rbd: clean up a few dout() calls

There was a dout() call in rbd_do_request() that was reporting
the reporting the offset as the length and vice versa.  While
fixing that I did a quick scan of other dout() calls and fixed
a couple of other minor things.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: drop rbd_req_sync_exec() "ver" parameter

The only place that passes a version pointer to rbd_req_sync_exec()
is in rbd_header_add_snap(), and that spot ignores the result.

The only thing rbd_req_sync_exec() does with its "ver" parameter is
pass it directly to rbd_req_sync_op().  So we can just use a null
pointer there, and drop the "ver" parameter to rbd_req_sync_exec().

Signed-off-by: Alex Elder <elder@inktank.com>
ceph: define snap counts as u32 everywhere

There are two structures in which a count of snapshots are
maintained:

    struct ceph_snap_context {
	...
        u32 num_snaps;
	...
    }
and
    struct ceph_snap_realm {
	...
        u32 num_prior_parent_snaps;   /*  had prior to parent_since */
	...
        u32 num_snaps;
	...
    }

These fields never take on negative values (e.g., to hold special
meaning), and so are really inherently unsigned.  Furthermore they
take their value from over-the-wire or on-disk formatted 32-bit
values.

So change their definition to have type u32, and change some spots
elsewhere in the code to account for this change.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: have __rbd_add_snap_dev() return a pointer

It's not obvious whether the snapshot pointer whose address is
provided to __rbd_add_snap_dev() will be assigned by that function.
Change it to return the snapshot, or a pointer-coded errno in the
event of a failure.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: fixes in rbd_header_from_disk()

This fixes a few issues in rbd_header_from_disk():
    - The memcmp() call at the beginning of the function is really
      looking at the "text" field of struct rbd_image_header_ondisk.
      While it does lie at the beginning of the structure, the
      comparison should be done against the field, not the structure
      as a whole.
    - There is a check intended to catch overflow, but it's wrong in
      two ways.
	- First, the type we don't want to overflow is size_t, not
	  unsigned int, and there is now a SIZE_MAX we can use for
	  use with that type.
	- Second, we're allocating the snapshot ids and snapshot
	  image sizes separately (each has type u64; on disk they
          grouped together as a rbd_image_header_ondisk structure).
	  So we can use the size of u64 in this overflow check.
    - If there are no snapshots, then there should be no snapshot
      names.  Enforce this, and issue a warning if we encounter a
      header with no snapshots but a non-zero snap_names_len.
    - When saving the snapshot names into the header, be more direct
      in defining the offset in the on-disk structure from which
      they're being copied by using "snap_count" rather than "i"
      in the array index.
    - If an error occurs, the "snapc" and "snap_names" fields are
      freed at the end of the function.  Make those fields be null
      pointers after they're freed, to be explicit that they are
      no longer valid.
    - Finally, move the definition of the local variable "i" to the
      innermost scope in which it's needed.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: make rbd_create_rw_ops() return a pointer

Either rbd_create_rw_ops() will succeed, or it will fail because a
memory allocation failed.  Have it just return a valid pointer or
null rather than stuffing a pointer into a provided address and
returning an errno.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: always pass ops array to rbd_req_sync_op()

All of the callers of rbd_req_sync_op() except one pass a non-null
"ops" pointer.  The only one that does not is rbd_req_sync_read(),
which passes CEPH_OSD_OP_READ as its "opcode" and, CEPH_OSD_FLAG_READ
for "flags".

By allocating the ops array in rbd_req_sync_read() and moving the
special case code for the null ops pointer into it, it becomes
clear that much of that code is not even necessary.

In addition, the "opcode" argument to rbd_req_sync_op() is never
actually used, so get rid of that.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: pass flags to rbd_req_sync_exec()

In order to allow both read requests and write requests to be
initiated using rbd_req_sync_exec(), add an OSD flags value
which can be passed down to rbd_req_sync_op().  Rename the "data"
and "len" parameters to be more clear that they represent data
that is outbound.

At this point, this function is still only used (and works) for
write requests.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: set r_num_pages in rbd_do_request()

XXX I need to investigate this one a bit more XXX

For an osd request with incoming data, we need to indicate in the
request's r_num_pages field how many pages are present in the
request.  The r_page_alignment field should also be set.

    --> Is this even used?  Where?

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: support data returned from OSD methods

An OSD object method call can be made using rbd_req_sync_exec().
Until now this has only been used for creating a new RBD snapshot,
and that has only required sending data out, not receiving anything
back from the OSD.

We will now need to get data back from an OSD on a method call, so
add parameters to rbd_req_sync_exec() that allow a buffer into which
returned data should be placed to be specified, along with its size.

Previously, rbd_req_sync_exec() passed a null pointer and zero
size to rbd_req_sync_op(); change this so the new inbound buffer
information is provided instead.

Rename the "buf" and "len" parameters in rbd_req_sync_op() to
make it more obvious they are describing inbound data.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: do some header initialization earlier

Move some of the code that initializes an rbd header out of
rbd_init_disk and into its caller.  In order to do this we need
to supply the image size to rbd_init_disk().

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: initialize header even earlier

Now move the header initialization even earlier, before doing any
registration of the device with the system.

This was done in two steps in hopes it would make reviewing the
change a little easier.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: assign header name later

Move the assignment of the header name for an rbd image a bit later,
outside rbd_add_parse_args() and into its caller.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: define some new format constants

Define constant symbols related to the rbd format 2 object names.
This begins to bring this version of the "rbd_types.h" header
more in line with the current user-space version of that file.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: add an rbd features field

Record the snapshot features value for each rbd image.

This is close but not well tested.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: define rbd_dev_get_image_id()

New format 2 rbd images are permanently identified by a unique image
id.  Each rbd image also has a name, but the name can be changed.
A format 2 rbd image will have an object--whose name is based on the
image name--which maps an image's name to its image id.

Create a new function rbd_dev_get_image_id() that checks for the
existence of the image id object, and if it's found, records the
image id in the rbd_device structure.

Create a new rbd device attribute (/sys/bus/rbd/<num>/image_id) that
makes this information available.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: lay out header probe infrastructure

This defines a new function rbd_dev_header_probe() as a top-level
function for populating an rbd header.  It first checks for the
existence of a format 2 rbd image id object.  If it exists, the
image is assumed to be a format 2 rbd image, and another function
rbd_dev_header_v2() is called to finish populating header data for
that image.  If it does not exist, it is assumed to be an old
(format 1) rbd image, calls a similar function rbd_dev_header_v1()
to populate its header information.

So far, the format 2 images are not really supported; this is
laying the infrastructure for fleshing out that support.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: flesh out header version 2 support

This adds osd method calls to rbd_dev_header_v2() that fill in more
information in format 2 rbd image header:
    - rbd image size
    - object order
    - object prefix

Signed-off-by: Alex Elder <elder@inktank.com>