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Date: Fri, 6 Aug 2021 23:02:51 +1200 From: Barry Song <song.bao.hua@...ilicon.com> To: <andriy.shevchenko@...ux.intel.com>, <yury.norov@...il.com>, <gregkh@...uxfoundation.org>, <linux-kernel@...r.kernel.org> CC: <akpm@...ux-foundation.org>, <dave.hansen@...el.com>, <linux@...musvillemoes.dk>, <rafael@...nel.org>, <rdunlap@...radead.org>, <agordeev@...ux.ibm.com>, <sbrivio@...hat.com>, <jianpeng.ma@...el.com>, <valentin.schneider@....com>, <peterz@...radead.org>, <bristot@...hat.com>, <guodong.xu@...aro.org>, <tangchengchang@...wei.com>, <prime.zeng@...ilicon.com>, <yangyicong@...wei.com>, <tim.c.chen@...ux.intel.com>, <linuxarm@...wei.com>, Barry Song <song.bao.hua@...ilicon.com> Subject: [PATCH v9 5/5] bitmap: extend comment to bitmap_print_bitmask/list_to_buf From: Yury Norov <yury.norov@...il.com> Extend comment to new function to warn potential users about caveats. Signed-off-by: Yury Norov <yury.norov@...il.com> Signed-off-by: Barry Song <song.bao.hua@...ilicon.com> --- lib/bitmap.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/lib/bitmap.c b/lib/bitmap.c index 73746d96af81..663dd81967d4 100644 --- a/lib/bitmap.c +++ b/lib/bitmap.c @@ -568,6 +568,24 @@ static int bitmap_print_to_buf(bool list, char *buf, const unsigned long *maskp, * and it can break the size limit of converted decimal list and hexadecimal * bitmask. * + * WARNING! + * + * This function is not a replacement for sprintf() or bitmap_print_to_pagebuf(). + * It is intended to workaround sysfs limitations discussed above and should be + * used carefully in general case for the following reasons: + * - Time complexity is O(nbits^2/count), comparing to O(nbits) for snprintf(). + * - Memory complexity is O(nbits), comparing to O(1) for snprintf(). + * - @off and @count are NOT offset and number of bits to print. + * - If printing part of bitmap as list, the resulting string is not a correct + * list representation of bitmap. Particularly, some bits within or out of + * related interval may be erroneously set or unset. The format of the string + * may be broken, so bitmap_parselist-like parser may fail parsing it. + * - If printing the whole bitmap as list by parts, user must ensure the order + * of calls of the function such that the offset is incremented linearly. + * - If printing the whole bitmap as list by parts, user must keep bitmap + * unchanged between the very first and very last call. Otherwise concatenated + * result may be incorrect, and format may be broken. + * * Returns the number of characters actually printed to @buf */ int bitmap_print_bitmask_to_buf(char *buf, const unsigned long *maskp, -- 2.25.1
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