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2012-12-20rbd: get rid of rbd_{get,put}_dev()Alex Elder
The functions rbd_get_dev() and rbd_put_dev() are trivial wrappers that add no value, and their existence suggests they may do more than what they do. Get rid of them. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Dan Mick <dan.mick@inktank.com>
2012-12-17rbd: don't use ENOTSUPPAlex Elder
ENOTSUPP is not a standard errno (it shows up as "Unknown error 524" in an error message). This is what was getting produced when the the local rbd code does not implement features required by a discovered rbd image. Change the error code returned in this case to ENXIO. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Sage Weil <sage@inktank.com>
2012-12-17rbd: get rid of RBD_MAX_SEG_NAME_LENAlex Elder
RBD_MAX_SEG_NAME_LEN represents the maximum length of an rbd object name (i.e., one of the objects providing storage backing an rbd image). Another symbol, MAX_OBJ_NAME_SIZE, is used in the osd client code to define the maximum length of any object name in an osd request. Right now they disagree, with RBD_MAX_SEG_NAME_LEN being too big. There's no real benefit at this point to defining the rbd object name length limit separate from any other object name, so just get rid of RBD_MAX_SEG_NAME_LEN and use MAX_OBJ_NAME_SIZE in its place. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Sage Weil <sage@inktank.com>
2012-12-17rbd: do not allow remove of mounted-on imageAlex Elder
There is no check in rbd_remove() to see if anybody holds open the image being removed. That's not cool. Add a simple open count that goes up and down with opens and closes (releases) of the device, and don't allow an rbd image to be removed if the count is non-zero. Protect the updates of the open count value with ctl_mutex to ensure the underlying rbd device doesn't get removed while concurrently being opened. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Sage Weil <sage@inktank.com>
2012-11-01rbd: get additional info in parent specAlex Elder
When a layered rbd image has a parent, that parent is identified only by its pool id, image id, and snapshot id. Images that have been mapped also record *names* for those three id's. Add code to look up these names for parent images so they match mapped images more closely. Skip doing this for an image if it already has its pool name defined (this will be the case for images mapped by the user). It is possible that an the name of a parent image can't be determined, even if the image id is valid. If this occurs it does not preclude correct operation, so don't treat this as an error. On the other hand, defined pools will always have both an id and a name. And any snapshot of an image identified as a parent for a clone image will exist, and will have a name (if not it indicates some other internal error). So treat failure to get these bits of information as errors. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-11-01rbd: get parent spec for version 2 imagesAlex Elder
Add support for getting the the information identifying the parent image for rbd images that have them. The child image holds a reference to its parent image specification structure. Create a new entry "parent" in /sys/bus/rbd/image/N/ to report the identifying information for the parent image, if any. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-11-01rbd: allow null image nameAlex Elder
Format 2 parent images are partially identified by their image id, but it may not be possible to determine their image name. The name is not strictly needed for correct operation, so we won't be treating it as an error if we don't know it. Handle this case gracefully in rbd_name_show(). Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-11-01rbd: allow null image nameAlex Elder
We will know the image id for format 2 parent images, but won't initially know its image name. Avoid making the query for an image id in rbd_dev_image_id() if it's already known. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-11-01rbd: encapsulate last part of probeAlex Elder
Group the activities that now take place after an rbd_dev_probe() call into a single function, and move the call to that function into rbd_dev_probe() itself. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-11-01rbd: define rbd_dev_{create,destroy}() helpersAlex Elder
Encapsulate the creation/initialization and destruction of rbd device structures. The rbd_client and the rbd_spec structures provided on creation hold references whose ownership is transferred to the new rbd_device structure. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-11-01rbd: consolidate rbd_dev init in rbd_add()Alex Elder
Group the allocation and initialization of fields of the rbd device structure created in rbd_add(). Move the grouped code down later in the function, just prior to the call to rbd_dev_probe(). This is for the most part simple code movement. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-11-01rbd: don't pass rbd_dev to rbd_get_client()Alex Elder
