truncate_pagecache() doesn't care about old size since commit
cedabed4 ("vfs: Fix vmtruncate() regression").  Let's drop it.
Signed-off-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The feature prevents mistrusted filesystems (ie: FUSE mounts created by
unprivileged users) to grow a large number of dirty pages before
throttling.  For such filesystems balance_dirty_pages always check bdi
counters against bdi limits.  I.e.  even if global "nr_dirty" is under
"freerun", it's not allowed to skip bdi checks.  The only use case for now
is fuse: it sets bdi max_ratio to 1% by default and system administrators
are supposed to expect that this limit won't be exceeded.

The feature is on if a BDI is marked by BDI_CAP_STRICTLIMIT flag.  A
filesystem may set the flag when it initializes its BDI.

The problematic scenario comes from the fact that nobody pays attention to
the NR_WRITEBACK_TEMP counter (i.e.  number of pages under fuse
writeback).  The implementation of fuse writeback releases original page
(by calling end_page_writeback) almost immediately.  A fuse request queued
for real processing bears a copy of original page.  Hence, if userspace
fuse daemon doesn't finalize write requests in timely manner, an
aggressive mmap writer can pollute virtually all memory by those temporary
fuse page copies.  They are carefully accounted in NR_WRITEBACK_TEMP, but
nobody cares.

To make further explanations shorter, let me use "NR_WRITEBACK_TEMP
problem" as a shortcut for "a possibility of uncontrolled grow of amount
of RAM consumed by temporary pages allocated by kernel fuse to process
writeback".

The problem was very easy to reproduce.  There is a trivial example
filesystem implementation in fuse userspace distribution: fusexmp_fh.c.  I
added "sleep(1);" to the write methods, then recompiled and mounted it.
Then created a huge file on the mount point and run a simple program which
mmap-ed the file to a memory region, then wrote a data to the region.  An
hour later I observed almost all RAM consumed by fuse writeback.  Since
then some unrelated changes in kernel fuse made it more difficult to
reproduce, but it is still possible now.

Putting this theoretical happens-in-the-lab thing aside, there is another
thing that really hurts real world (FUSE) users.  This is write-through
page cache policy FUSE currently uses.  I.e.  handling write(2), kernel
fuse populates page cache and flushes user data to the server
synchronously.  This is excessively suboptimal.  Pavel Emelyanov's patches
("writeback cache policy") solve the problem, but they also make resolving
NR_WRITEBACK_TEMP problem absolutely necessary.  Otherwise, simply copying
a huge file to a fuse mount would result in memory starvation.  Miklos,
the maintainer of FUSE, believes strictlimit feature the way to go.

And eventually putting FUSE topics aside, there is one more use-case for
strictlimit feature.  Using a slow USB stick (mass storage) in a machine
with huge amount of RAM installed is a well-known pain.  Let's make simple
computations.  Assuming 64GB of RAM installed, existing implementation of
balance_dirty_pages will start throttling only after 9.6GB of RAM becomes
dirty (freerun == 15% of total RAM).  So, the command "cp 9GB_file
/media/my-usb-storage/" may return in a few seconds, but subsequent
"umount /media/my-usb-storage/" will take more than two hours if effective
throughput of the storage is, to say, 1MB/sec.

After inclusion of strictlimit feature, it will be trivial to add a knob
(e.g.  /sys/devices/virtual/bdi/x:y/strictlimit) to enable it on demand.
Manually or via udev rule.  May be I'm wrong, but it seems to be quite a
natural desire to limit the amount of dirty memory for some devices we are
not fully trust (in the sense of sustainable throughput).

[akpm@linux-foundation.org: fix warning in page-writeback.c]
Signed-off-by: NMaxim Patlasov <MPatlasov@parallels.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Drop a subtree when we find that it has moved or been delated.  This can be
done as long as there are no submounts under this location.

If the directory was moved and we come across the same directory in a
future lookup it will be reconnected by d_materialise_unique().
Signed-off-by: NAnand Avati <avati@redhat.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

On errors unrelated to the filesystem's state (ENOMEM, ENOTCONN) return the
error itself from ->d_revalidate() insted of returning zero (invalid).

