lib/kasprintf.c: introduce kvasprintf_const (0a9df786) · Commits · 戴 / test

This adds kvasprintf_const which tries to use kstrdup_const if possible: If the format string contains no % characters, or if the format string is exactly "%s", we delegate to kstrdup_const. Otherwise, we fall back to kvasprintf. Just as for kstrdup_const, the main motivation is to save memory by reusing .rodata when possible. The return value should be freed by kfree_const, just like for kstrdup_const. There is deliberately no kasprintf_const: In the vast majority of cases, the format string argument is a literal, so one can determine statically whether one could instead use kstrdup_const directly (which would also require one to change all corresponding kfree calls to kfree_const). Signed-off-by:

Rasmus Villemoes <linux@rasmusvillemoes.dk> Cc: Greg KH <greg@kroah.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

include/linux/kernel.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -413,6 +413,8 @@ extern __printf(2, 3)
		char kasprintf(gfp_t gfp, const char fmt, ...);
		extern __printf(2, 0)
		char kvasprintf(gfp_t gfp, const char fmt, va_list args);
		extern __printf(2, 0)
		const char kvasprintf_const(gfp_t gfp, const char fmt, va_list args);

		extern __scanf(2, 3)
		int sscanf(const char , const char , ...);

lib/kasprintf.c

+16 −0

Original line number	Diff line number	Diff line
		@@ -31,6 +31,22 @@ char kvasprintf(gfp_t gfp, const char fmt, va_list ap)
		}
		EXPORT_SYMBOL(kvasprintf);

		/*
		* If fmt contains no % (or is exactly %s), use kstrdup_const. If fmt
		* (or the sole vararg) points to rodata, we will then save a memory
		* allocation and string copy. In any case, the return value should be
		* freed using kfree_const().
		*/
		const char kvasprintf_const(gfp_t gfp, const char fmt, va_list ap)
		{
		if (!strchr(fmt, '%'))
		return kstrdup_const(fmt, gfp);
		if (!strcmp(fmt, "%s"))
		return kstrdup_const(va_arg(ap, const char*), gfp);
		return kvasprintf(gfp, fmt, ap);
		}
		EXPORT_SYMBOL(kvasprintf_const);

		char kasprintf(gfp_t gfp, const char fmt, ...)
		{
		va_list ap;

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