Introduce a new truncate calling sequence into fs/mm subsystems. Rather than
setattr > vmtruncate > truncate, have filesystems call their truncate sequence
from ->setattr if filesystem specific operations are required. vmtruncate is
deprecated, and truncate_pagecache and inode_newsize_ok helpers introduced
previously should be used.

simple_setattr is introduced for simple in-ram filesystems to implement
the new truncate sequence. Eventually all filesystems should be converted
to implement a setattr, and the default code in notify_change should go
away.

simple_setsize is also introduced to perform just the ATTR_SIZE portion
of simple_setattr (ie. changing i_size and trimming pagecache).

To implement the new truncate sequence:
- filesystem specific manipulations (eg freeing blocks) must be done in
  the setattr method rather than ->truncate.
- vmtruncate can not be used by core code to trim blocks past i_size in
  the event of write failure after allocation, so this must be performed
  in the fs code.
- convert usage of helpers block_write_begin, nobh_write_begin,
  cont_write_begin, and *blockdev_direct_IO* to use _newtrunc postfixed
  variants. These avoid calling vmtruncate to trim blocks (see previous).
- inode_setattr should not be used. generic_setattr is a new function
  to be used to copy simple attributes into the generic inode.
- make use of the better opportunity to handle errors with the new sequence.

Big problem with the previous calling sequence: the filesystem is not called
until i_size has already changed.  This means it is not allowed to fail the
call, and also it does not know what the previous i_size was. Also, generic
code calling vmtruncate to truncate allocated blocks in case of error had
no good way to return a meaningful error (or, for example, atomically handle
block deallocation).

Cc: Christoph Hellwig <hch@lst.de>
Acked-by: NJan Kara <jack@suse.cz>
Signed-off-by: NNick Piggin <npiggin@suse.de>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

We don't name our generic fsync implementations very well currently.
The no-op implementation for in-memory filesystems currently is called
simple_sync_file which doesn't make too much sense to start with,
the the generic one for simple filesystems is called simple_fsync
which can lead to some confusion.

This patch renames the generic file fsync method to generic_file_fsync
to match the other generic_file_* routines it is supposed to be used
with, and the no-op implementation to noop_fsync to make it obvious
what to expect.  In addition add some documentation for both methods.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

__aio_put_req() plays sick games with file refcount.  What
it wants is fput() from atomic context; it's almost always
done with f_count > 1, so they only have to deal with delayed
work in rare cases when their reference happens to be the
last one.  Current code decrements f_count and if it hasn't
hit 0, everything is fine.  Otherwise it keeps a pointer
to struct file (with zero f_count!) around and has delayed
work do __fput() on it.

Better way to do it: use atomic_long_add_unless( , -1, 1)
instead of !atomic_long_dec_and_test().  IOW, decrement it
only if it's not the last reference, leave refcount alone
if it was.  And use normal fput() in delayed work.

I've made that atomic_long_add_unless call a new helper -
fput_atomic().  Drops a reference to file if it's safe to
do in atomic (i.e. if that's not the last one), tells if
it had been able to do that.  aio.c converted to it, __fput()
use is gone.  req->ki_file *always* contributes to refcount
now.  And __fput() became static.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

This is an implementation of ->llseek useable for the rare special case
when userspace expects the seek to succeed but the (device) file is
actually not able to perform the seek.  In this case you use noop_llseek()
instead of falling back to the default implementation of ->llseek.
Signed-off-by: NJan Blunck <jblunck@suse.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Because BTRFS can do RAID and such, we need our own submit hook so we can setup
the bio's in the correct fashion, and handle checksum errors properly.  So there
are a few changes here

1) The submit_io hook.  This is straightforward, just call this instead of
submit_bio.

2) Allow the fs to return -ENOTBLK for reads.  Usually this has only worked for
writes, since writes can fallback onto buffered IO.  But BTRFS needs the option
of falling back on buffered IO if it encounters a compressed extent, since we
need to read the entire extent in and decompress it.  So if we get -ENOTBLK back
from get_block we'll return back and fallback on buffered just like the write
case.