The only reason rbd_dev is passed to rbd_get_client() is so its rbd_client field can get assigned. Instead, just return the rbd_client pointer as a result and have the caller do the assignment. Change rbd_put_client() so it takes an rbd_client structure, so follows the more typical symmetry with rbd_get_client(). Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-11-01rbd: fill rbd_spec in rbd_add_parse_args()Alex Elder
Pass the address of an rbd_spec structure to rbd_add_parse_args(). Use it to hold the information defining the rbd image to be mapped in an rbd_add() call. Use the result in the caller to initialize the rbd_dev->id field. This means rbd_dev is no longer needed in rbd_add_parse_args(), so get rid of it. Now that this transformation of rbd_add_parse_args() is complete, correct and expand on the its header documentation to reflect the new reality. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-11-01rbd: add reference counting to rbd_specAlex Elder
With layered images we'll share rbd_spec structures, so add a reference count to it. It neatens up some code also. A silly get/put pair is added to the alloc routine just to avoid "defined but not used" warnings. It will go away soon. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-30rbd: define image specification structureAlex Elder
Group the fields that uniquely specify an rbd image into a new reference-counted rbd_spec structure. This structure will be used to describe the desired image when mapping an image, and when probing parent images in layered rbd devices. Replace the set of fields in the rbd device structure with a pointer to a dynamically allocated rbd_spec. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-30rbd: have rbd_add_parse_args() return errorAlex Elder
Change the interface to rbd_add_parse_args() so it returns an error code rather than a pointer. Return the ceph_options result via a pointer whose address is passed as an argument. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-30rbd: pass and populate rbd_options structureAlex Elder
Have the caller pass the address of an rbd_options structure to rbd_add_parse_args(), to be initialized with the information gleaned as a result of the parse. I know, this is another near-reversal of a recent change... Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-30rbd: remove snap_name arg from rbd_add_parse_args()Alex Elder
The snapshot name returned by rbd_add_parse_args() just gets saved in the rbd_dev eventually. So just do that inside that function and do away with the snap_name argument, both in rbd_add_parse_args() and rbd_dev_set_mapping(). Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-30rbd: remove options args from rbd_add_parse_args()Alex Elder
They "options" argument to rbd_add_parse_args() (and it's partner options_size) is now only needed within the function, so there's no need to have the caller allocate and pass the options buffer. Just allocate the options buffer within the function using dup_token(). Also distinguish between failures due to failed memory allocation and failing because a required argument was missing. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-30rbd: get rid of snap_name_lenAlex Elder
The value returned in the "snap_name_len" argument to rbd_add_parse_args() is never actually used, so get rid of it. The snap_name_len recorded in rbd_dev_v2_snap_name() is not useful either, so get rid of that too. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-30rbd: do all argument parsing in one placeAlex Elder
This patch makes rbd_add_parse_args() be the single place all argument parsing occurs for an image map request: - Move the ceph_parse_options() call into that function - Use local variables rather than parameters to hold the list of monitor addresses supplied - Rather than returning it, pass the snapshot name (and its length) back via parameters - Have the function return a ceph_options structure pointer Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-30rbd: move ceph_parse_options() call upAlex Elder
Move option parsing out of rbd_get_client() and into its caller. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-30rbd: rename snap_exists fieldAlex Elder
A Boolean field "snap_exists" in an rbd mapping is used to indicate whether a mapped snapshot has been removed from an image's snapshot context, to stop sending requests for that snapshot as soon as we know it's gone. Generalize the interpretation of this field so it applies to non-snapshot (i.e. "head") mappings. That is, define its value to be false until the mapping has been set, and then define it to be true for both snapshot mappings or head mappings. Rename the field "exists" to reflect the broader interpretation. The rbd_mapping structure is on its way out, so move the field back into the rbd_device structure. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-30rbd: move snap info out of rbd_mapping structAlex Elder
