... returning -E... upon error and amount of data left in iter after
(possible) truncation upon success.  Note, that normal case gives
a non-zero (positive) return value, so any tests for != 0 _must_ be
updated.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Conflicts:
	fs/ext4/file.c

	Alignment checks for dio depend upon the range truncation done by
generic_write_checks().  They can be done as soon as we got ocfs2_rw_lock()
and that actually makes ocfs2_prepare_inode_for_write() simpler.

	The only thing to watch out for is restoring the original count
in "unlock and redo without dio" case.  Position doesn't need to be
restored, since we change it only in O_APPEND case and in that case it
will be reassigned anyway.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

it's &iocb->ki_pos; no need to obfuscate.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

it's easier to do generic_write_checks() first
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

already done by caller.  We used to call __fuse_direct_write(), which
called generic_write_checks(); now the former got expanded, bringing
the latter to the surface.  It used to be called all along and calling
it from there had been wrong all along...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

simpler that way...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

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

all remaining callers are passing 0; some just obscure that fact.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

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

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

A side effect worth noting: in O_APPEND case we set ->ki_pos early,
so if it turns out to be an error or a zero-length write, we'll
end up with ->ki_pos modified.  Safe, since all callers never
look at the ->ki_pos after the call of __generic_file_write_iter()
returning non-positive, all the way to caller of ->write_iter() and
those discard ->ki_pos when getting that.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

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

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

That allows ->write_iter() instances much more convenient life wrt
iocb->ki_pos (and fixes several filesystems with borderline POSIX
violations when zero-length write succeeds and changes the current
position).
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Now that no one is using rw, remove it completely.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

The rw parameter to direct_IO is redundant with iov_iter->type, and
treated slightly differently just about everywhere it's used: some users
do rw & WRITE, and others do rw == WRITE where they should be doing a
bitwise check. Simplify this with the new iov_iter_rw() helper, which
always returns either READ or WRITE.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

And use iov_iter_rw() instead.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Most filesystems call through to these at some point, so we'll start
here.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Get either READ or WRITE out of iter->type.
Signed-off-by: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

no remaining users
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

readv() and writev() should _not_ ignore all but the first ->iov_len,
among other things.  Really weird abuse of those syscalls - it
expects a vector element per channel, with identical lengths (it
actually assumes them to be identical - no checking is done).
readv() and writev() are really bad match for that.  Unfortunately,
userland API is userland API and we can't do anything about them.

Converted to ->read_iter/->write_iter.  Please, _please_ don't do
anything of that kind when designing new interfaces.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

	Things Not To Do When Writing A Driver, part 1001st:
have writev() and write() on the same file doing completely
different things.  As in, "interpret very different sets of
commands".

	We _can_ handle that, but it's a bloody bad idea.
Don't do that in new drivers.  Ever.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

all remaining instances of aio_{read,write} (all 4 of them) have explicit
->read and ->write resp.; do_sync_read/do_sync_write is never called by
__vfs_read/__vfs_write anymore and no other users had been left.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

store reference to iter instead of that to iovec
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

we just change the calling conventions here; more work to follow.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Note that _these_ guys have ->read() and ->write() left in place - they are
eqiuvalent to what we'd get if we replaced those with NULL, but we are
talking about hot paths here.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

All places outside of core VFS that checked ->read and ->write for being NULL or
called the methods directly are gone now, so NULL {read,write} with non-NULL
{read,write}_iter will do the right thing in all cases.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

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

all writable files that might be used as backing store for /dev/loop
already support ->write_iter()
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

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

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

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

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

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

... and fix the case when the area we are asked to read crosses
a hugepage boundary
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... and request the same from the local cache - all filesystems with
anything usable for that support those already.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

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

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