[v4,0/7] iov_iter: Add extraction helpers

Message

David Howells Jan. 7, 2023, 12:33 a.m. UTC

Hi Al,

Here are patches clean up some use of READ/WRITE and ITER_SOURCE/DEST,
patches to provide support for extracting pages from an iov_iter and a
patch to use the primary extraction function in the block layer bio code if
you could take a look?

[!] NOTE that I've switched the functions to be exported GPL-only at
    Christoph's request[1].  They are, however, intended as a replacement
    for iov_iter_get_pages*(), which is not marked _GPL - so that
    functionality will probably become unavailable to non-GPL 3rd party
    modules in future.

The first three patches deal with ITER_SOURCE/DEST:

 (1) Switch ITER_SOURCE/DEST to an enum and add a couple of helper
     functions to query if an iterator represents a source or a destination
     buffer.  Using an enum may allow extra consistency warnings from the
     compiler.

 (2) Use the ITER_SOURCE/DEST values in the iov_iter core functions rather
     than READ/WRITE.

 (3) Get rid of most of the callers of iov_iter_rw(), using the IOCB_WRITE
     and IOMAP_WRITE instead where available.  This leaves only two places
     looking at the this value: a consistency check in cifs and a single
     place in the block layer.

The next patch adds a replacement for iov_iter_get_pages*(), including
Logan's new version:

 (4) Add a function to list-only, get or pin pages from an iterator as a
     future replacement for iov_iter_get_pages*().  Pointers to the pages
     are placed into an array (which will get allocated if not provided)
     and, depending on the iterator type and direction, the pages will have
     a ref or a pin get on them or be left untouched (on the assumption
     that the caller manages their lifetime).

     The determination is:

	UBUF/IOVEC + DEST	-> pin
	UBUF/IOVEC + SOURCE	-> get
	PIPE + DEST		-> list-only
	BVEC/XARRAY		-> list-only
	Anything else		-> EFAULT

     The function also returns an indication of which of "list only, get or
     pin" the extraction function did to aid in cleaning up (returning 0,
     FOLL_GET or FOLL_PIN as appropriate).

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

 (5) Add a netfslib function to use (4) to extract pages from an ITER_IOBUF
     or ITER_UBUF iterator into an ITER_BVEC iterator.  This will get or
     pin the pages as appropriate.

 (6) Add a netfslib function 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 (4) is used for a UBUF and IOVEC iterators, so those
     need cleaning up afterwards.  BVEC and XARRAY iterators are ungot and
     unpinned and may be rendered into elements that span multiple pages,
     for example if large folios are present.

Finally, there's an example test patch for the extract pages:

 (7) Make the block layer's BIO code pin pages or leave pages unaltered
     rather than getting a ref on the pages when the circumstances warrant,
     and noting in the bio struct what cleanups should be performed so that
     the bio cleanup code then does the right thing.

Changes:
========
ver #4)
 - Drop the patch to move the FOLL_* flags to linux/mm_types.h as they're
   no longer referenced by linux/uio.h.
 - Add patches 1-3 and 7.
 - Make patches 4-6 use ITER_SOURCE/DEST.
 - Allow additional gup_flags to be passed into iov_iter_extract_pages().

ver #3)
 - Switch to using EXPORT_SYMBOL_GPL to prevent indirect 3rd-party access
   to get/pin_user_pages_fast()[1].

ver #2)
 - Rolled the extraction cleanup mode query function into the extraction
   function, returning the indication through the argument list.
 - Fixed patch 4 (extract to scatterlist) to actually use the new
   extraction API.

I've pushed the patches here also:

	https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=iov-extract

David

Link: https://lore.kernel.org/r/Y3zFzdWnWlEJ8X8/@infradead.org/ [1]
Link: https://lore.kernel.org/r/[e-mail]/ # rfc
Link: https://lore.kernel.org/r/[e-mail]/ # rfc
Link: https://lore.kernel.org/r/[e-mail]/ # rfc
Link: https://lore.kernel.org/r/[e-mail]/ # rfc
Link: https://lore.kernel.org/r/[e-mail]/ # v2
Link: https://lore.kernel.org/r/[e-mail]/ # v3

---
David Howells (7):
      iov_iter: Change the direction macros into an enum
      iov_iter: Use the direction in the iterator functions
      iov_iter: Use IOCB/IOMAP_WRITE if available rather than iterator direction
      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
      iov_iter, block: Make bio structs pin pages rather than ref'ing if appropriate


 block/bio.c               |  47 +++--
 block/fops.c              |   8 +-
 fs/9p/vfs_addr.c          |   2 +-
 fs/affs/file.c            |   4 +-
 fs/ceph/file.c            |   2 +-
 fs/dax.c                  |   6 +-
 fs/direct-io.c            |  22 +--
 fs/exfat/inode.c          |   6 +-
 fs/ext2/inode.c           |   2 +-
 fs/f2fs/file.c            |  10 +-
 fs/fat/inode.c            |   4 +-
 fs/fuse/dax.c             |   2 +-
 fs/fuse/file.c            |   8 +-
 fs/hfs/inode.c            |   2 +-
 fs/hfsplus/inode.c        |   2 +-
 fs/iomap/direct-io.c      |   6 +-
 fs/jfs/inode.c            |   2 +-
 fs/netfs/Makefile         |   1 +
 fs/netfs/iterator.c       | 367 ++++++++++++++++++++++++++++++++++
 fs/nfs/direct.c           |   2 +-
 fs/nilfs2/inode.c         |   2 +-
 fs/ntfs3/inode.c          |   2 +-
 fs/ocfs2/aops.c           |   2 +-
 fs/orangefs/inode.c       |   2 +-
 fs/reiserfs/inode.c       |   2 +-
 fs/udf/inode.c            |   2 +-
 include/linux/blk_types.h |   1 +
 include/linux/netfs.h     |   7 +
 include/linux/uio.h       |  59 ++++--
 lib/iov_iter.c            | 407 +++++++++++++++++++++++++++++++++++---
 mm/vmalloc.c              |   1 +
 31 files changed, 889 insertions(+), 103 deletions(-)
 create mode 100644 fs/netfs/iterator.c