.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 ...
+.br
+.B fusefile \fB-dump\fR \fR[\fIfuse-opts\fR] \fBmountpoint\fR \fR[\fIoverlay\fR] \fIfilename/from-to\fR ...
+.br
+.B fusefile \fB-push\fR \fR[\fIfuse-opts\fR] \fBmountpoint\fR \fR[\fIoverlay\fR] \fIfilename/from-to\fR ...
+.br
+.B fusedisk \fR[\fIfuse-opts\fR] \fBmountpoint\fR \fR[\fIoverlay\fR] \fIfilename/from-to\fR ...
.SH DESCRIPTION
-\fBfusefile\fR 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. 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
-\fB-overlay:\fIfilename\fR 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).
+\fBfusefile\fR is a FUSE \fIfile mount\fR that presents a series of
+fragments of other files as a contiguous concatenation. Technically it
+bind mounts a driver on top of the filename mountpoint to provide
+access to the given file fragments as if in a single, contiguous file.
+
+\fBfusefile\fR accepts over-writing on the fused file (i.e. the
+mountpoint) which gets distributed accordingly to the fragments. But
+neither the fused file nor the fragments can change size; any writing
+thus merely over-writes content without truncating fragments. All
+fragment files are held open while \fBfusefile\fR is active.
+
+By using the optional \fB-overlay:\fIfilename\fR argument between the
+mount point and the fragments, an overlay file may be set up. The
+overlay file will then be used by \fBfusefile\fR for capturing writes
+to the fused file (i.e. the mountpoint). The overlay file will contain
+any new written fused file regions followed by meta data to
+distinguish between new, written content and old content that comes
+from the fragments.
+
+By instead using the \fB-overlay:\fIlist\fR argument where \fIlist\fR
+is a colon-separated list of filenames, \fBfusefile\fR will use those
+as an ordered stack of overlays and "inject" them as fragments on top
+of each other.
+
+The option \fB-dump\fR as first argument together with a fusefile
+setup will print the setup to standard output rather than establishing
+a fusefile mount. This is of most use with a prior overlay setup where
+then the printout includes the portions of updates that have been
+captured in the overlay. The printout is the series of fusefile
+fragment argments to give in order to intersperse the captured overlay
+portions according to the overlay table.
+
+The option \fB-push\fR as first argument together with a fusefile
+setup will push the overlay into the sources (except for
+write-protected fragments). This is only of use with a prior overlay
+setup where then the updates that have been captured in the overlay
+get pushed into the fragments.
+
+\fBfusedisk\fR is a helper script to set up a \fBfusefile\fR as a
+block device (via \fIfuseblk\fR) by using the device mapper
+(\fBdmsetup\fR) to manage an empty block device mapping where content
+is handled at the mountpoint via \fBfusefile\fR. (Note that the same
+thing may be done with the device manager directly, but then all
+fragments need to be in sectors of N*512 bytes whereas with
+\fBfusedisk\fR, only the fused file as a whole is "clipped" at nearest
+N*512 bytes below actual size)
+
+.SH FRAGMENT ARGUMENTS
The fragment arguments include the filename of a source file, and
optionally start and end byte positions. All in all there five
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
+Character 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.
+.SH OPTIONS
+
+This section enumerates the most interesting options to use with
+\fBfuesfile\fR. See "man fuse" and "man mount" for more options.
+
+.TP
+\fB-dump\fR
+
+The \fB-dump\fR "option" tells \fBfusefile\fR to print out the
+applicable fragment sequence for the current setup, including the
+overlay table, if any. The printout is done instead of setting up a
+mount point.
+
+.TP
+\fB-o\fIallow_other\fB
+
+The fuse option \fI-oallow_other\fR is needed for sharing the fused
+file with other users who otherwise will not have access to it
+(including "root"). Note however that this must first be enabled in
+\fI/etc/fuse.conf\fR.
+
+.TP
+\fB-o\fInonempty\fR
+
+The fuse option \fI-ononempty\fR may need to be used when reusing an
+existing file as mountpoint.
