common: Fix mismatched output from standard mkswap

With older util-linux(e.g. v2.17.2), running some tests(e.g.
generic/472, generic/495) got the following output:
-------------------------------------------------------
+mkswap: /mnt/xfstests/scratch/swap: warning: don't erase bootbits sectors
+        on whole disk. Use -f to force.
+mkswap: unable to relabel /mnt/xfstests/scratch/swap to system_u:object_r:swapfile_t:s0: Operation not supported
-------------------------------------------------------

1) Before commit c1f1b30 of util-linux, standard mkswap didn't zap bootbits
   sectors and printed a warning until force option(i.e. -f) was given.  We
   define "mkswap -f" as MKSWAP_PROG and replace all standard mkswap with
   $MKSWAP_PROG.

2) With mounting default SELinux context(e.g. system_u:object_r:root_t:s0),
   standard mkswap tried to reset the type of default context to swapfile_t
   if it is not swapfile_t, and then it failed and returned ENOTSUP expectedly
   as we don't want to create any SELinux attr on purpose.  standard mkswap
   ignored this relabel error by commit d97dc0e of util-linux, but it still
   reported the error before commit d97dc0e.  We try to skip the reset step
   in standard mkswap by mounting swapfile context directly.

Note:
We just mount swapfile context in related tests, and keep default context
in the rest of tests.

[Eryu: make mkswap a non-mandatory requirement and add comments on
"-f" option]

Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

common/config

@@ -132,6 +132,11 @@ export DF_PROG="$(type -P df)"
 export XFS_IO_PROG="$(type -P xfs_io)"
 [ "$XFS_IO_PROG" = "" ] && _fatal "xfs_io not found"
 
+export MKSWAP_PROG="$(type -P mkswap)"
+# mkswap from util-linux v2.17.2 or older needs "-f" option to force to erase
+# bootbits sectors
+MKSWAP_PROG="$MKSWAP_PROG -f"
+
 export XFS_LOGPRINT_PROG="$(type -P xfs_logprint)"
 export XFS_REPAIR_PROG="$(type -P xfs_repair)"
 export XFS_DB_PROG="$(type -P xfs_db)"

common/rc

@@ -2210,15 +2210,28 @@ _format_swapfile() {
 	# Swap files must be nocow on Btrfs.
 	$CHATTR_PROG +C "$fname" > /dev/null 2>&1
 	_pwrite_byte 0x61 0 "$sz" "$fname" >> $seqres.full
-	mkswap "$fname" >> $seqres.full
+	$MKSWAP_PROG "$fname" >> $seqres.full
 }
 
 # Check that the filesystem supports swapfiles
 _require_scratch_swapfile()
 {
 	_require_scratch
+	_require_command "$MKSWAP_PROG" "mkswap"
 
 	_scratch_mkfs >/dev/null
+
+	# With mounting SELinux context(e.g. system_u:object_r:root_t:s0),
+	# standard mkswap tried to reset the type of default context to
+	# swapfile_t if it's not swapfile_t, and then it failed and returned
+	# ENOTSUP expectedly as we don't want to create any SELinux attr on
+	# purpose.  standard mkswap ignored this relabel error by commit
+	# d97dc0e of util-linux, but it still reported the error before
+	# commit d97dc0e.  We mount swapfile context directly to skip the
+	# reset step.
+	[ -n "$SELINUX_MOUNT_OPTIONS" ] && export \
+		SELINUX_MOUNT_OPTIONS="-o context=system_u:object_r:swapfile_t:s0"
+
 	_scratch_mount
 
 	# Minimum size for mkswap is 10 pages

tests/btrfs/173

@@ -41,7 +41,7 @@ rm -f "$SCRATCH_MNT/swap"
 touch "$SCRATCH_MNT/swap"
 chmod 0600 "$SCRATCH_MNT/swap"
 _pwrite_byte 0x61 0 $(($(get_page_size) * 10)) "$SCRATCH_MNT/swap" >> $seqres.full
-mkswap "$SCRATCH_MNT/swap" >> $seqres.full
+$MKSWAP_PROG "$SCRATCH_MNT/swap" >> $seqres.full
 swapon "$SCRATCH_MNT/swap" 2>&1 | _filter_scratch
 swapoff "$SCRATCH_MNT/swap" >/dev/null 2>&1
 

tests/xfs/419

@@ -47,7 +47,7 @@ $XFS_IO_PROG -c "open -f -R $testdir/dummy" $testdir >> $seqres.full
 echo moo >> $testdir/dummy
 $XFS_IO_PROG -c "open -f -R $testdir/file1" $testdir >> $seqres.full
 _pwrite_byte 0x61 0 $((blocks * blksz)) $testdir/file1 >> $seqres.full
-mkswap -U 27376b42-ff65-42ca-919f-6c9b62292a5c $testdir/file1 >> $seqres.full
+$MKSWAP_PROG -U 27376b42-ff65-42ca-919f-6c9b62292a5c $testdir/file1 >> $seqres.full
 
 echo "Try to swapon"
 swapon $testdir/file1 2>&1 | _filter_scratch