I've tested these changes with fsx and everything seems to work.  Thanks,
Signed-off-by: NJosef Bacik <josef@redhat.com>
Signed-off-by: NChris Mason <chris.mason@oracle.com>

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

 >  =============================================
 >  [ INFO: possible recursive locking detected ]
 >  2.6.31-2-generic #14~rbd3
 >  ---------------------------------------------
 >  firefox-3.5/4162 is trying to acquire lock:
 >   (&s->s_vfs_rename_mutex){+.+.+.}, at: [<ffffffff81139d31>] lock_rename+0x41/0xf0
 >
 >  but task is already holding lock:
 >   (&s->s_vfs_rename_mutex){+.+.+.}, at: [<ffffffff81139d31>] lock_rename+0x41/0xf0
 >
 >  other info that might help us debug this:
 >  3 locks held by firefox-3.5/4162:
 >   #0:  (&s->s_vfs_rename_mutex){+.+.+.}, at: [<ffffffff81139d31>] lock_rename+0x41/0xf0
 >   #1:  (&sb->s_type->i_mutex_key#11/1){+.+.+.}, at: [<ffffffff81139d5a>] lock_rename+0x6a/0xf0
 >   #2:  (&sb->s_type->i_mutex_key#11/2){+.+.+.}, at: [<ffffffff81139d6f>] lock_rename+0x7f/0xf0
 >
 >  stack backtrace:
 >  Pid: 4162, comm: firefox-3.5 Tainted: G         C 2.6.31-2-generic #14~rbd3
 >  Call Trace:
 >   [<ffffffff8108ae74>] print_deadlock_bug+0xf4/0x100
 >   [<ffffffff8108ce26>] validate_chain+0x4c6/0x750
 >   [<ffffffff8108d2e7>] __lock_acquire+0x237/0x430
 >   [<ffffffff8108d585>] lock_acquire+0xa5/0x150
 >   [<ffffffff81139d31>] ? lock_rename+0x41/0xf0
 >   [<ffffffff815526ad>] __mutex_lock_common+0x4d/0x3d0
 >   [<ffffffff81139d31>] ? lock_rename+0x41/0xf0
 >   [<ffffffff81139d31>] ? lock_rename+0x41/0xf0
 >   [<ffffffff8120eaf9>] ? ecryptfs_rename+0x99/0x170
 >   [<ffffffff81552b36>] mutex_lock_nested+0x46/0x60
 >   [<ffffffff81139d31>] lock_rename+0x41/0xf0
 >   [<ffffffff8120eb2a>] ecryptfs_rename+0xca/0x170
 >   [<ffffffff81139a9e>] vfs_rename_dir+0x13e/0x160
 >   [<ffffffff8113ac7e>] vfs_rename+0xee/0x290
 >   [<ffffffff8113c212>] ? __lookup_hash+0x102/0x160
 >   [<ffffffff8113d512>] sys_renameat+0x252/0x280
 >   [<ffffffff81133eb4>] ? cp_new_stat+0xe4/0x100
 >   [<ffffffff8101316a>] ? sysret_check+0x2e/0x69
 >   [<ffffffff8108c34d>] ? trace_hardirqs_on_caller+0x14d/0x190
 >   [<ffffffff8113d55b>] sys_rename+0x1b/0x20
 >   [<ffffffff81013132>] system_call_fastpath+0x16/0x1b

The trace above is totally reproducible by doing a cross-directory
rename on an ecryptfs directory.

The issue seems to be that sys_renameat() does lock_rename() then calls
into the filesystem; if the filesystem is ecryptfs, then
ecryptfs_rename() again does lock_rename() on the lower filesystem, and
lockdep can't tell that the two s_vfs_rename_mutexes are different.  It
seems an annotation like the following is sufficient to fix this (it
does get rid of the lockdep trace in my simple tests); however I would
like to make sure I'm not misunderstanding the locking, hence the CC
list...
Signed-off-by: NRoland Dreier <rdreier@cisco.com>
Cc: Tyler Hicks <tyhicks@linux.vnet.ibm.com>
Cc: Dustin Kirkland <kirkland@canonical.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Now that the last user passing a NULL file pointer is gone we can remove
the redundant dentry argument and associated hacks inside vfs_fsynmc_range.

