FUSE: Implement atomic lookup + open

FUSE, as of now, makes aggressive lookup calls into libfuse in certain code
paths. These lookup calls possibly can be avoided in some cases. Incoming
two patches addresses the issue of aggressive lookup calls.

First patch handles the case where we open first time a file/dir or create
a file (O_CREAT) but do a lookup first on it. After lookup is performed
we make another call into libfuse to open the file. Now these two separate
calls into libfuse can be combined and performed as a single call into
libfuse.

Second patch handles the case when we are opening an already existing file
(positive dentry). Before this open call, we re-validate the inode and
this re-validation does a lookup on the file and verify the inode.
This separate lookup also can be avoided (for non-dir) and combined
with open call into libfuse.

Here is the link to libfuse patches which implement atomic open

https://github.com/d-hans/libfuse/commit/5255ce89decac719...
https://github.com/d-hans/libfuse/commit/346b9feb2de5b6ff...
https://github.com/d-hans/libfuse/commit/ac010dac446a9267...


Dharmendra Singh (2):
  FUSE: Implement atomic lookup + open
  FUSE: Avoid lookup in d_revalidate()

 fs/fuse/dir.c             | 170 +++++++++++++++++++++++++++++++++-----
 fs/fuse/file.c            |  30 ++++++-
 fs/fuse/fuse_i.h          |  13 ++-
 fs/fuse/inode.c           |   4 +-
 fs/fuse/ioctl.c           |   2 +-
 include/uapi/linux/fuse.h |   2 +
 6 files changed, 195 insertions(+), 26 deletions(-)

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2.17.1