fusefile
========

This project implements a "fuse" device to mount as a single file that
is a concatenation of fragments of one or more files. By default the
fused file is read-only.

A writeable fused file is set up by associating the mount with a
"scratch pad file"

FUSE file mount for combining file fragments.
 
== SYNOPSIS
 *fusefile* [_fuse options_] *mountpoint* _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.

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). 

 * *pad=*_filename_ when this is given as first argument, the fused
 file is set up as a writable random-access file, where the write
 events are captured appended to the nominated "pad" file. The new
 content is inserted into the fused file but not the original files,
 and fragments are split up and adjusted as needed so as to make the
 write events appear as insertions inteo the fused file.

## EXAMPLES

Insert file "y" into file "x" at position 1200:
  
    $ fusefile -ononempty x x/-1200 y x/1200
The bind mount shadows the original file "x", and presents the
composite instead.

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

    $ fusefile y x/2442 x/-2442

## 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, anything may happen.

If the mountpoint file doesn't exist, then **fusefile** creates it,
and removes it when unmounted.

When a "pad" file is used, it is updated as an "ar" archive where each
write event is a new member appended at the end. The "pad" member has
two additional, newline-terminated text lines with the insertion
position and the member size (ascii decimal digits), before the actual
insertion event content.

## AUTHOR

Ralph Rönnquist <ralph.ronnquist@gmail.com>