Ceph » CephFS

this illustrates the problem:

mkdir mnt/foo
echo asdf > mnt/foo/a
mkdir mnt/foo/.snap/s
ln mnt/foo/a mnt/foo/b
cat mnt/foo/.snap/s/a
echo "this will hang..." 
echo qwer >> mnt/foo/b   
echo "oh, it didn't hang! good job." 
rmdir mnt/foo/.snap/s

the 'ln' clones the cap (badness). the cat of the snapped version revokes the cloned cap, which makes the client state diverge from the mds state for the live cap. the append then hangs because the client doesn't have the w caps but the mds thinks it does.

ok, the cap tracking is done.

remaining issues:
- how to make an OPEN or STAT on the snapped inode trigger the head lock to sync.
- delayed cap writeback of dir attributes (needs to go into old_inodes)
- rdlock on snapped dir shouldn't succeed when in filelock is in EXCL state

incompat bit?

need a way to remove bad (in)compat bits from mdsmap compatset (via teh montior)