X-Git-Url: https://git.rrq.au/?a=blobdiff_plain;f=fusefile.8;h=b952f5574075e2ae9b0df699ead855873618a772;hb=cc21d1ab7c157da459a33ddd6b30d862cd144eec;hp=b4bd50d314f7b3504677285e7660e1fbc17da885;hpb=a56b1315a88e0c89573e99a22e7ae6353f845760;p=rrq%2Ffusefile.git diff --git a/fusefile.8 b/fusefile.8 index b4bd50d..b952f55 100644 --- a/fusefile.8 +++ b/fusefile.8 @@ -1,19 +1,67 @@ .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[fuse options\fR] \fBmountpoint\fR \fIfilename/from-to\fR ... +.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. +\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 @@ -39,46 +87,153 @@ 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 +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 +.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 +\fB$ partx -oNR,START,SECTORS \fIA\fR + NR START SECTORS + 1 2048 2097152 + 2 2099200 409600 + 3 2508800 14268383 +.RE +.br +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 +.RE +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. + +.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. -If the mountpoint file doesn't exist, then \fBfusefile\fR creates it, -and removes it when unmounted. +Unmounting is done with "\fBfusermount -u\fR \fImountpoint\fR" as +usual. A \fBfusedisk\fR mount is unmounted by \fIroot\fR using +\fBumount\fR. +.SH SEE ALSO +\fBfuse, fusermount, mount, dmsetup\fR .SH AUTHOR -Ralph Rönnquist +Ralph Rönnquist . +