populate: support compressing metadumps

If the test runner passed in a DUMP_COMPRESSOR program, make it so that
the metadumps we generate are also compressed.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>

README

@@ -111,6 +111,11 @@ Preparing system for tests:
                the module is the same as FSTYP.
              - Set DUMP_CORRUPT_FS=1 to record metadata dumps of XFS
                filesystems if a filesystem check fails.
+             - Set DUMP_COMPRESSOR to a compression program to compress
+               metadumps of filesystems.  This program must accept '-f' and the
+               name of a file to compress; and it must accept '-d -f -k' and
+               the name of a file to decompress.  In other words, it must
+               emulate gzip.
 
         - or add a case to the switch in common/config assigning
           these variables based on the hostname of your test

common/populate

@@ -824,6 +824,17 @@ _scratch_populate_cache_tag() {
 _scratch_populate_restore_cached() {
 	local metadump="$1"
 
+	# If we're configured for compressed dumps and there isn't already an
+	# uncompressed dump, see if we can use DUMP_COMPRESSOR to decompress
+	# something.
+	if [ -n "$DUMP_COMPRESSOR" ]; then
+		for compr in "$metadump".*; do
+			[ -e "$compr" ] && $DUMP_COMPRESSOR -d -f -k "$compr" && break
+		done
+	fi
+
+	test -r "$metadump" || return 1
+
 	case "${FSTYP}" in
 	"xfs")
 		xfs_mdrestore "${metadump}" "${SCRATCH_DEV}" && return 0
@@ -855,7 +866,6 @@ _scratch_populate_cached() {
 		rm -rf "${POPULATE_METADUMP}"
 
 	# Try to restore from the metadump
-	test -r "${POPULATE_METADUMP}" && \
 	_scratch_populate_restore_cached "${POPULATE_METADUMP}" && \
 		return
 
@@ -867,6 +877,13 @@ _scratch_populate_cached() {
 		_scratch_xfs_populate $@
 		_scratch_xfs_populate_check
 		_scratch_xfs_metadump "${POPULATE_METADUMP}"
+
+		local logdev=
+		[ "$USE_EXTERNAL" = yes -a ! -z "$SCRATCH_LOGDEV" ] && \
+			logdev=$SCRATCH_LOGDEV
+
+		_xfs_metadump "$POPULATE_METADUMP" "$SCRATCH_DEV" "$logdev" \
+			compress
 		;;
 	"ext2"|"ext3"|"ext4")
 		_scratch_ext4_populate $@