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SubjectRe: [patch 1/8] documentation and scripts
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Add reference to similar functionality in drivers/md/faulty.c .

Clarify debugfs descriptions.

Add an entry for fault-injection to
Documentation/kernel-parameters.txt .


Signed-off-by: Don Mullis <dwm@meer.net>

---
Documentation/fault-injection/fault-injection.txt | 85 ++++++++++------------
Documentation/kernel-parameters.txt | 7 +
2 files changed, 47 insertions(+), 45 deletions(-)
Index: linux-2.6.17/Documentation/fault-injection/fault-injection.txt
===================================================================
--- linux-2.6.17.orig/Documentation/fault-injection/fault-injection.txt
+++ linux-2.6.17/Documentation/fault-injection/fault-injection.txt
@@ -1,6 +1,9 @@
Fault injection capabilities infrastructure
===========================================

+See also drivers/md/faulty.c .
+
+
Available fault injection capabilities
--------------------------------------

@@ -14,58 +17,49 @@ o fail_page_alloc

o fail_make_request

- injects disk IO errors on permitted devices by /sys/block/<device>/make-it-fail
- or /sys/block/<device>/<partition>/make-it-fail. (generic_make_request())
+ injects disk IO errors on permitted devices by
+ /sys/block/<device>/make-it-fail or
+ /sys/block/<device>/<partition>/make-it-fail. (generic_make_request())

Configure fault-injection capabilities behavior
-----------------------------------------------

-Example for failslab:
-
o debugfs entries

fault-inject-debugfs kernel module provides some debugfs entries for runtime
-configuration for fault-injection capabilities.
-
-- /debug/failslab/probability:
+configuration of fault-injection capabilities.

- specifies how often it should fail in percent.
+- /debug/*/probability:

-- /debug/failslab/interval:
-
- specifies the interval of failures.
-
-- /debug/failslab/times:
-
- specifies how many times failures may happen at most.
+ likelihood of failure injection, in percent.

-- /debug/failslab/space:
+- /debug/*/interval:

- specifies the size of free space where memory can be allocated
- safely in bytes.
+ specifies the interval between failures, for calls to
+ should_fail() that pass all the other tests.

-- /debug/failslab/process-filter:
+ Note that if you enable this, by setting interval>1, you will
+ probably want to set probability=100.

- specifies whether the process filter is enabled or not.
- It allows failing only permitted processes by /proc/<pid>/make-it-fail
+- /debug/*/times:

-- /debug/failslab/stacktrace-depth:
-
- specifies the maximum stacktrace depth walking allowed.
- A value '0' means stacktrace filter is disabled.
+ specifies how many times failures may happen at most.
+ A value of -1 means "no limit".

-- /debug/failslab/address-start:
-- /debug/failslab/address-end:
+- /debug/*/space:

- specifies the range of virtual address.
- It allows failing only if the stacktrace hits in this range.
+ specifies an initial resource "budget", decremented by "size"
+ on each call to should_fail(,size). Failure injection is
+ suppressed until "space" reaches zero.

o Boot option

In order to inject faults while debugfs is not available (early boot time),
-We can use boot option.
+use the boot option:

-- failslab=<interval>,<probability>,<space>,<times>
+ failslab=
+ fail_page_alloc=
+ fail_make_request=<interval>,<probability>,<space>,<times>

How to add new fault injection capability
-----------------------------------------
@@ -77,44 +71,42 @@ o define the fault attributes
DEFINE_FAULT_INJECTION(name);

Please see the definition of struct fault_attr in fault-inject.h
- for the detail.
+ for details.

o provide the way to configure fault attributes

- boot option

- If you need to enable the fault injection capability ealier boot time,
+ If you need to enable the fault injection capability from boot time,
you can provide boot option to configure it. There is a helper function for it.

setup_fault_attr(attr, str);

- module parameters

- If the scope of the fault injection capability is limited by a kernel module,
- It is better to provide module parameters to configure the member of fault
- attributes.
+ If the scope of the fault injection capability is limited to a
+ single kernel module, it is better to provide module parameters to
+ configure the fault attributes.

- debugfs entries

failslab, fail_page_alloc, and fail_make_request use this way.
-
- But now there is no helper functions to provides debugfs entries for
+ But now there is no helper functions to provide debugfs entries for
fault injection capabilities. Please refer to lib/fault-inject-debugfs.c
to know how to do. And please try not to add new one into
fault-inject-debugfs module.
-
- Because failslab, fail_page_alloc, and fail_make_request are used ealier
- boot time before debugfs is available and the slab allocator,
- the page allocator, and the block layer cannot be built as module.
+ Because failslab, fail_page_alloc, and fail_make_request are used from
+ boot time, before debugfs is available, the slab allocator,
+ the page allocator, and the block layer cannot be built as modules.

o add a hook to insert failures

should_fail() returns 1 when failures should happen.

- should_fail(attr);
+ should_fail(attr,size);

-Tests
------
+Application Examples
+--------------------

o inject slab allocation failures into module init/cleanup code

@@ -148,3 +140,6 @@ echo 25 > /debug/failslab/probability

------------------------------------------------------------------------------

+
+
+
Index: linux-2.6.17/Documentation/kernel-parameters.txt
===================================================================
--- linux-2.6.17.orig/Documentation/kernel-parameters.txt
+++ linux-2.6.17/Documentation/kernel-parameters.txt
@@ -544,6 +544,13 @@ running once the system is up.
eurwdt= [HW,WDT] Eurotech CPU-1220/1410 onboard watchdog.
Format: <io>[,<irq>]

+ failslab=
+ fail_page_alloc=
+ fail_make_request=[KNL]
+ General fault injection mechanism.
+ Format: <interval>,<probability>,<space>,<times>
+ See also /Documentation/fault-injection/.
+
fd_mcs= [HW,SCSI]
See header of drivers/scsi/fd_mcs.c.


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