tests: fix async allocation race on BTRFS

* tests/dd/sparse.sh: Sync files before checking allocations,
which may be done asynchronously on NFS and BTRFS at least.
Also mark this test as very expensive on remote file systems.
* tests/du/2g.sh: Likewise, also use fallocate if available
to efficiently allocate the large file, otherwise skip
on remote file systems.
* tests/tail-2/inotify-rotate-resources.sh: Use the more
standard is_local_dir_() to check remoteness.
* tests/cp/fiemap-empty.sh: Comment on the sync issue
for this currerntly unused test.
Fixes http://bugs.gnu.org/20570

tests/cp/fiemap-empty.sh

@@ -22,6 +22,7 @@ print_ver_ cp
 # FIXME: enable any part of this test that is still relevant,
 # or, if none are relevant (now that cp does not handle unwritten
 # extents), just remove the test altogether.
+# Note also if checking allocations may need to sync first on BTRFS at least
 skip_ 'disabled for now'
 
 touch fiemap_chk

tests/dd/sparse.sh

@@ -17,6 +17,7 @@
 
 . "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
 print_ver_ dd
+is_local_dir_ . || very_expensive_
 require_sparse_support_
 
 # Ensure basic sparse generation works
@@ -50,6 +51,9 @@ dd if=/dev/zero    of=file.in bs=1M count=1 seek=1 conv=notrunc || fail=1
 
 kb_alloc() { du -k "$1"|cut -f1; }
 
+# sync out data for async allocators like NFS/BTRFS
+# sync file.in || fail=1
+
 # If our just-created input file appears to be too small,
 # skip the remaining tests.  On at least Solaris 10 with NFS,
 # file.in is reported to occupy <= 1KiB for about 50 seconds
@@ -58,7 +62,10 @@ if test $(kb_alloc file.in) -gt 3000; then
 
   # Ensure NUL blocks smaller than the block size are not made sparse.
   # Here, with a 2MiB block size, dd's conv=sparse must *not* introduce a hole.
-  dd if=file.in of=file.out bs=2M conv=sparse
+  dd if=file.in of=file.out bs=2M conv=sparse || fail=1
+
+  # Intermittently BTRFS returns 0 allocation for file.out unless synced
+  sync file.out || framework_failure_
   test 2500 -lt $(kb_alloc file.out) || fail=1
 
   # Note we recreate a sparse file first to avoid

tests/du/2g.sh

@@ -24,7 +24,6 @@ print_ver_ du
 # Creating a 2GB file counts as 'very expensive'.
 very_expensive_
 
-
 # Get number of free kilobytes on current partition, so we can
 # skip this test if there is insufficient free space.
 free_kb=$(df -k --output=avail . | tail -n1)
@@ -42,15 +41,22 @@ test $min_kb -lt $free_kb ||
 }
 
 big=big
-rm -f $big
-{
-  for i in $(seq 100); do
-    # Note: 2147483648 == 2^31. Print floor(2^31/100) per iteration.
-    printf %21474836s x || fail=1
-  done
-  # After the final iteration, append the remaining 48 bytes.
-  printf %48s x || fail=1
-} > $big || fail=1
+
+if ! fallocate -l2G $big; then
+  rm -f $big
+  {
+    is_local_dir_ . || skip 'Not writing 2GB data to remote'
+    for i in $(seq 100); do
+      # Note: 2147483648 == 2^31. Print floor(2^31/100) per iteration.
+      printf %21474836s x || fail=1
+    done
+    # After the final iteration, append the remaining 48 bytes.
+    printf %48s x || fail=1
+  } > $big || fail=1
+fi
+
+# The allocation may be done asynchronously (BTRFS for example)
+sync $big || framework_failure_
 
 du -k $big > out1 || fail=1
 rm -f $big

tests/tail-2/inotify-rotate-resources.sh

@@ -25,7 +25,7 @@ grep '^#define HAVE_INOTIFY 1' "$CONFIG_HEADER" >/dev/null \
 require_strace_ 'inotify_add_watch,inotify_rm_watch'
 
 # Quickly skip on remote file systems
-df --local . >/dev/null 2>&1 ||
+is_local_dir . >/dev/null 2>&1 ||
   skip_ 'inotify not used on remote file system'
 
 check_tail_output()