[RFC PATCH 00/12] smb3: Add iter helpers and use iov_iters down to the network transport

[David Howells]

Hi Steve, Al, Christoph,

Here's an updated version of a subset of my branch to make the cifs/smb3
driver pass iov_iters down to the lowest layers where they can be passed to
the network transport.

The first couple of patches provide iov_iter general stuff:

 (1) Move the FOLL_* flags to linux/mm_types.h so that linux/uio.h can make
     use of them.

 (2) Add a function to extract/get/pin pages from an iterator as a future
     replacement for iov_iter_get_pages*().  It also adds a function by
     which the caller can determine which of "extract/get/pin" the
     extraction function will actually do to aid in cleaning up.

Then there are a couple of patches that add stuff to netfslib that I want
to use there as well as in cifs:

 (3) Add a netfslib function to use (2) to extract pages from an ITER_IOBUF
     or ITER_UBUF iterator into an ITER_BVEC iterator.

 (4) Add a netfslib function to use (2) to extract pages from an iterator
     that's of type ITER_UBUF/IOVEC/BVEC/KVEC/XARRAY and add them to a
     scatterlist.  The function in (2) is used for a UBUF and IOVEC
     iterators, so those need cleaning up afterwards; BVEC and XARRAY
     iterators can be rendered into elements that span multiple pages.

Then there are some cifs helpers that work with iterators:

 (5) Implement cifs_splice_read() to use an ITER_BVEC rather than an
     ITER_PIPE, bulk-allocating the pages, attaching them to the bvec,
     doing the I/O and then pushing the pages into the pipe.  This avoids
     the problem with cifs wanting to split the pipe iterator in a later
     patch.

 (6) Add a function to walk through an ITER_BVEC/KVEC/XARRAY iterator and
     add elements to an RDMA SGE list.  Only the DMA addresses are stored,
     and an element may span multiple pages (say if an xarray contains a
     multipage folio).

 (7) Add a function to walk through an ITER_BVEC/KVEC/XARRAY iterator and
     pass the contents into a shash function.

 (8) Add functions to walk through an ITER_XARRAY iterator and perform
     various sorts of cleanup on the folios held therein, to be used on I/o
     completion.

 (9) Add a function to read from the transport TCP socket directly into an
     iterator.

Then come the patches that actually do the work of iteratorising cifs:

(10) The main patch.  Replace page lists with iterators.  It extracts the
     pages from ITER_UBUF and ITER_IOVEC iterators to an ITER_BVEC
     iterator, pinning or getting refs on them, before passing them down as
     the I/O may be done from a worker thread.

     The iterator is extracted into a scatterlist in order to talk to the
     crypto interface or to do RDMA.

(11) In the cifs RDMA code, extract the iterator into an RDMA SGE[] list,
     removing the scatterlist intermediate - at least for smbd_send().
     There appear to be other ways for cifs to talk to the RDMA layer that
     don't go through that that I haven't managed to work out.

(12) Remove a chunk of now-unused code.

Note also that I haven't managed to test all the combinations of transport.
Samba doesn't support RDMA and ksmbd doesn't support encryption.  I can
test them separately, but not together.  That said, rdma, sign, seal and
sign+seal seem to work.

I've pushed the patches here also:

	https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=cifs-for-viro

Note that this is based on a merge of Al's work.iov_iter branch with
v6.1-rc2.

David

Link: https://lore.kernel.org/r/166697254399.61150.1256557652599252121.stgit@xxxxxxxxxxxxxxxxxxxxxx/
---
David Howells (12):
      mm: Move FOLL_* defs to mm_types.h
      iov_iter: Add a function to extract a page list from an iterator
      netfs: Add a function to extract a UBUF or IOVEC into a BVEC iterator
      netfs: Add a function to extract an iterator into a scatterlist
      cifs: Implement splice_read to pass down ITER_BVEC not ITER_PIPE
      cifs: Add a function to build an RDMA SGE list from an iterator
      cifs: Add a function to Hash the contents of an iterator
      cifs: Add some helper functions
      cifs: Add a function to read into an iter from a socket
      cifs: Change the I/O paths to use an iterator rather than a page list
      cifs: Build the RDMA SGE list directly from an iterator
      cifs: Remove unused code


 fs/cifs/Kconfig          |    1 +
 fs/cifs/cifsencrypt.c    |  172 +++-
 fs/cifs/cifsfs.c         |   12 +-
 fs/cifs/cifsfs.h         |    6 +
 fs/cifs/cifsglob.h       |   31 +-
 fs/cifs/cifsproto.h      |   11 +-
 fs/cifs/cifssmb.c        |   13 +-
 fs/cifs/connect.c        |   16 +
 fs/cifs/file.c           | 1793 ++++++++++++++++++--------------------
 fs/cifs/fscache.c        |   22 +-
 fs/cifs/fscache.h        |   10 +-
 fs/cifs/misc.c           |  127 +--
 fs/cifs/smb2ops.c        |  378 ++++----
 fs/cifs/smb2pdu.c        |   45 +-
 fs/cifs/smbdirect.c      |  503 +++++++----
 fs/cifs/smbdirect.h      |    4 +-
 fs/cifs/transport.c      |   57 +-
 fs/netfs/Makefile        |    1 +
 fs/netfs/iterator.c      |  346 ++++++++
 include/linux/mm.h       |   74 --
 include/linux/mm_types.h |   73 ++
 include/linux/netfs.h    |    5 +
 include/linux/uio.h      |   29 +
 lib/iov_iter.c           |  333 +++++++
 24 files changed, 2390 insertions(+), 1672 deletions(-)
 create mode 100644 fs/netfs/iterator.c