generic/{472,496}: fix swap file creation on Btrfs

The swap file must be set nocow before it is written to, otherwise it is
ignored and Btrfs refuses to activate it as swap.

Fixes: 25ce974 ("generic: test swapfile creation, activation, and deactivation")
Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/472

@@ -42,13 +42,15 @@ _scratch_mount >>$seqres.full 2>&1
 
 swapfile=$SCRATCH_MNT/swap
 len=$((2 * 1048576))
-page_size=$(get_page_size)
 
 swapfile_cycle() {
 	local swapfile="$1"
+	local len="$2"
 
+	touch $swapfile
 	# Swap files must be nocow on Btrfs.
 	$CHATTR_PROG +C $swapfile >> $seqres.full 2>&1
+	_pwrite_byte 0x58 0 $len $swapfile >> $seqres.full
 	"$here/src/mkswap" $swapfile >> $seqres.full
 	"$here/src/swapon" $swapfile 2>&1 | _filter_scratch
 	swapoff $swapfile 2>> $seqres.full
@@ -57,20 +59,16 @@ swapfile_cycle() {
 
 # Create a regular swap file
 echo "regular swap" | tee -a $seqres.full
-_pwrite_byte 0x58 0 $len $swapfile >> $seqres.full
-swapfile_cycle $swapfile
+swapfile_cycle $swapfile $len
 
 # Create a swap file with a little too much junk on the end
 echo "too long swap" | tee -a $seqres.full
-_pwrite_byte 0x58 0 $((len + 3)) $swapfile >> $seqres.full
-swapfile_cycle $swapfile
+swapfile_cycle $swapfile $((len + 3))
 
 # Create a ridiculously small swap file.  Each swap file must have at least
 # two pages after the header page.
 echo "tiny swap" | tee -a $seqres.full
-tiny_len=$((page_size * 3))
-_pwrite_byte 0x58 0 $tiny_len $swapfile >> $seqres.full
-swapfile_cycle $swapfile
+swapfile_cycle $swapfile $(($(get_page_size) * 3))
 
 status=0
 exit

tests/generic/496

@@ -49,8 +49,6 @@ page_size=$(get_page_size)
 swapfile_cycle() {
 	local swapfile="$1"
 
-	# Swap files must be nocow on Btrfs.
-	$CHATTR_PROG +C $swapfile >> $seqres.full 2>&1
 	"$here/src/mkswap" $swapfile >> $seqres.full
 	"$here/src/swapon" $swapfile 2>&1 | _filter_scratch
 	swapoff $swapfile 2>> $seqres.full
@@ -59,8 +57,10 @@ swapfile_cycle() {
 
 # Create a fallocated swap file
 echo "fallocate swap" | tee -a $seqres.full
-$XFS_IO_PROG -f -c "falloc 0 $len" $swapfile >> $seqres.full
+touch $swapfile
+# Swap files must be nocow on Btrfs.
 $CHATTR_PROG +C $swapfile >> $seqres.full 2>&1
+$XFS_IO_PROG -f -c "falloc 0 $len" $swapfile >> $seqres.full
 "$here/src/mkswap" $swapfile
 "$here/src/swapon" $swapfile >> $seqres.full 2>&1 || \
 	_notrun "fallocated swap not supported here"