de.9

Unix操作系统minix 2.0源码

.CD "de \(en disk editor"
.SX "de\fR [\fB\(enw\fR] \fIblock_device"
.SX "de \(enr \fIfile
.FL "\(enr" "Recover a file that has been removed"
.FL "\(enw" "Enable writing, so device can be modified"
.EX "de \(enr /usr/ast/prog.c" "Undo the effects of: \fIrm /usr/ast/prog.c\fR"
.EX "de \(enw /dev/fd0" "Edit \fI/dev/fd0\fR for writing"
.PP
The \fIde\fR program allows a system administrator to examine and modify
a \s-2MINIX\s0 file system device. 
Commands are available to move to any address on the disk
and display the disk block contents. This information may
be presented in one of three visual modes: as two-byte words,
as ASCII characters or as a bit map. The disk may be searched
for a string of characters. If the \fB\(enw\fR option is given,
\fIde\fR will open the device for writing and words may be
modified.
Without this flag, writing is prohibited.
Lost blocks and files can be recovered using a variety of
commands. The \fB\(enr\fR option supports automated recovery of
files removed by \fIunlink\fR.
.SS "Positioning"
.PP
Disks are divided into blocks (also called \*(OQzones\*(CQ) of 1024
bytes. \fIDe\fR keeps a current address on the disk as a
block number and a byte offset within the block. In some
visual modes the offset is rounded off, for example, in
\*(OQword\*(CQ mode the offset must be even.
.PP
There are different types of blocks on a file system device,
including a super block, bit maps, i-nodes and data blocks.
\fIDe\fR knows the type of the current block, but will allow
most positioning commands and visual modes to function
anywhere on the disk.
.PP
The \fIf\fR command (or PGDN on the keypad) moves forward to the
next block, similarly \fIb\fR (PGUP) moves backwards one block.
\fIF\fR (END) moves to the last block and \fIB\fR (HOME) moves to the
first block.
.PP
The arrow keys (or 
\fIu\fR, \fId\fR, \fIl\fR, and \fIr\fR) change the current
address by small increments. The size of the increment
depends on the current display mode, as shown below. The
various sizes suit each display and pointers move on the
screen to follow each press of an arrow key.
.HS
.if t .ta .75iR 1.5iR 2.25iR 3.0iR 3.75iR
.if n .ta .75i 1.5i 2.25i 3.0i 3.75i
.nf
\fB	Mode	Up	Down	Left	Right\fR
	Word	\(mi2	+2	\(mi32	+32
	Block	\(mi64	+64	\(mi1	+1
	Map	\(mi256	+256	\(mi4	+4
.fi
.HS
The \fIg\fR command allows movement to any specified block.
Like all commands that take arguments, a prompt and
subsequent input are written to the bottom line of the
screen. Numerical entry may be decimal, octal or
hexadecimal, for example 234, \(mi1, 070, 0xf3, \(miX3C.
.PP
While checking an i-node one may want to move to a block
listed as a zone of the file. The \fIG\fR command takes the
contents at the current address in the device as a block
number and indirectly jumps to that block.
.PP
The address may be set to the start of any i-node using
the \fI\fR command and supplying an i-node number. The \fII\fR
command maps a given file name into an i-node address.
The file must exist on the current device and this
device must be mounted.
.SS "The Display"
.PP
The first line of the display contains the device name,
the name of the current output file (if one is open) and
the current search string. If \fIde\fR is being run with
the \fB\(enw\fR option then the device name is flagged with \*(OQ(w).\*(CQ
If a string is too long to fit on the line it is marked with \*(OQ...\*(CQ.
.PP
The second line contains the current block number, the
total number of blocks, and the type of the current block.
The types are: boot, super, i-node bit map, zone bit map,
i-nodes and data block.
If the current address is
within a data block then the string \*(OQin use\*(CQ is displayed
if the block corresponds to a set in the zone bit map.
.PP
The third line shows the offset in the current block. If
the current address is within either the i-node or zone bit
maps then the i-node or block number corresponding to the
current bit is shown. If the current address is within an
i-node then the i-node number and \*(OQin use\*(CQ status is displayed.
If the address is within a bit map or i-node block, but past
the last usable entry, then the string \*(OQpadding\*(CQ is shown.
