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From: "Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>
To: Yury Norov <yury.norov@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
Cc: "dave.hansen@intel.com" <dave.hansen@intel.com>,
	"linux@rasmusvillemoes.dk" <linux@rasmusvillemoes.dk>,
	"rafael@kernel.org" <rafael@kernel.org>,
	"rdunlap@infradead.org" <rdunlap@infradead.org>,
	"agordeev@linux.ibm.com" <agordeev@linux.ibm.com>,
	"sbrivio@redhat.com" <sbrivio@redhat.com>,
	"jianpeng.ma@intel.com" <jianpeng.ma@intel.com>,
	"valentin.schneider@arm.com" <valentin.schneider@arm.com>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"bristot@redhat.com" <bristot@redhat.com>,
	"guodong.xu@linaro.org" <guodong.xu@linaro.org>,
	tangchengchang <tangchengchang@huawei.com>,
	"Zengtao (B)" <prime.zeng@hisilicon.com>,
	yangyicong <yangyicong@huawei.com>,
	"tim.c.chen@linux.intel.com" <tim.c.chen@linux.intel.com>,
	Linuxarm <linuxarm@huawei.com>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"andriy.shevchenko@linux.intel.com" 
	<andriy.shevchenko@linux.intel.com>
Subject: RE: [PATCH] bitmap: extend comment to bitmap_print_to_buf
Date: Thu, 29 Jul 2021 06:04:09 +0000	[thread overview]
Message-ID: <eec4210a5d724cccb2931a3f4403e5be@hisilicon.com> (raw)
In-Reply-To: <20210728185831.215079-1-yury.norov@gmail.com>



> -----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


      reply	other threads:[~2021-07-29  6:04 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-15 11:58 [PATCH v7 0/4] use bin_attribute to break the size limitation of cpumap ABI Barry Song
2021-07-15 11:58 ` [PATCH v7 1/4] cpumask: introduce cpumap_print_to_buf to support large bitmask and list Barry Song
2021-07-15 15:28   ` Yury Norov
2021-07-15 21:08     ` Song Bao Hua (Barry Song)
2021-07-16  0:57     ` Song Bao Hua (Barry Song)
2021-07-15 11:58 ` [PATCH v7 2/4] topology: use bin_attribute to break the size limitation of cpumap ABI Barry Song
2021-07-16  8:49   ` Song Bao Hua (Barry Song)
2021-07-16 20:04     ` Yury Norov
2021-07-17  0:16       ` Song Bao Hua (Barry Song)
2021-07-17  1:12         ` Yury Norov
2021-07-19  9:07           ` andriy.shevchenko
2021-07-19 11:10             ` Song Bao Hua (Barry Song)
2021-07-19 17:10               ` Yury Norov
2021-07-21  9:30                 ` Song Bao Hua (Barry Song)
2021-07-15 11:58 ` [PATCH v7 3/4] drivers/base/node.c: " Barry Song
2021-07-15 11:58 ` [PATCH v7 4/4] lib: test_bitmap: add bitmap_print_to_buf test cases Barry Song
2021-07-15 12:09   ` Andy Shevchenko
2021-07-15 20:47     ` Yury Norov
2021-07-15 21:32       ` Andy Shevchenko
2021-07-15 23:23         ` Yury Norov
2021-07-16  0:41           ` Song Bao Hua (Barry Song)
2021-07-21 11:40           ` Greg Kroah-Hartman
2021-07-22 17:09             ` Yury Norov
2021-07-22 17:47               ` Greg Kroah-Hartman
2021-07-22 18:27                 ` Yury Norov
2021-07-22 18:36                   ` Andy Shevchenko
2021-07-22 18:45                   ` Greg Kroah-Hartman
2021-07-28  9:08                     ` Song Bao Hua (Barry Song)
2021-07-28  9:24                       ` Andy Shevchenko
2021-07-15 15:36   ` Yury Norov
2021-07-28 13:41 ` [PATCH v7 0/4] use bin_attribute to break the size limitation of cpumap ABI Greg KH
2021-07-28 14:53   ` Yury Norov
2021-07-28 15:25     ` Greg KH
2021-07-28 18:58 ` [PATCH] bitmap: extend comment to bitmap_print_to_buf Yury Norov
2021-07-29  6:04   ` Song Bao Hua (Barry Song) [this message]

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