` David Howells
2018-09-17 20:58 ` David Howells
2018-09-13 15:52 ` [PATCH 05/10] afs: Better tracing of protocol errors David Howells
2018-09-13 15:52 ` [PATCH 06/10] afs: Set up the iov_iter before calling afs_extract_data() David Howells
2018-09-13 15:52 ` [PATCH 07/10] afs: Use ITER_MAPPING for writing David Howells
2018-09-13 15:52 ` [PATCH 08/10] afs: Add O_DIRECT read support David Howells
2018-09-13 15:52 ` [PATCH 09/10] afs: Add a couple of tracepoints to log I/O errors David Howells
2018-09-13 15:52 ` [PATCH 10/10] afs: Don't invoke the server to read data beyond EOF David Howells
2018-09-13 16:10 ` [PATCH 00/10] iov_iter: Add new iters and use with AFS Matthew Wilcox
2018-09-13 16:18 ` David Howells
2018-09-13 16:43 ` Matthew Wilcox
2018-09-13 17:05 ` David Howells
2018-09-13 17:58 ` Al Viro
-- strict thread matches above, loose matches on Subject: below --
2018-08-06 13:16 David Howells
2018-08-06 13:17 ` [PATCH 04/10] iov_iter: Add mapping and discard iterator types David Howells
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