The next step will be removig the dentry argument from ->fsync, but given
the luck with the last round of method prototype changes I'd rather
defer this until after the main merge window.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

The entries in xattr handler table should be immutable (ie const)
like other operation tables.

Later patches convert common filesystems. Uncoverted filesystems
will still work, but will generate a compiler warning.
Signed-off-by: NStephen Hemminger <shemminger@vyatta.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Currently the way we do freezing is by passing sb>s_bdev to freeze_bdev and then
letting it do all the work.  But freezing is more of an fs thing, and doesn't
really have much to do with the bdev at all, all the work gets done with the
super.  In btrfs we do not populate s_bdev, since we can have multiple bdev's
for one fs and setting s_bdev makes removing devices from a pool kind of tricky.
This means that freezing a btrfs filesystem fails, which causes us to corrupt
with things like tux-on-ice which use the fsfreeze mechanism.  So instead of
populating sb->s_bdev with a random bdev in our pool, I've broken the actual fs
freezing stuff into freeze_super and thaw_super.  These just take the
super_block that we're freezing and does the appropriate work.  It's basically
just copy and pasted from freeze_bdev.  I've then converted freeze_bdev over to
use the new super helpers.  I've tested this with ext4 and btrfs and verified
everything continues to work the same as before.

The only new gotcha is multiple calls to the fsfreeze ioctl will return EBUSY if
the fs is already frozen.  I thought this was a better solution than adding a
freeze counter to the super_block, but if everybody hates this idea I'm open to
suggestions.  Thanks,
Signed-off-by: NJosef Bacik <josef@redhat.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

... and switch the simple "loop over superblocks and do something"
loops to it.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

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

At the same time we can kill s_need_restart and local mutex in there.
__put_super() made public for a while; will be gone later.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

use atomic_inc_not_zero(&sb->s_active) instead of playing games with
checking ->s_count > S_BIAS
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

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

It will be used in suspend code and serves as an easy wrap around
copy_from_user. Similar to simple_read_from_buffer, it takes care
of transfers with proper lengths depending on available and count
parameters and advances ppos appropriately.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>

Currently, device claiming for exclusive open is done after low level
open - disk->fops->open() - has completed successfully.  This means
that exclusive open attempts while a device is already exclusively
open will fail only after disk->fops->open() is called.

cdrom driver issues commands during open() which means that O_EXCL
open attempt can unintentionally inject commands to in-progress
command stream for burning thus disturbing burning process.  In most
cases, this doesn't cause problems because the first command to be
issued is TUR which most devices can process in the middle of burning.
However, depending on how a device replies to TUR during burning,
cdrom driver may end up issuing further commands.

This can't be resolved trivially by moving bd_claim() before doing
actual open() because that means an open attempt which will end up
failing could interfere other legit O_EXCL open attempts.
ie. unconfirmed open attempts can fail others.

This patch resolves the problem by introducing claiming block which is
started by bd_start_claiming() and terminated either by bd_claim() or
bd_abort_claiming().  bd_claim() from inside a claiming block is
guaranteed to succeed and once a claiming block is started, other
bd_start_claiming() or bd_claim() attempts block till the current
claiming block is terminated.

bd_claim() can still be used standalone although now it always
synchronizes against claiming blocks, so the existing users will keep
working without any change.

blkdev_open() and open_bdev_exclusive() are converted to use claiming
blocks so that exclusive open attempts from these functions don't
interfere with the existing exclusive open.

This problem was discovered while investigating bko#15403.

  https://bugzilla.kernel.org/show_bug.cgi?id=15403

The burning problem itself can be resolved by updating userspace
probing tools to always open w/ O_EXCL.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-by: NMatthias-Christian Ott <ott@mirix.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>

This cleans up a few of the complaints of __generic_block_fiemap.  I've
fixed all the typing stuff, used inline functions instead of macros,
gotten rid of a couple of variables, and made sure the size and block
requests are all block aligned.  It also fixes a problem where sometimes
FIEMAP_EXTENT_LAST wasn't being set properly.
Signed-off-by: NJosef Bacik <josef@redhat.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kill_fasync() uses a central rwlock, candidate for RCU conversion, to
avoid cache line ping pongs on SMP.

fasync_remove_entry() and fasync_add_entry() can disable IRQS on a short
section instead during whole list scan.

