258 lines
8.1 KiB
Groff
258 lines
8.1 KiB
Groff
.\"
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.\" Copyright (c) 2009 Isilon Inc http://www.isilon.com/
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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(s), this list of conditions and the following disclaimer as
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.\" the first lines of this file unmodified other than the possible
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.\" addition of one or more copyright notices.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice(s), 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 COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
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.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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.\" DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
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.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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.\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
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.\" DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd March 15, 2016
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.Dt FAIL 9
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.Os
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.Sh NAME
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.Nm KFAIL_POINT_CODE ,
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.Nm KFAIL_POINT_CODE_FLAGS ,
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.Nm KFAIL_POINT_CODE_COND ,
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.Nm KFAIL_POINT_RETURN ,
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.Nm KFAIL_POINT_RETURN_VOID ,
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.Nm KFAIL_POINT_ERROR ,
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.Nm KFAIL_POINT_GOTO ,
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.Nm KFAIL_POINT_SLEEP_CALLBACKS ,
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.Nm fail_point ,
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.Nm DEBUG_FP
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.Nd fail points
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.Sh SYNOPSIS
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.In sys/fail.h
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.Fn KFAIL_POINT_CODE "parent" "name" "code"
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.Fn KFAIL_POINT_CODE_FLAGS "parent" "name" "flags" "code"
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.Fn KFAIL_POINT_CODE_COND "parent" "name" "cond" "flags" "code"
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.Fn KFAIL_POINT_RETURN "parent" "name"
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.Fn KFAIL_POINT_RETURN_VOID "parent" "name"
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.Fn KFAIL_POINT_ERROR "parent" "name" "error_var"
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.Fn KFAIL_POINT_GOTO "parent" "name" "error_var" "label"
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.Fn KFAIL_POINT_SLEEP_CALLBACKS "parent" "name" "pre_func" "pre_arg" "post_func" "post_arg" "code"
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.Sh DESCRIPTION
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Fail points are used to add code points where errors may be injected
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in a user controlled fashion.
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Fail points provide a convenient wrapper around user-provided error
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injection code, providing a
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.Xr sysctl 9
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MIB, and a parser for that MIB that describes how the error
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injection code should fire.
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.Pp
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The base fail point macro is
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.Fn KFAIL_POINT_CODE
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where
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.Fa parent
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is a sysctl tree (frequently
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.Sy DEBUG_FP
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for kernel fail points, but various subsystems may wish to provide
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their own fail point trees), and
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.Fa name
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is the name of the MIB in that tree, and
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.Fa code
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is the error injection code.
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The
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.Fa code
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argument does not require braces, but it is considered good style to
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use braces for any multi-line code arguments.
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Inside the
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.Fa code
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argument, the evaluation of
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.Sy RETURN_VALUE
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is derived from the
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.Fn return
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value set in the sysctl MIB.
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.Pp
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Additionally,
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.Fn KFAIL_POINT_CODE_FLAGS
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provides a
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.Fa flags
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argument which controls the fail point's behaviour.
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This can be used to e.g., mark the fail point's context as non-sleepable,
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which causes the
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.Sy sleep
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action to be coerced to a busy wait.
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The supported flags are:
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.Bl -ohang -offset indent
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.It FAIL_POINT_USE_TIMEOUT_PATH
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Rather than sleeping on a
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.Fn sleep
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call, just fire the post-sleep function after a timeout fires.
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.It FAIL_POINT_NONSLEEPABLE
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Mark the fail point as being in a non-sleepable context, which coerces
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.Fn sleep
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calls to
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.Fn delay
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calls.
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.El
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.Pp
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Likewise,
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.Fn KFAIL_POINT_CODE_COND
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supplies a
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.Fa cond
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argument, which allows you to set the condition under which the fail point's
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code may fire.
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This is equivalent to:
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.Bd -literal
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if (cond)
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KFAIL_POINT_CODE_FLAGS(...);
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.Ed
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See
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.Sx SYSCTL VARIABLES
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below.
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.Pp
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The remaining
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.Fn KFAIL_POINT_*
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macros are wrappers around common error injection paths:
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.Bl -inset
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.It Fn KFAIL_POINT_RETURN parent name
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is the equivalent of
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.Sy KFAIL_POINT_CODE(..., return RETURN_VALUE)
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.It Fn KFAIL_POINT_RETURN_VOID parent name
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is the equivalent of
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.Sy KFAIL_POINT_CODE(..., return)
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.It Fn KFAIL_POINT_ERROR parent name error_var
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is the equivalent of
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.Sy KFAIL_POINT_CODE(..., error_var = RETURN_VALUE)
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.It Fn KFAIL_POINT_GOTO parent name error_var label
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is the equivalent of
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.Sy KFAIL_POINT_CODE(..., { error_var = RETURN_VALUE; goto label;})
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.El
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.Sh SYSCTL VARIABLES
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The
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.Fn KFAIL_POINT_*
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macros add sysctl MIBs where specified.