.PP
The rest of the screen is used to display data from the
current block. There are three visual display modes:
\*(OQword,\*(CQ \*(OQblock,\*(CQ and \*(OQmap.\*(CQ 
The \fIv\fR command followed by
\fIw\fR, \fIb\fR, or \fIm\fR sets the current display mode.
.PP
In \*(OQword\*(CQ mode 16 words, of two bytes each, are shown in
either base 2, 8, 10 or 16. The current base is displayed
to the far right of the screen. It can be changed using the
\fIo\fR command followed by either an \fIh\fR (hexadecimal), \fId\fR
(decimal), \fIo\fR (octal) or \fIb\fR (binary).
.PP
\fIDe\fR knows where i-nodes are, and will display the
contents in a readable format, including the \fIrwx\fR bits,
the user name and the time field. If the current page
is at the beginning of the super block, or an executable
file or an \fIar\fR archive, then \fIde\fR will also inform
the user. In all other cases the contents of the 16
words are shown to the right as equivalent ASCII
characters.
.PP
In \*(OQblock\*(CQ mode a whole block of 1024 bytes is displayed
as ASCII characters, 64 columns by 16 lines. Control codes
are shown as highlighted characters. If the high order bit
is set in any of the 1024 bytes then an \*(OQMSB\*(CQ flag is shown
on the far right of the screen, but these bytes are not
individually marked.
.PP
In \*(OQmap\*(CQ mode 2048 bits (256 bytes) are displayed from the
top to the bottom (32 bits) and from the left to the right
of the screen. Bit zero of a byte is towards the top of the
screen. This visual mode is generally used to observe
the bit map blocks. The number of set bits displayed is
written on the far right of the screen.
.SS "Searching"
.PP
A search for an ASCII string is initiated by the \fI/\fR command.
Control characters not used for other purposes may be
entered in the search string, for example CTRL-J is an end-of-line 
character. The search is from the current position to
the end of the current device.
.PP
Once a search string has been defined by a use of \fI/\fR, the
next search may be initiated with the \fIn\fR command, (a \fI/\fR
followed immediately by an ENTER is equivalent to an \fIn\fR).
.PP
Whenever a search is in progress \fIde\fR will append
one \fI.\fR to the prompt line for every 500 blocks searched. If the
string is found between the end of the file system and the
actual end of the device, then the current address is set to
the end of the file system.
.PP
Some of the positioning commands push the current address
and visual mode in a stack before going to a new address.
These commands are 
\fIB\fR, \fIF\fR, \fIg\fR, \fIG\fR, \fIi\fR, \fII\fR, \fIn\fR, \fIx\fR and 
\fI/\fR. 
The \fIp\fR
(previous) command pops the last address and visual mode
from the stack. This stack is eight entries deep.
.SS "Modifying the File System"
.PP
The \fIs\fR command will prompt for a data word and store it at
the current address on the disk. This is used to change
information that can not be easily changed by any other
means.
.PP
The data word is 16 bits wide, it may be entered in decimal,
octal or hexadecimal. Remember that the \fB\(enw\fR option must
be specified for the \fIs\fR command to operate. Be careful
when modifying a mounted file system.
.SS "Recovering Files"
.PP
Any block on the disk may be written to an output file.
This is used to recover blocks marked as free on the
disk. A write command will request a file name the first
time it is used, on subsequent writes the data is appended
to the current output file.
.PP
The name of the current output file is changed using the
\fIc\fR command. This file should be on a different file system,
to avoid overwriting an i-node or block before it is
recovered.
.PP
An ASCII block is usually recovered using the \fIw\fR command.
All bytes will have their most significant bit cleared before
being written to the output file. Bytes containing '\\0'
or '\\177' are not copied. The \fIW\fR command writes the current
block (1024 bytes exactly) to the output file.
.PP
When a file is deleted using \fIunlink\fR the i-node number
in the directory is zeroed, but before its removal, it is
copied into the end of the file name field. This allows
the i-node of a deleted file to be found by searching
through a directory. The \fIx\fR command asks for the path
name of a lost file, extracts the old i-node number and
changes the current disk address to the start of the
i-node.
.PP
Once an i-node is found, all of the freed blocks may be
recovered by checking the i-node zone fields, using 'G'
to go to a block, writing it back out using 'w', going
back to the i-node with \fIp\fR and advancing to the next
block. This file extraction process is automated by using
the \fIX\fR command, which goes through the i-node, indirect
and double indirect blocks finding all the block pointers
and recovering all the blocks of the file.
