simillar to iov_iter_fault_in_readable() but differs in that it is
not limited to faulting in the first iovec and instead faults in
"bytes" bytes iterating over the iovecs as necessary.

Also, instead of only faulting in the first and last page of the
range, all pages are faulted in.

This function is needed by NTFS when it does multi page file
writes.
Signed-off-by: NAnton Altaparmakov <anton@tuxera.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

iovec-backed iov_iter instances are assumed to satisfy several properties:
	* no more than UIO_MAXIOV elements in iovec array
	* total size of all ranges is no more than MAX_RW_COUNT
	* all ranges pass access_ok().

The problem is, invariants of data structures should be established in the
primitives creating those data structures, not in the code using those
primitives.  And iov_iter_init() violates that principle.  For a while we
managed to get away with that, but once the use of iov_iter started to
spread, it didn't take long for shit to hit the fan - missed check in
sys_sendto() had introduced a roothole.

We _do_ have primitives for importing and validating iovecs (both native and
compat ones) and those primitives are almost always followed by shoving the
resulting iovec into iov_iter.  Life would be considerably simpler (and safer)
if we combined those primitives with initializing iov_iter.

That gives us two new primitives - import_iovec() and compat_import_iovec().
Calling conventions:
	iovec = iov_array;
	err = import_iovec(direction, uvec, nr_segs,
			   ARRAY_SIZE(iov_array), &iovec,
			   &iter);
imports user vector into kernel space (into iov_array if it fits, allocated
if it doesn't fit or if iovec was NULL), validates it and sets iter up to
refer to it.  On success 0 is returned and allocated kernel copy (or NULL
if the array had fit into caller-supplied one) is returned via iovec.
On failure all allocations are undone and -E... is returned.  If the total
size of ranges exceeds MAX_RW_COUNT, the excess is silently truncated.

compat_import_iovec() expects uvec to be a pointer to user array of compat_iovec;
otherwise it's identical to import_iovec().

Finally, import_single_range() sets iov_iter backed by single-element iovec
covering a user-supplied range -

	err = import_single_range(direction, address, size, iovec, &iter);

does validation and sets iter up.  Again, size in excess of MAX_RW_COUNT gets
silently truncated.

Next commits will be switching the things up to use of those and reducing
the amount of iov_iter_init() instances.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Copy iter and kmemdup the underlying array for the copy.  Returns
a pointer to result of kmemdup() to be kfree()'d later.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

similar to iov_iter_kvec(), for ITER_BVEC ones
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

BTW, do we want memcpy_nocache()?
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

initialization of kvec-backed iov_iter
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

... without bothering with copy_..._user()
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Just have copy_page_{to,from}_iter() fall back to kmap_atomic +
copy_{to,from}_iter() + kunmap_atomic() in ITER_BVEC case.  As
the matter of fact, that's what we want to do for any iov_iter
kind that isn't blocking - e.g. ITER_KVEC will also go that way
once we recognize it on iov_iter.c primitives level
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

same as iterate_all_kinds, but iterator is moved to the position past
the last byte we'd handled.

iov_iter_advance() converted to it
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

iterate_all_kinds(iter, size, ident, step_iovec, step_bvec)
iterates through the ranges covered by iter (up to size bytes total),
repeating step_iovec or step_bvec for each of those.  ident is
declared in expansion of that thing, either as struct iovec or
struct bvec, and it contains the range we are currently looking
at.  step_bvec should be a void expression, step_iovec - a size_t
one, with non-zero meaning "stop here, that many bytes from this
range left".  In the end, the amount actually handled is stored
in size.

iov_iter_copy_from_user_atomic() and iov_iter_alignment() converted
to it.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

The branches of the if (i->type & ITER_BVEC) statement in
iov_iter_single_seg_count() are the wrong way around; if ITER_BVEC is
clear then we use i->bvec, when we should be using i->iov.  This fixes
it.

In my case, the symptom that this caused was that a KVM guest doing
filesystem operations on a virtual disk would result in one of qemu's
threads on the host going into an infinite loop in
generic_perform_write().  The loop would hit the copied == 0 case and
call iov_iter_single_seg_count() to reduce the number of bytes to try
to process, but because of the error, iov_iter_single_seg_count()
would just return i->count and the loop made no progress and continued
forever.

Cc: stable@vger.kernel.org # 3.16+
Signed-off-by: NPaul Mackerras <paulus@samba.org>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

For DAX, we want to be able to copy between iovecs and kernel addresses
that don't necessarily have a struct page.  This is a fairly simple
rearrangement for bvec iters to kmap the pages outside and pass them in,
but for user iovecs it gets more complicated because we might try various
different ways to kmap the memory.  Duplicating the existing logic works
out best in this case.

We need to be able to write zeroes to an iovec for reads from unwritten
ranges in a file.  This is performed by the new iov_iter_zero() function,
again patterned after the existing code that handles iovec iterators.

[AV: and export the buggers...]
Signed-off-by: NMatthew Wilcox <willy@linux.intel.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

The third argument of fuse_get_user_pages() "nbytesp" refers to the number of
bytes a caller asked to pack into fuse request. This value may be lesser
than capacity of fuse request or iov_iter.  So fuse_get_user_pages() must
ensure that *nbytesp won't grow.

Now, when helper iov_iter_get_pages() performs all hard work of extracting
pages from iov_iter, it can be done by passing properly calculated
"maxsize" to the helper.

The other caller of iov_iter_get_pages() (dio_refill_pages()) doesn't need
this capability, so pass LONG_MAX as the maxsize argument here.

Fixes: c9c37e2e ("fuse: switch to iov_iter_get_pages()")
Reported-by: NWerner Baumann <werner.baumann@onlinehome.de>
Tested-by: NMaxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

... instead of maximal size.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

New variant of iov_iter - ITER_BVEC in iter->type, backed with
bio_vec array instead of iovec one.  Primitives taught to deal
with such beasts, __swap_write() switched to using that kind
of iov_iter.

Note that bio_vec is just a <page, offset, length> triple - there's
nothing block-specific about it.  I've left the definition where it
was, but took it from under ifdef CONFIG_BLOCK.

Next target: ->splice_write()...
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

if we'd ended up in the end of a segment, jump to the
beginning of the next one (iov_offset = 0, iov++),
rather than having the next primitive deal with that.

Ought to be folded back...
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

parallel to copy_page_to_iter().  pipe_write() switched to it (and became
->write_iter()).
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

same as iov_iter_get_pages(), except that pages array is allocated
(kmalloc if possible, vmalloc if that fails) and left for caller to
free.  Lustre and NFS ->direct_IO() switched to it.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

counts the pages covered by iov_iter, up to given limit.
do_block_direct_io() and fuse_iter_npages() switched to
it.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

iov_iter_get_pages(iter, pages, maxsize, &start) grabs references pinning
the pages of up to maxsize of (contiguous) data from iter.  Returns the
amount of memory grabbed or -error.  In case of success, the requested
area begins at offset start in pages[0] and runs through pages[1], etc.
Less than requested amount might be returned - either because the contiguous
area in the beginning of iterator is smaller than requested, or because
the kernel failed to pin that many pages.

direct-io.c switched to using iov_iter_get_pages()
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

For now, just use the same thing we pass to ->direct_IO() - it's all
iovec-based at the moment.  Pass it explicitly to iov_iter_init() and
account for kvec vs. iovec in there, by the same kludge NFS ->direct_IO()
uses.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

returns the value aligned as badly as the worst remaining segment
in iov_iter is.  Use instead of open-coded equivalents.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

all callers can use copy_page_from_iter() and it actually simplifies
them.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>