Also make a common label for invalidating the dentry.  This will be used by
the next patch.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Use d_materialise_unique() instead of d_splice_alias().  This allows dentry
subtrees to be moved to a new place if there moved, even if something is
referencing a dentry in the subtree (open fd, cwd, etc..).

This will also allow us to drop a subtree if it is found to be replaced by
something else.  In this case the disconnected subtree can later be
reconnected to its new location.

d_materialise_unique() ensures that a directory entry only ever has one
alias.  We keep fc->inst_mutex around the calls for d_materialise_unique()
on directories to prevent a race with mkdir "stealing" the inode.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Userspace can add names containing a slash character to the directory
listing.  Don't allow this as it could cause all sorts of trouble.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Cc: stable@vger.kernel.org

The way how fuse calls truncate_pagecache() from fuse_change_attributes()
is completely wrong. Because, w/o i_mutex held, we never sure whether
'oldsize' and 'attr->size' are valid by the time of execution of
truncate_pagecache(inode, oldsize, attr->size). In fact, as soon as we
released fc->lock in the middle of fuse_change_attributes(), we completely
loose control of actions which may happen with given inode until we reach
truncate_pagecache. The list of potentially dangerous actions includes
mmap-ed reads and writes, ftruncate(2) and write(2) extending file size.

The typical outcome of doing truncate_pagecache() with outdated arguments
is data corruption from user point of view. This is (in some sense)
acceptable in cases when the issue is triggered by a change of the file on
the server (i.e. externally wrt fuse operation), but it is absolutely
intolerable in scenarios when a single fuse client modifies a file without
any external intervention. A real life case I discovered by fsx-linux
looked like this:

1. Shrinking ftruncate(2) comes to fuse_do_setattr(). The latter sends
FUSE_SETATTR to the server synchronously, but before getting fc->lock ...
2. fuse_dentry_revalidate() is asynchronously called. It sends FUSE_LOOKUP
to the server synchronously, then calls fuse_change_attributes(). The
latter updates i_size, releases fc->lock, but before comparing oldsize vs
attr->size..
3. fuse_do_setattr() from the first step proceeds by acquiring fc->lock and
updating attributes and i_size, but now oldsize is equal to
outarg.attr.size because i_size has just been updated (step 2). Hence,
fuse_do_setattr() returns w/o calling truncate_pagecache().
4. As soon as ftruncate(2) completes, the user extends file size by
write(2) making a hole in the middle of file, then reads data from the hole
either by read(2) or mmap-ed read. The user expects to get zero data from
the hole, but gets stale data because truncate_pagecache() is not executed
yet.

The scenario above illustrates one side of the problem: not truncating the
page cache even though we should. Another side corresponds to truncating
page cache too late, when the state of inode changed significantly.
Theoretically, the following is possible:

1. As in the previous scenario fuse_dentry_revalidate() discovered that
i_size changed (due to our own fuse_do_setattr()) and is going to call
truncate_pagecache() for some 'new_size' it believes valid right now. But
by the time that particular truncate_pagecache() is called ...
2. fuse_do_setattr() returns (either having called truncate_pagecache() or
not -- it doesn't matter).
3. The file is extended either by write(2) or ftruncate(2) or fallocate(2).
4. mmap-ed write makes a page in the extended region dirty.

The result will be the lost of data user wrote on the fourth step.

The patch is a hotfix resolving the issue in a simplistic way: let's skip
dangerous i_size update and truncate_pagecache if an operation changing
file size is in progress. This simplistic approach looks correct for the
cases w/o external changes. And to handle them properly, more sophisticated
and intrusive techniques (e.g. NFS-like one) would be required. I'd like to
postpone it until the issue is well discussed on the mailing list(s).

