fuse: close file synchronously

Hi,

There is a long-standing demand for syncronous behaviour of fuse_release:

http://sourceforge.net/mailarchive/message.php?msg_id=19343889
http://sourceforge.net/mailarchive/message.php?msg_id=29814693

A few months ago Avati and me explained why such a feature would be useful:

http://sourceforge.net/mailarchive/message.php?msg_id=29889055
http://sourceforge.net/mailarchive/message.php?msg_id=29867423

In short, the problem is that fuse_release (that's called on last user close(2)) sends FUSE_RELEASE to userspace and returns without waiting for ACK from userspace. Consequently, there is a gap when user regards the file released while userspace fuse is still working on it. An attempt to access the file from another node leads to complicated synchronization problems because the first node still "holds" the file.

The patch-set resolves the problem by making fuse_release synchronous:
wait for ACK from userspace for FUSE_RELEASE if the feature is ON.

To keep single-threaded userspace implementations happy the patch-set ensures that by the time fuse_release_common calls fuse_file_put, no more in-flight I/O exists. Asynchronous fuse callbacks (like fuse_readpages_end) cannot trigger FUSE_RELEASE anymore. Hence, we'll never block in contexts other than close().

Thanks,
Maxim

---

Maxim Patlasov (5):
fuse: add close_wait flag to fuse_conn
fuse: cosmetic rework of fuse_send_readpages
fuse: wait for end of IO on release
fuse: enable close_wait feature
fuse: fix synchronous case of fuse_file_put()

 fs/fuse/file.c            |   82 ++++++++++++++++++++++++++++++++++++++-------
 fs/fuse/fuse_i.h          |    3 ++
 fs/fuse/inode.c           |    5 ++-
 include/uapi/linux/fuse.h |    7 +++-
 4 files changed, 82 insertions(+), 15 deletions(-)

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