Messages in this thread Patch in this message | | | From | Barry Song <> | Subject | [PATCH v8 5/5] bitmap: extend comment to bitmap_print_to_buf | Date | Thu, 29 Jul 2021 17:42:08 +1200 |
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From: Yury Norov <yury.norov@gmail.com>
Extend comment to new function to warn potential users about caveats.
Signed-off-by: Yury Norov <yury.norov@gmail.com> Signed-off-by: Barry Song <song.bao.hua@hisilicon.com> --- lib/bitmap.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)
diff --git a/lib/bitmap.c b/lib/bitmap.c index 56bcffe2fa8c..608b79eabd43 100644 --- a/lib/bitmap.c +++ b/lib/bitmap.c @@ -545,6 +545,24 @@ EXPORT_SYMBOL(bitmap_print_to_pagebuf); * mainly serves bin_attribute which doesn't work with exact one page, 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_to_buf(bool list, char *buf, const unsigned long *maskp, -- 2.25.1
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