rbd: new request tracking code

This patch fully implements the new request tracking code for rbd
I/O requests.

Each I/O request to an rbd image will get an rbd_image_request
structure allocated to track it.  This provides access to all
information about the original request, as well as access to the
set of one or more object requests that are initiated as a result
of the image request.

An rbd_obj_request structure defines a request sent to a single osd
object (possibly) as part of an rbd image request.  An rbd object
request refers to a ceph_osd_request structure built up to represent
the request; for now it will contain a single osd operation.  It
also provides space to hold the result status and the version of the
object when the osd request completes.

An rbd_obj_request structure can also stand on its own.  This will
be used for reading the version 1 header object, for issuing
acknowledgements to event notifications, and for making object
method calls.

All rbd object requests now complete asynchronously with respect
to the osd client--they supply a common callback routine.

This resolves:
    http://tracker.newdream.net/issues/3741

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: kill rbd_rq_fn() and all other related code

Now that the request function has been replaced by one using the new
request management data structures the old one can go away.
Deleting it makes rbd_dev_do_request() no longer needed, and
deleting that makes other functions unneeded, and so on.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: kill rbd_req_coll and rbd_request

The two remaining callers of rbd_do_request() always pass a null
collection pointer, so the "coll" and "coll_index" parameters are
not needed.  There is no other use of that data structure, so it
can be eliminated.

Deleting them means there is no need to allocate a rbd_request
structure for the callback function.  And since that's the only use
of *that* structure, it too can be eliminated.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: implement sync object read with new code

Reimplement the synchronous read operation used for reading a
version 1 header using the new request tracking code.  Name the
resulting function rbd_obj_read_sync() to better reflect that
it's a full object operation, not an object request.  To do this,
implement a new OBJ_REQUEST_PAGES object request type.

This implements a new mechanism to allow the caller to wait for
completion for an rbd_obj_request by calling rbd_obj_request_wait().

This partially resolves:
    http://tracker.newdream.net/issues/3755

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: get rid of rbd_req_sync_read()

Delete rbd_req_sync_read() is no longer used, so get rid of it.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: implement watch/unwatch with new code

Implement a new function to set up or tear down a watch event
for an mapped rbd image header using the new request code.

Create a new object request type "nodata" to handle this.  And
define rbd_osd_trivial_callback() which simply marks a request done.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: get rid of rbd_req_sync_watch()

Get rid of rbd_req_sync_watch(), because it is no longer used.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: use new code for notify ack

Use the new object request tracking mechanism for handling a
notify_ack request.

Move the callback function below the definition of this so we don't
have to do a pre-declaration.

This resolves:
    http://tracker.newdream.net/issues/3754

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: get rid of rbd_req_sync_notify_ack()

Get rid rbd_req_sync_notify_ack() because it is no longer used.
As a result rbd_simple_req_cb() becomes unreferenced, so get rid
of that too.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: send notify ack asynchronously

When we receive notification of a change to an rbd image's header
object we need to refresh our information about the image (its
size and snapshot context).  Once we have refreshed our rbd image
we need to acknowledge the notification.

This acknowledgement was previously done synchronously, but there's
really no need to wait for it to complete.

Change it so the caller doesn't wait for the notify acknowledgement
request to complete.  And change the name to reflect it's no longer
synchronous.

This resolves:
    http://tracker.newdream.net/issues/3877

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: implement sync method with new code

Reimplement synchronous object method calls using the new request
tracking code.  Use the name rbd_obj_method_sync()

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: get rid of rbd_req_sync_exec()

Get rid rbd_req_sync_exec() because it is no longer used.  That
eliminates the last use of rbd_req_sync_op(), so get rid of that
too.  And finally, that leaves rbd_do_request() unreferenced, so get
rid of that.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: unregister linger in watch sync routine

Move the code that unregisters an rbd device's lingering header
object watch request into rbd_dev_header_watch_sync(), so it
occurs in the same function that originally sets up that request.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: track object rather than osd request for watch

Switch to keeping track of the object request pointer rather than
the osd request used to watch the rbd image header object.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: decrement obj request count when deleting

Decrement the obj_request_count value when deleting an object
request from its image request's list.  Rearrange a few lines
in the surrounding code.

This resolves:
    http://tracker.ceph.com/issues/3940

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: don't drop watch requests on completion

When we register an osd request to linger, it means that request
will stay around (under control of the osd client) until we've
unregistered it.  We do that for an rbd image's header object, and
we keep a pointer to the object request associated with it.

Keep a reference to the watch object request for as long as it is
registered to linger.  Drop it again after we've removed the linger
registration.

This resolves:
    http://tracker.ceph.com/issues/3937

(Note: this originally came about because the osd client was
issuing a callback more than once.  But that behavior will be
changing soon, documented in tracker issue 3967.)

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: define flags field, use it for exists flag

Define a new rbd device flags field, manipulated using bit
operations.  Replace the use of the current "exists" flag with a bit
in this new "flags" field.  Add a little commentary about the
"exists" flag, which does not need to be manipulated atomically.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: prevent open for image being removed

An open request for a mapped rbd image can arrive while removal of
that mapping is underway.  We need to prevent such an open request
from succeeding.  (It appears that Maciej Galkiewicz ran into this
problem.)

Define and use a "removing" flag to indicate a mapping is getting
removed.  Set it in the remove path after verifying nothing holds
the device open.  And check it in the open path before allowing the
open to proceed.  Acquire the rbd device's lock around each of these
spots to avoid any races accessing the flags and open_count fields.

This addresses:
    http://tracker.newdream.net/issues/3427

Reported-by: Maciej Galkiewicz <maciejgalkiewicz@ragnarson.com>
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
libceph: add a compatibility check interface

An upcoming change implements semantic change that could lead to
a crash if an old version of the libceph kernel module is used with
a new version of the rbd kernel module.

In order to preclude that possibility, this adds a compatibilty
check interface.  If this interface doesn't exist, the modules are
obviously not compatible.  But if it does exist, this provides a way
of letting the caller know whether it will operate properly with
this libceph module.

Perhaps confusingly, it returns false right now.  The semantic
change mentioned above will make it return true.

This resolves:
    http://tracker.ceph.com/issues/3800

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
rbd: don't take extra bio reference for osd client

Currently, if the OSD client finds an osd request has had a bio list
attached to it, it drops a reference to it (or rather, to the first
entry on that list) when the request is released.

The code that added that reference (i.e., the rbd client) is
therefore required to take an extra reference to that first bio
structure.

The osd client doesn't really do anything with the bio pointer other
than transfer it from the osd request structure to outgoing (for
writes) and ingoing (for reads) messages.  So it really isn't the
right place to be taking or dropping references.

Furthermore, the rbd client already holds references to all bio
structures it passes to the osd client, and holds them until the
request is completed.  So there's no need for this extra reference
whatsoever.

So remove the bio_put() call in ceph_osdc_release_request(), as
well as its matching bio_get() call in rbd_osd_req_create().

This change could lead to a crash if old libceph.ko was used with
new rbd.ko.  Add a compatibility check at rbd initialization time to
avoid this possibilty.

This resolves:
    http://tracker.ceph.com/issues/3798    and
    http://tracker.ceph.com/issues/3799

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>