Fedora 28: misc bounds check compiler warnings

[tonyhutter]

System information

Type	Version/Name
Distribution Name	Fedora
Distribution Version	28
Linux Kernel	4.16
Architecture	x86-64
ZFS Version	master
SPL Version	master

Describe the problem you're observing

Building ZFS under Fedora 28 produces a number of bounds check warnings. Fedora 28 comes with GCC 8.0.1.

Describe how to reproduce the problem

make

Include any warning/errors/backtraces from the system logs

Some samples:

  CC       lauxlib.lo
In file included from ../../include/sys/zfs_context.h:100,
                 from ../../module/zfs/zio.c:28:
In function ‘umem_cache_create.constprop’,
    inlined from ‘zio_init’ at ../../module/zfs/zio.c:182:23:
../../lib/libspl/include/umem.h:149:3: warning: ‘strncpy’ output may be truncated copying 31 bytes from a string of length 35 [-Wstringop-truncation]
   strncpy(cp->cache_name, name, UMEM_CACHE_NAMELEN);
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In function ‘umem_cache_create.constprop’,
    inlined from ‘zio_init’ at ../../module/zfs/zio.c:186:28:
../../lib/libspl/include/umem.h:149:3: warning: ‘strncpy’ output may be truncated copying 31 bytes from a string of length 35 [-Wstringop-truncation]
   strncpy(cp->cache_name, name, UMEM_CACHE_NAMELEN);
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  CC       lbaselib.lo


make[7]: Entering directory '/home/hutter/fedora28/tests/zfs-tests/tests/functional/cli_root/zfs_diff'
  CC       socket.o
socket.c: In function ‘main’:
socket.c:39:2: warning: ‘strncpy’ specified bound 108 equals destination size [-Wstringop-truncation]
  strncpy(sock.sun_path, (char *)path, sizeof (sock.sun_path));
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  CCLD     socket
make[7]: Leaving directory '/home/hutter/fedora28/tests/zfs-tests/tests/functional/cli_root/zfs_diff'
Making all in zfs_get


make[5]: Entering directory '/home/hutter/fedora28/tests/zfs-tests/cmd/mkbusy'
  CC       mkbusy.o
mkbusy.c: In function ‘main’:
mkbusy.c:141:10: warning: ‘strncpy’ output truncated before terminating nul copying as many bytes from a string as its length [-Wstringop-truncation]
   (void) strncpy(fpath, dname, dlen);
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~
mkbusy.c:129:10: note: length computed here
   dlen = strlen(dname);
          ^~~~~~~~~~~~~
mkbusy.c:143:10: warning: ‘strncat’ output truncated before terminating nul copying as many bytes from a string as its length [-Wstringop-truncation]
   (void) strncat(fpath, fname, flen);
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~
mkbusy.c:130:10: note: length computed here
   flen = strlen(fname);
          ^~~~~~~~~~~~~
  CCLD     mkbusy
make[5]: Leaving directory '/home/hutter/fedora28/tests/zfs-tests/cmd/mkbusy'


Making all in zvol_id
make[3]: Entering directory '/home/hutter/fedora28/cmd/zvol_id'
  CC       zvol_id_main.o
zvol_id_main.c: In function ‘main’:
zvol_id_main.c:92:10: warning: ‘-part’ directive output may be truncated writing 5 bytes into a region of size between 1 and 256 [-Wformat-truncation=]
       "%s-part%d", zvol_name, dev_part);
          ^~~~~
zvol_id_main.c:92:7: note: directive argument in the range [1, 15]
       "%s-part%d", zvol_name, dev_part);
       ^~~~~~~~~~~
zvol_id_main.c:91:3: note: ‘snprintf’ output between 7 and 263 bytes into a destination of size 256
   snprintf(zvol_name_part, ZFS_MAX_DATASET_NAME_LEN,
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
       "%s-part%d", zvol_name, dev_part);
       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  CCLD     zvol_id
make[3]: Leaving directory '/home/hutter/fedora28/cmd/zvol_id'