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From: Yury Norov <yury.norov@gmail.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Barry Song <song.bao.hua@hisilicon.com>,
	akpm@linux-foundation.org, andriy.shevchenko@linux.intel.com,
	linux-kernel@vger.kernel.org, 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@huawei.com, prime.zeng@hisilicon.com,
	yangyicong@huawei.com, tim.c.chen@linux.intel.com,
	linuxarm@huawei.com
Subject: Re: [PATCH v7 0/4] use bin_attribute to break the size limitation of cpumap ABI
Date: Wed, 28 Jul 2021 07:53:59 -0700	[thread overview]
Message-ID: <YQFvhyAggX1fUm2t@yury-ThinkPad> (raw)
In-Reply-To: <YQFebNhDUD4VPN/P@kroah.com>

On Wed, Jul 28, 2021 at 03:41:00PM +0200, Greg KH wrote:
> On Thu, Jul 15, 2021 at 11:58:52PM +1200, Barry Song wrote:
> > v7:
> >   - update doc in code for new APIs according to the comments of
> >     Andy Shevchenko;
> >   - other minor cleanup and commit log fix according to the comments
> >     of Andy Shevchenko
> 
> I'm lost to tell if this is the latest version or if there are more
> changes?  Can you send this again with the latest changes so I can
> review it?

Barry, Greg,

If you decide to keep bitmap_print_to_buf in lib/bitmap.c, could you
please add the following patch to the series.

Thanks,
Yury


From 58602766dc2877d2103a334db6c2c2e1e6b8c89b Mon Sep 17 00:00:00 2001
From: Yury Norov <yury.norov@gmail.com>
Date: Wed, 28 Jul 2021 07:39:30 -0700
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>
---
 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() 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


  reply	other threads:[~2021-07-28 14:54 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-15 11:58 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 [this message]
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)

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