Tests: use a portable way to flush kernel cache

On Linux, kernel cache can be flushed using
echo 3 > /proc/sys/vm/drop_caches

This non-portable approach can be replaced by an on-purpose
failed attempt to unmount: if the mount point is the current
directory and umount is called, the kernel will flush inodes
until it realize it cannot complete the operation because
root of filesystem is busy:
( cd $M0 ; umount $M0 )

Unfortunately this does not flush everything. Entries may
still be present in the kenrel FUSE cache. Using $GFS to
mount the filesystem ensure --entry-timeout=0 and clears
this problem.

Some stall information may also remain in glusterfs caches,
and that may have to be adressed by appropriate volume option.
For instance tests/bugs/rpc/bug-954057.t needs to disable
performance.stat-prefetch. Qtherwise, root's new credentials
are not evaluated after root-quash is enabled. The test could
also be done with performance.stat-prefetch enabled using
various tricks: copying the file to read, creating a hard link
on it, or just waiting long enough for metadata cache to expire.

Backport of: I54929e899d55c04dcd9d947809133549f01fd0e1
BUG: 1212676
Signed-off-by: Emmanuel Dreyfus <manu@netbsd.org>

Change-Id: I2849a27acaa0334ef30aae3b852019b5a6eeb419
Reviewed-on: http://review.gluster.org/10648
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Tested-by: NetBSD Build System

1 files changed, 2 insertions, 10 deletions

diff --git a/tests/bugs/glusterfs/bug-867253.t b/tests/bugs/glusterfs/bug-867253.t
index 3df49a1bd61..aee27c87158 100644
--- a/tests/bugs/glusterfs/bug-867253.t
+++ b/tests/bugs/glusterfs/bug-867253.t
@@ -4,14 +4,6 @@
 . $(dirname $0)/../../volume.rc
 . $(dirname $0)/../../nfs.rc
 
-# Skip the entire test if /proc/sys/vm/drop_caches does not exist
-if [ ! -f /proc/sys/vm/drop_caches ] ; then
-    echo "Skip test using /proc/sys/vm/drop_caches, "\
-         "which does not exists on this system" >&2
-    SKIP_TESTS
-    exit 0
-fi
-
 cleanup;
 
 function file_count()
@@ -45,7 +37,7 @@ touch $M0/files{1..1000};
 # Kill a brick process
 kill -9 `cat $GLUSTERD_WORKDIR/vols/$V0/run/$H0-d-backends-${V0}0.pid`;
 
-echo 3 >/proc/sys/vm/drop_caches;
+( cd $M0 ; umount $M0 ) # fail but drops kernel cache
 
 ls -l $M0 >/dev/null;
 
@@ -56,7 +48,7 @@ TEST $CLI volume start $V0 force
 # Kill a brick process
 kill -9 `cat $GLUSTERD_WORKDIR/vols/$V0/run/$H0-d-backends-${V0}1.pid`;
 
-echo 3 >/proc/sys/vm/drop_caches;
+( cd $M0 ; umount $M0 )
 
 ls -l $M0 >/dev/null;