Moving the snap_id and snap_name fields into the separate rbd_mapping structure was misguided. (And in time, perhaps we'll do away with that structure altogether...) Move these fields back into struct rbd_device. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-30rbd: make pool_id a 64 bit valueAlex Elder
If a format 2 image has a parent, its pool id will be specified using a 64-bit value. Change the pool id we save for an image to match that. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-30rbd: remove snapshots on error in rbd_add()Alex Elder
If rbd_dev_snaps_update() has ever been called for an rbd device structure there could be snapshot structures on its snaps list. In rbd_add(), this function is called but a subsequent error path neglected to clean up any of these snapshots. Add a call to rbd_remove_all_snaps() in the appropriate spot to remedy this. Change a couple of error labels to be a little clearer while there. Drop the leading underscores from the function name; there's nothing special about that function that they might signify. As suggested in review, the leading underscores in __rbd_remove_snap_dev() have been removed as well. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-30rbd: simplify rbd_rq_fn()Alex Elder
When processing a request, rbd_rq_fn() makes clones of the bio's in the request's bio chain and submits the results to osd's to be satisfied. If a request bio straddles the boundary between objects backing the rbd image, it must be represented by two cloned bio's, one for the first part (at the end of one object) and one for the second (at the beginning of the next object). This has been handled by a function bio_chain_clone(), which includes an interface only a mother could love, and which has been found to have other problems. This patch defines two new fairly generic bio functions (one which replaces bio_chain_clone()) to help out the situation, and then revises rbd_rq_fn() to make use of them. First, bio_clone_range() clones a portion of a single bio, starting at a given offset within the bio and including only as many bytes as requested. As a convenience, a request to clone the entire bio is passed directly to bio_clone(). Second, bio_chain_clone_range() performs a similar function, producing a chain of cloned bio's covering a sub-range of the source chain. No bio_pair structures are used, and if successful the result will represent exactly the specified range. Using bio_chain_clone_range() makes bio_rq_fn() a little easier to understand, because it avoids the need to pass very much state information between consecutive calls. By avoiding the need to track a bio_pair structure, it also eliminates the problem described here: http://tracker.newdream.net/issues/2933 Note that a block request (and therefore the complete length of a bio chain processed in rbd_rq_fn()) is an unsigned int, while the result of rbd_segment_length() is u64. This change makes this range trunctation explicit, and trips a bug if the the segment boundary is too far off. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-26rbd: kill rbd_device->rbd_optsAlex Elder
The rbd_device structure has an embedded rbd_options structure. Such a structure is needed to work with the generic ceph argument parsing code, but there's no need to keep it around once argument parsing is done. Use a local variable to hold the rbd options used in parsing in rbd_get_client(), and just transfer its content (it's just a read_only flag) into the field in the rbd_mapping sub-structure that requires that information. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com> Reviewed-by: Dan Mick <dan.mick@inktank.com>
2012-10-26rbd: simplify rbd_merge_bvec()Alex Elder
The aim of this patch is to make what's going on rbd_merge_bvec() a bit more obvious than it was before. This was an issue when a recent btrfs bug led us to question whether the merge function was working correctly. Use "obj" rather than "chunk" to indicate the units whose boundaries we care about we call (rados) "objects". Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Dan Mick <dan.mick@inktank.com>
2012-10-26rbd: increase maximum snapshot name lengthAlex Elder
Change RBD_MAX_SNAP_NAME_LEN to be based on NAME_MAX. That is a practical limit for the length of a snapshot name (based on the presence of a directory using the name under /sys/bus/rbd to represent the snapshot). The /sys entry is created by prefixing it with "snap_"; define that prefix symbolically, and take its length into account in defining the snapshot name length limit. Enforce the limit in rbd_add_parse_args(). Also delete a dout() call in that function that was not meant to be committed. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Dan Mick <dan.mick@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-26rbd: verify rbd image order valueAlex Elder