Changed in v2:
 - improved patch description to cover both sides of the issue.
Signed-off-by: NMaxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Cc: stable@vger.kernel.org

Calls like setxattr and removexattr result in updation of ctime.
Therefore invalidate inode attributes to force a refresh.
Signed-off-by: NAnand Avati <avati@redhat.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Cc: stable@vger.kernel.org

The patch fixes a race between ftruncate(2), mmap-ed write and write(2):

1) An user makes a page dirty via mmap-ed write.
2) The user performs shrinking truncate(2) intended to purge the page.
3) Before fuse_do_setattr calls truncate_pagecache, the page goes to
   writeback. fuse_writepage_locked fills FUSE_WRITE request and releases
   the original page by end_page_writeback.
4) fuse_do_setattr() completes and successfully returns. Since now, i_mutex
   is free.
5) Ordinary write(2) extends i_size back to cover the page. Note that
   fuse_send_write_pages do wait for fuse writeback, but for another
   page->index.
6) fuse_writepage_locked proceeds by queueing FUSE_WRITE request.
   fuse_send_writepage is supposed to crop inarg->size of the request,
   but it doesn't because i_size has already been extended back.

Moving end_page_writeback to the end of fuse_writepage_locked fixes the
race because now the fact that truncate_pagecache is successfully returned
infers that fuse_writepage_locked has already called end_page_writeback.
And this, in turn, infers that fuse_flush_writepages has already called
fuse_send_writepage, and the latter used valid (shrunk) i_size. write(2)
could not extend it because of i_mutex held by ftruncate(2).
Signed-off-by: NMaxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Cc: stable@vger.kernel.org

The dev_attrs field of struct class is going away soon, dev_groups
should be used instead.  This converts the cuse class code to use the
correct field.
Acked-by: NMiklos Szeredi <mszeredi@suse.cz>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Niels noted that we don't need the 'dentry = NULL' line.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
CC: Niels de Vos <ndevos@redhat.com>

If we got the inode through fuse_iget() then the attributes are already
up-to-date.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Fuse does instantiation slightly differently from NFS/CIFS which use
d_materialise_unique().
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
CC: stable@vger.kernel.org

Add sanity checks before adding or updating an entry with data received
from readdirplus.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
CC: stable@vger.kernel.org

In case d_lookup() returns a dentry with d_inode == NULL, the dentry is not
returned with dput(). This results in triggering a BUG() in
shrink_dcache_for_umount_subtree():

  BUG: Dentry ...{i=0,n=...} still in use (1) [unmount of fuse fuse]

[SzM: need to d_drop() as well]
Reported-by: NJustin Clift <jclift@redhat.com>
Signed-off-by: NNiels de Vos <ndevos@redhat.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Tested-by: NBrian Foster <bfoster@redhat.com>
Tested-by: NNiels de Vos <ndevos@redhat.com>
CC: stable@vger.kernel.org

The global variable num_physpages is scheduled to be removed, so use
totalram_pages instead of num_physpages at runtime.
Signed-off-by: NJiang Liu <jiang.liu@huawei.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: James Morris <jmorris@namei.org>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Cc: Patrick McHardy <kaber@trash.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

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

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

Changing size of a file on server and local update (fuse_write_update_size)
should be always protected by inode->i_mutex. Otherwise a race like this is
possible:

1. Process 'A' calls fallocate(2) to extend file (~FALLOC_FL_KEEP_SIZE).
fuse_file_fallocate() sends FUSE_FALLOCATE request to the server.
2. Process 'B' calls ftruncate(2) shrinking the file. fuse_do_setattr()
sends shrinking FUSE_SETATTR request to the server and updates local i_size
by i_size_write(inode, outarg.attr.size).
3. Process 'A' resumes execution of fuse_file_fallocate() and calls
fuse_write_update_size(inode, offset + length). But 'offset + length' was
obsoleted by ftruncate from previous step.

Changed in v2 (thanks Brian and Anand for suggestions):
 - made relation between mutex_lock() and fuse_set_nowrite(inode) more
   explicit and clear.
 - updated patch description to use ftruncate(2) in example
Signed-off-by: NMaxim V. Patlasov <MPatlasov@parallels.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

The bug was introduced with async_dio feature: trying to optimize short reads,
we cut number-of-bytes-to-read to i_size boundary. Hence the following example:

	truncate --size=300 /mnt/file
	dd if=/mnt/file of=/dev/null iflag=direct

led to FUSE_READ request of 300 bytes size. This turned out to be problem
for userspace fuse implementations who rely on assumption that kernel fuse
does not change alignment of request from client FS.

