linux-kernel - [PATCH] cpumask: Omit terminating null byte in cpumap_print_{list,bitmask}_to

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Date:   Fri, 17 Sep 2021 00:27:05 +0200
From:   Tobias Klauser <tklauser@...tanz.ch>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Tian Tao <tiantao6@...ilicon.com>,
        Barry Song <song.bao.hua@...ilicon.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Yury Norov <yury.norov@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] cpumask: Omit terminating null byte in cpumap_print_{list,bitmask}_to_buf

The changes in the patch series [1] introduced a terminating null byte
when reading from cpulist or cpumap sysfs files, for example:

  $ xxd /sys/devices/system/node/node0/cpulist
  00000000: 302d 310a 00                             0-1..

Before this change, the output looked as follows:

  $ xxd /sys/devices/system/node/node0/cpulist
  00000000: 302d 310a                                0-1.

Fix this regression by excluding the terminating null byte from the
returned length in cpumap_print_list_to_buf and
cpumap_print_bitmask_to_buf.

[1] https://lore.kernel.org/all/20210806110251.560-1-song.bao.hua@hisilicon.com/

Fixes: 1fae562983ca ("cpumask: introduce cpumap_print_list/bitmask_to_buf to support large bitmask and list")
Signed-off-by: Tobias Klauser <tklauser@...tanz.ch>
---
 include/linux/cpumask.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 5d4d07a9e1ed..1e7399fc69c0 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -996,14 +996,15 @@ cpumap_print_to_pagebuf(bool list, char *buf, const struct cpumask *mask)
  * cpumask; Typically used by bin_attribute to export cpumask bitmask
  * ABI.
  *
- * Returns the length of how many bytes have been copied.
+ * Returns the length of how many bytes have been copied, excluding
+ * terminating '\0'.
  */
 static inline ssize_t
 cpumap_print_bitmask_to_buf(char *buf, const struct cpumask *mask,
 		loff_t off, size_t count)
 {
 	return bitmap_print_bitmask_to_buf(buf, cpumask_bits(mask),
-				   nr_cpu_ids, off, count);
+				   nr_cpu_ids, off, count) - 1;
 }
 
 /**
@@ -1018,7 +1019,7 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask,
 		loff_t off, size_t count)
 {
 	return bitmap_print_list_to_buf(buf, cpumask_bits(mask),
-				   nr_cpu_ids, off, count);
+				   nr_cpu_ids, off, count) - 1;
 }
 
 #if NR_CPUS <= BITS_PER_LONG
-- 
2.33.0