completed overlay option

[rrq/fusefile.git] / fusefile.8

diff --git a/fusefile.8 b/fusefile.8
index b4bd50d314f7b3504677285e7660e1fbc17da885..183a362bce8c42bff4b27764ba01a4930625b37e 100644 (file)
--- a/fusefile.8
+++ b/fusefile.8
@@ -4,7 +4,7 @@
 fusefile \- FUSE file mount for combining file fragments
 
 .SH SYNOPSIS
-.B fusefile \fR[fuse options\fR] \fBmountpoint\fR \fIfilename/from-to\fR ...
+.B fusefile \fR[\fIfuse-opts\fR] \fBmountpoint\fR \fR[\fIoverlay\fR] \fIfilename/from-to\fR ...
 
 .SH DESCRIPTION
 
@@ -15,6 +15,13 @@ as a 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 the "-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:
@@ -66,6 +73,14 @@ position 2442:
 \fB$ fusefile y x/2442: x/:2442\fR
 .RE
 
+Protect raw disk image file with an overlay:
+.RS
+\fB# fusefile -ononempty disk.raw -overlay:today disk.raw
+.RE
+By this 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.
+
 .SH NOTES
 
 Note that \fBfusefile\fR opens the nominated source file or files
@@ -78,6 +93,10 @@ If a source is reduced in size, access will be inconsistent.
 If the mountpoint file doesn't exist, then \fBfusefile\fR creates it,
 and removes it when unmounted.
 
+Using an overlay file makes the fused file writable regardless of the
+fused fragemnts 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.
 
 .SH AUTHOR