Use a spinlock per fasync_struct to synchronize kill_fasync_rcu() and
fasync_{remove|add}_entry(). This spinlock is IRQ safe, so sock_fasync()
doesnt need its own implementation and can use fasync_helper(), to
reduce code size and complexity.

We can remove __kill_fasync() direct use in net/socket.c, and rename it
to kill_fasync_rcu().
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Requested by hch, for consistency now it is exported.

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Anton Blanchard <anton@samba.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jan Kara <jack@suse.cz>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Commit 148f948b (vfs: Introduce new
helpers for syncing after writing to O_SYNC file or IS_SYNC inode) broke
the raw driver.

We now call through generic_file_aio_write -> generic_write_sync ->
vfs_fsync_range.  vfs_fsync_range has:

        if (!fop || !fop->fsync) {
                ret = -EINVAL;
                goto out;
        }

But drivers/char/raw.c doesn't set an fsync method.

We have two options: fix it or remove the raw driver completely.  I'm
happy to do either, the fact this has been broken for so long suggests it
is rarely used.

The patch below adds an fsync method to the raw driver.  My knowledge of
the block layer is pretty sketchy so this could do with a once over.

If we instead decide to remove the raw driver, this patch might still be
useful as a backport to 2.6.33 and 2.6.32.
Signed-off-by: NAnton Blanchard <anton@samba.org>
Reviewed-by: NJan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <jens.axboe@oracle.com>
Reviewed-by: NJeff Moyer <jmoyer@redhat.com>
Tested-by: NJeff Moyer <jmoyer@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

It was tolerable until Eric went and added 8388608.

Cc: Eric Paris <eparis@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This fixes inefficient page-by-page reads on POSIX_FADV_RANDOM.

POSIX_FADV_RANDOM used to set ra_pages=0, which leads to poor performance:
a 16K read will be carried out in 4 _sync_ 1-page reads.

In other places, ra_pages==0 means
- it's ramfs/tmpfs/hugetlbfs/sysfs/configfs
- some IO error happened
where multi-page read IO won't help or should be avoided.

POSIX_FADV_RANDOM actually want a different semantics: to disable the
*heuristic* readahead algorithm, and to use a dumb one which faithfully
submit read IO for whatever application requests.

So introduce a flag FMODE_RANDOM for POSIX_FADV_RANDOM.

Note that the random hint is not likely to help random reads performance
noticeably.  And it may be too permissive on huge request size (its IO
size is not limited by read_ahead_kb).

In Quentin's report (http://lkml.org/lkml/2009/12/24/145), the overall
(NFS read) performance of the application increased by 313%!
Tested-by: NQuentin Barnes <qbarnes+nfs@yahoo-inc.com>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: <stable@kernel.org>			[2.6.33.x]
Cc: <qbarnes+nfs@yahoo-inc.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This gives the filesystem more information about the writeback that
is happening.  Trond requested this for the NFS unstable write handling,
and other filesystems might benefit from this too by beeing able to
distinguish between the different callers in more detail.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Add a new UMOUNT_NOFOLLOW flag to umount(2).  This is needed to prevent
symlink attacks in unprivileged unmounts (fuse, samba, ncpfs).

Additionally, return -EINVAL if an unknown flag is used (and specify
an explicitly unused flag: UMOUNT_UNUSED).  This makes it possible for
the caller to determine if a flag is supported or not.

CC: Eugene Teo <eugene@redhat.com>
CC: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

apply function to vfsmounts in set returned by collect_mounts(),
stop if it returns non-zero.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Analog of is_subdir for vfsmount,dentry pairs, moved from audit_tree.c
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

No one is calling this anymore as everyone has switched to
invalidate_mapping_pages long time ago.  Also update a few
references to it in comments.  nfs has two more, but I can't
easily figure what they are actually referring to, so I left
them as-is.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

re-order structure super_block to remove 16 bytes of alignment padding
on 64bit builds.

