This is a note to let you know that I've just added the patch titled
string.h: Add str_has_prefix() helper function
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
string.h-add-str_has_prefix-helper-function.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From stable+bounces-43483-greg=kroah.com@xxxxxxxxxxxxxxx Thu May 9 04:30:28 2024
From: George Guo <dongtai.guo@xxxxxxxxx>
Date: Thu, 9 May 2024 10:29:24 +0800
Subject: string.h: Add str_has_prefix() helper function
To: gregkh@xxxxxxxxxxxxxxxxxxx, rostedt@xxxxxxxxxxx, mhiramat@xxxxxxxxxx, tom.zanussi@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx, Tom Zanussi <zanussi@xxxxxxxxxx>, Namhyung Kim <namhyung@xxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Joe Perches <joe@xxxxxxxxxxx>, Andreas Schwab <schwab@xxxxxxxxxxxxxx>, George Guo <guodongtai@xxxxxxxxxx>
Message-ID: <20240509022931.3513365-7-dongtai.guo@xxxxxxxxx>
From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
commit 72921427d46bf9731a1ab7864adc64c43dfae29f upstream.
A discussion came up in the trace triggers thread about converting a
bunch of:
strncmp(str, "const", sizeof("const") - 1)
use cases into a helper macro. It started with:
strncmp(str, const, sizeof(const) - 1)
But then Joe Perches mentioned that if a const is not used, the
sizeof() will be the size of a pointer, which can be bad. And that
gcc will optimize strlen("const") into "sizeof("const") - 1".
Thinking about this more, a quick grep in the kernel tree found several
(thousands!) of cases that use this construct. A quick grep also
revealed that there's probably several bugs in that use case. Some are
that people forgot the "- 1" (which I found) and others could be that
the constant for the sizeof is different than the constant (although, I
haven't found any of those, but I also didn't look hard).
I figured the best thing to do is to create a helper macro and place it
into include/linux/string.h. And go around and fix all the open coded
versions of it later.
Note, gcc appears to optimize this when we make it into an always_inline
static function, which removes a lot of issues that a macro produces.
Link: http://lkml.kernel.org/r/e3e754f2bd18e56eaa8baf79bee619316ebf4cfc.1545161087.git.tom.zanussi@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20181219211615.2298e781@xxxxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/CAHk-=wg_sR-UEC1ggmkZpypOUYanL5CMX4R7ceuaV4QMf5jBtg@xxxxxxxxxxxxxx
Cc: Tom Zanussi <zanussi@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Suggestions-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Suggestions-by: Joe Perches <joe@xxxxxxxxxxx>
Suggestions-by: Andreas Schwab <schwab@xxxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Signed-off-by: George Guo <guodongtai@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/linux/string.h | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -492,4 +492,24 @@ static inline void memcpy_and_pad(void *
memcpy(dest, src, dest_len);
}
+/**
+ * str_has_prefix - Test if a string has a given prefix
+ * @str: The string to test
+ * @prefix: The string to see if @str starts with
+ *
+ * A common way to test a prefix of a string is to do:
+ * strncmp(str, prefix, sizeof(prefix) - 1)
+ *
+ * But this can lead to bugs due to typos, or if prefix is a pointer
+ * and not a constant. Instead use str_has_prefix().
+ *
+ * Returns: 0 if @str does not start with @prefix
+ strlen(@prefix) if @str does start with @prefix
+ */
+static __always_inline size_t str_has_prefix(const char *str, const char *prefix)
+{
+ size_t len = strlen(prefix);
+ return strncmp(str, prefix, len) == 0 ? len : 0;
+}
+
#endif /* _LINUX_STRING_H_ */
Patches currently in stable-queue which might be from kroah.com@xxxxxxxxxxxxxxx are
queue-4.19/tracing-consolidate-trace_add-remove_event_call-back-to-the-nolock-functions.patch
queue-4.19/tracing-split-up-onmatch-action-data.patch
queue-4.19/tracing-remove-unnecessary-var_ref-destroy-in-track_data_destroy.patch
queue-4.19/tracing-use-str_has_prefix-helper-for-histogram-code.patch
queue-4.19/tracing-simplify-creation-and-deletion-of-synthetic-events.patch
queue-4.19/tracing-refactor-hist-trigger-action-code.patch
queue-4.19/string.h-add-str_has_prefix-helper-function.patch
queue-4.19/tracing-remove-unneeded-synth_event_mutex.patch
queue-4.19/tracing-add-unified-dynamic-event-framework.patch
queue-4.19/tracing-use-dyn_event-framework-for-synthetic-events.patch
queue-4.19/tracing-use-str_has_prefix-instead-of-using-fixed-sizes.patch
queue-4.19/tracing-generalize-hist-trigger-onmax-and-save-action.patch
queue-4.19/tracing-have-the-historgram-use-the-result-of-str_has_prefix-for-len-of-prefix.patch
