Clear pointer to mds request after dropping the reference to
ensure we don't drop it again, as there is at least one error
path through this function that does not reset fi->last_readdir
to a new value.
Signed-off-by: NSage Weil <sage@newdream.net>

Define supported and required feature set.  Fail connection if the server
requires features we do not support (TAG_FEATURES), or if the server does
not support features we require.
Signed-off-by: NSage Weil <sage@newdream.net>

We need to hold session s_mutex for __ceph_mdsc_drop_dentry_lease(), which
we don't, so skip it.  It was purely an optimization.
Signed-off-by: NSage Weil <sage@newdream.net>

We need to skip /.ceph in (cached) readdir results, and exclude "/.ceph"
from the cached ENOENT lookup check.
Signed-off-by: NSage Weil <sage@newdream.net>

It was hidden from sync readdir, but not the cached dcache version.
Signed-off-by: NSage Weil <sage@newdream.net>

This simplifies much of the error handling during mount.  It also means
that we have the mount args before client creation, and we can initialize
based on those options.
Signed-off-by: NSage Weil <sage@newdream.net>

Directory operations, including lookup, are defined here.  We take
advantage of lookup intents when possible.  For the most part, we just
need to build the proper requests for the metadata server(s) and
pass things off to the mds_client.

The results of most operations are normally incorporated into the
client's cache when the reply is parsed by ceph_fill_trace().
However, if the MDS replies without a trace (e.g., when retrying an
update after an MDS failure recovery), some operation-specific cleanup
may be needed.

We can validate cached dentries in two ways.  A per-dentry lease may
be issued by the MDS, or a per-directory cap may be issued that acts
as a lease on the entire directory.  In the latter case, a 'gen' value
is used to determine which dentries belong to the currently leased
directory contents.

We normally prepopulate the dcache and icache with readdir results.
This makes subsequent lookups and getattrs avoid any server
interaction.  It also lets us satisfy readdir operation by peeking at
the dcache IFF we hold the per-directory cap/lease, previously
performed a readdir, and haven't dropped any of the resulting
dentries.
Signed-off-by: NSage Weil <sage@newdream.net>