This shrinks the size of super_block from 712 to 696 bytes so requiring
one fewer 64 byte cache lines.
Signed-off-by: NRichard Kennedy <richard@rsk.demon.co.uk>

-----
patch against 2.6.33-rc5
compiled & tested on x86_64 AMDX2 desktop machine.

I've been running with this patch applied for several weeks with no
problems.

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

Remove the EXPORT_UNUSED_SYMBOL of simple_prepare_write

Collapse simple_prepare_write into it's only caller, though
making it simpler and clearer to understand.
Signed-off-by: NBoaz Harrosh <bharrosh@panasas.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

This removes 8 bytes of padding from struct inode on 64bit builds, and
so allows 1 more object/slab in the inode_cache when using slub.
Signed-off-by: NRichard Kennedy <richard@rsk.demon.co.uk>
----
patch against 2.6.33-rc8
compiled & tested on x86_64 AMDX2

I've been running this patch for over a week with no obvious problems
regards
Richard
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

commit 5300990c had stepped on a rather
nasty mess: definitions of ACC_MODE used to be different.  Fixed the
resulting breakage, converting them to variant that takes O_... value;
all callers have that and it actually simplifies life (see tomoyo part
of changes).
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Quota code requires unlocked version of this function. Off course
we can just copy-paste the code, but copy-pasting is always an evil.
Signed-off-by: NDmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: NJan Kara <jack@suse.cz>

This question was determined to be a bug which was fixed in
commit 4a3b0a49.
Signed-off-by: NAndreas Gruenbacher <agruen@suse.de>
Cc: Jan Blunck <jblunck@suse.de>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

* pull ACC_MODE to fs.h; we have several copies all over the place
* nightmarish expression calculating f_mode by f_flags deserves a helper
too (OPEN_FMODE(flags))
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

After I_SYNC was split from I_LOCK the leftover is always used together with
I_NEW and thus superflous.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

We recently go rid of all callers of do_sync_file_range as they're better
served with vfs_fsync or the filemap_write_and_wait.  Now that
do_sync_file_range is down to a single caller fold it into it so that people
don't start using it again accidentally.  While at it also switch it from
using __filemap_fdatawrite_range(..., WB_SYNC_ALL) to the more clear
filemap_fdatawrite_range().
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Change all async metadata buffers to use [READ|WRITE]_META I/O types
so that the I/O doesn't get issued immediately. This allows merging of
adjacent metadata requests but still prioritises them over bulk data.
This shows a 10-15% improvement in sequential create speed of small
files.

Don't include the log buffers in this classification - leave them as
sync types so they are issued immediately.
Signed-off-by: NDave Chinner <dgc@sgi.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAlex Elder <aelder@sgi.com>

Currently the locking in blockdev_direct_IO is a mess, we have three different
locking types and very confusing checks for some of them.  The most
complicated one is DIO_OWN_LOCKING for reads, which happens to not actually be
used.

This patch gets rid of the DIO_OWN_LOCKING - as mentioned above the read case
is unused anyway, and the write side is almost identical to DIO_NO_LOCKING.
The difference is that DIO_NO_LOCKING always sets the create argument for
the get_blocks callback to zero, but we can easily move that to the actual
get_blocks callbacks.  There are four users of the DIO_NO_LOCKING mode:
gfs already ignores the create argument and thus is fine with the new
version, ocfs2 only errors out if create were ever set, and we can remove
this dead code now, the block device code only ever uses create for an
error message if we are fully beyond the device which can never happen,
and last but not least XFS will need the new behavour for writes.

Now we can replace the lock_type variable with a flags one, where no flag
means the DIO_NO_LOCKING behaviour and DIO_LOCKING is kept as the first
flag.  Separate out the check for not allowing to fill holes into a separate
flag, although for now both flags always get set at the same time.

Also revamp the documentation of the locking scheme to actually make sense.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>