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

0 files changed, 0 insertions, 0 deletions