[Libguestfs] [virt-v2v PATCH v2 1/3] lib/utils: add the "Utils.with_nbd_connect_unix" helper function

Connecting to an NBD server temporarily, for a "one-shot" operation, is quite similar to "Std_utils.with_open_in" and "Std_utils.with_open_out", as there are cleanup operations regardless of whether the "one-shot" operation completes successfully or throws an exception. Introduce the "Utils.with_nbd_connect_unix" function, which takes a Unix domain socket pathname, a list of metadata contexts to request from the NBD server, and calls a function with the live NBD server connection. Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2027598 Signed-off-by: Laszlo Ersek <lersek(a)redhat.com&gt; --- Notes: v2: - move the function to the Utils module, from Nbdkit [Rich] - rename the function to "with_nbd_connect_unix" (from "with_connect_unix") - update the commit message lib/Makefile.am | 2 +- lib/utils.mli | 10 ++++++++++ lib/utils.ml | 12 ++++++++++++ 3 files changed, 23 insertions(+), 1 deletion(-) diff --git a/lib/Makefile.am b/lib/Makefile.am index c274b9ecf6c7..1fab25b326f5 100644 --- a/lib/Makefile.am +++ b/lib/Makefile.am @@ -80,7 +80,7 @@ BOBJECTS = config.cmo $(SOURCES_ML:.ml=.cmo) XOBJECTS = $(BOBJECTS:.cmo=.cmx) OCAMLPACKAGES = \ - -package str,unix \ + -package str,unix,nbd \ -I $(builddir) \ -I $(top_builddir)/common/mlgettext \ -I $(top_builddir)/common/mlpcre \ diff --git a/lib/utils.mli b/lib/utils.mli index c9b4bd631d65..f41e825e747d 100644 --- a/lib/utils.mli +++ b/lib/utils.mli @@ -77,3 +77,13 @@ val metaversion : string Eventually we may switch to using an "open metadata" format instead (eg. XML). *) + +val with_nbd_connect_unix : socket:string -> + meta_contexts:string list -> + f:(NBD.t -> 'a) -> + 'a +(** [with_nbd_connect_unix socket meta_contexts f] calls function [f] with the + NBD server at Unix domain socket [socket] connected, and the metadata + contexts 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. *) diff --git a/lib/utils.ml b/lib/utils.ml index c18a467cb57c..86967f342e6e 100644 --- a/lib/utils.ml +++ b/lib/utils.ml @@ -164,3 +164,15 @@ let rec wait_for_file filename timeout = ) let metaversion = Digest.to_hex (Digest.string Config.package_version_full) + +let with_nbd_connect_unix ~socket ~meta_contexts ~f = + let nbd = NBD.create () in + protect + ~f:(fun () -> + List.iter (NBD.add_meta_context nbd) meta_contexts; + NBD.connect_unix nbd socket; + protect + ~f:(fun () -> f nbd) + ~finally:(fun () -> NBD.shutdown nbd) + ) + ~finally:(fun () -> NBD.close nbd) -- 2.19.1.3.g30247aa5d201