fixup: add a public osdmap_full_flag and use it

... instead of having lots of places where we lock
objecter, look at osdmap, unlock object.

Squash into: various

Signed-off-by: John Spray <john.spray@redhat.com>
fixup: remove stale comment in MClientCaps

... the canonical record of which version adds
which fields is the ::encode/::decode source,
and we don't have comments like this elsewhere.

Squash into: messages: add osd_epoch_barrier to cap msgs
fixup: remove overly verbose MDS comment in favor of docs

Squash into: "mds: implement osd epoch barrier on caps"

Signed-off-by: John Spray <john.spray@redhat.com>
doc: add cephfs ENOSPC and eviction information

Adding this at this time to give us a sensible place
to talk about the epoch barrier stuff.  The eviction
stuff will probably get simplified once we add a mon-side
eviction command that handles blacklisting and MDS session
eviction in one go.

Signed-off-by: John Spray <john.spray@redhat.com>
osdc: implement Objecter::set_epoch_barrier

For use in MDS and Client when they want to wait
for a particular OSDMap epoch before using caps
that depend on a prior blacklist or op cancellation.

Signed-off-by: John Spray <john.spray@redhat.com>
osdc: remove spurious _maybe_request_map return value

This was always zero: make the function return void, and
remove all the places we asserted on its return value.

Signed-off-by: John Spray <john.spray@redhat.com>
fixup: mds: use objecter epoch barrier instead of holding up cap messages

... so that we don't break the ordering on mds session messages.

Squash into: "mds: implement osd epoch barrier on caps"
fixup: client: use objecter epoch barrier

squash into: "client: track osd epoch barrier"

Signed-off-by: John Spray <john.spray@redhat.com>
client: propagate flush errors to fclose/fsync

Ensure that all calls to _flush get an explicit
context (rather than implicit PutInode used
before), which tags any error onto the Inode object.

Later, read the error from the Inode object in _release_fh
and ensure all callers of _release_fh properly handle
its return code.

Signed-off-by: John Spray <john.spray@redhat.com>