fix gcc 10.1 stringop-truncation error

[gamanakis]

Compiling with gcc 10.1 fails with:

zpool_main.c: In function ‘zpool_do_events_short’:
zpool_main.c:8901:9: error: ‘strncpy’ output may be truncated copying 6 bytes from a string of length 21 [-Werror=stringop-truncation]
 8901 |  (void) strncpy(str, ctime_str+4,  6);  /* 'Jun 30' */
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
zpool_main.c:8902:9: error: ‘strncpy’ output may be truncated copying 4 bytes from a string of length 5 [-Werror=stringop-truncation]
 8902 |  (void) strncpy(str+7, ctime_str+20, 4);  /* '1993' */
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
zpool_main.c:8903:9: error: ‘strncpy’ output may be truncated copying 8 bytes from a string of length 14 [-Werror=stringop-truncation]
 8903 |  (void) strncpy(str+12, ctime_str+11, 8); /* '21:49:08' */
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

As we do not expect the destination of these strncpy calls to be NUL terminated, substitute them with memcpy per https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wstringop-truncation

Signed-off-by: George Amanakis gamanakis@gmail.com

Motivation and Context

Description

How Has This Been Tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the ZFS on Linux code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
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[tonyhutter]

I think you can simplify it further to:

/*
 * Take a date like 'Mon May 18 15:23:11 2020' and trim off the day
 * of the week (first three chars + space).
 */
memcpy(str, ctime_str + 4,  20);

[gamanakis]

@tonyhutter I think that would change the format of the date though.
I find it more functional the way it has been: May 18 2020 15:23:11.xxxxx, instead of May 18 15:23:11.xxxxx 2020

[codecov-commenter]

Codecov Report

Merging #10346 into master will increase coverage by 0.24%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #10346      +/-   ##
==========================================
+ Coverage   79.24%   79.48%   +0.24%     
==========================================
  Files         390      390              
  Lines      123336   123336              
==========================================
+ Hits        97737    98036     +299     
+ Misses      25599    25300     -299     

Flag	Coverage Δ
#kernel	79.94% <ø> (+0.03%)	⬆️
#user	66.02% <100.00%> (+1.85%)	⬆️

Impacted Files	Coverage Δ
cmd/zpool/zpool_main.c	80.43% <100.00%> (+0.02%)	⬆️
module/lua/lmem.c	83.33% <0.00%> (-4.17%)	⬇️
module/zfs/dsl_synctask.c	92.40% <0.00%> (-2.54%)	⬇️
module/zfs/zap_micro.c	85.35% <0.00%> (-1.26%)	⬇️
module/os/linux/zfs/zfs_file_os.c	84.15% <0.00%> (-1.00%)	⬇️
module/zfs/dmu_traverse.c	96.34% <0.00%> (-0.67%)	⬇️
module/zfs/vdev_raidz.c	93.13% <0.00%> (-0.66%)	⬇️
module/zfs/vdev_queue.c	94.49% <0.00%> (-0.62%)	⬇️
module/zfs/zil.c	91.25% <0.00%> (-0.57%)	⬇️
module/zfs/bpobj.c	90.61% <0.00%> (-0.54%)	⬇️
... and 58 more

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[tonyhutter]

@gamanakis ah you're right, I see what you mean. Approved