The patch turns off the optimization if async_dio is disabled. And, if it's
enabled, the patch fixes adjustment of number-of-bytes-to-read to preserve
alignment.

Note, that we cannot throw out short read optimization entirely because
otherwise a direct read of a huge size issued on a tiny file would generate
a huge amount of fuse requests and most of them would be ACKed by userspace
with zero bytes read.
Signed-off-by: NMaxim Patlasov <MPatlasov@parallels.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

If request submission fails for an async request (i.e.,
get_user_pages() returns -ERESTARTSYS), we currently skip the
-EIOCBQUEUED return and drop into wait_for_sync_kiocb() forever.

Avoid this by always returning -EIOCBQUEUED for async requests. If
an error occurs, the error is passed into fuse_aio_complete(),
returned via aio_complete() and thus propagated to userspace via
io_getevents().
Signed-off-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NMaxim Patlasov <MPatlasov@parallels.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Fix bug introduced by commit 4582a4ab "FUSE: Adapt readdirplus to application
usage patterns".

We need to check for a positive dentry; negative dentries are not added by
readdirplus.  Secondly we need to advise the use of readdirplus on the *parent*,
otherwise the whole thing is useless.  Thirdly all this is only relevant if
"readdirplus_auto" mode is selected by the filesystem.

We advise the use of readdirplus only if the dentry was still valid.  If we had
to redo the lookup then there was no use in doing the -plus version.
Reported-by: NBernd Schubert <bernd.schubert@itwm.fraunhofer.de>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
CC: Feng Shuo <steve.shuo.feng@gmail.com>
CC: stable@vger.kernel.org

An fallocate request without FALLOC_FL_KEEP_SIZE set can extend the
size of a file. Update the inode size after a successful fallocate.

Also invalidate the inode attributes after a successful fallocate
to ensure we pick up the latest attribute values (i.e., i_blocks).
Signed-off-by: NBrian Foster <bfoster@redhat.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

fuse supports hole punch via the fallocate() FALLOC_FL_PUNCH_HOLE
interface. When a hole punch is passed through, the page cache
is not cleared and thus allows reading stale data from the cache.

This is easily demonstrable (using FOPEN_KEEP_CACHE) by reading a
smallish random data file into cache, punching a hole and creating
a copy of the file. Drop caches or remount and observe that the
original file no longer matches the file copied after the hole
punch. The original file contains a zeroed range and the latter
file contains stale data.

Protect against writepage requests in progress and punch out the
associated page cache range after a successful client fs hole
punch.
Signed-off-by: NBrian Foster <bfoster@redhat.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Commit 8b41e671 introduced explicit background checking for fuse_req
structures with BUG_ON() checks for the appropriate type of request in
in the associated send functions. Commit bcba24cc introduced the ability
to send dio requests as background requests but does not update the
request allocation based on the type of I/O request. As a result, a
BUG_ON() triggers in the fuse_request_send_background() background path if
an async I/O is sent.

Allocate a request based on the async state of the fuse_io_priv to avoid
the BUG.
Signed-off-by: NBrian Foster <bfoster@redhat.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Faster kernel compiles by way of fewer unnecessary includes.

[akpm@linux-foundation.org: fix fallout]
[akpm@linux-foundation.org: fix build]
Signed-off-by: NKent Overstreet <koverstreet@google.com>
Cc: Zach Brown <zab@redhat.com>
Cc: Felipe Balbi <balbi@ti.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Asai Thambi S P <asamymuthupa@micron.com>
Cc: Selvan Mani <smani@micron.com>
Cc: Sam Bradshaw <sbradshaw@micron.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Reviewed-by: N"Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Without async DIO write requests to a single file were always serialized.
With async DIO that's no longer the case.

