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Subject[PATCH] docs: fault-injection: fix non-working usage of negative values
Date
Fault injection uses debugfs in a way that the provided values via sysfs
are interpreted as u64. Providing negative numbers results in an error:

/sys/kernel/debug/fail_function# echo -1 > times
sh: write error: Invalid argument

Update the docs and examples to use "printf %#x <val>" in these cases.
For "retval", reword the paragraph a little and fix a typo.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
---
.../fault-injection/fault-injection.rst | 24 +++++++++++--------
1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/Documentation/fault-injection/fault-injection.rst b/Documentation/fault-injection/fault-injection.rst
index 31ecfe44e5b4..f47d05ed0d94 100644
--- a/Documentation/fault-injection/fault-injection.rst
+++ b/Documentation/fault-injection/fault-injection.rst
@@ -78,8 +78,10 @@ configuration of fault-injection capabilities.

- /sys/kernel/debug/fail*/times:

- specifies how many times failures may happen at most.
- A value of -1 means "no limit".
+ specifies how many times failures may happen at most. A value of -1
+ means "no limit". Note, though, that this file only accepts unsigned
+ values. So, if you want to specify -1, you better use 'printf' instead
+ of 'echo', e.g.: $ printf %#x -1 > times

- /sys/kernel/debug/fail*/space:

@@ -167,11 +169,13 @@ configuration of fault-injection capabilities.
- ERRNO: retval must be -1 to -MAX_ERRNO (-4096).
- ERR_NULL: retval must be 0 or -1 to -MAX_ERRNO (-4096).

-- /sys/kernel/debug/fail_function/<functiuon-name>/retval:
+- /sys/kernel/debug/fail_function/<function-name>/retval:

- specifies the "error" return value to inject to the given
- function for given function. This will be created when
- user specifies new injection entry.
+ specifies the "error" return value to inject to the given function.
+ This will be created when the user specifies a new injection entry.
+ Note that this file only accepts unsigned values. So, if you want to
+ use a negative errno, you better use 'printf' instead of 'echo', e.g.:
+ $ printf %#x -12 > retval

Boot option
^^^^^^^^^^^
@@ -255,7 +259,7 @@ Application Examples
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
+ printf %#x -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
@@ -309,7 +313,7 @@ Application Examples
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
+ printf %#x -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
@@ -336,11 +340,11 @@ Application Examples
FAILTYPE=fail_function
FAILFUNC=open_ctree
echo $FAILFUNC > /sys/kernel/debug/$FAILTYPE/inject
- echo -12 > /sys/kernel/debug/$FAILTYPE/$FAILFUNC/retval
+ printf %#x -12 > /sys/kernel/debug/$FAILTYPE/$FAILFUNC/retval
echo N > /sys/kernel/debug/$FAILTYPE/task-filter
echo 100 > /sys/kernel/debug/$FAILTYPE/probability
echo 0 > /sys/kernel/debug/$FAILTYPE/interval
- echo -1 > /sys/kernel/debug/$FAILTYPE/times
+ printf %#x -1 > /sys/kernel/debug/$FAILTYPE/times
echo 0 > /sys/kernel/debug/$FAILTYPE/space
echo 1 > /sys/kernel/debug/$FAILTYPE/verbose

--
2.30.2
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