What is hdfuse?
===============

hdfuse is a filesystem in userspace (FUSE https://github.com/libfuse/libfuse or
MacFUSE https://osxfuse.github.io/) to explore data stored in
hierarchical hdf5 files (see https://www.hdfgroup.org/solutions/hdf5/).

All files in the directory given as the hdfuse5 root are mirrored into the
mountpoint with all hdf5 files being presented as a directories. HDF5 Groups
within the files are mapped into further directories, data arrays are files,
and attributes are shown as extended filesystem attributes. Non-hdf5 files
and directories are just mirrored unchanged.

The main purpose is to enable a quick access to the contents of hdf5 files
with normal system tools (grep, find, cat, file browser, etc.).

What do I need to run hdfuse?
==============================

 * python (https://www.python.org/)
 * h5py (https://www.h5py.org/)
 * fusepy (https://github.com/fusepy/fusepy)
 * FUSE or MacFUSE support in you operating system and the required
   permissions to use it. That rules out any Windows variants.

Most distributions have a 'fuse' user group you need to be a member of in
order to be allowed to use fuse (and therefore hdfuse5).

What do I need to do?
=====================


    $ pip install hdfuse
    # This will put you inside the editor (by default Vim), browsing
    # the directory that was mounted with `-d`
    $ hdfuse -d directory_containing_nxs_file


To go back to a shell from Vim you can do `:sh`. The directory path should be
visible just above where the new shell starts. If you `cd` to it then you can
browse it like a normal directory:


    $ # what's in the mountpoint now? a directory for the file!
    $ ls -l tmppath
    total 0
    drwxr-xr-x 1 user user 14704 2011-06-17 16:55 NXtest.h5
    $ # explore the structure
    $ find tmppath -ls
    1    0 drwxr-xr-x   2 user user     4096 Jun 17 16:55 tmppath
    2    0 drwxr-xr-x   1 user user    14704 Jun 17 16:55 tmppath/NXtest.h5
    3    0 drwxr-xr-x   1 user user        0 Jun 17 16:55 tmppath/NXtest.h5/entry
    4    0 -rw-r--r--   1 user user       10 Jun 17 16:55 tmppath/NXtest.h5/entry/ch_data
    5    0 drwxr-xr-x   1 user user        0 Jun 17 16:55 tmppath/NXtest.h5/entry/data
    6    0 -rw-r--r--   1 user user     8000 Jun 17 16:55 tmppath/NXtest.h5/entry/data/comp_data
    7    0 -rw-r--r--   1 user user       28 Jun 17 16:55 tmppath/NXtest.h5/entry/data/flush_data
    8    0 -rw-r--r--   1 user user      160 Jun 17 16:55 tmppath/NXtest.h5/entry/data/r8_data
    9    0 -rw-r--r--   1 user user        4 Jun 17 16:55 tmppath/NXtest.h5/entry/i1_data
    10    0 -rw-r--r--   1 user user        8 Jun 17 16:55 tmppath/NXtest.h5/entry/i2_data
    11    0 -rw-r--r--   1 user user       16 Jun 17 16:55 tmppath/NXtest.h5/entry/i4_data
    12    0 -rw-r--r--   1 user user       32 Jun 17 16:55 tmppath/NXtest.h5/entry/i8_data
    13    0 -rw-r--r--   1 user user       80 Jun 17 16:55 tmppath/NXtest.h5/entry/r4_data
    14    0 -rw-r--r--   1 user user      160 Jun 17 16:55 tmppath/NXtest.h5/entry/r8_data
    15    0 drwxr-xr-x   1 user user        0 Jun 17 16:55 tmppath/NXtest.h5/entry/sample
    16    0 -rw-r--r--   1 user user       20 Jun 17 16:55 tmppath/NXtest.h5/entry/sample/ch_data
    17    0 drwxr-xr-x   1 user user        0 Jun 17 16:55 tmppath/NXtest.h5/link
    18    0 -rw-r--r--   1 user user      160 Jun 17 16:55 tmppath/NXtest.h5/link/renLinkData
    19    0 drwxr-xr-x   1 user user        0 Jun 17 16:55 tmppath/NXtest.h5/link/renLinkGroup
    20    0 -rw-r--r--   1 user user       20 Jun 17 16:55 tmppath/NXtest.h5/link/renLinkGroup/ch_data
    21    0 drwxr-xr-x   1 user user        0 Jun 17 16:55 tmppath/NXtest.h5/link/sample
    22    0 -rw-r--r--   1 user user       20 Jun 17 16:55 tmppath/NXtest.h5/link/sample/ch_data
    $ # find out the attributes of a dataset
    $ getfattr -d tmppath/NXtest.h5/entry/data/comp_data
    # file: tmppath/NXtest.h5/entry/data/comp_data
    user.dtype="int32"
    user.dtype.itemsize="4"
    user.itemsize="4"
    user.ndim="2"
    user.shape="(100, 20)"
    user.size="2000"
    $ # explore the data (see "man od")
    $ od -t dI -w4 -v tmppath/NXtest.h5/entry/data/comp_data | head -30
    0000000           0
    0000004           0
    0000010           0
    0000014           0
    0000020           0
    0000024           0
    0000030           0
    0000034           0
    0000040           0
    0000044           0
    0000050           0
    0000054           0
    0000060           0
    0000064           0
    0000070           0
    0000074           0
    0000100           0
    0000104           0
    0000110           0
    0000114           0
    0000120           1
    0000124           1
    0000130           1
    0000134           1
    0000140           1
    0000144           1
    0000150           1
    0000154           1
    0000160           1
    0000164           1
    $ grep -ar sample tmppath # find some sample information
    mnt/NXtest.h5/entry/sample/ch_data:NeXus sample
    mnt/NXtest.h5/link/renLinkGroup/ch_data:NeXus sample
    mnt/NXtest.h5/link/sample/ch_data:NeXus sample


After you exit the shell and Vim the file will be automatically closed.


Random other questions
======================

What kind of performance can I expect?
--------------------------------------

None. hdfuse was coded as a proof of principle. It holds no state, there
is no caching, no optimisations whatsoever. This left the code quite simple
and concise but still proved to be good enough for the main application:
quick inspection of the file structure of a limited number of files.

It is not recommended to run this on a directory with hundreds of HDF5 files.


Why do I have to mount a directory? Why can't I mount a single file?
--------------------------------------------------------------------

This would be simple to support. The motivation at the time was to be able
explore to multiple files easily with "grep" or similar tools.


Can I have write support?
-------------------------

It is best to use `h5py` directly for this, that way you can be more
confident that the data is correct.

Any drawbacks?
--------------

hdf5 files cannot be opened "normally" by HDF5 aware tools in the tree
mounted via hdfuse5, because to the operating system they look like directories.


Any future plans?
-----------------

Links in hdf5 could be presented as symbolic link in the mounted directory.
Pull requests welcome.

Another idea would get to present data that could be interpreted as image
data in the hdf5 in a format that could be read by standard image file
readers, e.g. as tiff.