So don't turn on async DIO by default for fear of breaking backward
compatibility.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

The patch improves error handling in fuse_direct_IO(): if we successfully
submitted several fuse requests on behalf of synchronous direct write
extending file and some of them failed, let's try to do our best to clean-up.

Changed in v2: reuse fuse_do_setattr(). Thanks to Brian for suggestion.
Signed-off-by: NMaxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

If user requested direct read beyond EOF, we can skip sending fuse requests
for positions beyond EOF because userspace would ACK them with zero bytes read
anyway. We can trust to i_size in fuse_direct_IO for such cases because it's
called from fuse_file_aio_read() and the latter updates fuse attributes
including i_size.
Signed-off-by: NMaxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

In case of synchronous DIO request (i.e. read(2) or write(2) for a file
opened with O_DIRECT), the patch submits fuse requests asynchronously, but
waits for their completions before return from fuse_direct_IO().

In case of asynchronous DIO request (i.e. libaio io_submit() or a file opened
with O_DIRECT), the patch submits fuse requests asynchronously and return
-EIOCBQUEUED immediately.

The only special case is async DIO extending file. Here the patch falls back
to old behaviour because we can't return -EIOCBQUEUED and update i_size later,
without i_mutex hold. And we have no method to wait on real async I/O
requests.

The patch also clean __fuse_direct_write() up: it's better to update i_size
in its callers. Thanks Brian for suggestion.
Signed-off-by: NMaxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

The patch implements passing "struct fuse_io_priv *io" down the stack up to
fuse_send_read/write where it is used to submit request asynchronously.
io->async==0 designates synchronous processing.

Non-trivial part of the patch is changes in fuse_direct_io(): resources
like fuse requests and user pages cannot be released immediately in async
case.
Signed-off-by: NMaxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

The patch implements a framework to process an IO request asynchronously. The
idea is to associate several fuse requests with a single kiocb by means of
fuse_io_priv structure. The structure plays the same role for FUSE as 'struct
dio' for direct-io.c.

The framework is supposed to be used like this:
 - someone (who wants to process an IO asynchronously) allocates fuse_io_priv
   and initializes it setting 'async' field to non-zero value.
 - as soon as fuse request is filled, it can be submitted (in non-blocking way)
   by fuse_async_req_send()
 - when all submitted requests are ACKed by userspace, io->reqs drops to zero
   triggering aio_complete()

In case of IO initiated by libaio, aio_complete() will finish processing the
same way as in case of dio_complete() calling aio_complete(). But the
framework may be also used for internal FUSE use when initial IO request
was synchronous (from user perspective), but it's beneficial to process it
asynchronously. Then the caller should wait on kiocb explicitly and
aio_complete() will wake the caller up.
Signed-off-by: NMaxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

fuse_release_user_pages() will be indirectly used by fuse_send_read/write
in future patches.
Signed-off-by: NMaxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Normally blocked_waitq will be inactive, so optimize this case.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

The patch solves thundering herd problem. So far as previous patches ensured
that only allocations for background may block, it's safe to wake up one
waiter. Whoever it is, it will wake up another one in request_end() afterwards.
Signed-off-by: NMaxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

A task may have at most one synchronous request allocated. So these
requests need not be otherwise limited.

The patch re-works fuse_get_req() to follow this idea.
Signed-off-by: NMaxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Existing flag fc->blocked is used to suspend request allocation both in case
of many background request submitted and period of time before init_reply
arrives from userspace. Next patch will skip blocking allocations of
synchronous request (disregarding fc->blocked). This is mostly OK, but
we still need to suspend allocations if init_reply is not arrived yet. The
patch introduces flag fc->initialized which will serve this purpose.
Signed-off-by: NMaxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

There are two types of processing requests in FUSE: synchronous (via
fuse_request_send()) and asynchronous (via adding to fc->bg_queue).

Fortunately, the type of processing is always known in advance, at the time
of request allocation. This preparatory patch utilizes this fact making
fuse_get_req() aware about the type. Next patches will use it.
Signed-off-by: NMaxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

it's used only as a flag to distinguish normal pipes/FIFOs from the
internal per-task one used by file-to-file splice.  And pipe->files
would work just as well for that purpose...
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>