check-block.sh: passthrough -jN flag of make to -j N flag of check

This improves performance of running iotests during "make -jN check".

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20211223183933.1497037-1-vsementsov@virtuozzo.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tests/check-block.sh

@@ -74,10 +74,17 @@ cd tests/qemu-iotests
 # QEMU_CHECK_BLOCK_AUTO is used to disable some unstable sub-tests
 export QEMU_CHECK_BLOCK_AUTO=1
 export PYTHONUTF8=1
+# If make was called with -jN we want to call ./check with -j N. Extract the
+# flag from MAKEFLAGS, so that if it absent (or MAKEFLAGS is not defined), JOBS
+# would be an empty line otherwise JOBS is prepared string of flag with value:
+# "-j N"
+# Note, that the following works even if make was called with "-j N" or even
+# "--jobs N", as all these variants becomes simply "-jN" in MAKEFLAGS variable.
+JOBS=$(echo "$MAKEFLAGS" | sed -n 's/\(^\|.* \)-j\([0-9]\+\)\( .*\|$\)/-j \2/p')
 
 ret=0
 for fmt in $format_list ; do
-    ${PYTHON} ./check -makecheck -$fmt $group || ret=1
+    ${PYTHON} ./check $JOBS -makecheck -$fmt $group || ret=1
 done
 
 exit $ret