tests: determine if SEEK_HOLE is enabled

Upcomming gnulib changes may disable SEEK_HOLE
even if the system supports it, so dynamically
check if we've SEEK_HOLE enabled.

* init.cfg (seek_data_capable_): SEEK_DATA may be disabled in the build
if the system support is deemed insufficient, so also use `cp --debug`
to determine if it's enabled.
* tests/cp/sparse-2.sh: Adjust to a more general diagnostic.
* tests/cp/sparse-extents-2.sh: Likewise.
* tests/cp/sparse-extents.sh: Likewise.
* tests/cp/sparse-perf.sh: Likewise.

init.cfg

@@ -546,6 +546,18 @@ require_kill_group_()
 # which SEEK_DATA support exists.
 seek_data_capable_()
 {
+  # Check that SEEK_HOLE support is enabled
+  # Note APFS was seen to not create sparse files < 16MiB
+  if ! truncate -s16M file.sparse_; then
+      warn_ "can't create a sparse file: assuming not SEEK_DATA capable"
+      return 1
+  fi
+  if ! cp --debug --reflink=never file.sparse_ file.sparse_.cp \
+       | grep SEEK_HOLE; then
+      return 1
+  fi
+
+  # Check that SEEK_HOLE is supported on the passed file
   { python3 < /dev/null && PYTHON_=python3; } ||
   { python  < /dev/null && PYTHON_=python; }
 

tests/cp/sparse-2.sh

@@ -21,7 +21,7 @@ print_ver_ cp stat dd
 
 touch sparse_chk
 seek_data_capable_ sparse_chk \
-  || skip_ "this file system lacks SEEK_DATA support"
+  || skip_ "insufficient SEEK_DATA support"
 
 # Exercise the code that handles a file ending in a hole.
 printf x > k || framework_failure_

tests/cp/sparse-extents-2.sh

@@ -26,7 +26,7 @@ touch sparse_chk
 if seek_data_capable_ sparse_chk && ! df -t ext3 . >/dev/null; then
   : # Current partition has working extents.  Good!
 else
-  skip_ "current file system has insufficient SEEK_DATA support"
+  skip_ "insufficient SEEK_DATA support"
 
   # It's not;  we need to create one, hence we need root access.
   require_root_

tests/cp/sparse-extents.sh

@@ -23,7 +23,7 @@ require_sparse_support_
 
 touch sparse_chk || framework_failure_
 seek_data_capable_ sparse_chk ||
-  skip_ 'this file system lacks SEEK_DATA support'
+  skip_ 'insufficient SEEK_DATA support'
 
 fallocate --help >/dev/null || skip_ 'The fallocate utility is required'
 touch falloc.test || framework_failure_

tests/cp/sparse-perf.sh

@@ -28,7 +28,7 @@ timeout 10 truncate -s1T f ||
 # between the creation of the file and the use of SEEK_DATA,
 # for it to determine it's an empty file (return ENXIO).
 seek_data_capable_ f ||
-  skip_ "this file system lacks appropriate SEEK_DATA support"
+  skip_ "insufficient SEEK_DATA support"
 
 # Nothing can read that many bytes in so little time.
 timeout 10 cp --reflink=never f f2 || fail=1