+
+.TP
+\fB-o\fIuid=...\fR and \fB-o\fIgid=...\fR,
+
+These mount options, where \fI...\fR is a user or group id
+respectively, are useful for root when using \fBfusedisk\fR and
+thereby give user or group ownership for the mount to the nominated
+user or group.
+
.SH EXAMPLES
+This section illustrates uses of \fBfusefile\fR.
-Insert file "y" into file "x" at position 1200:
+.SS Exanple 1.
+Insert a file "y" into a file "x" at position 1200.
.RS
\fB$ fusefile -ononempty x x/:1200 y x/1200:\fR
.RE
-The bind mount shadows the original file "x", and presents the
-fused file instead.
+This also shadows the original file "x" and presents the fused file
+instead.
+.SS Example 2.
Make fused file y be a swap of the beginning and end of file "x", at
-position 2442:
+position 2442.
.RS
\fB$ fusefile y x/2442: x/:2442\fR
.RE
-Replace a partition in an image file with a different file
+.SS Example 3.
+Replace partition 2 of an image file, \fIA\fR, with a different
+file, \fIX\fR. For this example the partition table looks as follows.
.RS
-# Check the partition table
-.br
-\fB$ partx -oNR,START,SECTORS disk.raw\fR
+\fB$ partx -oNR,START,SECTORS \fIA\fR
NR START SECTORS
1 2048 2097152
2 2099200 409600
3 2508800 14268383
+.RE
.br
-# Replace partition 2 of 409600 sectors from 2099200 with
-.br
-# the file "insert.fat" clipped to 409600 sectors.
-.br
-\fB$ fusefile -ononempty disk.raw \\
- disk.raw/0:$(( 2099200*512 )) \\
- insert.fat/0:$(( 409600*512 )) \\
- disk.raw/$(( (2099200+409600)*512 )):\fR
+As each sector is 512 bytes the clipping points around partition 2 are
+1074790400 and 1284505600 and the insertion size is 209715200 bytes.
+The \fBfusefile\fR comman will therefore be as follows.
+.RS
+\fB$ fusefile -ononempty \fIA\fB \fIA\fB/:1074790400 \fIX\fB/:209715200 \fIA\fB/1284505600\fR
.RE
+Note that the fused file shadows the original file \fIA\fR.
+.SS Example 4.
Protect raw disk image file with an overlay:
.RS
\fB$ fusefile -ononempty disk.raw -overlay:today disk.raw\fR
file, "disk.raw" from changes, and also override the pathname
"disk.raw" to be the fused file.
+.SS Example 5.
+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.
+
+.RS
+\fB$ fusefile -ononempty \fIA\fR \fB-overlay:\fIB\fB \fIA\fR
+.RE
+
+The overlay file, \fIB\fR in the example, contains all changes to the
+shadowed original file, \fIA\fR. The overlay file contains only the
+newly written regions and content is otherwise obtained from the
+original file.
+
+To that end, the overlay file also contains a "marker table" at the
+end as if appended to the fused file. That part of the file is outside
+of the fused file; and it's simply an element count followed by pairs
+of byte addresses that tell which regions of the fused file have been
+captured into the overlay file. (The marker table is of course
+maintained so that adjoining regions are collapsed)
+
+Thus, an overlay file may be reused to later re-establish the same
+fused file with overlay as previously, to continue capturing more
+changes.
+
+.SS Example 6.
+As final example, we set up a fused block device \fIy\fR 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
-before bind mounting. With the fuse option \fI-ononempty\fR 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 the fused file will present the new content.
-If a source is reduced in size, access will be inconsistent.
+\fBfusefile\fR opens the nominated source files before any bind
+mounting. With the fuse option \fI-ononempty\fR it will bind over an
+non-empty file, which may be useful. The source files remain open, but
+the source fragments are not recomputed. If a source file changes the
+fused file will present the new content. 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.
+usual. A \fBfusedisk\fR mount is unmounted by \fIroot\fR using
+\fBumount\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.
+.SH SEE ALSO
+\fBfuse, fusermount, mount, dmsetup\fR
.SH AUTHOR
projects / rrq / fusefile.git / blobdiff