fusefile
========
:colon: :
:noop:

This project implements a "fuse" device to mount as a single file that
is a concatenation of fragments of one or more files. The fused file
allows overwriting the parts files, but not changing their sizes, and
only for parts files that are writable upon first access.

FUSE file mount for combining file fragments.
 
== SYNOPSIS

====
*fusefile* [ _fuse options_ ] *mountpoint*  [ _overlay_ ] +_filename_/from:to+ ...
====

## DESCRIPTION

*fusefile* is FUSE file mount that presents a series of fragments of
other files as a contiguous concatenation. It bind mounts a driver on
top of the file mountpoint to present the nominated file fragments as
a single, contiguous file. single, contiguous file. It accepts
over-writing on the fused file which gets distributed accordingly to
the fragments, but cannot change size.

An optional overlay file is declared with an
**-overlay:**__filename__ argument between the mount point and
the fragments. This file is then set up as an overlay for capturing
writes to the fused file. The overlay file will contain the written
fused file regions, followed by meta data to distinguish between
written content and "holes" (where content comes from the fused
fragments).
       
The fragment arguments include the filename of a source file, and
optionally start and end byte positions. All in all there five
variations:

 * __filename__ include all of the file.

 * __filename/__ include all of the file named with "/" in the pathname. This case requires a final "/", since the last "/" separates the filename from the position details.

 * __filename/from__ include the file from the given start position, to end.

 * __filename/-to__ include the file from beginning to the given end position (not included).

 * __filename/from:to__ include the file from the given start position, up to the given end position (not included). 

## EXAMPLES

.Insert file "y" into file "x" at position 1200:
  
    $ fusefile -ononempty x x/:1200 y x/1200:

That mount will shadow the original file "x", and presents the
fused file instead.

.Make file y be a swap of the beginning and end of file "x", at position 2442:

    $ fusefile y x/2442: x/:2442

.Replace a partition in an image file with a different file

    $ partx -oNR,START,SECTORS disk.raw
    NR   START  SECTORS
     1    2048  2097152
     2 2099200   409600
     3 2508800 14268383
    # Replace partition 2 of 409600 sectors from 2099200 with
    # the file "insert.fat" clipped to 409600 sectors.
    $ fusefile -ononempty disk.raw \
         disk.raw/0:$(( 2099200*512 )) \
         insert.fat/0:$(( 409600*512 )) \
         disk.raw/$(( (2099200+409600)*512 )):

.Protect raw disk image file with an overlay:
    $ fusefile -ononempty disk.raw -overlay:today disk.raw

By that set up, the overlay file, "today", will protect the disk image
file, "disk.raw" from changes, and also override the pathname
"disk.raw" to be the fused file.


## NOTES

Note that **fusefile** opens the nominated source file(s) before bind
mounting. With the fuse option __-ononempty__ it will bind over an
non-empty file, which may be useful. The source file descriptors
remain open, but the source fragments are not recomputed. If a source
file changes or reduces in size "behind" the fused file, then anything
may happen.

If the mountpoint file doesn't exist, then **fusefile** creates it.

Unmounting is done with "**fusermount -u** __mountpoint__" as usual.

Using an overlay file makes the fused file writable regardless of the
fused fragments with the overlay file containing any changes to the
original. The overlay file is reusable for subsequent fusing of the
same fragments for reconstructing a prior session with changes.

## AUTHOR

Ralph Rönnquist <ralph.ronnquist@gmail.com>.