From 0bee0cece2a6a71ccc347fdc1d46cf638cd5fd1c Mon Sep 17 00:00:00 2001 From: Yury Norov Date: Mon, 3 Feb 2020 17:37:20 -0800 Subject: lib/string: add strnchrnul() Patch series "lib: rework bitmap_parse", v5. Similarl to the recently revisited bitmap_parselist(), bitmap_parse() is ineffective and overcomplicated. This series reworks it, aligns its interface with bitmap_parselist() and makes it simpler to use. The series also adds a test for the function and fixes usage of it in cpumask_parse() according to the new design - drops the calculating of length of an input string. bitmap_parse() takes the array of numbers to be put into the map in the BE order which is reversed to the natural LE order for bitmaps. For example, to construct bitmap containing a bit on the position 42, we have to put a line '400,0'. Current implementation reads chunk one by one from the beginning ('400' before '0') and makes bitmap shift after each successful parse. It makes the complexity of the whole process as O(n^2). We can do it in reverse direction ('0' before '400') and avoid shifting, but it requires reverse parsing helpers. This patch (of 7): New function works like strchrnul() with a length limited string. Link: http://lkml.kernel.org/r/20200102043031.30357-2-yury.norov@gmail.com Signed-off-by: Yury Norov Reviewed-by: Andy Shevchenko Cc: Rasmus Villemoes Cc: Amritha Nambiar Cc: Willem de Bruijn Cc: Kees Cook Cc: Matthew Wilcox Cc: "Tobin C . Harding" Cc: Will Deacon Cc: Miklos Szeredi Cc: Vineet Gupta Cc: Chris Wilson Cc: Arnaldo Carvalho de Melo Cc: Steffen Klassert Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/string.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) (limited to 'lib/string.c') diff --git a/lib/string.c b/lib/string.c index 08ec58cc673b..f607b967d978 100644 --- a/lib/string.c +++ b/lib/string.c @@ -434,6 +434,23 @@ char *strchrnul(const char *s, int c) EXPORT_SYMBOL(strchrnul); #endif +/** + * strnchrnul - Find and return a character in a length limited string, + * or end of string + * @s: The string to be searched + * @count: The number of characters to be searched + * @c: The character to search for + * + * Returns pointer to the first occurrence of 'c' in s. If c is not found, + * then return a pointer to the last character of the string. + */ +char *strnchrnul(const char *s, size_t count, int c) +{ + while (count-- && *s && *s != (char)c) + s++; + return (char *)s; +} + #ifndef __HAVE_ARCH_STRRCHR /** * strrchr - Find the last occurrence of a character in a string -- cgit v1.2.3