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The 'reqs' member of fuse_io_priv serves two purposes. First is to track
the number of oustanding async requests to the server and to signal that
the io request is completed. The second is to be a reference count on the
structure to know when it can be freed.

For sync io requests these purposes can be at odds.  fuse_direct_IO() wants
to block until the request is done, and since the signal is sent when
'reqs' reaches 0 it cannot keep a reference to the object. Yet it needs to
use the object after the userspace server has completed processing
requests. This leads to some handshaking and special casing that it
needlessly complicated and responsible for at least one race condition.

It's much cleaner and safer to maintain a separate reference count for the
object lifecycle and to let 'reqs' just be a count of outstanding requests
to the userspace server. Then we can know for sure when it is safe to free
the object without any handshaking or special cases.

The catch here is that most of the time these objects are stack allocated
and should not be freed. Initializing these objects with a single reference
that is never released prevents accidental attempts to free the objects.

Fixes: 9d5722b7

 ("fuse: handle synchronous iocbs internally")
Cc: stable@vger.kernel.org # v4.1+
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

A useful performance improvement for accessing virtual machine images
via FUSE mount.

See https://bugzilla.redhat.com/show_bug.cgi?id=1220173

 for a use-case
for glusterFS.
Signed-off-by: Ravishankar N <ravishankar@redhat.com>
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>

Make each fuse device clone refer to a separate processing queue.  The only
constraint on userspace code is that the request answer must be written to
the same device clone as it was read off.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

Allow fuse device clones to refer to be distinguished.  This patch just
adds the infrastructure by associating a separate "struct fuse_dev" with
each clone.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reviewed-by: Ashish Samant <ashish.samant@oracle.com>

When an unlocked request is aborted, it is moved from fpq->io to a private
list.  Then, after unlocking fpq->lock, the private list is processed and
the requests are finished off.

To protect the private list, we need to mark the request with a flag, so if
in the meantime the request is unlocked the list is not corrupted.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reviewed-by: Ashish Samant <ashish.samant@oracle.com>

Add a fpq->lock for protecting members of struct fuse_pqueue and FR_LOCKED
request flag.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reviewed-by: Ashish Samant <ashish.samant@oracle.com>

This will allow checking ->connected just with the processing queue lock.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reviewed-by: Ashish Samant <ashish.samant@oracle.com>

This is just two fields: fc->io and fc->processing.

This patch just rearranges the fields, no functional change.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reviewed-by: Ashish Samant <ashish.samant@oracle.com>

This will allow checking ->connected just with the input queue lock.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reviewed-by: Ashish Samant <ashish.samant@oracle.com>

The input queue contains normal requests (fc->pending), forgets
(fc->forget_*) and interrupts (fc->interrupts).  There's also fc->waitq and
fc->fasync for waking up the readers of the fuse device when a request is
available.

The fc->reqctr is also moved to the input queue (assigned to the request
when the request is added to the input queue.

This patch just rearranges the fields, no functional change.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reviewed-by: Ashish Samant <ashish.samant@oracle.com>

Use flags for representing the state in fuse_req.  This is needed since
req->list will be protected by different locks in different states, hence
we'll want the state itself to be split into distinct bits, each protected
with the relevant lock in that state.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

FUSE_REQ_INIT is actually the same state as FUSE_REQ_PENDING and
FUSE_REQ_READING and FUSE_REQ_WRITING can be merged into a common
FUSE_REQ_IO state.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reviewed-by: Ashish Samant <ashish.samant@oracle.com>

Reuse req->waitq.lock for protecting FR_ABORTED and FR_LOCKED flags.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reviewed-by: Ashish Samant <ashish.samant@oracle.com>

Finer grained locking will mean there's no single lock to protect
modification of bitfileds in fuse_req.

So move to using bitops.  Can use the non-atomic variants for those which
happen while the request definitely has only one reference.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reviewed-by: Ashish Samant <ashish.samant@oracle.com>

Based on a patch from Maxim Patlasov <MPatlasov@parallels.com>.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Theoretically we need to order setting of various fields in fc with
fc->initialized.

No known bug reports related to this yet.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

The following pattern is repeated many times:

	req = fuse_get_req_nopages(fc);
	/* Initialize req->(in|out).args */
	fuse_request_send(fc, req);
	err = req->out.h.error;
	fuse_put_request(req);

Create a new replacement helper:

	/* Initialize args */
	err = fuse_simple_request(fc, &args);

In addition to reducing the code size, this will ease moving from the
complex arg-based to a simpler page-based I/O on the fuse device.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

The third out-arg is never actually used.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

path_put() in release could trigger a DESTROY request in fuseblk.  The
possible deadlock was worked around by doing the path_put() with
schedule_work().

