freebsd-skq/usr.sbin/fdread/fdread.1

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.Dd May 14, 2001
.Os
.Dt FDREAD 1
.Sh NAME
.Nm fdread
.Nd read floppy disks
.Sh SYNOPSIS
.Nm
.Op Fl qr
.Op Fl d Ar device
.Op Fl f Ar fillbyte
.Op Fl o Ar file
.Sh DESCRIPTION
The
.Nm
utility reads floppy disks.  Effective read blocking based on the track
size is performed, and floppy-specific error recovery of otherwise
bad blocks can be enabled.
.Pp
.Nm
will always read an entire floppy medium, and write its contents to
the respective output file.  Unlike other tools like
.Xr dd 1 ,
.Nm
automatically uses a read block size that is more efficient than
reading single blocks (usually one track of data at a time), but
falls back to reading single floppy sectors in case of an input/output
error occurred, in order to obtain as much valid data as possible.
While
.Nm
is working, kernel error reporting for floppy errors is turned off, so
the console and/or syslog are not flooded with kernel error messages.
.Pp
The
.Nm
utility accepts the following options:
.Bl -tag -width indent
.It Fl q
Turn on quiet mode.  By default, the medium parameters of the device
are being written to standard error output, progress will be indicated
by the approximate number of kilobytes read so far, and errors will be
printed out in detail, including the information about the location of
recovered data in the output.  In quiet mode, none of these messages
will be generated.
.It Fl r
Enable error recovery.  By default,
.Nm
stops after the first unrecovered read error, much like
.Xr dd 1
does.  In recovery mode, however, one of two recovery actions will be
taken:
.Bl -bullet
.It
If the error was a CRC error in the data field, the
kernel is told to ignore the error, and data are transferred to the
output file anyway.
.Bf -emphasis
Note that this will cause the erroneous data
to be included in the output file!
.Ef
Still, this is the best recovery action that can be taken at all.
.It
All other errors are really fatal (usually, the FDC didn't find the
sector ID fields), thus a dummy block with fill
bytes will be included in the output file.
.El
.Pp
Unless operating in quiet mode, the action taken and the location of
the error in the output file will be displayed.
.It Fl d Ar device
Specify the input floppy device, defaulting to
.Pa /dev/fd0 .
The parameter
.Ar device
must be a valid floppy disk device.
.It Fl f Ar fillbyte
Value of the fill byte used for dummy blocks in the output file in
recovery mode.  Defaults to
.Ql 0xf0 .
(Mnemonic:
.Dq foo . )
The value can be specified using the usual C language notation of
the number base.
.It Fl o Ar file
Specify the output file to be
.Ar file .
By default, the data will be written to standard output.
.El
.Sh FILES
.Bl -tag -width /dev/fd0
.It Pa /dev/fd0
Default device to read from.
.El
.Sh DIAGNOSTICS
.Nm
sets the exit value according to
.Xr sysexits 3 .
In recovery mode, the exit value will be set to
.Dv EX_IOERR
if any error occurred during processing (even in quiet mode).
.Pp
Unless running in quiet mode, upon encountering an error, the status
of the floppy disc controller (FDC) will be printed out, both in
hexadecimal form, followed by a textual description that translates
those values into a human-readable form for the most common error
cases that can happen in a PC environment.
.Pp
The FDC error status includes the three FDC status registers
.Ql ST0 ,
.Ql ST1 ,
and
.Ql ST2 ,
as well as the location of the error (physical cylinder, head, and sector
number, plus the
.Dq sector shift value ,
respectively).  See the manual for the NE765 or compatible for details
about the status register contents.
.Pp
The FDC's status is then examined to determine whether the error is
deemed to be recoverable.  If error recovery was requested, the
location of the bad block in the output file is indicated by its
(hexadecimal) bounds.  Also, a summary line indicating the total number
of transfer errors will be printed before exiting.
.Sh SEE ALSO
.Xr dd 1 ,
.Xr fdwrite 1 ,
.Xr sysexits 3 ,
.Xr fdc 4 ,
.Xr fdcontrol 8
.Sh HISTORY
The
.Nm
utility was written mainly to provide a means of recovering at least some of
the data on bad media, and to obviate the need to invoke
.Xr dd 1
with too many hard to memorize options that might be useful to handle
a floppy.
.Pp
The command appeared in
.Fx 5.0 .
.Sh AUTHORS
Program and man page by
.An J\(:org Wunsch .
.Sh BUGS
Concurrent traffic on the second floppy drive located at the same FDC
will make error recovery attempts pointless, since the FDC status
obtained after a read error occurred cannot be guaranteed to actually
belong to the erroneous transfer.  Thus using option
.Fl r
is only reliable if
.Ar device
is the only active drive on that controller.
.Pp
No attempt beyond the floppy error retry mechanism of
.Xr fdc 4
is made in order to see whether bad sectors could still be read
without errors by trying multiple times.
.Pp
Bits that are (no longer) available on the floppy medium cannot be
guessed by
.Nm .