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Many base kernel MIBs can be found in the
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.Sy debug.fail_point
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tree (referenced in code by
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.Sy DEBUG_FP ) .
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.Pp
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The sysctl variable may be set in a number of ways:
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.Bd -literal
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[<pct>%][<cnt>*]<type>[(args...)][-><more terms>]
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.Ed
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.Pp
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The <type> argument specifies which action to take; it can be one of:
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.Bl -tag -width ".Dv return"
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.It Sy off
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Take no action (does not trigger fail point code)
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.It Sy return
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Trigger fail point code with specified argument
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.It Sy sleep
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Sleep the specified number of milliseconds
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.It Sy panic
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Panic
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.It Sy break
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Break into the debugger, or trap if there is no debugger support
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.It Sy print
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Print that the fail point executed
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.It Sy pause
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Threads sleep at the fail point until the fail point is set to
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.Sy off
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.It Sy yield
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Thread yields the cpu when the fail point is evaluated
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.It Sy delay
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Similar to sleep, but busy waits the cpu.
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(Useful in non-sleepable contexts.)
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.El
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.Pp
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The <pct>% and <cnt>* modifiers prior to <type> control when
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<type> is executed.
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The <pct>% form (e.g. "1.2%") can be used to specify a
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probability that <type> will execute.
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This is a decimal in the range (0, 100] which can specify up to
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1/10,000% precision.
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The <cnt>* form (e.g. "5*") can be used to specify the number of
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times <type> should be executed before this <term> is disabled.
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Only the last probability and the last count are used if multiple
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are specified, i.e. "1.2%2%" is the same as "2%".
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When both a probability and a count are specified, the probability
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is evaluated before the count, i.e. "2%5*" means "2% of the time,
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but only 5 times total".
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.Pp
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The operator -> can be used to express cascading terms.
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If you specify <term1>-><term2>, it means that if <term1> does not
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.Ql execute ,
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<term2> is evaluated.
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For the purpose of this operator, the return() and print() operators
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are the only types that cascade.
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A return() term only cascades if the code executes, and a print()
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term only cascades when passed a non-zero argument.
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A pid can optionally be specified.
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The fail point term is only executed when invoked by a process with a
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matching p_pid.
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.Sh EXAMPLES
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.Bl -tag -width Sy
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.It Sy sysctl debug.fail_point.foobar="2.1%return(5)"
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21/1000ths of the time, execute
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.Fa code
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with RETURN_VALUE set to 5.
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.It Sy sysctl debug.fail_point.foobar="2%return(5)->5%return(22)"
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2/100ths of the time, execute
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.Fa code
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with RETURN_VALUE set to 5.
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If that does not happen, 5% of the time execute
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.Fa code
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with RETURN_VALUE set to 22.
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.It Sy sysctl debug.fail_point.foobar="5*return(5)->0.1%return(22)"
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For 5 times, return 5.
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After that, 1/1000th of the time, return 22.
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.It Sy sysctl debug.fail_point.foobar="0.1%5*return(5)"
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Return 5 for 1 in 1000 executions, but only 5 times total.
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.It Sy sysctl debug.fail_point.foobar="1%*sleep(50)"
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1/100th of the time, sleep 50ms.
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.It Sy sysctl debug.fail_point.foobar="1*return(5)[pid 1234]"
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Return 5 once, when pid 1234 executes the fail point.
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.El
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.Sh AUTHORS
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.An -nosplit
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This manual page was written by
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.Pp
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.An Matthew Bryan Aq Mt matthew.bryan@isilon.com
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and
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.Pp
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.An Zach Loafman Aq Mt zml@FreeBSD.org .
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.Sh CAVEATS
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It is easy to shoot yourself in the foot by setting fail points too
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aggressively or setting too many in combination.
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For example, forcing
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.Fn malloc
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to fail consistently is potentially harmful to uptime.
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.Pp
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The
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.Fn sleep
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sysctl setting may not be appropriate in all situations.
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Currently,
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.Fn fail_point_eval
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does not verify whether the context is appropriate for calling
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.Fn msleep .
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You can force it to evaluate a
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.Sy sleep
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action as a
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.Sy delay
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action by specifying the
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.Sy FAIL_POINT_NONSLEEPABLE
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flag at the point the fail point is declared.
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