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-Fault injection capabilities infrastructure
-===========================================
-
-See also drivers/md/faulty.c and "every_nth" module option for scsi_debug.
-
-
-Available fault injection capabilities
---------------------------------------
-
-o failslab
-
- injects slab allocation failures. (kmalloc(), kmem_cache_alloc(), ...)
-
-o fail_page_alloc
-
- injects page allocation failures. (alloc_pages(), get_free_pages(), ...)
-
-o fail_make_request
-
- injects disk IO errors on devices permitted by setting
- /sys/block/<device>/make-it-fail or
- /sys/block/<device>/<partition>/make-it-fail. (generic_make_request())
-
-o fail_mmc_request
-
- injects MMC data errors on devices permitted by setting
- debugfs entries under /sys/kernel/debug/mmc0/fail_mmc_request
-
-Configure fault-injection capabilities behavior
------------------------------------------------
-
-o debugfs entries
-
-fault-inject-debugfs kernel module provides some debugfs entries for runtime
-configuration of fault-injection capabilities.
-
-- /sys/kernel/debug/fail*/probability:
-
- likelihood of failure injection, in percent.
- Format: <percent>
-
- Note that one-failure-per-hundred is a very high error rate
- for some testcases. Consider setting probability=100 and configure
- /sys/kernel/debug/fail*/interval for such testcases.
-
-- /sys/kernel/debug/fail*/interval:
-
- specifies the interval between failures, for calls to
- should_fail() that pass all the other tests.
-
- Note that if you enable this, by setting interval>1, you will
- probably want to set probability=100.
-
-- /sys/kernel/debug/fail*/times:
-
- specifies how many times failures may happen at most.
- A value of -1 means "no limit".
-
-- /sys/kernel/debug/fail*/space:
-
- specifies an initial resource "budget", decremented by "size"
- on each call to should_fail(,size). Failure injection is
- suppressed until "space" reaches zero.
-
-- /sys/kernel/debug/fail*/verbose
-
- Format: { 0 | 1 | 2 }
- specifies the verbosity of the messages when failure is
- injected. '0' means no messages; '1' will print only a single
- log line per failure; '2' will print a call trace too -- useful
- to debug the problems revealed by fault injection.
-
-- /sys/kernel/debug/fail*/task-filter:
-
- Format: { 'Y' | 'N' }
- A value of 'N' disables filtering by process (default).
- Any positive value limits failures to only processes indicated by
- /proc/<pid>/make-it-fail==1.
-
-- /sys/kernel/debug/fail*/require-start:
-- /sys/kernel/debug/fail*/require-end:
-- /sys/kernel/debug/fail*/reject-start:
-- /sys/kernel/debug/fail*/reject-end:
-
- specifies the range of virtual addresses tested during
- stacktrace walking. Failure is injected only if some caller
- in the walked stacktrace lies within the required range, and
- none lies within the rejected range.
- Default required range is [0,ULONG_MAX) (whole of virtual address space).
- Default rejected range is [0,0).
-
-- /sys/kernel/debug/fail*/stacktrace-depth:
-
- specifies the maximum stacktrace depth walked during search
- for a caller within [require-start,require-end) OR
- [reject-start,reject-end).
-
-- /sys/kernel/debug/fail_page_alloc/ignore-gfp-highmem:
-
- Format: { 'Y' | 'N' }
- default is 'N', setting it to 'Y' won't inject failures into
- highmem/user allocations.
-
-- /sys/kernel/debug/failslab/ignore-gfp-wait:
-- /sys/kernel/debug/fail_page_alloc/ignore-gfp-wait:
-
- Format: { 'Y' | 'N' }
- default is 'N', setting it to 'Y' will inject failures
- only into non-sleep allocations (GFP_ATOMIC allocations).
-
-- /sys/kernel/debug/fail_page_alloc/min-order:
-
- specifies the minimum page allocation order to be injected
- failures.
-
-o Boot option
-
-In order to inject faults while debugfs is not available (early boot time),
-use the boot option:
-
- failslab=
- fail_page_alloc=
- fail_make_request=
- mmc_core.fail_request=<interval>,<probability>,<space>,<times>
-
-How to add new fault injection capability
------------------------------------------
-
-o #include <linux/fault-inject.h>
-
-o define the fault attributes
-
- DECLARE_FAULT_INJECTION(name);
-
- Please see the definition of struct fault_attr in fault-inject.h
- for details.
-
-o provide a way to configure fault attributes
-
-- boot option
-
- 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);
-
-- debugfs entries
-
- failslab, fail_page_alloc, and fail_make_request use this way.
- Helper functions:
-
- fault_create_debugfs_attr(name, parent, attr);
-
-- module parameters
-
- 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.
-
-o add a hook to insert failures
-
- Upon should_fail() returning true, client code should inject a failure.
-
- should_fail(attr, size);
-
-Application Examples
---------------------
-
-o Inject slab allocation failures into module init/exit code
-
-#!/bin/bash
-
-FAILTYPE=failslab
-echo Y > /sys/kernel/debug/$FAILTYPE/task-filter
-echo 10 > /sys/kernel/debug/$FAILTYPE/probability
-echo 100 > /sys/kernel/debug/$FAILTYPE/interval
-echo -1 > /sys/kernel/debug/$FAILTYPE/times
-echo 0 > /sys/kernel/debug/$FAILTYPE/space
-echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
-echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
-
-faulty_system()
-{
- bash -c "echo 1 > /proc/self/make-it-fail && exec $*"
-}
-
-if [ $# -eq 0 ]
-then
- echo "Usage: $0 modulename [ modulename ... ]"
- exit 1
-fi
-
-for m in $*
-do
- echo inserting $m...
- faulty_system modprobe $m
-
- echo removing $m...
- faulty_system modprobe -r $m
-done
-
-------------------------------------------------------------------------------
-
-o Inject page allocation failures only for a specific module
-
-#!/bin/bash
-
-FAILTYPE=fail_page_alloc
-module=$1
-
-if [ -z $module ]
-then
- echo "Usage: $0 <modulename>"
- exit 1
-fi
-
-modprobe $module
-
-if [ ! -d /sys/module/$module/sections ]
-then
- echo Module $module is not loaded
- exit 1
-fi
-
-cat /sys/module/$module/sections/.text > /sys/kernel/debug/$FAILTYPE/require-start
-cat /sys/module/$module/sections/.data > /sys/kernel/debug/$FAILTYPE/require-end
-
-echo N > /sys/kernel/debug/$FAILTYPE/task-filter
-echo 10 > /sys/kernel/debug/$FAILTYPE/probability
-echo 100 > /sys/kernel/debug/$FAILTYPE/interval
-echo -1 > /sys/kernel/debug/$FAILTYPE/times
-echo 0 > /sys/kernel/debug/$FAILTYPE/space
-echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
-echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
-echo 1 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-highmem
-echo 10 > /sys/kernel/debug/$FAILTYPE/stacktrace-depth
-
-trap "echo 0 > /sys/kernel/debug/$FAILTYPE/probability" SIGINT SIGTERM EXIT
-
-echo "Injecting errors into the module $module... (interrupt to stop)"
-sleep 1000000
-