generic: add write vs fcollapse test

This test exposed a problem with XFS where it failed to write back a
partial page correctly during a fcollapse operation. This left a
stray dirty buffer on the page, and hence invalidation of the page
then failed of the fcollapse returned an EBUSY error.

Make this a generic test so that we can ensure that all filesystems
handle the case correctly. Test case originally worked out and
written by Brian Foster.

Signed-off-by: Dave Chinner <>

3 files changed