This adds a verification that an rbd image's object order is within the upper and lower bounds supported by this implementation. It must be at least 9 (SECTOR_SHIFT), because the Linux bio system assumes that minimum granularity. It also must be less than 32 (at the moment anyway) because there exist spots in the code that store the size of a "segment" (object backing an rbd image) in a signed int variable, which can be 32 bits including the sign. We should be able to relax this limit once we've verified the code uses 64-bit types where needed. Note that the CLI tool already limits the order to the range 12-25. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-26rbd: consolidate rbd_do_op() callsAlex Elder
The two calls to rbd_do_op() from rbd_rq_fn() differ only in the value passed for the snapshot id and the snapshot context. For reads the snapshot always comes from the mapping, and for writes the snapshot id is always CEPH_NOSNAP. The snapshot context is always null for reads. For writes, the snapshot context always comes from the rbd header, but it is acquired under protection of header semaphore and could change thereafter, so we can't simply use what's available inside rbd_do_op(). Eliminate the snapid parameter from rbd_do_op(), and set it based on the I/O direction inside that function instead. Always pass the snapshot context acquired in the caller, but reset it to a null pointer inside rbd_do_op() if the operation is a read. As a result, there is no difference in the read and write calls to rbd_do_op() made in rbd_rq_fn(), so just call it unconditionally. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-26rbd: drop rbd_do_op() opcode and flagsAlex Elder
The only callers of rbd_do_op() are in rbd_rq_fn(), where call one is used for writes and the other used for reads. The request passed to rbd_do_op() already encodes the I/O direction, and that information can be used inside the function to set the opcode and flags value (rather than passing them in as arguments). So get rid of the opcode and flags arguments to rbd_do_op(). Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-26rbd: kill rbd_req_{read,write}()Alex Elder
Both rbd_req_read() and rbd_req_write() are simple wrapper routines for rbd_do_op(), and each is only called once. Replace each wrapper call with a direct call to rbd_do_op(), and get rid of the wrapper functions. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-26rbd: fix read-only option nameAlex Elder
The name of the "read-only" mapping option was inadvertently changed in this commit: f84344f3 rbd: separate mapping info in rbd_dev Revert that hunk to return it to what it should be. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Dan Mick <dan.mick@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-26rbd: zero return code in rbd_dev_image_id()Alex Elder
When rbd_dev_probe() calls rbd_dev_image_id() it expects to get a 0 return code if successful, but it is getting a positive value. The reason is that rbd_dev_image_id() returns the value it gets from rbd_req_sync_exec(), which returns the number of bytes read in as a result of the request. (This ultimately comes from ceph_copy_from_page_vector() in rbd_req_sync_op()). Force the return value to 0 when successful in rbd_dev_image_id(). Do the same in rbd_dev_v2_object_prefix(). Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com> Reviewed-by: Dan Mick <dan.mick@inktank.com>
2012-10-26rbd: fix bug in rbd_dev_id_put()Alex Elder
In rbd_dev_id_put(), there's a loop that's intended to determine the maximum device id in use. But it isn't doing that at all, the effect of how it's written is to simply use the just-put id number, which ignores whole purpose of this function. Fix the bug. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-10rbd: activate v2 image supportAlex Elder
Now that v2 images support is fully implemented, have rbd_dev_v2_probe() return 0 to indicate a successful probe. (Note that an image that implements layering will fail the probe early because of the feature chekc.) Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-10rbd: implement feature checksAlex Elder
Version 2 images have two sets of feature bit fields. The first indicates features possibly used by the image. The second indicates features that the client *must* support in order to use the image. When an image (or snapshot) is first examined, we need to make sure that the local implementation supports the image's required features. If not, fail the probe for the image. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-10rbd: define rbd_dev_v2_refresh()Alex Elder
Define a new function rbd_dev_v2_refresh() to update/refresh the snapshot context for a format version 2 rbd image. This function will update anything that is not fixed for the life of an rbd image--at the moment this is mainly the snapshot context and (for a base mapping) the size. Update rbd_refresh_header() so it selects which function to use based on the image format. Rename __rbd_refresh_header() to be rbd_dev_v1_refresh() to be consistent with the naming of its version 2 counterpart. Similarly rename rbd_refresh_header() to be rbd_dev_refresh(). Unrelated--we use rbd_image_format_valid() here. Delete the other use of it, which was primarily put in place to ensure that function was referenced at the time it was defined. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-10rbd: define rbd_update_mapping_size()Alex Elder
