[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>
---
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
+ )
--
2.19.1.3.g30247aa5d201