The fileattr API conversion broke lsattr on ntfs3g.

Previously the ioctl(... FS_IOC_GETFLAGS) returned an EINVAL error, but
after the conversion the error returned by the fuse filesystem was not
propagated back to the ioctl() system call, resulting in success being
returned with bogus values.

Fix by checking for outarg.result in fuse_priv_ioctl(), just as generic
ioctl code does.

Reported-by: Jean-Pierre André <jean-pierre.andre@wanadoo.fr>
Fixes: 72227eac177d ("fuse: convert to fileattr")
Cc: <stable@vger.kernel.org> # v5.13
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Due to the introduction of kmap_local_*, the storage of slots used for
short-term mapping has changed from per-CPU to per-thread.  kmap_atomic()
disable preemption, while kmap_local_*() only disable migration.

There is no need to disable preemption in several kamp_atomic places used
in fuse.

Link: https://lwn.net/Articles/836144/
Signed-off-by: Peng Hao <flyingpeng@tencent.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Since fuse just passes ioctl args through to/from server, converting to the
fileattr API is more involved, than most other filesystems.

Both .fileattr_set() and .fileattr_get() need to obtain an open file to
operate on.  The simplest way is with the following sequence:

  FUSE_OPEN
  FUSE_IOCTL
  FUSE_RELEASE

If this turns out to be a performance problem, it could be optimized for
the case when there's already a file (any file) open for the inode.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Next patch will expand ioctl code and fuse/file.c is large enough as it is.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>