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.

BUG: 1129939
Change-Id: I54929e899d55c04dcd9d947809133549f01fd0e1
Signed-off-by: Emmanuel Dreyfus <manu@netbsd.org>
Reviewed-on: http://review.gluster.org/10411
Reviewed-by: Dan Lambright <dlambrig@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>

1 files changed, 16 insertions, 5 deletions

diff --git a/tests/bugs/rpc/bug-954057.t b/tests/bugs/rpc/bug-954057.t
index 9c48207b711..faaf261d88b 100755
--- a/tests/bugs/rpc/bug-954057.t
+++ b/tests/bugs/rpc/bug-954057.t
@@ -3,15 +3,25 @@
 . $(dirname $0)/../../include.rc
 . $(dirname $0)/../../volume.rc
 
-#This script checks if use-readdirp option works as accepted in mount options
-
+# This script checks if use-readdirp option works as accepted in mount options
+
+# Note on re-reading $M0/new after enabling root-squash:
+# Since we have readen it once, the file is present in various caches.
+# In order to actually fail on second attempt we must:
+# 1) drop kernel cache, by ( cd $M0 ; umount $M0 )
+# 2) make sure FUSE does not cache the entry. This is also
+#    in the kernel, but not flushed by a failed umount.
+#    Using $GFS enforces this because it sets --entry-timeout=0
+# 3) make sure reading new permissins does not produce stale
+#    information from glusterfs metadata cache. Setting volume
+#    option performance.stat-prefetch off enforces that.
 
 TEST glusterd
 TEST pidof glusterd
 TEST $CLI volume create $V0 $H0:$B0/${V0}
 TEST $CLI volume start $V0
 
-TEST glusterfs --volfile-id=/$V0 --volfile-server=$H0 $M0
+TEST $GFS --volfile-id=/$V0 --volfile-server=$H0 $M0
 
 TEST mkdir $M0/dir
 TEST mkdir $M0/nobody
@@ -21,8 +31,9 @@ TEST cp $M0/file $M0/new
 TEST chmod 700 $M0/new
 TEST cat $M0/new
 
+TEST $CLI volume set $V0 performance.stat-prefetch off
 TEST $CLI volume set $V0 server.root-squash enable
-TEST `echo 3 > /proc/sys/vm/drop_caches`
+( cd $M0 ; umount $M0 ) # fails but drops kernel cache
 TEST ! mkdir $M0/other
 TEST mkdir $M0/nobody/other
 TEST cat $M0/file
@@ -30,7 +41,7 @@ TEST ! cat $M0/new
 TEST `echo "nobody" >> $M0/nobody/file`
 
 #mount the client without root-squashing
-TEST glusterfs --volfile-id=/$V0 --volfile-server=$H0 --no-root-squash=yes $M1
+TEST $GFS --volfile-id=/$V0 --volfile-server=$H0 --no-root-squash=yes $M1
 TEST mkdir $M1/m1_dir
 TEST `echo "file" >> $M1/m1_file`
 TEST cp $M0/file $M1/new