Warning from ddt_load breaking -Werror

[rincebrain]

System information

Type	Version/Name
Distribution Name	Debian
Distribution Version	11
Kernel Version	5.10.0-27-amd64
Architecture	amd64
OpenZFS Version	af4da5c

Describe the problem you're observing

I'm guessing this is fallout from something in the recent DDT series, but I'm not sure why the CI wouldn't have screamed about it...

I was cutting a build to test something, and got this on vanilla git:

In file included from ./include/sys/spa.h:46,
                 from module/zfs/ddt.c:30:
module/zfs/ddt.c: In function ‘ddt_load’:
./include/sys/dmu.h:377:24: warning: ‘%s’ directive output may be truncated writing likely 5 or more bytes into a region of size between 1 and 104 [-Wformat-truncation=]
  377 | #define DMU_POOL_DDT   "DDT-%s-%s-%s"
      |                        ^~~~~~~~~~~~~~
module/zfs/ddt.c:377:37: note: in expansion of macro ‘DMU_POOL_DDT’
  377 |  (void) snprintf(name, DDT_NAMELEN, DMU_POOL_DDT,
      |                                     ^~~~~~~~~~~~
./include/sys/dmu.h:377:35: note: format string is defined here
  377 | #define DMU_POOL_DDT   "DDT-%s-%s-%s"
      |                                   ^~
./include/sys/dmu.h:377:24: note: assuming directive output of 5 bytes
  377 | #define DMU_POOL_DDT   "DDT-%s-%s-%s"
      |                        ^~~~~~~~~~~~~~
module/zfs/ddt.c:377:37: note: in expansion of macro ‘DMU_POOL_DDT’
  377 |  (void) snprintf(name, DDT_NAMELEN, DMU_POOL_DDT,
      |                                     ^~~~~~~~~~~~
module/zfs/ddt.c:377:9: note: ‘snprintf’ output 7 or more bytes (assuming 115) into a destination of size 110
  377 |  (void) snprintf(name, DDT_NAMELEN, DMU_POOL_DDT,
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  378 |      zio_checksum_table[ddt->ddt_checksum].ci_name,
      |      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  379 |      ddt_ops[type]->ddt_op_name, ddt_class_name[class]);
      |      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Describe how to reproduce the problem

Just build on Debian 11, I assume.

Include any warning/errors/backtraces from the system logs

See above.

[robn]

Sigh this thing. What compiler version?

[rincebrain]

Sorry, I meant to include that and forgot.

 $ gcc --version
gcc (Debian 10.2.1-6) 10.2.1 20210110
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[behlendorf]

Fixed by #15908