minor editing and document fusedisk

diff --git a/fusefile.8 b/fusefile.8
index f9ca25db611e0a89d1ef3ef2d4d4cf07abd1d316..148609b6086083a005c56c1febbeded0c902569e 100644 (file)
--- a/fusefile.8
+++ b/fusefile.8
@@ -1,10 +1,11 @@
 .mso www.tmac
 .TH fusefile 8
 .SH NAME
-fusefile \- FUSE file mount for combining file fragments
+fusefile, fusedisk \- FUSE file mount for combining file fragments
 
 .SH SYNOPSIS
 .B fusefile \fR[\fIfuse-opts\fR] \fBmountpoint\fR \fR[\fIoverlay\fR] \fIfilename/from-to\fR ...
+.B fusedisk \fR[\fIfuse-opts\fR] \fBmountpoint\fR \fR[\fIoverlay\fR] \fIfilename/from-to\fR ...
 
 .SH DESCRIPTION
 
@@ -46,18 +47,22 @@ relative to the end of the file. If "length" is negative or omitted it
 means that position relative to the end.
 
 .TP
-\fIfilename/start\fR
-include bytes from the given start. This is the same as "/start+"
+\fIfilename/start\fR include bytes from the given start. This is the
+same as "/start+"
 
 .P
 Note that a negative start position is clipped to 0 and a too large
-end position  is clipped to the end of the file.
+end position is clipped to the end of the file.
 
 .P
 Charater devices are treated as being of any given finite size, but
 have size 0 by default. For example, "/dev/zero/:100" means a fragment
 of 100 NUL bytes.
 
+\fBfusedisk\fR is a helper script to set up a fused file as a block
+device. This uses the device mapper (\fBdmsetup\fR) to manage empty
+block device mappings where content is handled via \fBfusefile\fR.
+
 .SH EXAMPLES
 
 Insert file "y" into file "x" at position 1200:
@@ -101,6 +106,15 @@ 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.
 
+As final example, make a fused block device y as a swap of the
+beginning and end of file "x", at position 2442:
+.RS
+\fB$ sudo fusedisk -ouid=1000 y x/2442: x/:2442\fR
+.RE
+Note the use of \fBsudo\fR for becoming \fIroot\fR, which is required
+for block device handling, and also the \fB-ouid=1000\fR option so as
+to make the block device \fIy\fR be owned by the user with id 1000.
+
 .SH NOTES
 
 Note that \fBfusefile\fR opens the nominated source file or files
@@ -112,13 +126,33 @@ If a source is reduced in size, access will be inconsistent.
 
 If the mountpoint file doesn't exist, then \fBfusefile\fR creates it.
 
-Unmounting is done with "\fBfusermount -u\fR \fImountpoint\fR" as
-usual.
+The fuse option \fI-oallow_other\fR is needed for sharing the fused
+file with other users (including "root"). Note however that this
+option must first be enabled in \fI/etc/fuse.conf\fR.
 
-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.
+Unmount is done with "\fBfusermount -u\fR \fImountpoint\fR" as usual.
+
+.P
+\fBUsing overlay file\fR
+
+.P
+A fusefile mount with an \fIoverlay file\fR is writable regardless of
+the fused fragments, but all updates are written to the overlay file
+instead of to the fragments.
+
+  $ fusefile -oallow_other -ononempty disk.raw \fB-overlay:today\fR disk.raw
+
+The overlay file ("today" in the example) contains all changes to the
+original file ("disk.raw" in the exmaple). It also contains a marker
+table at the end, as if appended to the fused file. This part of the
+overlay file is outside of the fused file; it consists of an element
+count followed by pairs of byte addresses to mark out which regions
+have been written into the overlay file, and the marker table is
+maintained so that adjoining regions are collapsed.
+
+That means that an overlay file may be reused to later re-establish
+the same fused file with overlay as previously, to continue capturing
+more changes.
 
 .SH AUTHOR