Re: [Libguestfs] [virt-v2v PATCH 2/3] lib/nbdkit: add the "Nbdkit.get_disk_allocated" helper function

Add the "Nbdkit.get_disk_allocated" helper function, which calculates the number of allocated bytes in an output disk image, through a corresponding NBD server connection. Original "NBD.block_status" summation example code by Rich Jones (thanks!), chunking, metadata context simplification, and virt-v2v integration by myself. Chunking added because "NBD.block_status" is not 64-bit clean just yet (Eric Blake is working on it). Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2027598 Signed-off-by: Laszlo Ersek <lersek(a)redhat.com&gt; --- lib/nbdkit.mli | 8 ++++++ lib/nbdkit.ml | 30 ++++++++++++++++++++ 2 files changed, 38 insertions(+) diff --git a/lib/nbdkit.mli b/lib/nbdkit.mli index 825755e61dbe..03107dab109d 100644 --- a/lib/nbdkit.mli +++ b/lib/nbdkit.mli @@ -117,3 +117,11 @@ val with_connect_unix : socket:string -> in [meta_contexts] requested (each of which is not necessarily supported by the server though). The connection is torn down either on normal return or if the function [f] throws an exception. *) + +val get_disk_allocated : dir:string -> disknr:int -> int64 option +(** Callable only in the finalization step. [get_disk_allocated dir disknr] + examines output disk [disknr] through the corresponding NBD server socket + that resides in [dir]. Returns the number of bytes allocated in the disk + image, according to the "base:allocation" metadata context. If the context + is not supported by the NBD server behind the socket, the function returns + None. *)

diff --git a/lib/nbdkit.ml b/lib/nbdkit.ml index 43e0fc5c728a..e142c210c66f 100644 --- a/lib/nbdkit.ml +++ b/lib/nbdkit.ml @@ -229,3 +229,33 @@ let with_connect_unix ~socket ~meta_contexts ~f = ~finally:(fun () -> NBD.shutdown nbd) ) ~finally:(fun () -> NBD.close nbd) + +let get_disk_allocated ~dir ~disknr = + let socket = sprintf "%s/out%d" dir disknr + and alloc_ctx = "base:allocation" in + with_connect_unix ~socket ~meta_contexts:[alloc_ctx] + ~f:(fun nbd -> + if NBD.can_meta_context nbd alloc_ctx then ( + (* Get the list of extents, using a 2GiB chunk size as hint. *) + let size = NBD.get_size nbd + and allocated = ref 0_L + and fetch_offset = ref 0_L in + while !fetch_offset < size do + let remaining = size -^ !fetch_offset in + let fetch_size = min 0x8000_0000_L remaining in + NBD.block_status nbd fetch_size !fetch_offset + (fun ctx offset entries err -> + assert (ctx = alloc_ctx); + for i = 0 to Array.length entries / 2 - 1 do + let len = Int64.of_int32 entries.(i * 2) + and typ = entries.(i * 2 + 1) in + if Int32.logand typ 1_l = 0_l then + allocated := !allocated +^ len; + fetch_offset := !fetch_offset +^ len + done; + 0 + ) + done; + Some !allocated + ) else None + )