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?
[!] 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 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).
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 #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/166697254399.61150.1256557652599252121.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # rfc
Link: https://lore.kernel.org/r/166722777223.2555743.162508599131141451.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # rfc
Link: https://lore.kernel.org/r/166732024173.3186319.18204305072070871546.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # rfc
Link: https://lore.kernel.org/r/166869687556.3723671.10061142538708346995.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # 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
