diff options
author | Steven Rostedt (VMware) <rostedt@goodmis.org> | 2018-12-21 18:10:14 -0500 |
---|---|---|
committer | Steven Rostedt (VMware) <rostedt@goodmis.org> | 2018-12-22 22:50:29 -0500 |
commit | 72921427d46bf9731a1ab7864adc64c43dfae29f (patch) | |
tree | b41bbec2205c7bc8d0d24f442352eafd9bcd1a4e /include/linux/string.h | |
parent | 1cce377df1800154301525a8ee04100dd83c9633 (diff) | |
download | linux-stable-72921427d46bf9731a1ab7864adc64c43dfae29f.tar.gz linux-stable-72921427d46bf9731a1ab7864adc64c43dfae29f.tar.bz2 linux-stable-72921427d46bf9731a1ab7864adc64c43dfae29f.zip |
string.h: Add str_has_prefix() helper function
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@linux.intel.com
Link: http://lkml.kernel.org/r/20181219211615.2298e781@gandalf.local.home
Link: http://lkml.kernel.org/r/CAHk-=wg_sR-UEC1ggmkZpypOUYanL5CMX4R7ceuaV4QMf5jBtg@mail.gmail.com
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Suggestions-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggestions-by: Joe Perches <joe@perches.com>
Suggestions-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'include/linux/string.h')
-rw-r--r-- | include/linux/string.h | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/include/linux/string.h b/include/linux/string.h index 27d0482e5e05..7927b875f80c 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -456,4 +456,24 @@ static inline void memcpy_and_pad(void *dest, size_t dest_len, 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_ */ |