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    Subject[PATCH v2 0/4] iov_iter: Add extraction helpers
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    Hi Al,

    Here are four patches to provide support for extracting pages from an
    iov_iter, where such a thing makes sense, if you could take a look?

    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 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 left untouched (on the assumption that
    the caller manages their lifetime).

    The determination is:

    UBUF/IOVEC + READ -> pin
    UBUF/IOVEC + WRITE -> get
    PIPE + READ -> 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).

    [!] NOTE that this function is not marked EXPORT_SYMBOL_GPL because
    it's intended as a replacement for iov_iter_get_pages*(), which is
    not itself marked _GPL.

    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. This will get or
    pin the pages as appropriate.

    (4) 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 (2) 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.

    Changes:
    ========
    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/166697254399.61150.1256557652599252121.stgit@warthog.procyon.org.uk/ # rfc
    Link: https://lore.kernel.org/r/166722777223.2555743.162508599131141451.stgit@warthog.procyon.org.uk/ # rfc
    Link: https://lore.kernel.org/r/166732024173.3186319.18204305072070871546.stgit@warthog.procyon.org.uk/ # rfc
    Link: https://lore.kernel.org/r/166869687556.3723671.10061142538708346995.stgit@warthog.procyon.org.uk/ # rfc

    ---
    David Howells (4):
    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


    fs/netfs/Makefile | 1 +
    fs/netfs/iterator.c | 367 +++++++++++++++++++++++++++++++++++++++
    include/linux/mm.h | 74 --------
    include/linux/mm_types.h | 73 ++++++++
    include/linux/netfs.h | 7 +
    include/linux/uio.h | 4 +
    lib/iov_iter.c | 350 +++++++++++++++++++++++++++++++++++++
    mm/vmalloc.c | 1 +
    8 files changed, 803 insertions(+), 74 deletions(-)
    create mode 100644 fs/netfs/iterator.c


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