userlandfs: implement get_fs_info using ioctl

This avoids introducing an entirely custom hook in FUSE.
It uses the ioctl hook in an unconventional way (calling it with no
valid fuse_file_info) but this can be fixed if a filesystem requires it
(by opening a file handle on /, doing the ioctl, then closing again).

An updated version of fusesmb-haiku is available and confirmed working:
https://github.com/haikuarchives/fusesmb-haiku

Change-Id: If1268113874363fa035e5340be75e9f5198216d6
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5199
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>

FUSE compat: add Haiku extension

* Add a way for a FUSE module to supply Haiku-specific extensions.
This allows it to integrate better with Haiku while only requiring
minimal changes on the FUSE module itself.

* For now, there is only one extension: another function pointer for
"get_fs_info", which lets the FUSE module fill in an fs_info struct.
FUSE provides no good way to otherwise communicate extra information,
such as the volume flags (e.g. B_FS_IS_SHARED).

* A FUSE module can signal that it supports the Haiku extensions by
a) defining HAS_HAIKU_FUSE_EXTENSIONS before including the fuse
headers
b) setting the global variable gHasHaikuFuseExtensions to 1 in
its initialization
Otherwise, the Haiku extensions are completely invisible to the
FUSE module.

* Our error codes are already negative, so return ENOSYS instead of -ENOSYS.
* fuse_fs_utimens(): Fall back to the utime() hook, if utimens() is not
available.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@29720 a95241bf-73f2-0310-859d-f6bbb57e9c96

* Added "fuse_api.h" header wrapping the inclusion of <fuse.h>.
* Implemented the fuse_fs_*() functions.
* More work on the initialization procedure for the client file system. We do
now start a separate thread which calls the main() function. It won't return
from fuse_main_real() until unmounting the FS. We create a fuse_fs structure
and call the client FS initialization and cleanup hooks.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@29613 a95241bf-73f2-0310-859d-f6bbb57e9c96

* Our error codes are already negative, so return ENOSYS instead of -ENOSYS.
* fuse_fs_utimens(): Fall back to the utime() hook, if utimens() is not
available.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@29720 a95241bf-73f2-0310-859d-f6bbb57e9c96

* Added "fuse_api.h" header wrapping the inclusion of <fuse.h>.
* Implemented the fuse_fs_*() functions.
* More work on the initialization procedure for the client file system. We do
now start a separate thread which calls the main() function. It won't return
from fuse_main_real() until unmounting the FS. We create a fuse_fs structure
and call the client FS initialization and cleanup hooks.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@29613 a95241bf-73f2-0310-859d-f6bbb57e9c96