.\" Copyright (c) 2015 The DragonFly BSD Project.
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.\" This code is derived from software contributed to The DragonFly BSD Project
.\" by Tomohiro Kusumi <tkusumi@netbsd.org>
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.Dd November 17, 2015
.Dt DM_TARGET_FLAKEY 4
.Os
.Sh NAME
.Nm dm_target_flakey
.Nd Device-mapper flakey target
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following lines in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device dm"
.Cd "device dm_target_flakey"
.Ed
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
dm_target_flakey_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
target for
.Xr dm 4
provides periodic unreliable I/O behavior to simulate failing devices for testing purposes.
.Dq Nm dmsetup Cm create
takes the following list of parameters for the
.Nm
table.
.Bd -ragged -offset indent
.Cd "<device_path> <offset> <up_interval> <down_interval> [<num_feature_parameters> [<feature_parameters>]]"
.Ed
.Pp
The first four parameters are mandatory.
.Nm
is similar to
.Xr dm_target_linear 4
except that
.Nm
has parameters for periodic unreliable I/O behavior.
.Pp
<device_path> is a path to the underlying device.
<offset> is the starting sector within the device.
<up_interval> is the number of seconds device is available.
<down_interval> is the number of seconds device returns errors.
The device has periodic unreliable I/O behavior for <down_interval>
seconds every other <up_interval> seconds starting from the time
the table is loaded by
.Xr dmsetup 8 .
.Pp
Optional <feature_parameters> are as follows.
<num_feature_parameters> takes the number of parameters for <feature_parameters>.
In other words <num_feature_parameters> is the number of parameters after this.
If <feature_parameters> are not specified, all I/Os return error during <down_interval>.
.Pp
.Dq Nm drop_writes
feature takes no additional parameters.
All write I/Os are silently ignored.
.Bd -ragged -offset indent
.Cd "[drop_writes]"
.Ed
.Pp
.Dq Nm corrupt_bio_byte
feature takes four additional mandatory parameters.
It replaces <Nth_byte> of the
.Dq Nm struct Cm buf
data
whose direction is <direction> with <value> during <down_interval>.
.Bd -ragged -offset indent
.Cd "[corrupt_bio_byte <Nth_byte> <direction> <value> <flags>]"
.Ed
.Pp
<Nth_byte> is the offset of the
.Dq Nm struct Cm buf
data to replace. Counting starts at 1 to replace the first byte of the data.
<direction> is either 'r' for reads or 'w' for writes. Using 'w' is imcompatible with
.Dq Nm drop_writes
feature.
<value> is the value to replace which must be between 0 and 255.
<flags> makes
.Nm
perform the replacement only if
.Dq Nm b_flags
field of
.Dq Nm struct Cm buf
has all the specified flags set.
.Sh SEE ALSO
.Xr dm 4 ,
.Xr dmsetup 8
.Sh HISTORY
The
.Nm
.Xr dm 4
target first appeared in
.Dx 4.3 .
.Sh AUTHORS
.An Tomohiro Kusumi Aq Mt tkusumi@netbsd.org