This complexity isn't needed if we just hold the inode instead of the path.
Since we now flush all requests before destroying the super block we can be
sure that all held inodes will be dropped.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

Use fuse_abort_conn() instead of fuse_conn_kill() in fuse_put_super().
This flushes and aborts requests still on any queues.  But since we've
already reset fc->connected, those requests would not be useful anyway and
would be flushed when the fuse device is closed.

Next patches will rely on requests being flushed before the superblock is
destroyed.

Use fuse_abort_conn() in cuse_process_init_reply() too, since it makes no
difference there, and we can get rid of fuse_conn_kill().
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

... to fuse_direct_{read,write}().  ->direct_IO() path uses the
iov_iter passed by the caller instead.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Support RENAME_EXCHANGE and RENAME_NOREPLACE flags on the userspace ABI.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

The patch extends fuse_setattr_in, and extends the flush procedure
(fuse_flush_times()) called on ->write_inode() to send the ctime as well as
mtime.
Signed-off-by: Maxim Patlasov <MPatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

...and flush mtime from this.  This allows us to use the kernel
infrastructure for writing out dirty metadata (mtime at this point, but
ctime in the next patches and also maybe atime).
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fuse_ctl_cleanup is only called by __exit fuse_exit
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

The problem is:

1. write cached data to a file
2. read directly from the same file (via another fd)

The 2nd operation may read stale data, i.e. the one that was in a file
before the 1st op. Problem is in how fuse manages writeback.

When direct op occurs the core kernel code calls filemap_write_and_wait
to flush all the cached ops in flight. But fuse acks the writeback right
after the ->writepages callback exits w/o waiting for the real write to
happen. Thus the subsequent direct op proceeds while the real writeback
is still in flight. This is a problem for backends that reorder operation.

Fix this by making the fuse direct IO callback explicitly wait on the
in-flight writeback to finish.
Signed-off-by: Maxim Patlasov <MPatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

Let the kernel maintain i_mtime locally:
 - clear S_NOCMTIME
 - implement i_op->update_time()
 - flush mtime on fsync and last close
 - update i_mtime explicitly on truncate and fallocate

Fuse inode flag FUSE_I_MTIME_DIRTY serves as indication that local i_mtime
should be flushed to the server eventually.
Signed-off-by: Maxim Patlasov <MPatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

Off (0) by default. Will be used in the next patches and will be turned
on at the very end.
Signed-off-by: Maxim Patlasov <MPatlasov@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

open/release operations require userspace transitions to keep track
of the open count and to perform any FS-specific setup.  However,
for some purely read-only FSs which don't need to perform any setup
at open/release time, we can avoid the performance overhead of
calling into userspace for open/release calls.

This patch adds the necessary support to the fuse kernel modules to prevent
open/release operations from hitting in userspace. When the client returns
ENOSYS, we avoid sending the subsequent release to userspace, and also
remember this so that future opens also don't trigger a userspace
operation.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

Various read operations (e.g. readlink, readdir) invalidate the cached
attrs for atime changes.  This patch adds a new function
'fuse_invalidate_atime', which checks for a read-only super block and
avoids the attr invalidation in that case.
Signed-off-by: Andrew Gallagher <andrewjcg@fb.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

makes ->permission() and ->d_revalidate() safety in RCU mode independent
from vfsmount_lock.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

...which just returns -EBUSY if a directory alias would be created.

This is to be used by fuse mkdir to make sure that a buggy or malicious
userspace filesystem doesn't do anything nasty.  Previously fuse used a
private mutex for this purpose, which can now go away.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

As Maxim Patlasov pointed out, it's possible to get a dirty page while it's
copy is still under writeback, despite fuse_page_mkwrite() doing its thing
(direct IO).

This could result in two concurrent write request for the same offset, with
data corruption if they get mixed up.

To prevent this, fuse needs to check and delay such writes.  This
implementation does this by:

 1. check if page is still under writeout, if so create a new, single page
    secondary request for it

 2. chain this secondary request onto the in-flight request

 2/a. if a seconday request for the same offset was already chained to the
    in-flight request, then just copy the contents of the page and discard
    the new secondary request.  This makes sure that for each page will
    have at most two requests associated with it

 3. when the in-flight request finished, send off all secondary requests
    chained onto it
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

Doing dput(parent) is not valid in RCU walk mode.  In RCU mode it would
probably be okay to update the parent flags, but it's actually not
necessary most of the time...

So only set the FUSE_I_ADVISE_RDPLUS flag on the parent when the entry was
recently initialized by READDIRPLUS.

This is achieved by setting FUSE_I_INIT_RDPLUS on entries added by
READDIRPLUS and only dropping out of RCU mode if this flag is set.
FUSE_I_INIT_RDPLUS is cleared once the FUSE_I_ADVISE_RDPLUS flag is set in
the parent.
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Miklos 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: Maxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: stable@vger.kernel.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: Miklos 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: Maxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: Miklos 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: Maxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: Miklos 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: Maxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: Miklos 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: Maxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>