Messages in this thread | | | From | "Song Bao Hua (Barry Song)" <> | Subject | RE: [PATCH] bitmap: extend comment to bitmap_print_to_buf | Date | Thu, 29 Jul 2021 06:04:09 +0000 |
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> -----Original Message----- > From: Yury Norov [mailto:yury.norov@gmail.com] > Sent: Thursday, July 29, 2021 6:59 AM > To: linux-kernel@vger.kernel.org; gregkh@linuxfoundation.org; Song Bao Hua > (Barry Song) <song.bao.hua@hisilicon.com> > Cc: Yury Norov <yury.norov@gmail.com>; dave.hansen@intel.com; > linux@rasmusvillemoes.dk; rafael@kernel.org; rdunlap@infradead.org; > agordeev@linux.ibm.com; sbrivio@redhat.com; jianpeng.ma@intel.com; > valentin.schneider@arm.com; peterz@infradead.org; bristot@redhat.com; > guodong.xu@linaro.org; tangchengchang <tangchengchang@huawei.com>; Zengtao (B) > <prime.zeng@hisilicon.com>; yangyicong <yangyicong@huawei.com>; > tim.c.chen@linux.intel.com; Linuxarm <linuxarm@huawei.com>; > akpm@linux-foundation.org; andriy.shevchenko@linux.intel.com > Subject: [PATCH] bitmap: extend comment to bitmap_print_to_buf > > Extend comment to new function to warn potential users about caveats. > > Signed-off-by: Yury Norov <yury.norov@gmail.com> > ---
Looks awesome. Thanks, Yury. I have integrated your patch into the latest series v8.
> lib/bitmap.c | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/lib/bitmap.c b/lib/bitmap.c > index 56bcffe2fa8c..b9f557ca668c 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, > -- > 2.30.2
Thanks Barry
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