Encapsulate the code that handles updating the size of a mapping after an rbd image has been refreshed. This is done in anticipation of the next patch, which will make this common code for format 1 and 2 images. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-01rbd: BUG on invalid layoutSage Weil
This shouldn't actually be possible because the layout struct is constructed from the RBD header and validated then. [elder@inktank.com: converted BUG() call to equivalent rbd_assert()] Signed-off-by: Sage Weil <sage@inktank.com> Reviewed-by: Alex Elder <elder@inktank.com>
2012-10-01rbd: update remaining header fields for v2Alex Elder
There are three fields that are not yet updated for format 2 rbd image headers: the version of the header object; the encryption type; and the compression type. There is no interface defined for fetching the latter two, so just initialize them explicitly to 0 for now. Change rbd_dev_v2_snap_context() so the caller can be supplied the version for the header object. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-01rbd: get snapshot name for a v2 imageAlex Elder
Define rbd_dev_v2_snap_name() to fetch the name for a particular snapshot in a format 2 rbd image. Define rbd_dev_v2_snap_info() to to be a wrapper for getting the name, size, and features for a particular snapshot, using an interface that matches the equivalent function for version 1 images. Define rbd_dev_snap_info() wrapper function and use it to call the appropriate function for getting the snapshot name, size, and features, dependent on the rbd image format. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-01rbd: get the snapshot context for a v2 imageAlex Elder
Fetch the snapshot context for an rbd format 2 image by calling the "get_snapcontext" method on its header object. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-01rbd: get image features for a v2 imageAlex Elder
The features values for an rbd format 2 image are fetched from the server using a "get_features" method. The same method is used for getting the features for a snapshot, so structure this addition with a generic helper routine that can get this information for either. The server will provide two 64-bit feature masks, one representing the features potentially in use for this image (or its snapshot), and one representing features that must be supported by the client in order to work with the image. For the time being, neither of these is really used so we keep things simple and just record the first feature vector. Once we start using these feature masks, what we record and what we expose to the user will most likely change. Signed-off-by: Alex Elder <elder@inktank.com>
2012-10-01rbd: get the object prefix for a v2 rbd imageAlex Elder
The object prefix of an rbd format 2 image is fetched from the server using a "get_object_prefix" method. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-01rbd: add code to get the size of a v2 rbd imageAlex Elder
The size of an rbd format 2 image is fetched from the server using a "get_size" method. The same method is used for getting the size of a snapshot, so structure this addition with a generic helper routine that we can get this information for either. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-01rbd: lay out header probe infrastructureAlex Elder
This defines a new function rbd_dev_probe() as a top-level function for populating detailed information about an rbd device. 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_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, and calls a similar function rbd_dev_v1() to populate its header information. A new field, rbd_dev->format, is defined to record which version of the rbd image format the device represents. For a valid mapped rbd device it will have one of two values, 1 or 2. So far, the format 2 images are not really supported; this is laying out the infrastructure for fleshing out that support. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
2012-10-01rbd: encapsulate code that gets snapshot infoAlex Elder
Create a function that encapsulates looking up the name, size and features related to a given snapshot, which is indicated by its index in an rbd device's snapshot context array of snapshot ids. This interface will be used to hide differences between the format 1 and format 2 images. At the moment this (looking up the name anyway) is slightly less efficient than what's done currently, but we may be able to optimize this a bit later on by cacheing the last lookup if it proves to be a problem. Signed-off-by: Alex Elder <elder@inktank.com> Reviewed-by: Josh Durgin <josh.durgin@inktank.com>