.PP
The \fIX\fR command closes the current output file and asks
for the name of a new output file. All of the disk blocks
must be marked as free, if they are not the command stops
and the file must be recovered manually.
.PP
When extracting lost blocks \fIde\fR will maintain \*(OQholes\*(CQ in
the file. Thus, a recovered sparse file does not allocate
unused blocks and will keep its efficient storage scheme.
This property of the \fIX\fR command may be used to move a sparse
file from one device to another.
.PP
Automatic recovery may be initiated by the \fB\(enr\fR option on
the command line. Also specified is the path name of a
file just removed by \fIunlink\fR. \fIDe\fR determines which
mounted file system device held the file and opens it for
reading. The lost i-node is found and the file extracted by
automatically performing an \fIx\fR and an \fIX\fR command.
.PP
The recovered file will be written to \fI/tmp\fR. \fIDe\fR will
refuse to automatically recover a file on the same file
system as \fI/tmp\fR. The lost file must have belonged to the
user. If automatic recovery will not complete, then manual
recovery may be performed.
.SS "Miscellaneous"
.PP
The user can terminate a session with \fIde\fR by typing
\fIq\fR, CTRL-D, or the key associated with SIGQUIT.
.PP
The \fIm\fR command invokes the \s-2MINIX\s0 \fIsh\fR shell as a subprocess.
.PP
For help while using \fIde\fR use \fIh\fR.
.SS "Command Summary"
.LP
.ta 0.25i 1.0i 1.5i
.nf
.sp
	PGUP	b	Back one block
	PGDN	f	Forward one block
	HOME	B	Goto first block
	END	F	Goto last block
	UP	u	Move back 2/64/256 bytes
	DOWN	d	Move forward 2/64/256 bytes
	LEFT	l	Move back 32/1/4 bytes
	RIGHT	r	Move forward 32/1/4 bytes
		g	Goto specified block
		G	Goto block indirectly
		i	Goto specified i-node
		I	Filename to i-node
		/	Search
		n	Next occurrence
		p	Previous address
		h	Help
	EOF	q	Quit
		m	\s-2MINIX\s0 shell
		v	Visual mode (w b m)
		o	Output base (h d o b)
		c	Change file name
		w	Write ASCII block
		W	Write block exactly
		x	Extract lost directory entry
		X	Extract lost file blocks
		s	Store word
.fi
.sp
NOTES:
When entering a line in response to a prompt from \fIde\fR
there are a couple of editing characters available. The
previous character may be erased by typing CTRL-H and the
whole line may be erased by typing CTRL-U. ENTER terminates
the input. If DELETE or a non-ASCII character is typed
then the command requesting the input is aborted.
.PP
The commands \fIG\fR, \fIs\fR and \fIX\fR will only function if
the current visual display mode is \*(OQword.\*(CQ 
The commands
\fIi\fR, \fII\fR and \fIx\fR change the mode to \*(OQword\*(CQ on
completion. The commands \fIG\fR and \fI/\fR change the mode
to \*(OQblock\*(CQ. These restrictions and automatic mode
conversions are intended to aid the user.
.PP
The \*(OQmap\*(CQ mode uses special graphic characters, and
only functions if the user is at the console.
.PP
\fIDe\fR generates warnings for illegal user input or if
erroneous data is found on the disk, for example a
corrupted magic number. Warnings appear in the middle
of the screen for two seconds, then the current page
is redrawn. Some minor errors, for example, setting
an unknown visual mode, simply ring the bell. Major
errors, for example I/O problems on the file system
device cause an immediate exit from \fIde\fR.
.PP
The i-node and zone bit maps are read from the device
when \fIde\fR starts up. These determine whether \*(OQin use\*(CQ
or \*(OQnot in use\*(CQ is displayed in the status field at
the top of the screen. The bit maps are not re-read
while using \fIde\fR and will become out-of-date if
observing a mounted file system.
.PP
\fIDe\fR requires termcap definitions for \*(OQcm\*(CQ and \*(OQcl\*(CQ.
Furthermore, \*(OQso\*(CQ and \*(OQse\*(CQ will also be used if available. 
The ANSI strings generated by the keypad arrows are recognized,
as well as any single character codes defined by \*(OQku\*(CQ,
\*(OQkd\*(CQ, \*(OQkl\*(CQ and \*(OQkr\*(CQ.
.SS "Author"
.PP
The \fIde\fR program was written by Terrence Holm.