Steven Rostedt (VMware) 1415e7a48b
string.h: Add str_has_prefix() helper function ...
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@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 >
Signed-off-by: George Guo <guodongtai@kylinos.cn >
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org >
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1415e7a48b