linux-kernel - Re: [PATCH v3] string.h: Add str_has

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Message-ID: <20181221182507.2fdc756f@gandalf.local.home>
Date:   Fri, 21 Dec 2018 18:25:07 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Joe Perches <joe@...ches.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Tom Zanussi <zanussi@...nel.org>
Subject: Re: [PATCH v3] string.h: Add str_has_prefix() helper

On Fri, 21 Dec 2018 15:19:33 -0800
Joe Perches <joe@...ches.com> wrote:

> I believe this should be bool.
> 
> I don't find a use for non-zero assigned len value in the kernel
> for strncmp and I believe the function should simply be:
> 
> static inline bool str_has_prefix(const char *str, const char prefix[])
> {
> 	return !strncmp(str, prefix, strlen(prefix));
> }

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 3bb2b3351e35..e4566b9c2553 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -172,8 +172,8 @@ cache_type_store(struct device *dev, struct device_attribute *attr,
 		 * it's not worth the risk */
 		return -EINVAL;
 
-	if (strncmp(buf, temp, sizeof(temp) - 1) == 0) {
-		buf += sizeof(temp) - 1;
+	if ((len = str_has_prefix(buf, temp))) {
+		buf += len;
 		sdkp->cache_override = 1;
 	} else {
 		sdkp->cache_override = 0;

And there's more places like this.

> 
> It's hard to believe __always_inline vs inline matters
> for any single line function.

I've been burnt by gcc deciding to not inline single functions before.
Why take the chance? It also documents that I must be inlined, and not
just a hint.

-- Steve