b97809a770
Its main purpose is to adapt automatically to the floppy parameters (in particular the track size for efficient reading), and to allow a simple error recovery for CRC-errored sectors. Requires the newly added fdc(4) options.
185 lines
6.2 KiB
Groff
185 lines
6.2 KiB
Groff
.\"
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.\" Copyright (c) 2001 Joerg Wunsch
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.\"
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.\"
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.Dd May 14, 2001
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.Os FreeBSD
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.Dt FDREAD 1
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.Sh NAME
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.Nm fdread
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.Nd read floppy disks
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.Sh SYNOPSIS
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.Nm
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.Op Fl q
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.Op Fl r
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.Op Fl d Ar device
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.Op Fl f Ar fillbyte
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.Op Fl o Ar file
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.Sh DESCRIPTION
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.Nm Fdread
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reads floppy disks. Effective read blocking based on the track
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size is performed, and floppy-specific error recovery of otherwise
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bad blocks can be enabled.
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.Pp
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.Nm Fdread
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will always read an entire floppy medium, and write its contents to
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the respective output file. Unlike other tools like
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.Xr dd 1 ,
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.Nm
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automatically uses a read block size that is more efficient than
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reading single blocks (usually one track of data at a time), but
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falls back to reading single floppy sectors in case of an input/output
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error occurred, in order to obtain as much valid data as possible.
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While
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.Nm
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is working, kernel error reporting for floppy errors is turned off, so
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the console and/or syslog are not flooded with kernel error messages.
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.Sh Options
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The options are as follows:
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.Bl -tag -width XXXX -offset indent
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.It Fl q
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Turn on quiet mode. By default, the medium parameters of the device
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are being written to standard error output, progress will be indicated
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by the approximate number of kilobytes read so far, and errors will be
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printed out in detail, including the information about the location of
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recovered data in the output. In quiet mode, none of these messages
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will be generated.
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.It Fl r
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Enable error recovery. By default,
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.Nm
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stops after the first unrecovered read error, much like
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.Xr dd 1
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does. In recovery mode, however, one of two recovery actions will be
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taken:
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.Bl -bullet -offset indent
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.It
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If the error was a CRC error in the data field, the
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kernel is told to ignore the error, and data are transferred to the
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output file anyway.
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.Em Note that this will cause the erroneous data
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.Em to be included in the output file !
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Still, this is the best recovery action that can be taken at all.
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.It
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All other errors are really fatal (usually, the FDC didn't find the
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sector ID fields), thus a dummy block with fill
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bytes will be included in the output file.
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.El
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.Pp
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Unless operating in quiet mode, the action taken and the location of
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the error in the output file will be displayed.
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.It Fl d Ar device
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Specify the input floppy device, defaulting to
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.Pa /dev/fd0 .
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The parameter
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.Ar device
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must be a valid floppy disk device.
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.It Fl f Ar fillbyte
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Value of the fill byte used for dummy blocks in the output file in
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recovery mode. Defaults to
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.Ql 0xf0 .
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(Mnemonic:
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.Dq foo . )
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The value can be specified using the usual C language notation of
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the number base.
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.It Fl o Ar file
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Specify the output file to be
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.Ar file .
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By default, the data will be written to standard output.
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.El
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.Sh FILES
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.Bl -tag -width XXXXXXXX -offset indent
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.It Pa /dev/fd0
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Default device to read from.
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.Sh DIAGNOSTICS
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.Nm Fdread
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sets the exit value according to
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.Xr sysexits 3 .
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In recovery mode, the exit value will be set to
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.Sy EX_IOERR
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if any error occurred during processing (even in quiet mode).
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.Pp
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Unless running in quiet mode, upon encountering an error, the status
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of the floppy disc controller (FDC) will be printed out, both in
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hexadecimal form, followed by a textual description that translates
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those values into a human-readable form for the most common error
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cases that can happen in a PC environment.
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.Pp
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The FDC error status includes the three FDC status registers
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.Ql ST0 ,
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.Ql ST1 ,
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and
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.Ql ST2 ,
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as well as the location of the error (physical cylinder, head, and sector
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number, plus the
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.Dq sector shift value ,
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respectively). See the manual for the NE765 or compatible for details
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about the status register contents.
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.Pp
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The FDC's status is then examined to determine whether the error is
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deemed to be recoverable. If error recovery was requested, the
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location of the bad block in the output file is indicated by its
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(hexadecimal) bounds. Also, a summary line indicating the total number
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of transfer errors will be printed before exiting.
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.Sh SEE ALSO
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.Xr dd 1 ,
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.Xr fdc 4 ,
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.Xr fdcontrol 8 ,
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.Xr fdwrite 1 ,
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.Xr sysexits 3
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.Sh HISTORY
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.Nm Fdread
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was written mainly to provide a means of recovering at least some of
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the data on bad media, and to obviate the need to invoke
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.Xr dd 1
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with too many hard to memorize options that might be useful to handle
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a floppy.
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.Pp
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The command appeared in
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.Fx 5.0 .
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.Sh AUTHORS
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Program and man page by
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.ie t J\(:org Wunsch.
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.el Joerg Wunsch.
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.Sh BUGS
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Concurrent traffic on the second floppy drive located at the same FDC
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will make error recovery attempts pointless, since the FDC status
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obtained after a read error occurred cannot be guaranteed to actually
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belong to the erroneous transfer. Thus using option
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.Fl r
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is only reliable if
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.Ar device
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is the only active drive on that controller.
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.Pp
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No attempt beyond the floppy error retry mechanism of
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.Xr fdc 4
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is made in order to see whether bad sectors could still be read
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without errors by trying multiple times.
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.Pp
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Bits that are (no longer) available on the floppy medium cannot be
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guessed by
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.Nm fdread .
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