generic: LVM and ram disks don't play well

The "brd" kernel ram disk abuses BLKFLSBUF to mean "free all memory
in the ram drive" when in fact it should mean "flush all dirty
buffers to stable storage". The brd driver ignores BLKFLSBUF if
there is an active reference to the block device, (e.g. a fs is
mounted on it), but when a device is layered over the top of it
(e.g. dm-flakey, lvm devices, etc) then the applications and
filesystems hold references to the upper device, not the brd device.
Hence when the upper device passes down BLKFLSBUF to brd, it removes
all the pages in the brd, effectively erasing it.  This causes all
sorts of problems.....

Fix this by black listing "/dev/ramXXX" devices from tests that
require DM in some way. The _requires_sane_bdev_flush() macro is
called by the _requires_dm.... checks so that we don't have to
remember to add this to all new tests that use dm in some way.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/common/rc b/common/rc
index c5db0ddf569460bd89045706ef55ed8b18c55e16..ca8da7f34fbcdb3d17502ca3d72041a06f25eca6 100644 (file)
--- a/common/rc
+++ b/common/rc
@@ -1305,26 +1305,38 @@ _require_block_device()
        fi
 }
 
+# brd based ram disks erase the device when they receive a flush command when no
+# active references are present. This causes problems for DM devices sitting on
+# top of brd devices as DM doesn't hold active references to the brd device.
+_require_sane_bdev_flush()
+{
+       echo $1 | grep -q "^/dev/ram[0-9]\+$"
+       if [ $? -eq 0 ]; then
+               _notrun "This test requires a sane block device flush"
+       fi
+}
+
 # this test requires the device mapper flakey target
 #
 _require_dm_flakey()
 {
-    # require SCRATCH_DEV to be a valid block device
-    _require_block_device $SCRATCH_DEV
-    _require_command "$DMSETUP_PROG" dmsetup
+       # require SCRATCH_DEV to be a valid block device with sane BLKFLSBUF
+       # behaviour
+       _require_block_device $SCRATCH_DEV
+       _require_sane_bdev_flush $SCRATCH_DEV
+       _require_command "$DMSETUP_PROG" dmsetup
 
-    modprobe dm-flakey >/dev/null 2>&1
-    $DMSETUP_PROG targets | grep flakey >/dev/null 2>&1
-    if [ $? -eq 0 ]
-    then
-       :
-    else
-       _notrun "This test requires dm flakey support"
-    fi
+       modprobe dm-flakey >/dev/null 2>&1
+       $DMSETUP_PROG targets | grep flakey >/dev/null 2>&1
+       if [ $? -ne 0 ]; then
+               _notrun "This test requires dm flakey support"
+       fi
 }
 
 _require_dm_snapshot()
 {
+       _require_block_device $SCRATCH_DEV
+       _require_sane_bdev_flush $SCRATCH_DEV
        _require_command "$DMSETUP_PROG" dmsetup
        modprobe dm-snapshot >/dev/null 2>&1
        $DMSETUP_PROG targets | grep -q snapshot

diff --git a/tests/generic/081 b/tests/generic/081
index e242c4cad22c6709261074b7a884df1863377c6f..5d38c11a0aff6592222d701dc1a795d0e7e54fd0 100755 (executable)
--- a/tests/generic/081
+++ b/tests/generic/081
@@ -50,7 +50,6 @@ _supported_os Linux
 _require_test
 _require_scratch_nocheck
 _require_dm_snapshot
-_require_block_device $SCRATCH_DEV
 _require_command $LVM_PROG lvm
 
 echo "Silence is golden"